OF  THL 

U N I VE.RS  ITY 
Of  ILLINOIS 


540 

M6I 

1867a 

v-Z 


Digitized  by  the  Internet  Archive 
in  2017  with  funding  from 

University  of  Illinois  Urbana-Champaign  Alternates 


https://archive.org/details/elementsofchemis02mill 


ELEMENTS  OF  CHEMISTRY 


THEORETICAL  AND  PRACTICAL. 


BY 

WILLIAM  ALLEN  MILLEE,  M.D.,  LL.l)., 

TREASURER  AND  VICE-PRESIDENT  OF  THE  ROYAL  SOCIETY; 
VICE-PRESIDENT  OP  THE  CHEMICAL  SOCIETY  ; 

PROFESSOR  OP  CHEMISTRY  IN  KING’S  COLLEGE,  LONDON  ; 

HON.  FELLOW  OF  KING’S  COLLEGE,  LONDON. 


PART  II. 

INOEGANIC  CITEAIISTRY. 


PROM 

THIRD  LONDON  EDITION,  WITH  ADDITIONS. 


NEW  YORK: 

JOHN  WILEY  & SON,  PUBLISHERS, 

2 Clinton  Hall,  Astok  Place. 

1868. 


The  New  York  Printing  Company, 
8i,  83,  and  85  Centre  Street, 
New  York. 


'H  ialMADGE 


^^0 

Mui 

V.Z  ! 


t 

TABLE  OF  CONTENTS. 


CHAPTER  I. 

NO.  OF 

PABAGKAPn.  PAGB 

Nomenclature — Classification  of  Elements , . . . 1 — 10 

331  Principles  of  Chemical  Nomenclature, 1 

332  Empirical  and  Rational  Formulae, 6 

333  General  Arrangement  of  the  Elements, 7 


CHAPTER  II. 

First  Division — N on-metallic  Elements^  , . . . 10 — 269 
The  Atmosphere — Oxygen — Nitrogen^  ....  11 — 30 


334  Compound  Nature  of  the  Atmosphere, 11 

335  § I.  Oxygen^ 12 

336  Nature  of  Combustion, 17 

337  Varieties  of  Oxides, 20 

338  Ozone 21 

339  § II.  Nitrogen^ 24 

§ III.  The  Atmosphere. 

340  Proportion  of  Oxygen — Its  Constancy, 2'6 

341  Proportion  of  Aqueous  Vapour  in  the  Air, 28 

342  Proportion  of  Carbonic  Anhydride, 29 

CHAPTER  III. 


Water — Hydrogen^ 30 — 47 

343  § I.  Water^ 30 

344  Various  kinds  of  Natural  Waters, 34 


TABLE  OF  CONTENTS. 


iv^ 

NO.  OF 
PARAGRAPH. 

345  § II.  Hydrogen^ 

346  Synthesis  of  Water — Eudiometers,  . 

347  Oxy hydrogen  Jet,  . 


PAGE 

. 38 


42 

46 


CHAPTER  IV. 


Carbon — Carbonic  Anhydride, 48 — 73 

348  § I.  Carbonic  Acid  {anhydride), 48 

349  Sources  of  Carbonic  Acid, 51 

350  Carbonates, 55 

351  § II.  Carbon, 57 

352  Diamond, 58 


353  Graphite — Coke — Graphon — Graphic  Acid — Consumption  of  Smoke,  59 

354  Charcoal — Lamp  Black — Animal  Charcoal, 64 

355  General  Properties  of  Carbon,  66 

356  Synthesis  of  Carbonic  Anhydride, 68 

357  Carbonic  Oxide,  \ 69 

CHAPTER  Y. 

Compounds  of  Nitrogen  with  Oxygen  and  with  Hydrogen,  73 — 98 


358  § I.  Compounds  of  Nitrogen  with  Oxygen,  , . .73 

359  Nitric  Acid, 73 

360  Action  of  Acids  on  Metals  and  Bases, 77 

361  Hydrates  of  Nitric  Acid, 79 

362  Nitric  Anhydride, 79 

363  Nitrates — Tests  for  Nitric  Acid, 80 

364  Nitrous  Oxide, 83 

365  Nitric  Oxide, 85 

366  Nitrous  Acid — Nitrites, 87 

367  Peroxide  of  Nitrogen, 89 

368  Difference  between  Mixture  and  Combination,  . . . .91 


§ II.  Compounds  of  Nitrogen  with  Hydrogen. 


369  Ammonia, 91 

370  Solution  of  Ammonia, 95 

871  Amidogen,  and  Ammonium, 97 


TABLE  OF  CONTENTS. 


V 


NO,  OF 

PARAGEAPH.  PAGE 

CHAPTER  VI. 

372  The  Halogens^ 98—141 

373  § /.  Chlorine — Chlorides, 98 

374  Hydrochloric  Acid, 101 

375  Solution  of  Hydrochloric  Acid, 103 

376  Action  of  Hydrochloric  Acid  on  Metallic  Oxides,  ....  105 

377  Aqua  Regia — Chloro-Hitric  and  Chloro-Nitrous  Gases,  . . . 107 

378  Oxides  of  Chlorine, 109 

379  Hypochlorous  Acid — Hypochlorites, 109 

380  Bleaching  Compounds — Chloride  of  Lime, 112 

381  Chlorimetry, 114 

382  Chloric  Acid — Chlorates, 115 

383  Perchloric  Acid — Perchlorates, 116 

384  Chlorous  Acid — Chlorites, 118 

385  Peroxide  of  Chlorine, 119 

386  Chloride  (?)  of  Nitrogen, 121 

387  Chlorides  of  Carbon, 122 

388  Chloro-Carbonic  or  Phosgene  Gas, 123 

389  § II.  Bromine, 123 

390  Hydrobromic  Acid,  . . * 125 

391  Bromides, 126 

392  Bromic  Acid, 127 

393  Other  Compounds  of  Bromine, 127 

394  § III.  Iodine, 128 

395  Hydriodic  Acid, 130 

396  Iodides, 131 

397  Oxides  of  Iodine — Iodic  Acid — lodates, 132 

398  Periodic  Acid — Periodates, 134 

399  Chlorides  and  Bromides  of  Iodine, 134 

400  Iodide  (?)  of  Nitrogen, 135 

401  Relations  of  the  Halogens  to  other  Elements,  . . . . 135 

402  § IV.  Fluorine, 137 

403  Hydrofluoric  Acid — Fluorides, 138 

404  Determination  of  the  Combining  Number  of  Fluorine,  . . 140 

CHAPTER  YII. 

Sulphur — Selenium — Tellurium, 141 — 184 

405  Natural  Relations  of  the  Sulphur  Group, 141 


vi  TAELE  OF  CONTEXTS. 

NO.  OF 

PARAGRAPH.  PAGE 

406  § I.  Sulphur 143 

407  Tarious  Forms  of  Sulphur, 145 

408  Electro-positive  and  Electro-negative  Sulphur,  ....  146 

409  Compounds  of  Sulphur  with  Oxygen, 148 

410  Sulphurous  Acid, 148 

411  Sulphites, 151 

412  Sulphuric  Acid — Theory  of  its  Formation, 153 

413  Sulphuric  Acid — Process  of  its  Manufacture, 155 

414  Hydrates  of  Sulphuric  Acid, 157 

415  Hordhausen  Sulphuric  Acid, 159 

416  Sulphuric  Anhydride, 159 

417  Common  Impurities  in  Sulphuric  Acid, 160 

418  Sulphates — Tests  for  Sulphuric  Acid, 161 

419  Hyposulphurous  Acid — Hyposulphites, 163 

420  Hyposulphuric  (Dithionic)  Acid, 166 

421  Trithionic  Acid, 166 

422  Tetrathionic  Acid, 167 

423  Pentathionic  Acid, 167 

424  Chlorosulphuric  Acid — lodosulphuric  Acid,  . ~ . . . .167 

425  Hitrosulphuric  Acid, 168 

426  Sulphazotised  Acids, 168 

427  Hydrosulphuric  Acid,  or  Sulphuretted  Hydrogen,  ....  169 

428  Hydrosulphates  and  Sulphides, 172 

429  Persulphide  of  Hydrogen, 174 

430  Bisulphide  of  Carbon, 175 

431  Chlorides,  Bromides,  and  Iodides  of  Sulphur,  . . . .177 

432  Sulphide  of  Nitrogen, 178 

433  § II.  Selenium, 178 

434  Selenious  Acid — Selenites, 180 

435  Selenic  Acid — Seleniates, 180 

436  Seleniuretted  Hydrogen, I8I 

437  Chlorides  of  Selenium, 181 

438  § III.  Tellurium, • . . 181 

439  TeUurous  Acid, 182 

440  Telluric  Acid, 183 

441  TeUuretted  Hydrogen, 183 

CHAPTER  VHI. 

Phosphorus, 184 — ^207 


442  Natural  Relations  of  the  Phosphorus  G-roup,  . 

443  Phosphorus, 


. 184 
. 185 


TAELE  OF  CONTENTS.  vil 

NO.  OF 

PARAGRAPH.  PAQB 

444  AUotropic  Modifications  of  Phosphorus, 188 

445  Oxides  of  Phosphorus, 191 

446  Phosphoric  Anhydride, 191 

447  Hydrates  of  Phosphoric  Acid, 192 

448  Orthophosphoric  or  Tribasic  Phosphoric  Acid,  . . . .193 

449  Pyrophosphoric  Acid, 195 

450  Monobasic,  or  Metaphosphoric  Acid, 197 

451  Phosphorous  Acid — Phosphites, 199 

452  Hypophosphorous  Acid — Hypophosphites, 200 

453  Oxide  of  Phosphorus, 201 

454  Phosphides  of  Hydrogen — Phosphuretted  Hydrogen  Gas,  . . 201 

455  Liquid  Phosphide  of  Hydrogen, 203 

456  Solid  Phosphide  of  Hydrogen, 204 

457  Chlorides  of  Phosphorus, 204 

458  Terchloride  of  Phosphorus, 204 

459  Pentachloride  of  Phosphorus 205 

460  Oxychloride  of  Phosphorus  (PCLO) 205 

461  Sulphochloride  of  Phosphorus  (POLS) 205 

462  Bromides  of  Phosphorus 206 

463  Iodides  of  Phosphorus 206 

464  Phospham 207 

465  Sulphides  of  Phosphorus,  . . . • 207 


CHAPTER  IX. 


Silicon — Boron^ 208 — 228 

466  Natural  Relations  of  Silicon, 208 

467  § I.  Silicon — Its  Different  Forms 208 

468  Silica,  or  Silicic  Anhydride, 211 

469  Hydrates  of  Silica, 212 

470  Silicates, 215 

471  Compounds  of  Silieon  with  Hydrogen  and  Oxygen,  . . . 216 

471aHydrated  Protoxide  of  Silicon  (Leukon), 217 

472  Hydride  of  Silicon, 218 

473  Nitride  of  Silicon, 218 

474  Sulphide  of  Silicon,  218 

475  Chloride  of  Silicon, 218 

476  Bromide  of  Silicon, 220 

477  Hydrochlorate  of  Chloride  of  Silicon, 220 

478  Fluoride  of  Silicon, 221 

479  Silicofluoric  Acid, 221 

480  § II.  Boron — Its  Different  Forms, 222 

481  Boracic  Anhydride — Boracic  Acid — Borates 224 


Vlll 


TABLE  OF  CONTENTS. 


NO.  OP 

PARAGRAPH.  page 

482  Sulphide  and  Chloride  of  Boron, 227 

483  Fluoride  of  Boron — Borofluoric  Acid — Hydrofluoboric  Acid,  . . 227 

484  Nitride  of  Boron, 228 

CHAPTER  X. 

Other  Compounds  of  the  Non-metallie  Elements  with  each 

other^ 228—269 

§ I.  Compounds  of  Hydrogen  and  Oxygen^ 

485  Peroxide  of  Hydrogen, 228 

§ II,  Compounds  of  Carbon  and  Hydrogen, 

486  Hydrocarbons,  . . 231 

487  Olefiant  Oas,  or  Ethylene, 231 

488  Dutch  Liquid — Action  of  Chlorine  upon  it,  . . . . .231 

489  Bibromide  of  Ethylene, 235 

490  Biniodide  of  Ethylene, 235 

491  Light  Carburetted  Hydrogen,  or  Marsh  Gas, 236 

492  Principle  of  the  Safety-lamp, 237 

493  Structure  of  Flame, 239 

494  Theory  of  the  Blowpipe, 242 

495  Use  of  the  Mouth  Blowpipe, 244 

496  Oil  Gas  (Tetrylene  or  Butylene), 246 

497  § III,  Oxides  of  Carbon, 246 

498  Oxalic  Acid — Oxalates, 246 

499  Rhodizonic  and  Croconic  Acids, 250 

500  Mellitic  Acid, 250 

§ /F.  Compounds  of  Carbon  with  Nitrogen, 

501  Cyanogen, 251 

502  Hydrocyanic  Acid, 253 

503  Cyanides, 255 

504  Cyanic  Acid, 257 

505  Fulminic  Acid, 258 

506  Isomerism, 259 

507  Paracyanogen, 259 

508  Chlorides  of  Cyanogen,  . . 260 

508aBromides  and  Iodides  of  Cyanogen, 261 

609  Other  Compounds  of  Cyanogen, 261 

§ F.  General  Remarks  on  Gas  Analysis, 

510  Modes  of  discriminating  different  Gases, 262 

611  Analytical  Classification  of  the  Gases, 263 


TABLE  OF  CONTENTS. 


ix 


NO.  OB’ 

PARAGRAPH.  PAGE 

512  (1)  Gases  Absorbable  by  Potash,  not  Inflammable,  . . . 263 

513  (2)  Gases  Absorbable  by  Potash,  but  Inflammable,  . . . 264 

514  (3)  Gases  not  Absorbable  by  Potash,  not  Inflammable,  . . . 264 

515  (4)  Gases  not  Absorbable  by  Potash,  but  Inflammable,  . . . 265 

516  Example  of  the  Analysis  of  Coal  Gas, 266 


CHAPTER  XL 


Second  Division — the  Metals, 270 — 722 

\ 

General  Remarks  on  the  Metals  and  on  their  Compounds — 

Theory  of  Salts, 270 — 326 

§ I.  General  Properties  of  the  Metals. 


517  Characteristics  of  a Metal, 270 

518  Lustre,  Opacity,  and  Colour — Odour  and  Taste,  ....  270 

519  Hardness,  Brittleness,  and  Tenacity, 271 

520  Malleability  and  Ductility, 273 

521  Specific  Gravity, 275 

522  Fusibility, 275 

523  Volatility, 276 

524  Conducting  Power  for  Heat  and  Electricity, 277 

525  Alloys, 277 

526  Condition  of  the  Metals  in  Nature, 279 

527  Distribution  of  the  Metals, 280 

528  Mining  Operations, 282 

529  Mechanical  Treatment  of  the  Ores, 284 

530  Roasting,  or  Oxidation, 287 

531  Reduction,  or  Smelting, 288 

532  Classification  of  the  Metals, 289 

§ II.  General  Properties  of  the  Compounds  of  the  Metals 
with  the  Non-metallic  Elements. 

533  The  Oxides, 293 

534  Estimation  of  Oxygen  in  Metallic  Oxides, 301 

535  The  Sulphides, 302 

536  Estimation  of  Sulphur  in  the  Metallic  Sulphides,  ....  305 

537  The  Selenides  and  Tellurides, 306 

538  Chlorides, 306 

539  Estimation  of  Chlorine, ^ . . . 310 

540  Bromides, 311 

541  Iodides, 311 

542  Fluorides, 312 

543  Nitrides, 312 

544  Phosphides, 313 

545  Compounds  of  Carbon,  of  Silicon,  and  of  Boron  with  Metals,  . . 313 

546  Compounds  of  Hydrogen  with  the  Metals, 313- 


X 


TABLE  OF  CONTEXTS. 


KO.  OF 

PARAGRAPH.  PAGE 

§ III,  Theory  of  Salts. 

547  Acids  and  Bases, . . 313 

548  Oxy acids  and  Hydracids, 314 

549  Binary  Theory  of  Salts, 315 

550  Objections  to  the  Binary  Theory, 317 

551  Sulpho-Salts, 318 

552  Varieties  of  Salts, 318 

553  Neutral  or  Normal  Salts, 318 

554  Acid  Salts — Polybasic  Acids, 319 

555  Double  Salts, 323 

556  Subsalts, 325 

557  Oxychlorides  and  Oxyiodides, 325 


CHAPTEE  XIL 


Group  I. — Metals  of  the  Alkalies., 326 — 399 

§ I.  Potassium. 

558  Notation  for  Mixtures  of  Isomorphous  Compounds,  ...  326 

559  Potassium, 328 

560  Preparation  of  Potassium, 329 

561  Tetroxide  and  Binoxide  of  Potassium, 331 

562  Potash — Hydrate  of  Potash, 332 

563  Sulphides  of  Potassium, 334 

564  Chloride  of  Potassium, 336 

565  Bromide  of  Potassium, 337 

566  Iodide  of  Potassium, 337 

567  Fluoride  of  Potassium, 338 

568  Sihcofluoride  of  Potassium, 338 

569  Sulphate  and  Bisulphate  of  Potassium, 338 

570  Nitrate  of  Potassium — Nitre  Plantations, 338 

571  Refining  of  Saltpetre, 340 

572  Grunpowder, 342 

573  Nitrite  of  Potassium,  . 345 

574  Chlorate  of  Potassium, 345 

575  Perchlorate  of  Potassium, 346 

576  Carbonate  of  Potassium, 346 

o77  Alkahmetry — Method  of  Neutralization,  .....  348 

578  Alkalimetry — Method  of  WiU  and  Fresenius, 350 

579  Bicarbonate  (Acid-carbonate  of  Potassium), 351 

580  Characters  of  the  Salts  of  Potassium, 351 

581  § II‘  Sodium, 352 

582  Soda — Hydrate  of  Soda — Sulphides  of  Sodium,  ....  353 

583  Chloride  of  Sodium, 354 

584  Bromide  of  Sodium, 357 

585  Iodide  of  Sodium, 357 

586  Sulphate  of  Sodium — Bisulphate  of  Sodium, 357 


TABLE  OF  CONTENTS. 


XI 


NO.  OF 

PARAGRAPH.  PAGE 

587  Sulphite  and  Bisulphite  of  Sodium, 360 

588  Nitrate  of  Sodium, 361 

589  Carbonate  of  Sodium — Process  of  its  Manufacture,  ....  361 

590  Bicarbonate  and  Sesquicarbonate  of  Sodium, 365 

591  Phosphates  of  Sodium, 367 

592  Borates  of  Sodium, 368 

593  Silicates  of  Sodium, 369 

594  Glass — Table  of  Chief  Varieties, 371 

595  Bohemian  Glass — Crown  Glass, 372 

596  Plate  Glass  and  Window  Glass, 373 

597  Bottle  Glass, 374 

598  Eeaumur’s  Porcelain — Devitrification, 375 

599  Flint  Glass — Optical  Glass, 375 

600  Coloured  Glasses, 377 

601  General  Properties  of  Glass, 379 

602  Characters  of  the  Salts  of  Sodium, 380 

603  § III.  Lithium.^ 381 

604  Lithia,  ............  381 

605  Compounds  of  Lithium, 382 

606  § lY.  Ruhidium^ 383 

607  Eubidia — Compounds  of  Eubidium, 384 

608  § Y.  Goesium., 384 

609  Coesia — Compounds  of  Coesium, 386 

§ YI  Salts  of  Ammonium., 

610  Compounds  of  Ammonia  with  Oxyacid  Anhydrides,  . . . 386 

611  Sulphuric  Ammonide — Sulphatammon, 387 

612  Sulphurous  Ammonides, 388 

613  Compounds  of  Ammonia  with  Hydracids, 388 

614  Theory  of  Ammonium, 388 

615  Solution  of  Ammonia, 389 

616  Sulphides  of  Ammonium — Ilydrosulphate  of  Ammonium,  . . 390 

617  Chloride  of  Ammonium, 391 

618  Sulphate  of  Ammonium, 392 

619  Nitrate  of  Ammonium, 393 

620  Carbonates  of  Ammonium, 393 

621  Phosphat  s of  Ammonium,  ........  394 

622  Ammoniated  Salts,  . 394 

623  Action  of  Ammonia  on  Metallic  Salts  in  Solution,  ....  395 

624  Characters  of  the  Compounds  of  Ammonium, 397 

625  Estimation  of  Ammonia  by  Precipitation,  .....  398 

326  Estimation  of  Ammonia  by  Acids, 399 


xn 


TABLE  OF  CONTEXTS. 


CHAPTEE  XIIL 

yo.  or 

PARAGRAPH.  PAGE 

Group  IL — 3Ietals  of  the  Alkaline  Earths^  . . 400 — 423 

627  § I.  Barium, 400 

628  Baryta — Peroxide  of  Barium, 400 

629  Sulphides  of  Barium, 402 

630  Chloride  of  Barium, 402 

631  Sdicofluoride  of  Barium,  .........  403 

632  Sulphate  of  Barium, 403 

633  ZSTitrate  of  Barium, 403 

634  Carbonate  of  Barium, 403 

635  Characters  of  the  Salts  of  Barium, 404 

636  ' § II.  Stro7itium, 405 

637  Strontia, 405 

638  Chloride  of  Strontium, . . 405 

639  Sulphate  of  Strontium,  405 

640  2S  itrate  of  Strontium, 406 

641  Carbonate  of  Strontium, 406 

642  Characters  of  the  Salts  of  Strontium, 406 

643  § III  Calcium, 407 

644  Lime — Quicklime — Slaked  Lime, 407 

645  Mortars  and  Cements,  . ‘ 409 

646  Hydraulic  Limes  and  Mortars, 410 

647  Other  Uses  of  Lime, 412 

648  Sulphides  of  Calcium, 413 

649  Phosphide  of  Calcium, 413 

649aSilicide  of  Calcium, 414 

650  Chloride  of  Calcium, 414 

651  Fluoride  of  Calcium, 415 

652  Sulphate  of  Calcium — Plaster  of  Paris, i 416 

653  Xitrate  of  Calcium,  . . 417 

654  Carbonate  of  Calcium, 417 

655  Calcareous  Waters — Clarks  Soap  Test, 418 

656  Building  Materials, 420 

657  Phosphates  of  Calcium, 421 

658  Boronatrocalcite, 422 

659  Characters  of  the  Salts  of  Calcium, 422 

CHAPTER  XTT. 

Group  III. — Metals  of  the  Earths,  ....  423 — 450 

660  § I Alummum, 423 

661  Properties  of  Aluminum, 425 

662  Alumina, 425 

663  Aluminate  of  Sodium, 427 


TABLE  OF  CONTENTS. 


Xlll 


NO.  OP 

PARAGRAPH.  PAGE 

664  Chloride  of  Aluminum, 428 

665  Fluorides  of  Aluminum, 429 

666  Sulphate  of  Aluminum, 430 

667  Different  Varieties  of  Alum, 430 

668  Phosphates  of  Aluminum, 433 

669  Silicates  of  Aluminum — Clays, 434 

670  Aluminous  Rocks  and  Minerals, 436 

671  Porcelain  and  Pottery  Ware, 438 

672  G-eneral  Remarks  on  Pottery, 440 

673  Ultramarine, 443 

674  Characters  of  the  Salts  of  Aluminum, 445 

675  Separation  of  Alumina  from  the  Alkaline  Earths,  ....  445 

676  § II.  Glucinum, 445 

677  Glucina  and  its  Salts, 446 

678  Characters  of  the  Compounds  of  G-lucinum, 447 

679  § III.  Zirconium, 447 

680  Zirconia  and  its  Salts, 447 

681  § Thorinum,  Yttrium,  and  Terbium,  . . , 448 

682  Yttria  and  Terbia, 449 

682a  § V.  Cerium,  Lanthanum,  and  Didymium,  . . . 449 


CHAPTER  XV. 


Group  IV,  Magnesian  Metals, 450 — 470 

683  § 1.  Magnesium, 450 

684  Magnesia,  452 

685  Sulphide  of  Magnesium, 452 

686  Chloride  of  Magnesium, 452 

687  Sulphate  of  Magnesium, 453 

688  Nitrate  of  Magnesium, 453 

689  Carbonates  of  Magnesium — Borate  of  Magnesium,  ....  453 

690  Silicates  of  Magnesium, 454 

691  Phosphates  of  Magnesium, 455 

692  Characters  of  the  Salts  of  Magnesium, 455 

693  Characters  of  the  Metals  of  the  First  Group,  .....  456 

694  Estimation  of  Potassium  and  Sodium, 456 

695  Conversion  of  the  Alkaline  Metals  into  Chlorides,  ....  457 

696  General  Characters  of  the  Metals  of  the  Second  Group,  . . . 457 

697  Separation  of  the  Alkaline  Earths  from  the  Alkalies,  . . . 457 

698  Separation  of  the  Alkaline  Earths  from  each  other,  . . . 458 

€99,  700  Mode  of  Collecting  and  Washing  Precipitates,  . . 458,  459 


XIV 


TABLE  OF  CONTEXTS. 


XO.  OF 

PARAGRAPH.  PAGE 

701  § II.  Zinc, 461 

702  Extraction  of  the  Metal — English  Method, 461 

703  Extraction  of  the  Metal — Silesian  Method, 462 

704  Extraction  of  the  Metal — Belgian  Method, 463 

705  Preparation  of  Pure  Zinc, 464 

706  Properties  of  Zinc, 464 

707  Its  Alloys  and  Industrial  Apphcations, 464 

708  Oxide  of  Zinc, 465 

709  Sulphide  of  Zinc,  or  Blende, 466 

710  Chloride  of  Zinc, 466 

711  Sulphate  of  Zinc, 466 

712  Carbonate  of  Zinc,  or  Calamine, 467 

713  Characters  of  the  Salts  of  Zinc, 467 

714  Estimation  of  Zinc  in  Analysis, 467 

715  Separation  of  Zinc  from  the  Alkahes  and  Earths,  ....  468 

716  § III.  Cadmium, 468 

717  Oxide  and  other  Compounds  of  Cadmium, 469 

718  Characters  of  the  Salts  of  Cadmium, 469 


CHAPTER  XVI. 


Group  V. — Metals  more  or  less  allied  to  Iron,  . . 470 — 551 

719  § I.  Cohalt, 470 

720  Oxides  of  Cobalt — Zaflfre — Smalt — Thenard’s  Blue,  . . . 472 

721  Ammoniacal  Compounds  of  Cobalt, 474 

722  Sulphides  of  Cobalt, 476 

723  Chloride  of  Cobalt, 477 

724  Sulphate  and  Nitrate  of  Cobalt, 477 

725  Carbonates  of  Cobalt, . 478 

726  Characters  of  the  Salts  of  Cobalt,  . . . . . . .478 

727  Estimation  of  Cobalt  in  Analysis, 478 

728  Separation  of  Cobalt  from  the  preceding  Metals,  ....  480 

729  § 11  Nickel, 480 

730  Oxides  of  Nickel, 482 

731  Sulphides  of  Nickel, 482 

732  Chloride  of  Nickel, 483 

733  Sulphate  of  Nickel,  483 

734  Carbonates  of  Nickel, 483 

735  Characters  of  the  Salts  of  Nickel, 483 

736  Estimation  of  Nickel  in  Analysis, 484 

737  Separation  of  Nickel  from  Cobalt, 484 


TABLE  OF  CONTENTS. 


XV 


KO.  OF 

PARAGRAPH.  PAGE 

738  § III.  Uranium, 485 

739  Oxides  of  Uranium, 486 

740  Chlorides  of  Uranium, 487 

741  Characters  of  the  Salts  of  Uranium, 487 

742  Estimation  of  Uranium, 488 

§ /U.  Iron, 488 

743  Iron  Ores: — Meteoric  Stones, 488 

744  Smelting  of  Clay  Ironstone, 491 

745  Theory  of  the  Blast  Furnace, 492 

746  Hot  Blast, 495 

747  Composition  and  Properties  of  Cast  Iron, 497 

748  Conversion  of  Cast  Iron  into  Wrought  Iron — Eefining,  . . . 500 

749  Puddling,  . 501 

750  Production  of  Wrought  Iron  direct  from  the  Ore,  ....  505 

751  Manufacture  of  Steel, 505 

752  Preparation  of  Pure  Iron, 509 

753  Properties  of  Bar-Iron — Busting  of  Iron, 510 

754  Passive  Condition  of  Iron  in  Nitric  Acid, 512 

755  Alloys  of  Iron,  ....  513 

756  Protoxide  of  Iron,  or  Ferrous  Oxide, 513 

757  Sesquioxide  of  Iron  or  Ferric  Oxide, 514 

758  Magnetic  Oxide  of  Iron, 516 

759  Ferric  Acid — Hydride  of  Iron, 517 

760  Nitride  of  Iron, 517 

761  Protosulphide  of  Iron, 518 

762  Bisulphide  of  Iron,  519 

763  Magnetic  Sulphides — Mispickel — Phosphide  of  Iron,  . . . 519 

764  Ferrous  Chloride, 520 

765  Ferric  Chloride, 520 

766  Bromides  and  Iodide  of  Iron, 521 

767  Sulphate  of  Iron,  or  Ferrous  Sulphate, 521 

768  Ferric  Sulphate, 522 

769  Nitrates  of  Iron, 523 

770  Carbonate  of  Iron, 523 

771  Oxalates  of  Iron, 524 

772  Phosphates  of  Iron, 524 

773  Character  of  the  Salts  of  Iron, 525 

774  Estimation  of  Iron,  and  Separation  from  the  Alkalies,  . . . 526 

775  Separation  of  Iron  from  Aluminum  and  Glucinum,  . . . 526 

776  Separation  from  Zinc,  Cobalt,  Nickel,  and  Manganese,  . . . 527 

777  Separation  of  Iron  from  Uranium,  .......  527 

778  Estimation  of  Mixed  Protoxide  and  Peroxide  of  Iron.  . . . 527 

779  Analysis  of  Cast  Iron,  Steel,  and  Bar-Iron, 529 

780  § ^*  Chromium,  530 

781  Protoxide  of  Chromium,  or  Chromous  Oxide,  ....  531 


XVI 


TABLE  OF  CONTEXTS. 


NO.  OP 

PARAGRAPH.  PAGE 

782  Sesquioxide  of  Chromium  or  Chromic  Oxide, 532 

783  Chrome  Iron-stone, 534 

784  Ammoniacal  Compounds  of  Chromium, 534 

785  Chromic  Acid, 534 

786  Chromates, 535 

787  Sulphide  of  Chromium, 537 

788  Chlorides  of  Chromium, 537 

789  Chlorochromic  Acid, 538 

790  Fluoride  of  Chromium, 538 

791  Kitride  of  Chromium, 539 

792  Sulphates  of  Chromium, 539 

793  Nitrate  of  Chromium, 540 

794  Oxalates  of  Chromium, 540 

795  Characters  of  the  Compounds  of  Chromium, 541 

796  Estimation  of  Chromium, 542 

797  § VI.  Manganese., 542 

798  Oxides  of  Manganese, 543 

799  Assay  of  Black  Oxide  of  Manganese, 544 

800  Manganic  Acid — Manganates,  545 

801  Permanganic  Acid, 546 

802  Sulphide  of  Manganese,  548 

803  Chlorides  of  Manganese, 548 

804  Sulphate  of  Manganese, 549 

805  Carbonate  of  Manganese, 549 

806  Characters  of  the  Salts  of  Manganese, 549 

807  Estimation  of  Manganese, 550 

CHAPTER  XVII. 

Group  VI. — Certain  Metals  which  form  Acids  with 

Oxygen, 551 — 607 

808  § I.  Tin, 551 

809  Processes  for  Extracting  the  Metal, 552 

810  Properties  of  Tin, 554 

811  Preparation  of  Tin-Plate, 555 

812  Alloys  of  Tin, 556 

813  Protoxide  of  Tin,  or  Stannous  Oxide, 558 

814  Binoxide  of  Tin — Metastannic  Acid, 558 

815  Stannic  Acid — Stannates, 559 

816  Sulphides  of  Tin, 560 

817  Stannous  Chloride,  or  Protochloride  of  Tin, 561 

818  Stannic  Chloride,  or  Bichloride  of  Tin, 562 

819  Characters  of  the  Salts  of  Tin, 562 

820  Estimation  of  Tin, 563 


TABLE  OF  CONTENTS. 


NO.  OF 
PARAGRAPH. 

821  § II,  Titanium^ 

822  Oxides  of  Titanium — Titanic  Acid, 

823  Other  Compounds  of  Titanium, 

824  Characters  of  the  Compounds  of  Titanium, 

825  Estimation  of  Titanium,  

826  § III.  Columbium — Tantalum^ 

827  § Molybdenum^ 

828  Oxides  of  Molybdenum, 

829  Molybdic  Anhydride — Molybdates, 

830  Other  Compounds  of  Molybdenum, 

831  Characters  of  the  Salts  of  Molybdenum, 

832  § V.  Tungsten^ 

833  Oxides  of  Tungsten — Tungstic  Acid — Tungstates,  . . . . 

834  Other  Compounds  of  Tungsten, 

835  Characters  of  the  Salts  of  Tungsten, 

836  I VI.  Vanadium^ 

837  Oxides,  and  other  Compounds  of  Vanadium, 

838  Characters  of  the  Compounds  of  Vanadium, 

839  § VII.  Arsenic, 

840  Arsenious  Acid — Arsenites, 

841  Arsenic  Acid — Arseniates, 

842  Sulphides  of  Arsenic — Realgar — Orpiment, 

843  Arseniuretted  Hydrogen, 

844  Other  Compounds  of  Arsenic, 

845  Characters  of  the  Compounds  of  Arsenic,  ..... 

846  Search  for  Arsenic  in  Organic  Mixtures — Reinsch’s  Test — Marsh’s 

Test, 

847  Estimation  of  Arsenic, 

848  Separation  of  Arsenic  from  other  Metals, 

849  § VIII.  Antimony, 

850  Properties  of  Antimony, 

851  Oxide  of  Antimony, 

852  Antimonic  Acid — Antimoniates,  ....... 

853  Metantimonic  Acid — Metantimoniates,  ...... 

854  Antimoniuretted  Hydrogen, 

855  Sulphides  of  Antimony,  

856  Chlorides  of  Antimony,  . . 


xvii 


PAGE 

564 

565 

566 

566 

567 

567 

567 

568 

569 

570 

570 

571 

571 

575 

576 

577 

577 

578 

578 

580 

582 

583 

585 

586 
586 

588 

592 

592 

592 

594 

596 

596 

598 

598 

599 

600 


XVUl 


TABLE  OF  CONTENTS. 


NO.  OF 

PARAGRAPH.  PAGE 

857  Characters  of  the  Compounds  of  Antimony, 601 

858  Estimation  of  Antimony, 602 

859  Separation  of  Antimony  from  other  Metals, 603 

860  § IX.  Bismuth^ 603 

861  Oxides  of  Bismuth, 605 

862  Sulphide  of  Bismuth, 605 

863  Terchloride  of  Bismuth, 606 

864  Nitrates  of  Bismuth,  606 

865  Characters  of  the  Salts  of  Bismuth, 606 

866  Estimation  of  Bismuth, 607 


CHAPTER  XVIIL 


Group  VII. — Copper;  Lead;  Thallium.,  . . . 607 — 647 

867  § I.  Copper, 607 

868  Welsh  Process  of  Copper  Smelting, 608 

869  Calcination  of  the  Ore, 609 

870  Melting  for  Coarse  and  for  Fine  Metal — Blister  Copper,  . . 610 

871  Poling,  or  Refining, 611 

872  Kernel-Roasting, 613 

873  Properties  of  Copper, 613 

874  Brass, 615 

875  Suboxide  of  Copper,  or  Cupreous  Oxide, 616 

876  Black  Oxide  of  Copper,  or  Cupric  Oxide, 617 

877  Hydride  of  Copper,  . . _ 618 

878  Nitride  of  Copper, 618 

879  Sulphides  of  Copper — G-rey  Copper  Ore — Selenide  of  Copper,  . 618 

880  Phosphide  of  Copper, : . 619 

881  Subchloride  of  Copper,  or  Cupreous  Chloride,  ....  620 

882  Chloride  of  Copper,  or  Cupric  Chloride, 620 

883  Bromides  of  Copper — Subiodide  of  Copper,  or  Cupreous  Iodide,  . 621 

884  Sulphates  of  Copper, 622 

885  Nitrates  of  Copper, 623 

886  Carbonates  of  Copper, 623 

887  Characters  of  the  Salts  of  Copper, 624 

888  Estimation  of  Copper, 625 

889  § IL  Lead, 626 

890  Extraction  of  Lead, 627 

891  Pattinson’s  Process  for  Extracting  Silver  from  Lead,  . . . 628 

892  Separation  of  Silver  from  Lead  by  CupeUation,  ....  629 

893  Other  Processes  for  Extracting  Lead, 630 

894  Properties  of  Lead, 631 


TABLE  OF  CONTENTS.  xix 

KO.  OF 

PARAGRAPH.  PAGH 

895  Combined  Action  of  Air  and  Water  on  Lead,  . . .631 

896  Uses,  and  Alloys  of  Lead, 633 

897  Compounds  of  Lead  with  Oxygen — Protoxide,  ....  633 

898  Eed  Oxide  of  Lead, 635 

899  Peroxide  of  Lead — Plumbates, 636 

900  Sulphides  of  Lead,  637 

901  Chloride,  Oxychlorides,  and  Bromide  of  Lead,  ....  638 

902  Iodide,  and  Fluoride  of  Lead, 638 

903  Sulphate,  and  Sulphite  of  Lead, 639 

904  Nitrates  of  Lead,  ..........  639 

905  Nitrites  of  Lead, 640 

906  Phosphates,  and  Borates  of  Lead, 640 

907  Carbonate  of  Lead — White  Lead, 641 

908  Characters  of  the  Salts  of  Lead, 643 

909  Estimation  of  Lead, 644 

910  § III.  Thallium^ 644 

911  Compounds  of  Thallium, 646 

912  Characters  of  the  Salts  of  Thallium, 646 

912a  Indium, 647 

CHAPTER  XIX. 

Group  VIII.  The  Nohle  Metals.^ 647 — 722 

913  G-eneral  Remarks  upon  this  Group, 647 

914  § /.  Mercury^ 647 

915  Properties  and  Uses  of  Mercury, 650 

916  Black  Oxide  of  Mercury,  or  Mercurous  Oxide,  ....  651 

917  Red  Oxide/ of  Mercury,  or  Mercuric  Oxide, 651 

918  Mercuramine, 652 

919  Sulphide  of  Mercury,  or  Mercurous  Sulphide, 653 

920  Cinnabar,  or  Vermilion,  .........  653 

921  Calomel,  or  Mercurous  Chloride,  .......  654 

922  Corrosive  Sublimate,  or  Mercuric  Chloride, 656 

923  Oxychlorides  of  Mercury, 656 

924  Action  of  Ammonia  on  Corrosive  Sublimate, 658 

925  Iodides  of  Mercury,  ..........  659 

926  Nitride  of  Mercury,  ..........  660 

927  Sulphates  of  Mercury,  661 

928  Nitrates  of  Mercury,  .........  661 

929  Characters  of  the  Salts  of  Mercury,  .......  662 

930  Estimation  of  Mercury, 663 


XX 


TABLE  OF  CONTENTS. 


NO.  OF 

PARAGRAPH.  PAGE 

931  § II.  Silver, 664 

932  Extraction  of  Silver  by  Amalgamation, 665 

933  American  Method  of  Amalgamation, 667 

934  Separation  of  Silver  from  Copper  by  Liquation,  ....  669 

935  Plating  and  Silvering, 669 

936  Silvering  of  Mirrors, 670 

937  Alloys  of  Silver,  . . . . . . . . . .671 

938  Assay  of  Silver  by  Cupellation, 672 

939  Assay  of  Silver  by  the  Humid  Process, 674 

940  Preparation  of  Fine  Silver,  ........  680 

941  Suboxide  of  Silver — Protoxide  of  Silver,  or  Argentic  Oxide,  . . 681 

942  Fulminating  Silver — Peroxide  of  Silver, 681,  682 

943  Sulphide  of  Silver, 682 

944  Chlorides  of  Silver, 683 

945  Bromide  of  Silver, . . . 684 

946  Iodide,  and  Fluoride  of  Silver,  . 685 

947  Sulphate  of  Silver, 685 

948  Nitrate  of  Silver, 686 

949  Phosphates  of  Silver, 686 

950  Characters  of  the  Salts  of  Silver, 687 

951  Estimation  of  Silver, 688 

952  Separation  of  Silver  from  other  Metals, 688 

953  § III.  Gold, 688 

954  Properties  of  Grold, 690 

955  Preparation  of  Fine  Gold, 690 

956  Processes  of  Gilding — Amalgams  of  Gold, 691 

957  Alloys  of  Gold, 692 

958  Assay  of  Gold, 694 

959  'Oxides  of  Gold,  . 696 

960  Sulphides  of  Gold, 697 

961  Chlorides  of  Gold, 697 

962  Bromides,  and  Iodides  of  Gold, 698 

963  Purple  of  Cassius,  699 

964  Characters  of  the  Salts  of  Gold,  . 699 

965  Estimation  of  Gold — Separation  from  other  Metals,  . . . 699 

966  § Platinum, 699 

967  Properties  of  Platinum, 702 

968  Platinum  Black,  . . . 703 

969  Applications  and  Alloys  of  Platinum, 703 

970  Oxides  of  Platinum, 704 

971  Sulphides  of  Platinum, 705 

972  Chlorides  of  Platinum,  . . .705 

973  Ammoniacal  Derivatives  from  the  Chlorides  of  Platinum,  . .706 

974  Other  Compounds  of  Platinum, 708 

975  Characters  of  the  Salts  of  Platinum, 709 

976  Estimation  of  Platinum,  709 


TABLE  OF  CONTENTS.  Xxi 

NO.  OF 

PARAGRAPH.  PAGE 

977  § F".  Palladium^ . 710 

978  Oxides  and  Sulphides  of  Palladium, 711 

979  Chloride,  Iodide,  Cyanide,  and  Nitrate  of  Palladium,  . . .711 


980  Characters  of  the  Salts  of  Palladium, 712 

981  § VI.  Rhodium^ 713 

982  Oxides,  Sulphides,  and  Chlorides  of  Ehodium,  ....  713 

983  Characters  of  the  Salts  of  Rhodium, 714 

§ VII.  Ruthenium. 

984  Treatment  of  the  Ore  of  Platinum, 715 

985  Ruthenium — its  Oxides  and  Chlorides, 716 

986  § VIII.  Osmium.^ 716 

987  Oxides  and  Sulphides  of  Osmium 717 

988  Chlorides  and  other  Salts  of  Osmium, 718 

989  § IX.  Iridium.^ 719 

990  Oxides  and  Sulphides  of  Iridium, 720 

991  Chlorides  and  other  Compounds  of  Iridium, 721 


CHAPTER  XX. 

On  some  Circumstances  which  modify  the  Action  of 
Chemical  Attraction., 722 — 773 

992  Cases  of  Simple  Chemical  Attraction, 722 

§ I.  Influence  of  Cohesion.,  Adhesion,  and  Elasticity  on 
Chemical  Attraction. 


993  Influence  of  Cohesion, 722 

994  Influence  of  Adhesion  and  Solution, 723 

995  Influence  of  Elasticity  on  Chemical  Attraction,  ....  723 

996  Aid  afforded  to  Chemical  Attraction  by  Mechanical  Action,  . . 725 

997  Influence  of  Pressure  in  preventing  Decomposition,  . . . 725 

998  Action  of  Acids  on  Salts  in  Solution, 726 

999  Action  of  Bases  on  Salts  in  Solution, 728 

1000  Mutual  Action  of  Salts  in  Solution, 728 

1001  Influence  of  Mass  on  the  Formation  of  Compounds,  . . . 731 

1002  Gladstone’s  Experiments  on  the  Influence  of  Mass,  . . . 732 

1003  Experiments  of  Bunsen  and  of  Debus  on  the  Effects  of  Mass,  . 734 

1004  Influence  of  Adhesion — Surface  Actions  of  Platinum,  . . . 736 


XXll 


TAELE  OF  CONTEXTS. 


NO.  OF 

PARAGEAPH.  PAGE 

1005  Other  Surface  Actions, 739 

1006  Catalysis — Liebig’s  Theory, 739 

1007  Effects  of  Motion  on  Chemical  Attraction, 740 

1008  Concurring  Attractions — Mercer’s  Theory  of  Catalysis,  . . . 741 


§ II.  Influence  of  Temperature. 

1009  Influence  of  Heat  upon  Chemical  Attraction, 745 

1010  Suspension  of  Chemical  Action  by  Depression  of  Temperature,  . 746 

§ III.  Influence  of  Light  on  Chemical  Attraction — 
Photography. 


1011  Supposed  Influence  of  Light  on  Crystallization,  . . . .747 

1012  Chemical  Actions  of  Light,  . . . . . . , . 747 

1013  Photochemical  Induction, 748 

1014  Influence  of  Light  on  Mixtures  of  Gases,  .....  748 

1015  Deoxidizing  Influence  of  Light  on  Metallic  Compounds,  . . 750 

1016  Photogenic,  or  Photographic  Printing, 751 

1017  Talbotype,  or  Calotype  Process, 752 

1018  Photography  on  Collodion, 754 

1019  Uses  of  Albumenized  Plates  in  Photography,  ....  756 

1020  Photographic  Engraving  and  Lithography, 756 

1021  Other  Photographic  Processes — Chrysotype, 758 

1022  Daguerreotype — Production  of  Images  on  Metallic  Plates,  . . 758 

1023  Prismatic  Analysis  of  the  Chemical  Effects  of  Light,  . . .761 

1024  Identity  of  Fluorescent  and  Chemical  Ptays, 763 

1025  Photographic  Transparency  of  Various  Media,  . . . .763 

1026  Photographic  Spectra  of  the  Elements, 768 

1027  Extinction  of  Chemical  Rays, 769 

1028  Opposite  Effects  of  the  Red  and  Violet  Extremity  of  the  Spec- 

trum,   771 

1029  Action  of  the  Solar  Spectrum  on  Vegetable  Colours,  . . . 773 


CHAPTER  XXI 

On  the  Determination  of  the  Comhining  Kumhers  and 


Atomic  Weights  of  the  Elementary  Bodies.^  . . 773 — 786 

1030  Aid  derived  from  Analysis  in  fixing  the  Atomic  IVeight  of  a Body,  773 

1031  Aid  derived  from  Isomorphism — Specific  Heat,  Ac.,  . . .774 

1032  Xumerical  Data  upon  which  the  Calculation  of  the  Atomic  W eight 

of  each  Element  is  founded, 776 

1033  Table  of  Atomic  Weights, 786 

1034  Numerical  Relations  of  Atomic  Weights, 786 

Index, 791 


[N.B. — In  the  formnlse  adopted  in  this  volume  the  symbols  for 
the  new  atomic  weights  are^  in  accordance  with  the  present  nsnal 
and  convenient  practice,  indicated  by  barred  letters,  instead  of  by 
italics,  as  in  the  first  \olnme.  The  conversion  of  any  formula  on 
the  new  notation  into  that  in  ordinary  use  is  effected  by  doubling 
the  numbers  attached  to  the  barred  symbols.  The  result  ob- 
tained will  either  be  the  ordinary  formula,  or  its  multiple  by- 
two.  KHO,  for  instance ^KHOa ; and  ■SnCl^=2  SnClj.] 


fmm..  . ' f "•  ■ f? 


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t^o.^  -^4  V*  ' rT. 


ELEMENTS  OE  CHEMISTRY. 


PART  II. 

INOKGANIC  CHEMISTRY. 


CHAPTER  I. 

NOMENCLATURE CLASSIFICATION  OF  THE  ELEMENTS. 

(331)  Principles  of  Chemical  Nomenclature. — Before  proceed- 
ing to  a description  of  the  chemical  properties  of  the  different 
elementary  substances,  and  of  the  compounds  which  are  the  result 
of  their  union  with  each  other,  it  will  be  needful  to  explain  the 
principles  upon  which  the  nomenclature  in  use  amongst  chemists 
has  been  founded.  The  object  of  the  inventors  of  this  language 
was,  not  merely  to  give  a distinguishing  name  to  the  substances 
spoken  of,  but  also  to  convey  a knowledge  of  their  components, 
and  even  of  the  proportions  in  which  those  components  occur.  In 
the  less  complicated  substances  with  which  the  chemist  has  to 
deal,  this  object  is  very  completely  attained.  In  those  of  a more 
complex  nature,  the  employment  of  symbols  (16)  becomes  neces- 
sary, in  order  to  enable  the  composition  of  the  body  to  be  fully 
indicated ; and  the  formula  of  a substance,  especially  if  the 
substance  be  derived  from  the  animal  or  the  vegetable  kingdom, 
becomes  an  indispensable  supplement  to  its  name. 

1.  Elements. — In  the  case  of  the  elementary  bodies,  the 
common  name  of  each  is  usually  that  by  which  it  is  distinguished 
in  chemical  language,  if  the  substance — as  is  the  case  with  many 
of  the  metals,  such  as  lead,  iron,  copper,  or  zinc — be  one  which  is 
familiarly  known : if  it  be  a body  which  the  researches  of  the 
chemist  have  brought  to  light,  the  name  is  generally  indicative  of 
some  marked  peculiarity  by  which  the  element  is  characterized. 
Thus  phosphorus  (from  0opk,  light  bearing)  is  so  named 
because  when  exposed  to  the  air  it  emits  a feeble  light  which  is 
visible  in  a darkened  room ; iodine  derives  its  name  from 
(violet),  in  reference  to  the  violet  colour  of  its  vapour ; hydrogen 
(producer  of  water,  yswaw)  is  so  called  from  the  circum- 

stance that  it  is  a necessary  component  of  water ; and  so  on. 

The  attempt  to  introduce  a strictly  systematic  nomenclature 
1 


2 


CHEmCAL  NOMEXCLATTJEE BINARY  COMPOUNDS. 


for  tlie  elementary  substances  has  failed,  owing  to  the  strong  hold 
which  the  popular  names  of  those  in  familiar  use  have  retained 
upon  the  language ; but  in  the  case  of  the  more  recently  discovered 
metals  a common  termination  in  has  been  assigned  to  them, 
as,  for  example,  palladium,  iridium,  osmium,  potassium,  sodium, 
aliuninum,  &c.  Among  the  non-metallic  elements  analogies  are 
also  pointed  out  by  a similarity  in  the  termination  of  the  name : 
for  instance,  chlorine,  iodine,  bromine,  and  fluorine,  have  similar 
properties ; and  the  existence  of  a certain  analogy  between  boron 
and  silicon  is  indicated  by  the  common  termination  of  both. 

2.  Binary  Comjyonnds. — ^hen  elements  combine  with  each 
other  to  form  a binary  compound — that  is  to  say,  a compound  in 
which  two  elements  only  are  present,  and  in  which  also  one  atomic 
proportion*  (13)  only  of  each  substance  is  concerned — the  nature 
of  both  the  components  is  specifled  by  the  name  employed ; the 
name  of  the  electro-negative  ingredient  (261),  being  that  which 
is  placed  first  as  the  generic  term,  whilst  that  of  the  electro- 
positive or  hasyloiis  element  follows  as  indicating  the  species : for 
instance,  a combination  of  oxygen  with  zinc  is  designated  oxide 
of  zinc — the  electro-negative  element  oxygen  standing  first  and 
undergoing  a modification  or  inflection  in  its  name.  The  follow- 
ing table  will  illustrate  the  manner  in  which  such  modifications 
are  applied ; the  symbols  of  the  different  compounds  are  given  in 
the  fourth  column.  It  is  to  be  observed  that  in  employing  sym- 
bols the  rule  observed  as  to  the  order  in  which  the  elements  are 
arranged  is  the  reverse  of  that  which  is  adopted  in  the  application 
of  the  name,  for  in  the  symbol  the  basylous  or  electro-positive 
element  is  usually  placed  first : — 


The  compouEds  of 

are  termed 

For  example  ; — 

Or  in  symbols 

Oxygen 

Oxides 

Oxide  of  Zinc 

Zn0 

Chlorine 

Chlorides 

Chloride  of  silver 

Ag  Cl 

Bromine 

Bromides 

Bromide  of  sodium 

Na  Br 

Iodine 

Iodides 

Iodide  of  potassium 

KI 

Fluorine 

Fluorides 

Fluoride  of  calcium 

0a  Fa 

Nitrogen 

Nitrides 

Nitride  of  boron 

B N 

Carbon 

_j 

i Carbides  or  ) 

1 Carburets  j 

Carbide  of  iron 

0640 

Sulphur 

\ 

I Sulphides  or  \ 

Sulphide  of  copper 

0u  S 

1 Sulphurets  ( 

Sulphuret  of  lead  | 

PbS 

Selenium 

1 

1 

) Selenides  or  ^ 

Selenide  of  mercury 

HgSo 

( 

1 Seleniurets  ) 

Seleniuret  of  cadmium 

0d  Se 

1 

Phosphorus 

j 

1 Phosphides  or  ) 

Phosphide  of  hydrogen 

H Pa 

1 

! Phosphurets  f 

Phosphuret  of  calcium 

0a  P 

* We  have  already  called  attention  (13)  to  the  loose  way  in  which  the  terms 
atom  and  equivdkni  are  often  employed  by  chemists,  and  have  pointed  out  the  essential 
difference  between  the  sis^nification  of  the  two  terms.  For  example,  an  acid  like  the 
citric  (H3O6H5O7),  will  require  three  times  as  much  potassium  to  form  with  it  a neu- 
tral salt,  as  is  required  by  another  acid,  such  as  the  nitric  (HNOs).  The  proportion 
of  citric  acid  represented  by  the  formula  (H366H5O7)  is  nevertheless  sometimes 
inaccurately  termed  its  equivalent,  and  the  same  term  is  also  applied  to  the  proportion 
of  nitric  acid  represented  by  the  formula  (HNO3);  yet  it  is  manifest  that  these  quau- 


NOMEXCLATUKE ^MULTIPLE  COMPOUNDS. 


3 


3.  Multiple  Compounds. — It  often  happens,  however,  in  con- 

sequence of  the  operation  of  the  law  of  multiple  proportions  (10), 
that  the  same  pair  of  elements  forms  two  or  more  compounds 
endowed  with  different  properties,  and  which  contain  different  pro- 
portions of  their  components : the  electro-negative  element  in  this 
case  is  usually  the  one  in  which  the  multiple  relation  is  observed ; 
and  the  number  of  atoms  in  which  it  enters  into  combination 
in  the  particular  case  is  indicated  by  prefixing  to  the  name  an 
abbreviation  of  the  corresponding  Greek  ordinal : first, 

5sjrs^og  second,  rpirog  third,  (fee.  For  examj)le,  there  are  four 
different  oxides  of  osmium  : — 

The  first  or  lowest  oxide  is  termed  the  protoxde  of  osmium,  or  ) 

simply,  oxide  of  osmium  f 

The  second  oxide  “ deutoxide  of  osmium 

The  third  oxide  “ tritoxide  of  osmium 

The  fourth  oxide  “ tessaroxide,  or  peroxide  ) 

of  osmium  . . . . ) 

Sometimes  the  Latin  prefixes  are  substituted  for  those  derived 
from  the  Greek  : thus  the  terms  dmoxide  and  deutoxide  of  tin  are 
used  indifferently  for  a combination  (SnG2)  of  one  atom  of  tin 
and  two  atoms  of  oxygen.  In  the  same  way  the  ^^rchloride  of 
antimony  (SbClg)  is  used  as  synonymous  with  the  tritochloride  of 
antimony.  The  more  complicated  relation  of  3 atoms  to  2 or  1^ 
to  1 is  expressed  by  the  Latin  prefix  sesqui,  which  means  ^ one  and 
a half.’  For  example,  we  speak  of  ^^s^msulphide  of  iron, 
(Fe2S3),  ^^^^moxide  of  chromium  (Oi^Og).  The  highest  oxide, 
chloride,  or  sulphide,  is  frequently  termed  t\\e  peroxide^^pereidoride^ 
or  j?^rsulphide.  For  example,  the  compound  SbCl^  is  termed  the 
perchloride  of  antimony,  and  OaS^  is  termed  indifferently  the  per- 
sulphide or  the  pentasulphide  of  calcium.  This  practice  of  using 
indifferently  a Greek  or  a Latin  prefix  in  the  names  of  compounds 
belonging  to  the  same  series  is  etymologically  reprehensible.  If, 
for  instance,  the  compound  of  tin  (SnS)  be  termed  the  protosul- 
fhide^  the  compound  (SnS^)  should,  in  order  to  preserve  consistency, 
be  termed  the  deutosulphide  / but  in  this  case  the  use  of  the  name 
bisulphide  is  so  generally  sanctioned  by  custom,  that  the  employ- 
ment of  the  term  deutosulphide  in  its  stead  would  have  a pedantic 
appearance. 

4.  Acids. — If  the  oxides  possess,  when  combined  with  the  ele- 
ments of  water,  acid  characters,  as,  for  example,  is  the  case  with 
some  of  the  higher  oxides  of  nitrogen,  a different  plan  is  adopted 
to  mark  this  important  peculiarity.  At  the  time  that  the  nomen- 
clature was  devised  by  Lavoisier  and  his  coadjutors,  oxygen  was 
considered  to  be  the  element  upon  whicli  the  existemje  of  the  acid 


Os  e 

Os  O2 
Os  O3 

Os  O4 


titles  of  the  two  acids  arc  not  really  equivalent  to  each  other,  inasmuch  as  one  of 
them  neutralizes  three  times  as  much  potassium  as  the  other. 

In  order,  therefore,  to  avoid  this  solecism,  and  at  the  same  time  to  secure  brevity 
in  our  descriptions,  it  will  be  convenient  to  speak  of  the  quantities  of  each  acid  above 
cited  as  an  airnn  of  their  respective  acids ; a term  warranted  by  the  fact  that  the  formula 
of  each  represents  the  simplest  expression  in  symbols  which  can  be  adopted  to  indicate 
the  smallest  particle  or  atom  of  the  compound  which  can  exist  in  a separate  form. 


4 


NOMENCLATUKE ACIDS. 


character  mainly  depended,  as  indeed  its  name  (signifying  gene- 
rator of  acids)  implies.  The  system  of  nomenclature  was  there- 
fore specially  adapted  to  this  idea.  It  frequently  happens  that  an 
element  forms  more  than  one  acid  with  oxygen  : the  compound 
which  contains  the  largest  proportion  of  oxygen  is  in  this  case 
indicated  hy  making  the  name  terminate  in  the  syllable  ISiitric 
acid  (HISrOg),  for  instance,  is  the  acid  of  nitrogen  in  which  the 
largest  quantity  of  oxygen  is  found  : in  like  manner  sulphuric  acid 
(HgSO^)  is  the  most  highly  oxidized  acid  of  sulphur.  A second 
acid  which  contains  the  same  elements  united  with  a smaller  pro- 
portion of  oxygen  receives  a name  which  ends  with  the  syllable 
ov^s : thus  nitrous  acid  (HllOg),  and  sulphurous  acid  (HgSOg) 
indicate  acids  in  which  a smaller  proportion  of  oxygen  is  present 
than  in  nitric  and  sulphuric  acids.  In  a few  cases  an  acid  has 
been  discovered  which  contains  still  more  oxygen  than  the  one  to 
which  the  termination  io  had  been  already  appropriated.  Chloric 
acid,  for  example,  is  represented  as  (HClOg),  but  an  acid  was  sub- 
sequently found  to  exist,  which  has  the  composition  (ITCIO^) ; in 
this  case  the  prefix  jyer  (which  is  an  abbreviation  for  u-rsp,  or 
super^  above)  is  employed,  the  new  compound  having  been 
termed  perchloric  acid.'^  When  an  acid  is  known  in  which  the 
proportion  of  oxygen  is  smaller  than  that  which  exists  in  the 
compound  to  which  the  termination  ous  has  been  appropriated, 
the  prefix  hypo  (from  u-tto  below)  is  usually  employed — for 
instance,  chlorous  acid  consists  of  IlClOg,  whilst  the  compound 
HCIO,  with  a still  smaller  amount  of  oxygen,  is  known  as  hypo- 
chlorous  acid. 

The  progress  of  research,  however,  has  revealed  other  acids  in 
which  oxygen  is  wanting,  but  which  are  compounds  of  hydrogen. 
These  acids  are  usually  distinguished  by  prefixing  the  word  hydro,, 
as  an  abbreviation  for  hydrogen:  thus  chlorine  and  hydrogen 
form  an  acid,  HCl,  hydrochloric  acid,  often  called  muriatic  acid : 
cyanogen  and  hydrogen  form  hydrocyanic  or  prussic  acid,  HCy, 
and  so  on.  Some  writers,  following  the  example  of  Thenard, 
transpose  these  terms : they  speak  of  chlorhydric  acid,  and  cyan- 
hydric  acid.  There  is  an  advantage  in  this  alteration,  since  it 
avoids  any  ambiguity  arising  from  the  use  of  the  prefix  hydro,, 
which  has  in  some  instances  been  applied  to  compounds  which 
contain  water. 

5.  Salts. — When  the  acids  by  their  action  upon  bases  form 
salts,  the  degree  of  oxidation  in  the  acid  is  still  indicated  by  the 

* The  term  acid  has  been  employed  by  chemical  writers  up  to  a late  period,  to 
designate  indifferently  either  the  anhydrous  bodies  formed  by  the  union  of  oxygen 
with  the  non-metallic  elements,  such  as  €^2  and  SO3  (now  more  commonly  termed 
anhydrides^  or  bodies  destitute  of  hydrogen),  or  the  hydrated  compounds  produced 
by  the  action  of  water  upon  the  anhydrides,  such  as  H2SO4,  oil  of  vitriol  or  sulphuric 
acid.  To  avoid  this  confusion,  produced  by  the  application  of  the  same  term  to  two 
substances  essentially  distinct,  it  will  be  convenient  to  follow  the  practice  of  many 
later  authors,  and  to  limit  the  term  acid  to  those  hydrated  bodies  which  are  really 
salts  of  hydrogen : II2SO4  is  then  true  sulphate  of  hydrogen,  or  sulphuric  acid ; 
HNO3  nitrate  of  hydrogen,  or  nitric  acid;  H^2H302  acetate  of  hydrogen,  or  acetic 
acid,  and  so  on. 


NOIilENCLATURE SALTS. 


O 


name  of  the  salt.  The  name  of  the  acid  stands  first  as  generic, 
the  name  of  the  metal  or  base  being  added  to  show  the  species. 

When  acids  ending  in  ic  form  salts,  in  naming  such  com- 
pounds the  termination  of  the  acid  is  changed  into  ate : thus  the 
salt  formed  by  the  action  of  nitric  acid  upon  lime  is  termed 
nitrate  of  lime,  or  frequently  nitrate  of  calcium  (-GajNOg).  When 
sulphuric  acid  acts  upon  oxide  of  iron,  the  salt  produced  is  called 
sulphate  of  protoxide  of  iron,  or  usually  sulphate  of  iron  (FeSO^) : 
perchloric  acid  by  its  action  upon  potash  furnishes  the  salt  called 
perchlorate  of  potassium  (KClOj.  If  the  name  of  the  acid  end 
in  ous^  the  termination  is  changed  to  ite  in  naming  the  salt ; thus 
sulphurous  acid  and  baryta  by  their  mutual  action  form  a salt 
called  sulphite  of  barium  (fiaSOg) : hypochlorous  acid  and  soda 
by  their  mutual  action  form  hypochlorite  of  sodium  (KaClO). 

It  may  here  be  well  to  caution  those  who  are  just  commencing 
the  study  of  chemistry,  of  the  necessity  of  distinguishing  clearly 
between  compounds  such  as  the  sulpln’i^(?5  and  the  sulpha?'^?^,  or 
the  sulph^c?^5  and  the  sulph^’z^^^.  Sulphide  of  sodium  (Jla^S),  for 
example,  is  a binary  compound,  containing  a direct  product  of 
the  combination  of  two  elementary  substances,  whereas  sul]3hite 
of  sodium  (Ha^SOg)  is  a more  complex  compound  formed  by  the 
action  of  two  compound  bodies  upon  each  other.  Sulphate  of 
sodium  (KagSOJ,  again,  contains  one  proportional  more  of  oxygen 
than  the  sulphite  of  this  metal. 

If  more  than  one  equivalent  of  the  radicle  of  an  acid  be  united 
with  one  equivalent  of  a metal,  there  is  no  difhculty  in  pointing 
this  out  in  the  name.  A compound  of  two  equivalents  of  sul- 
phuric acid  radicle  and  two  of  potassium  (KgSOJ  would  be 
spoken  of  simply  as  sulphate  of  potassium  ; but  there  is  another 
compound  of  potassium  with  sulphuric  acid,  in  which  two  equiva- 
lents of  the  acid  radicle  are  present  to  one  equivalent  of  the 
metal ; this  compound  is  commonly  known  as  the  bisulphate  of 
potash,  or  acid  sulphate  of  potassium  (KIIS0-J ; the  circum- 
stance of  the  additional  equivalent  of  acid  being  in  this  and  in 
other  analogous  cases  often  indicated  by  the  prefix  hi^  (from  the 
Latin  twice,)  which  is  made  to  precede  the  name  appropri- 
ated to  the  neutral  salt. 

Generally  speaking,  a metal  forms  only  one  basic  oxide — ^that 
is  to  say,  only  one  oxide  which  has  the  power  of  forming  salts  by 
interaction  with  acids;  but  there  are  several  exceptions  to  this 
rule.  Iron,  for  example,  may  form  salts  corresponding  to  the 
protoxide  (FeG).  Such  salts  are  frequently  distinguished  asy^rr;- 
tosalts:  (Fe0,S03.II0,6II0),  or  (FeSe,.IIgO,6Ii;G),  represents 
the  composition  of  the  crystallized  sulphate  of  protoxide  of  iron, 
often  described  as  protosulphate  of  iron  ; but  there  is  another 
series  of  salts  of  iron  derived  from  the  peroxide  or  sesquioxide 
(POgOg)  of  the  metal ; these  are  distinguished  as  the  jper salts ^ or 
sesqulsalts^  of  iron:  (FegOg,8SOg),  or  \Peg3S0-,),  represents  the 
sulphate  of  the  peroxide  (or  sesquioxide)  of  iron,  and  it  is 
frequently  termed  tlie  persulphate,  or  sesquisulphate  of  iron. 
Tliese  terms,  although  in  general  use,  are  not  free  from  ambi- 


6 


EMPIRICAL  AND  RATIONAL  FORIMIJLJE. 


guity.  Berzelius  preferred  to  call  the  protoxide  of  iron,  ferrous 
oxide,  and  the  protosulphate,  ferrous  sulphate,  whilst  the  sesqui- 
oxide  he  termed  ferric  oxide,  and  the  sesquisulphate  was  upon 
his  plan  called  ferric  sulphate.  This  form  of  nomenclature  unites 
brevity  with  precision,  and  may  frequently  be  employed  with 
advantage. 

Other  forms  of  nomenclature  are  applied  in  particular  cases, 
but  these  will  be  best  explained  as  the  examples  to  which  they 
refer  arise. 

(332)  Empirical  and  Rational  Formulce. — In  expressing  the 
composition  of  a body  by  the  use  of  symbols,  the  chemist  may 
either  content  himself  with  simply  stating  the  result  of  analysis 
by  a mere  enumeration  of  the  elements  and  the  relative  number 
of  proportionals  of  each ; in  which  case  he  gives  what  is  termed 
the  empirical  formula  of  the  body ; or  he  may  attempt  an  ex])la- 
nation  of  the  mode  in  which  he  conceives  those  elements  to  be 
associated  together,  and  by  the  arrangement  of  his  symbols  may 
give  expression  to  a theory  of  the  constitution  of  the  body,  and 
thus  assign  to  it  a rational  formula.  A body  can  have  but  one 
empirical  formula,  but  it  may  be  represented  by  a variety  of 
rational  formulse,  according  to  the  different  views  which  may  be 
taken  as  to  the  mode  in  which  its  components  are  arranged. 

Crystalhzed  sulphate  of  magnesium,  for  example,  adopting  the 
new  notation,  has  the  following  empirical  formula : — 

(1)  MgH„Se„ ; 

that  is  to  say,  its  constituents  are  present  in  the  ratio  of  1 atom 
of  magnesium,  14  of  hydrogen,  1 of  sulphur,  and  11  of  oxygen.  It 
is,  however,  never  so  written.  The  water  wffich  it  contains  may 
be  entirely  driven  off  by  a heat  a little  above  400°  F. ; and  it  is 
usually  represented  as  consisting  of  magnesia,  sulphuric  anhy- 
dride, and  water,  as  these  are  the  materials  out  of  which  it  is 
formed:  thus — 

(2)  MgO,  SO3  . 711,0. 

But  it  is  found  that  at  a heat  of  212°,  6 atoms  of  the  water  may 
be  expelled,  whilst  the  seventh  atom  requires  a much  higher 
temperature,  so  that  it  appears  to  occupy  a position  in  the  salt 
different  from  that  of  the  other  6 ; this  fact  may  be  indicated  by 
slightly  altering  the  second  formula,  as  follows : 

(3)  MgO,  SO3  . II,0,6H,0. 

Many  chemists,  however,  guided  partly  by  the  results  of  the 
electrolysis  of  the  salt,  suppose  that  when  once  an  acid  and  a 
base  have  reacted  on  each  other,  their  elements  are  arranged  in 
an  order  different  from  that  in  which  they  existed  when  separate, 
and  they  prefer  to  represent  the  salt  accordingly,  as 

(4)  Mg,SO, . 11,0,  6H,0. 

Each  of  the  last  three  formulje  is  a rational  formula  for  sul- 
phate of  magnesium ; and  each  conveys  far  more  information 
than  the  formula  Ko.  1.  Each  represents  a theory  founded  upon 


GENERAL  ARRANGE]VIENT  OF  THE  ELEMENTS.  T 

particular  modes  of  decomposition  which  the  salt  may  be  made 
to  experience. 

It  is  impossible  that  all  these  formulse  should  truly  indicate 
the  molecular  constitution  of  the  salt,  though  each  may  represent 
the  grouping  of  its  component  elements  under  particular  circum- 
stances. Rational  formulae  are  indeed  indispensable  as  the  expo- 
nents of  the  theories  which  guide  the  chemist  in  his  researches, 
or  which  aid  him  in  arranging  and  interpreting  phenomena ; but, 
like  the  theories  which  they  represent,  they  are  only  temporary 
expedients,  and  they  must  consequently  always  be  regarded  as 
such,  and  must  be  modified  or  discarded  when  they  no  longer 
faithfully  represent  the  conditions  of  our  knowledge  of  the  com- 
pounds which  they  are  employed  to  indicate.  A perfect  rational 
formula  would  embrace  all  the  modes  of  decomposition  of  which 
a compound  is  susceptible,  and  would  represent  the  constitution 
of  the  body  as  well  as  its  various  analogies  and  relations. 

(333)  U-eneral  Arrangement  of  the  Elements  adojpted  in  this 
Work. — The  general  division  of  the  elementary  bodies  into  non- 
metallic  and  metallic  has  been  already  pointed  out.  There  is, 
however,  no  strict  line  of  demarcation  between  the  non -metallic 
and  the  metallic  elements. 

The  bodies  which  are  considered  as  noii-metallic  constitute 
the  electro-negative  ingredient  in  the  binary  combinations  which 
they  form  with  the  metals,  and  are  most  of  them  insulators  of  the 
voltaic  current.  Carbon  and  silicon,  however,  in  certain  forms, 
act  as  conductors  of  electricity.  The  compounds  of  the  non- 
metallic  elements  with  oxygen  generally  show  but  little  tendency 
to  unite  with  acids  ; on  the  contrary,  the  higher  oxides  of  most 
of  them  form  compounds  which,  if  acted  on  by  water,  furnish 
powerful  acids.  These  acid-forming  oxides,  except  silica,  are 
readily  soluble  in  water ; and  even  silica,  under  certain  circum- 
stances, may  be  obtained  in  solution. 

The  metals,  on  the  other  hand,  are  characterized  by  a peculiar 
combination  of  opacity  and  compactness,  which  gives  them,  when 
polished,  a peculiar  brilliancy,  termed  the  metallic  lustre ; they 
are  good  conductors  of  heat  and  electricity,  and  most  of  them,  by 
combination  with  oxygen,  form  powerful  bases.  It  is,  neverthe- 
less, sometimes  difficult  to  determine  whether  a body  should  be 
regarded  as  a metal  or  not.  Arsenicum  has  a high  metallic 
lustre  ; but  it  is  more  closely  allied  to  phosphorus  than  to  any 
other  elementary  substance,  and  both  its  oxides,  when  dissolved 
in  water,  are  endowed  with  well-marked  acid  properties.  Tellu- 
rium also  exhibits  the  closest  analogy  with  selenium  and  with 
sulphur,  but  it  possesses  high  lustre,  and  some  conducting  power 
for  electricity. 

The  subdivision  of  the  simple  substances  into  non-metallic 
and  metallic  is,  however,  convenient  to  the  student,  and  it  will 
therefore  be  retained  in  this  work.  The  order  in  wliich  the 
different  elementary  bodies  will  be  treated  is  not  in  all  cases  that 
which  a rigid  adherence  to  analogy  would  indicate,  though  this 
has  been  adopted,  excepting  in  those  instances  in  which  it  seemed 


8 


GENERAL  ARRANGEMENT  OF  THE  ELEMENTS. 


more  advantageons  to  the  student  to  follow  a different  course. 
In  most  cases  we  shall  first  examine  the  chemical  properties 
which  are  exhibited  bj  each  of  the  elements  in  its  uncombined 
form ; we  shall  then  study  the  general  nature  of  its  actions  upon 
other  elements,  and  shall  afterwards  examine  the  more  important 
compounds  into  the  formation  of  which  it  enters. 

In  describing  the  properties  of  the  non-metallic  elements,  it 
will  be  found  a convenient  arrangement  to  consider  first  the  four 
elements  which  enter  into  the  composition  of  those  all-pervading 
and  all-important  substances,  air  and  water,  and  then  to  pass  on 
to  others,  classing  them  together  according  to  the  general  analogy 
of  theii’  properties.  Following  this  plan,  we  shall  consider  first 
the  properties  of  what  may  be  termed  the  atawspheric  group  of 
elements — viz.,  oxygen ; nitrogen  (and  the  atmosphere)  ; hydrogen 
(and  water)  ; carbon  (and  carbonic  acid). 

We  shall  next  examine  some  of  the  more  important  compounds 
which  these  bodies  form  with  each  other,  and  shall  then  describe 
the  well-marked  natural  group  constituting  what  Berzelius  termed 
the  Halogens^  from  the  circumstance  of  their  forming  with  the 
metals  saline  compounds  resembling  common  salt ; this  group 
comprises  chlorine,  bromine,  iodine,  and  fiuorine. 

Three  combustible  elements  will  be  taken  next  in  order — viz., 
sulphur,  selenium,  and  tellurium  : these  will  be  followed  by  phos- 
phorus, and  the  general  survey  of  the  non-metallic  elements  will 
be  completed  with  silicon  and  boron. 

For  the  convenience  of  description  and  of  reference,  the  metals 
will  be  arranged  in  eight  groups,  in  the  following  order.  The 
elements  which  compose  each  group  generally  present  some  natu- 
ral resemblance,  though,  as  already  stated,  the  classification  does 
not  in  all  cases  bring  "together  those  which,  in  chemical  habitudes, 
are  really  the  most  closely  allied. 


I.  Metals  of  the  Alkalies — 5 in  nuniber. 


1.  Potassium. 

2.  Sodium. 


3.  Lithium. 
L Coesium. 


5.  Pubidium. 


II.  Metals  of  the  Alkaline  Earths — 3 in  numher. 


1.  Barium.  | 2.  Strontium.  | 3.  Calcium. 


III.  Metals  of  the  Earths — 10  in  numher. 


1.  Aluminum. 

2.  Glucinum. 

3.  Zirconium. 

4.  Thorinum. 


5.  Yttrium. 

6.  Erbium. 

7.  Terbium. 


8.  Cerium. 

9.  Lanthanum. 

10.  Didymium. 


IV.  Magnesimi  Metals — 3 in  numher. 

1.  Magnesium.  | 2.  Zinc.  | 3.  Cadmium. 

Y.  Metals  rnare  or  less  analogous  to  Iron — 6 in  numher.  , 


1.  Cobalt. 

2.  FTickel. 


3.  Uranium.  5.  Chromium. 

4.  Iron.  6.  Manganese. 


GENERAL  ARRANGEMENT  OF  THE  ELEMENTS. 


9 


yi.  Metals  which  yield  Adds — 10  in  numher. 


1.  Tin. 

2.  Titaninm. 

3.  Columbium. 

4.  Tantalum. 


5.  Molybdenum. 

6.  Yanadium. 

7.  Tungsten. 

YII.  3 Metals. 


8.  Arsenic. 

9.  Antimony. 
10.  Bismuth. 


1.  Copper. 


2.  Lead. 


3.  Thallium. 


YIII.  Noble  Metals — 9 in  number. 


1.  Mercury. 

2.  Silver. 

3.  Gold. 


4.  Platinum. 

5.  Palladium. 

6.  Khodium. 


Y.  Kuthenium. 

8.  Osmium. 

9.  Iridium. 


If  a strictly  natural  order  were  to  be  followed  in  grouping  tlie 
elements,  it  would,  however,  be  necessary  to  modify  the  foregoing 
arrangement.  This  will  be  rendered  evident  by  pointing  out  the 
most  important  natural  groups  into  which  the  elementary  bodies 
admit  of  being  subdivided.  The  detailed  indication  of  the  points 
of  resemblance  between  the  members  composing  each  group  must 
be  deferred  until  the  properties  of  the  group  are  considered.  In 
many  instances  these  natural  relations  between  the  individual 
elements  thus  grouped  together  are  very  striking,  in  others  they 
are  more  obscurely  marked,  and  in  the  case  of  the  metals  of  the 
earths  proper,  as  well  as  of  the  noble  metals,  the  natural  chemical 
relations  of  these  elements  with  the  others  are  as  yet  but  incom- 
pletely known.  In  the  table  which  follows,  the  principal  elemen- 
tary bodies  are  represented  in  two  con  verging  series. 


Monads. 

Fluorine. 


Monads. 

Hydrogen. 


Chlorine. 

Bromine. 

Iodine. 


Dyads. 

Oxygen. 

Sulphur. 

Selenium. 

Tellurium, 


Triads. 

Nitrogen. 


Phosphorus. 

Arsenic. 

Antimony. 

Bismuth. 


Kuthenium. 

Khodium. 

Iridium. 

Gold. 


Boron. 


CoesiuLi. 

Kubidium. 

Potassium. 

Sodium. 

Lithium. 


Silver. 

Thallium. 


Barium. 

Strontium. 

Calcium. 


Dyads. 

Lead. 

Mercury. 


Magnesium. 

Zinc. 

Cadmium. 


Copper. 

Nickel. 

Cobalt. 


Iron. 

Chromium. 

Manganese. 

Uranium. 


10 


NON-METALLIC  ELEMEOTS. 


Teteads. 


Carbon. 


Silicon. 

Titanium. 

Tin. 

Zirconium. 

Niobium. 

Tantalum. 


Palladium. 

Platinum. 


DYADS. 

Cerium. 

Aluminum. 

Molybdenum. 

Yanadium. 

Tungsten. 


CHAPTEK  II. 

rmST  DIYISIOX. — non-metallic  elements. 

The  following  table  gives  a general  view  of  some  of  the  most 
important  of  the  constants  of  the  non-metallic  elements.  The 
squares  employed  in  the  column  headed  Atomic  Volume, ” indi- 
cate the  relative  volumes  occupied  by  a quantity  in  grains  of  each 
of  the  different  elements,  corresponding  to  the  numbers  given  in 
the  column  of  Atomic  Weights,”  assuming  that  the  space  occu- 
pied by  one  grain  of  hydrogen  under  similar  circumstances  of 
temperature  and  pressure,  would  hll  a space  of  one  square  or  one 
volume. 


TABLE  OF  NOX-METALLIC  ELEMENTS. 


1 Specific  gravity. 

1 

NAME. 

Symbol. 

Atomic 

weight 

Atomic 

vol. 

Gaseons. 

Fusing 
pt.  F° 

Boiling 
pt  F°. 

Solid. 

j Theory. 

Expt 

1 

Oxygen 

e 

16 

□ 

1-1056 

1-1056 

2 

Nitrogen 

N 

14 

□ 

0-9674 

0-9713 

3 

Hydrogen 

H 

1 

n 

0-0691 

0-0692 

4 

Carbon 

12 

? 

— 

— 

3-336 

never 

fused 

5 

Chlorine 

Cl 

35-5 

□ 

2-453 

2-47 

6 

Bromine 

Br 

80 

□ 

5-5281 

5-54 

3-187* 

9-5 

145-4 

1 

Iodine 

I 

121 

□ 

8 756 

8-716 

d-947 

225 

347 

8 

Fluorine 

F 

19 

□? 

1-313 

9 

Sulphur 

S 

32 

n 

2-2112 

2-2 

2-05 

239 

836 

10 

Selenium 

Se 

79-5 

□ 

5-486 

6-37 

4-788 

423 

5 below 

1 rnioess 

11 

Tellurium 

Te 

129 

□ 

8-913 

9-00 

6-65 

J above 
(800 

? 

12 

Phosphorus 

P 

31 

D 

4-284 

4-42 

1-83 

111-5 

550 

13 

Sihcon 

Si 

28 

? 

— 

— 

2-49 

? 

14 

Boron 

B 

10-9 

? 

— 

“ 1 

2-68 

? 

* Sp.  gr.  of  liquid  at  32°. 


COMPOUND  NATURE  OF  THE  ATMOSPHERE. 


11 


THE  ATMOSPHERE.  OXYGEN NITROGEN. 

(334)  Compound  Nature  of  the  Atmosphere. — The  chemical 
researches  of  the  philosophers  of  the  last  century  are  especially 
remarkable  on  account  of  the  important  information  which  they 
afforded  upon  the  nature  of  the  atmosphere.  Indeed,  the  know- 
ledge thus  obtained  may  be  regarded  as  the  starting-point  of  the 
brilliant  chemical  discoveries  which  have  since  succeeded  each 
other  with  such  rapidity.  These  researches  have  abundantly 
proved  that  the  air  is  far  from  being,  as  it  was  once  supposed  to 
be,  an  elementary  body.  It  has  been  found,  on  the  contrary,  to 
be  a mixture  of  several  substances,  some  of  which  are  elementary, 
others  (compound. 

The  most  remarkable  and  abundant  of  the  constituents  of  the 
air  are  the  elementary  bodies,  oxygen  and  nitrogen ; and  of  its 
compound  ingredients,  the  most  important  are  aqueous  vapour 
and  carbonic  acid,  or  rather  carbonic  anhydride,  as  it  must  be 
called,  in  order  to  preserve  consistency  in  our  nomenclature. 

The  most  direct  proofs  of  the  compound  character  of  the 
atmosphere  are  afforded  by  examining  the  effects  produced  upon 
it  by  burning  bodies.  Bodies,  as  is  well  known,  cannot  burn 
without  the  free  access  of  air.  On  placing  a lighted  taper  under 
the  receiver  of  the  air-pump  and  exhausting  the  air,  the  flame 
becomes  extinguished.  A limited  quantity  of  air  will  support 
combustion  for  but  a limited  period  : a lighted  taper  floating  on 
water  under  an  inverted  bell-glass,  the  edge  of  which  is  plunged 
beneath  the  water,  soon  begins  to  burn  dimly,  and  at  length 
becomes  extinct.  But  the  taper  ceases  to  burn  long  before  the 
air  is  all  spent ; the  receiver  still  contains  a large  quantity  of  a 
gaseous  body  in  which  a candle  will  not  burn.  The  results 
obtained  by  burning  a candle  in  a limited  portion  of  air  are,  how- 
ever, rather  complicated,  because  the  products  which  are  formed 
by  the  burning  body  rise  in  the  form  of  gas,  and  become  mixed 
with  the  remaining  portion  of  air.  Lavoisier  contrived  to  obviate 
this  inconvenience  by  acting  upon  the  air  with  a substance  which 
produced  a solid  body  as  the  result  of  the  chemical  action,  so  that 
it  left  the  air  unmixed  with  any  gas  which  rose  from  the  burning 
body.  The  material  which  he  employed  to  decompose  the  air 
was  metallic  mercury,  a substance  which  acts  very  slowly,  and 
which  does  not  burn  in  the  ordinary  sense  of  the  term.  The 
experiment  may  be  performed  as  follows  : — 

Into  the  bulb  of  a flask  or  retort  (a,  flg.  266),  provided  with  a 
neck  of  considerable  length,  an  ounce  or  two  of  metallic  mercury 
is  introduced : the  neck  of  the  flask  is  then  bent  in  the  manner 
shown  in  the  figure,  and  the  bent  portion  plunged  into  a mercu- 
rial bath,  so  as  to  leave  the  open  end  of  the  neck  projecting  above 
the  level  of  the  mercury,  into  a jar  partially  filled  with  atmos- 
pheric air.  The  bulk  of  this  portion  of  air  is  then  accurately  ob- 
served, and  the  temperature  and  barometric  pressure  at  the  time 
of  the  observation  are  recorded.  Heat  is  now  applied  to  the 


12 


PEOPERTIES  OF  OXYGEN. 


flask,  and  maintained  steadily  at  a point  jnst  below  that  required 
to  make  the  mercury  boil.  If  this  temperature  be  continued 

for  three  or  four 
consecutive  days, 
the  air  inclosed 
both  in  the  flask 
and  in  the  jar 
will  participate  in 
the  action.  The 
mercury  in  the 
flask  will  gradual- 
ly become  cover- 
ed with  red  scales, 
and  the  air,  which 
at  first  expanded 
from  the  action  of 
the  heat,  and  de- 
pressed the  level 
of  the  mercury  in 
the  jar,  will  slow- 
ly decrease  in  bulk  until  fresh  scales  no  longer  continue  to  be 
formed.  When  this  point  is  reached,  the  source  of  heat  may  be 
removed,  and  the  remaining  air,  when  cold,  wdll  be  found  to  mea- 
sure about  one-fifth  less  than  it  did  at  the  commencement.  If  a 
portion  of  this  residual  air  be  decanted  into  another  jar,  it  will  be 
found  to  be  unfit  for  the  support  of  animal  life  ; a mouse  or  other 
small  animal  introduced  into  it  speedily  dies,  and  the  flame  of  a 
candle  is  instantly  extinguished.  The  gas  which  has  been  thus 
obtained  is  an  elementary  body,  nearly  in  a state  of  purity, 
termed  nitrogen  (339).  In  this  experiment  the  heated  mercury 
has  been  slowly  effecting  the  removal  of  the  oxygen  from  the  air. 

§ I.  Oxygen.  O = 16  ; Atomic  Yol.  ; Molecule  in  free  state  ^ 
OO  III;  (0=8)  S^pecific  GrciA)ity^  1T056.* 

(335)  If  the  red  scales  which  are  formed  upon  mercury  when, 
as  in  the  foregoing  experiment,  it  is  heated  in  a confined  portion 
of  air,  be  introduced  into  a small  glass  retort  and  exposed  to  a 
strong  heat,  they  will  gradually  disappear  ; drops  of  mercury  will 
become  condensed  in  the  cool  part  of  the  retort,  and  a gas  will  be 

* In  tlie  former  editions  of  this  work,  in  accordance  with  general  usage,  the 
symbol  for  oxygen  has  been  taken  as  0 = 8,  and  the  volume  occupied  by  8 parts  by 
weight  of  oxygen  has  been  employed  as  the  unit  of  gaseous  volume.  The  arguments 
of  Gerhardt,  and  the  progress  of  research,  however,  seem  conclusively  to  indicate 
that  the  number  for  the  atomic  weight  of  oxygen  should  be  doubled,  if  that  of 
hydrogen  remain  unaltered.  Consequently  an  extensive  change  in  notation,  and 
indeed  in  the  interpretation  of  chemical  phenomena  generally,  becomes  necessary. 

If  the  atomic  weight  of  oxygen  be  represented  as  O = 16,  the  molecule  of  free 
oxygen  will  be  (0O) ; the  atomic  weight  of  hydrogen  being  (11=1).  the  molecule  of 
free  hydrogen  will  be  (HH),  occupying  the  same  volume  as  a molecule  of  oxygen ; 
and  the  molecular  weight  of  water  will  be  H2O  =18,  instead  of  HO  = 9.  The  mole- 
cular volume  of  compounds  wiU,  unless  specifically  stated  to  be  otherwise,  bo  repre- 
sented uniformly  by  2 volumes  instead  of  by  the  anomalous  method  of  representing 


PKOPEKTIES  OF  OXYGEN. 


13 


disengaged,  wliicli  may  be  collected  over  water.  If  the  experiment 
be  performed  with  accuracy  the  quantity  of  the  gas  obtained  wdll 
be  exactly  equal  in  volume  to  the  bulk  absorbed  from  the  air  by  the 
mercury.  To  this  gas  the  name  of  Oxygen  (generator  of  acids, 
from  sour,  and  yswaw  to  produce)  has  been  given.  It  is  an 
elementary  body,  and  from  the  abundance  in  which  it  occurs,  the 
number  and  the  variety  of  its  compounds,  and  the  necessary  part 
whicli  it  performs  in  the  maintenance  of  life,  it  must  be  regarded 
as  the  most  remarkable  and  important  of  the  simple  bodies. 

Properties. — Oxygen  possesses  extremely  powerful  chemical 
attractions  for  other  elementary  substances  ; one  element  only 
(fluorine)  being  known  with  which  it  does  not  combine.  Owing 
to  the  intensity  with  which  many  of  these  combinations  take 
place,  oxygen  gas  possesses  the  power  of  supporting  combustion 
in  an  eminent  degree.  If  a splinter  of  wood  with  a glowing  spark 
on  any  part  of  it  be  plunged  into  the  gas,  the  wood  will  instantly 
burst  into  flame,  and  will  burn  with  extraordinary  brilliancy. 
Many  bodies  which  burn  tranquilly  in  air  often  deflagrate  witli 
violence  in  oxygen.  Phosphorus  burns 
in  it  with  a brilliancy  which  is  painful 
to  the  eye,  and  in  like  manner  sulphur 
and  charcoal,  if  previously  kindled,  burn 
in  the  gas  with  great  vehemence  : many 
metals  also  burn  vividly  in  it ; a piece 
of  potassium  of  the  size  of  a pea,  if 
placed  in  a small  copper  spoon,  c,  fig. 

267,  and  heated  strongly  by  a spirit 
lamp,  bursts  into  flame  when  plunged 
into  the  gas;  if  a piece  of  German 
tinder  be  attached  to  a piece  of  watch- 
spring  or  thin  steel  wire  and  be  lighted, 
to  start  the  combustion  before  it  is  intro- 
duced into  the  oxygen,  the  wire  will  burn  with  brilliant  scintilla- 


Fig.  267. 


» some  compounds  by  2-,  others  by  4-volume  formulm,  as  heretofore  practised,  in  the 
various  equations  by  which  chemical  reactions  are  represented. 

Molecular  formulae  will  always  be  employed  where  it  is  practicable.  Such  molecu- 
lar formula*-  will  indicate  quantities  of  each  compound  the  volumes  of  wdiich  amount 
to  double  the  combining  volume  of  hydrogen,  if  H — 1 ; as  for  example : — 


Free  oxygen ... 

Equal 

vols. 

O0 

Molecular 

weight. 

32 

Free  hydrogen 

HH 

2 

Free  chlorine 

. . . ClCl 

71 

Free  nitrogen 

NN 

rr 

28 

Hydrochloric  acid 

HCl 

— 

36-5 

Steam 

. . . H2e 

18 

Sulphuretted  hydrogen 

lis 

= 

34 

Seleniuretted  hydrogen 

. . . Il2Se 

81-5 

Oxygen  belongs  to  a class  of  elements  including  sulphur,  selenium,  and  tellurium, 
which  may  be  termed  electro-negative  dyads.  They  are  characterized  by  their  power 
of  uniting  each  with  twice  its  volume  of  hydrogen,  furnishing  a gaseous  compound 
in  which  the  three  volumes  are  condensed  into  the  space  of  two ; one  atom  of  the  ele- 
ments belonging  to  this  group  may  bo  said  to  be  equivalent  in  combination  to  two 
atoms  of  hydrogen  or  of  the  halogens.  The  molecule  of  these  elements  contains  2 
atoms  ; e.g.  SS  or  S2=G4,  the  molecule  of  sulphur ; Se2=  159,  the  molecule  of  selenium. 


14 


PREPARATION  OF  OXYGEN. 


tioiis ; and  zinc  foil,  tipped  with  sulphur  and  kindled,  burns  in 
oxygen  with  an  intense  bluish  white  light. 


»xygen  is  essential  to  the  support  of  animal  life,  and  hence 
by  the  older  chemists  was  termed  mtal  air.  A small  animal  will 
live  in  a confined  space  filled  with  oxygen  for  a longer  period  than 
in  an  equal  bulk  of  air  ; but  the  gas  is  of  too  stimulating  a quality  to 
be  breathed  undiluted  with  impunity  for  any  considerable  time,  and 
before  long  it  produces  death  from  over-excitement  of  the  system. 

Oxygen,  like  air,  is  destitute  of  color,  taste,  and  smell.  Of 
all  known  substances  it  exerts  the  smallest  refracting  power  upon 
the  rays  of  light.  Hitherto  all  attempts  to  reduce  it  to  the  liquid 
form  by  the  combined  application  of  pressure  and  of  cold  have 
proved  fruitless.  Oxygen  has  been  proved  to  possess  weak  but 
decided  magnetic  properties,  like  those  of  iron,  and  like  this  sub- 
stance its  susceptibility  to  magnetization  is  diminished,  or  even 
temporarily  suspended,  by  a sufficient  elevation  of  temperature 
(325).  It  is  heavier  than  the  atmosphere,  its  specific  gravity, 
according  to  Regnault,  being  1*10563  ;*  100  cubic  inches  weigh- 
ing 34*203  grains  ; it  is  only  slightly  soluble  in  water,  which  takes 
up  about  of  its  bulk,  at  32°,  and  at  60°  ; 100  cubic  inches 
of  water,  according  to  Bunsen,  dissolving  4*11  cubic  inches  at 
32°,  and  2*99  cubic  inches  at  59°  F. 

Prejparation. — There  are  several  methods  of  procuring  oxygen 
gas,  the  simplest  of  which  consist  in  the  exposure  of  certain  metallic 
oxides  to  a high  temperature,  by  which  they  are  made  to  give  up, 
more  or  less  completely,  the  oxygen  with  wdiich  the  metals  had 
combined. 

1.  — The  original  method  of  Priestley,  by  which  he  first  isolated 
pure  oxygen,  in  17Y4,  consisted  in  heating  the  red  oxide  of  mer- 
cury to  700°  or  800°,  2 HgO  yielding  2 Hg  + O^ ; but  there  are 
other  modes  of  procuring  it  which  are  more  convenient  and  eco- 
nomical. 

2.  — For  the  supply  of  large  quantities  of  oxygen  it  is  usual  to 
employ  the  black  oxide  of  manganese  (MnO^)?  a mineral  which  at 
a red  heat  parts  with  one-third  of  the  oxygen  which  it  contains, 
whilst  a reddish-brown  oxide  of  manganese  remains  behind  ; 
3 MnO^  giving  MngO^  -f  Og.  The  mineral  must  be  reduced  to  small 
fragments  of  about  the  size  of  a pea,  and  introduced  into  an  iron 

268,  to  the  neck  of  which  an  iron  pipe  is  fitted  by 

grinding ; the 
Fig.  268.  bottle  is  heated 

in  a furnace, 
and  the  gas  is 
conveyed  to  the 
gas  - holder  by 
means  of  a piece 
of  flexible  me- 
tallic piping  of  suitable  length.  As  the  oxide  of  manganese 
usually  contains  water  as  well  as  a portion  of  nitrates  and  some 

* Dumas  and  Boussingault  found  the  density  of  oxygen  almost  exactly  the  same 
as  that  given  above — viz.  1-1057  ; De  Saussure  states  it  to  be  1-1056. 


bottle,  fig. 


PREPAKATION  OF  OXYGEN. 


15 


carbonate  of  calcium,  tlie  first  effect  of  heat  is  to  drive  off  a quan- 
tity of  steam  mixed  with  a gas  which  consists  principally  of  car- 
bonic anhydride  mixed  with  nitrogen,  which  last  gas,  liowever, 
usually  is  driven  off  at  a later  period,  and  contaminates  the  oxygen 
often  to  the  extent  of  5 or  6 per  cent.  When  the  gas  that  comes 
off  rekindles  a glowing  match,  it  may  be  collected  for  use.  Black 
oxide  of  manganese,  when  pure,  furnishes  about  one-ninth  of  its 
weight  of  oxygen  ; but  as  met  with  in  commerce  it  seldom  yields 
more  than  half  this  quantity,  a pound  giving  off  about  1400  cubic 
inches  of  the  gas. 

3. — A supply  of  very  pure  oxygen  may  also  be  obtained  readily 
by  the  action  of  heat  upon 
the  salt  known  as  chlorate 
of  potash,  or,  as  it  should 
be  called,  to  be  consistent, 
chlorate  of  potassium ; 

200  or  300  grains  of  this 
salt  may  be  heated  over 
a gas  fiame  or  a charcoal 
fire,  in  a green  glass  re- 
tort or  in  a Florence 
flask,  F (fig.  269),  fur- 
nished with  a cork  which 
is  adapted  to  a bent  tube 
for  delivering  the  gas ; 
the  salt  fuses  at  a heat 
below  redness,  and  at  a 
temperature  a little  above 
its  melting  point  emits  a 
large  quantity  of  gas,  which  may  be  collected  in  jars  over  water 
in  the  pneumatic  trough,  or  it  may,  if  not  wanted  for  immediate 
use,  be  stored  up  in  a gas-holder  (39).  If  a jar  of  the  gas  be 
closed  with  a glass  plate  it  may  readily  be  inverted,  as  at  a,  fig. 
270,  and  its  power  of  supporting  combustion  tested  by  a taper,  as 
shown  at  b.  The  oxygen  furnished  by  chlorate  of  potassium 
amounts  to  more  'han  one- 
third  of  the  weight  of  the 
salt  used;  1 ounce  of  the 
crystals  should  yield  about 
512  cubic  inches,  or  nearly 
2 gallons  of  the  gas.  Chlo- 
rate of  potassium  is  a com- 
pound of  chloric  acid  radi- 
cle with  potassium  (KClOg); 
when  heated  sufficiently, 
the  salt  is  decomposed,  and 
gives  up  all  its  oxygen  in 
the  gaseous  form,  whilst  the  chlorine  and  potassium  unite,  aud 
constitute  the  white  salt  which  remains  in  the  retort  when  the 
operation  is  over.  The  change  may  be  thus  represented  in  S3"m- 
bols:  2KCie3=2KCl-h3eg. 


Fig.  270. 


16  PEEPAEATION  OF  OXYGEN  FKOM  CHLORATE  OF  POTASSIUM. 


4. — When  tlie  quantities  of  chlorate  employed  are  rather  large, 
the  heat  required  is  apt  to  soften  the  glass  of  the  flask  in  which  it 
is  decomposed.  It  has,  however,  been  found  that  many  metallic 
oxides,  if  mixed  in  flne  powder  with  the  pulverized  chlorate  in  a 
proportion  of  not  less  than  one  part  to  ten  of  the  salt,  cause  the 
expulsion  of  the  gas  at  a much  lower  temperature,  ranging  between 
450°  and  500°  F.,  although  such  oxides  have  not  been  proved  to 
experience  any  chemical  change  during  the  operation  (1008).  It 
is  therefore  convenient  in  practice  to  mix  the  chlorate  of  potassium 
with  about  a fourth  of  its  weight  of  black  oxide  of  copper  (-BuO) 
or  of  oxide  of  manganese,  that  has  been  previously  heated  to  red- 
ness and  allowed  to  cool.  The  gas  which  is  obtained  in  this  way 
always  contains  traces  of  chlorine,  and  the  heat  must  be  carefully 
watched,  as  at  a particular  point  the  oxygen  is  disengaged  with 
very  great  rapidity. 

Oxygen  may  be  obtained  from  various  other  substances,  but 
those  already  mentioned  are  the  best,  and  are  the  materials  most 
frequently  employed.  Fed  lead,  and  the  peroxides  of  most  of  the 
metals,  such  as  those  of  silver  and  lead,  as  well  as  the  nitrates  of 
potassium,  sodium,  and  barium,  when  heated  strongly,  furnish  the 
gas ; it  may  also  be  obtained  by  heating  chloride  of  lime  or 
bleaching  powder ; and  a mixture  of  sulphuric  acid  in  its  concen- 
trated form,  with  half  its  weight  of  powdered  oxide  of  manganese, 
or  of  acid  chromate  of  potassium,  may  also  be  made  use  of  by 
applying  heat  to  the  materials  placed  in  a glass  retort.* 

* Acid  chromate  of  potassium  and  sulphuric  acid  when  heated  together  undergo 
a decomposition,  in  consequence  of  which,  oxygen,  acid  sulphate  of  potassium,  and 
sulphate  of  chromium  are  produced.  This  change  may  be  represented  in  the  follow- 
ing manner; — 

Acid  Chrom.  potass.  Sulph.  Acid.  Acid  Sulph.  Potass.  Sulph.  Chrom.  Water.  Oxygen. 

^ 2 K^-er^O,  -f-  10  = 4KHS^,  2 (er^SS^)  + 8 + 3 O2 

Part  of  the  sulphuric  acid  is  employed  in  displacing  the  chromic  acid  from  the 
acid  chromate  of  potassium,  and  in  forming  acid  sulphate  of  potassium  iu  its  stead, 
whilst  another  portion  of  the  sulphuric  acid  assists  in  decomposing  the  liberated 
chromic  acid,  which  loses  half  its  oxygen,  and  becomes  converted  into  oxide  of 
chromium  ; and  the  chromium  of  this  oxide,  b}""  exchanging  places  with  the  hydrogen 
of  the  sulphuric  acid,  forms  sulphate  of  chromium,  whilst  water  is  formed. 

When  oxygen  is  required  in  large  quantities,  as  iu  metallurgic  operations,  Deville 
and  Debray  recommend  the  decomposition  of  sulphuric  acid  by  heat  as  the  cheapest 
source  of  the  gas.  A tubulated  earthenware  retort  is  charged  with  fragments  of 
fire-brick,  an  iron  tube  sufficiently  long  to  reach  to  the  bottom  of  the  retort  is  luted 
into  the  tubulure,  and  when  the  retort  is  at  a full  red  heat,  the  acid  is  allowed  to 
pass  in,  drop  by  drop,  through  a bent  funnel.  In  this  operation  the  sulphuric  acid 
is  decomposed  into  sulphurous  acid,  oxygen,  and  water,  as  may  be  represented  by 
the  following  equation: — 

Sulphuric  Acid.  Sulphurous  anhydride. 

= 2 -f  2 SOa  -f  Oa. 

The  volatilized  products  are  transmitted  through  a small  spiral  condenser  to  liquefy 
the  water  and  undecomposed  acid,  whilst  the  sulphurous  anhydride  is  removed 
by  subsequent  washing  with  the  water,  and  the  oxygen  is  collected  in  the  usual 
manner. 

Dried  sulphate  of  zinc  likewise  furnishes  oxygen  and  sulphurous  anhydride 
readily  on  the  application  of  a full  red  heat,  while  oxide  of  zinc  remains  in  the 
i*Gt/Ort)  * 

2 ZnS04  = 2 ZnO  -t-  2 SO,  + O2. 


MATINEE  NOT  DESTROYED  BY  COMBUSTION. 


17 


(336)  Nature  of  Combustion. — The  distinguishing  feature  of 
oxygen  is  its  remarkable  power  of  supporting  combustion.  When- 
ever any  rapid  chemical  action  attended  with  extrication  of  light 
and  heat  takes  place,  combustion  is  said  to  occur.  In  order  to 
commence  this  action  it  is  generally  necessary  to  apply  heat ; 
afterwards  the  heat  whicli  is  liberated  during  the  process  is  more 
than  sufficient  to  carry  it  on,  and  the  act  of  combination  proceeds 
with  increasing  rapidity.  A stick  of  charcoal  may  be  kept  in 
oxygen  at  common  temperature  for  years  without  entering  into 
combination  with  the  gas,  but  the  smallest  spark  upon  the  surface 
of  the  charcoal  will  suffice  to  determine  its  immediate  and  vivid 
combustion. 

It  must  ever  be  borne  in  mind  that  in  the  case  of  combustion, 
as  in  every  instance  of  chemical  action,  how  completely  soever  the 
combustible,  or  body  which  is  burned,  may  change  its  form,  so  as 
even  to  disappear  from  our  sight,  there  is  no  actual  destruction 
of  matter  or  loss  of  weight.  A candle  in  burning  seems  to  be 
completely  destroyed ; and  when  the  combustion  is  over,  an  insig- 
nificant trace  of  ash  from  the  wick  is  all  that  remains  to  the  eye. 
It  is,  however,  easy  to 
show  that  there  is  no 
actual  destruction  of 
its  components  in  this 
operation,  but  that  the 
constituents  of  the 
candle  in  burning  have 
combined  with  a cer- 
tain proportion  of  oxy- 
gen, and  that  the  aeri- 
form compounds,  car- 
bonic anhydride  and 
aqueous  vapour,  which 
are  the  result  of  the 
combustion,  though  in- 
visible, really  weigh 
more  than  the  original 
candle ; the  gain  in 
weight  representing  the 
quantity  of  oxygen 
which  has  produced  the 
chemical  change  by  its 
combination  with  the 
materials  of  the  candle. 

The  experiment  may 
be  conducted  in  the  fol- 
lowing manner: — Take  a glass  tube,  a b,  fig.  271,  14:  or  15  inches 

Peroxide  of  barium  was  also  proposed  by  Boussinj^ault  as  a source  of  oxygen.  He 
hoped  alternately  to  convert  baryta  into  the  peroxide,  by  heating  it  to  dull  redness  in 
a current  of  air,  and  then  to  decompose  the  peroxide  by  a still  more  elevated  tem- 
perature, and  thus  to  be  able  to  extract  oxygen  from  the  atmosphere  with  the  same 
quantity  of  baryta  for  an  indefinite  number  of  times;  but  hitherto  the  difficulties 
attending  the  use  of  this  method  have  prevented  its  application  in  the  arts. 


18  SPONTANEOrS  COMBESTIOX QUICK  ANT)  SLOW  COMBUSTION. 

long,  and  incli  in  diameter;  thrust  a piece  of  wire  gauze, half 
wav  down  the  tube,  and  fill  the  upper  half  with  fi-agments  of  fused 
caustic  potash.  The  fused  potash  is  employed  to  retain  both  the  car- 
bonic anhydride  and  the  moisture,  which  are  the  only  compounds 
produced  by  the  burning  candle,  if  it  be  properly  supplied  with 
air.  To  the  lower  end  of  the  tube  fit  a cork  perforated  with 
three  or  four  holes  for  the  admission  of  air,  and  fasten  to  it  a 
short  piece  of  wax  taper.  To  the  other  end  of  the  tube  adapt 
a cork  through  which  a short  piece  of  tube,  y,  of  about  one- 
third  of  an  inch  in  diameter  is  passed.  iSTow  weigh  the  tube  and 
its  contents.  Connect  the  tube  g by  means  of  a piece  of  fiexible 
tubing,  c,  to  an  aspirator  jar,  n,  filled  with  water;  open  the  stop- 
cock, E,  and  let  the  water  flow.  The  water  cannot  escape  at  e 
till  its  place  is  supplied  by  atmospheric  air ; and  since  the  aspira- 
tor, through  the  tube  c,  is  connected  with  a b,  which  at  b com- 
municates freely  with  the  atmosphere,  a current  of  air  is  estab- 
lished through  A B.  Xow  withdraw  the  cork  b,  light  the  taper, 
and  quickly  replace  it  in  the  tube ; in  about  three  minutes’  time 
close  the  stopcock  of  the  aspirator ; the  taper  is  instantly  extin- 
guished. Detach  the  tube  c ; the  glass  a b,  when  cold,  will 
weigh  several  grains  heavier  than  before. 

At  the  ordinary  temperature  of  the  atmosphere  oxygen  fre- 
quently enters  slowly  into  combination  without  any  perceptible 
disengagement  of  heat,  as  when  a bar  of  iron  is  gradually  rusting 
in  the  air.*  In  other  instances,  where  the  process  is  moi-e  rapid, 
the  heat  accumulates,  and  sometimes  it  rises  high  enough  to  cause 
the  materials  to  burst  into  flame,  producing  what  are  called  cases 
of  spontaneous  combustion.  Charcoal  that  has  been  reduced  to 
fine  powder  as  a preliminary  to  the  manufacture  of  gunpowder, 
and  which  offers  a large  surface  to  the  air,  occasionally  exhibits 
this  phenomenon ; and  it  is  still  more  often  manifested  when  tow 
that  has  been  used  for  wiping  machinery  lubricated  with  oil  is 
laid  aside  in  heaps.  The  oil,  when  spread  over  so  large  a surface, 


* When  considerable  masses  of  iron  are  allowed  to  rust,  a distinct  elevation  of 
temperature  is  often  perceived.  This  is  seen  when  a heap  of  iron  turnings  of  from 
10  lb.  to  20  lb.  is  moistened  with  water  and  exposed  to  the  air;  and  a curious  illus- 
tration of  the  fact  was  afforded  during  the  manufacture  of  the  Mediterranean  Electric 
Cable.  The  copper  conducting  wire  of  this  cable  was  coated  with  gutta-percha,  this 
was  covered  with  a serving  of  tar  and  hemp,  and  the  whole  was  enclosed  in  a strong 
casing  of  iron  wire.  The  cable  as  it  was  manufactured  was  coiled  in  tanks  filled  with 
water.  These  tanks  leaked,  and  the  water  was  therefore  drawn  off,  leaving  a quan- 
tity of  cable,  about  163  nautical  miles  in  length,  coiled  into  a mass  about  30  feet  in 
diameter  with  an  eye  or  central  space  of  6 feet ; the  height  of  the  coil  was  about  8 
feet.  Rapid  oxidation  took  place,  and  the  temperature  at  the  centre  of  the  coil,  nearly 
3 feet  from  the  bottom,  rose  in  4 days  from  66°  to  79°,  although  the  temperature  of 
the  air  did  not  exceed  66°  during  the  period,  and  was  as  low  as  59°  part  of  the  time. 
In  other  parts  of  the  mass  the  heat  rose  so  high  as  to  cause  the  water  to  evaporate 
sufficiently  rapidly  to  produce  a visible  cloud  of  vapour,  and  to  give  rise  to  apprehen- 
sions that  the  insulating  power  of  the  cable  would  be  destroyed  by  the  softening  of 
the  gutta-percha.  No  doubt  the  rise  of  temperature  would  have  been  still  greater 
had  it  not  been  checked  by  the  affusion  of  cold  water;  but  the  oxidation  and  the 
heating  were  renewed  when  the  cooling  was  discontinued.  The  oxidation  occurred 
only  on  the  external  surface  of  the  iron  wires,  that  portion  in  contact  vdth  the  tarred 
hemp  remaining  perfectly  bright 


RAPID  AND  SLOW  OXIDATION. 


19 


absorbs  oxygen  rapidly,  and  the  temperature  goes  on  rising  until 
the  mass  bursts  into  flame. 

The  oxidation  of  the  metals  has  been  observed  to  take  place 
much  more  rapidly  in  a moist  than  in  a dry  atmosphere.  A bar 
of  polished  iron  will  remain  in  dry  air  unchanged  for  any  length 
of  time,  but  if  moisture  be  present  it  will  quickly  become  rusty  ; 
the  oxide  of  iron  in  this  case  combines  with  the  water  which  it 
absorbs  from  the  air  (753).  In  the  case  of  iron,  the  oxidation 
continues  to  spread  through  the  entire  mass  of  the  metal ; but  in 
other  instances,  as  occurs  with  lead  and  zinc,  a superficial  coat  of 
oxide  is  formed,  which  adheres  firmly  to  the  surface,  and  protects 
the  metal  beneath  from  further  change. 

The  more  the  oxygen  is  diluted,  whether  by  diminution  of 
pressure,  or  by  mixture  with  a gas  which  does  not  act  chemically 
upon  it,  as  with  the  nitrogen  of  the  atmosphere,  the  less  elevated 
is  the  temperature  which  is  produced  in  a given  time  by  combus- 
tion, because  fewer  particles  are  in  contact  with  the  burning  body, 
whilst  at  the  same  time  the  diluting  gas  must  have  its  tempera- 
ture raised,  and  the  more  slowly,  in  consequence,  does  the  opera- 
tion proceed.  The  activity  of  the  combustion  is  greatly  increased 
by  increasing  the  number  of  particles  of  oxygen  which  are  brought 
in  a given  time  into  contact  with  the  combustible,  and  by  carry- 
ing away  the  gaseous  products  of  combustion  which  are  incapable 
of  combining  with  the  fuel,  and  which,  if  suffered  to  accumulate, 
would  cut  oft*  the  supply  of  fresh  oxygen  ; in  this  way  the  action 
of  the  smith’s  bellows  and  the  blowing  machine  of  the  blast 
furnace  may  be  explained.  The  influence  of  a long  chimney  in 
producing  a powerful  heat  in  the  furnace  at  its  base  is  similar ; 
Avhilst  the  eff*ect  of  diminishing  the  supply  of  air  by  closing  the 
damper,  or  shutting  the  door  of  the  ash-pit,  is  seen  in  the  dimi- 
nished temperature  and  reduced  consumption  of  fuel  which  occurs 
under  such  circumstances. 

It  is,  however,  important  to  remark  that  the  quantity  of  heat 
emitted  during  the  combination  of  a given  quantity  of  oxygen  is 
definite,  and  is  dependent  in  part  upon  the  chemical  nature  of  the 
burning  body,  but  it  is  independent  of  the  rate  at  which  the  com- 
bustion is  eft'ected  (199  et  seq.). 

The  act  of  respiration  in  animals,  during  which  the  oxygen  of 
the  air  is  brought  into  contact  with  the  blood  through  the  agency 
of  the  lungs,  is  attended  with  a slow  change,  analogous  to  com- 
bustion, and  is  accompanied  by  extrication  of  heat ; an  oxidation 
of  a portion  of  the  constituents  of  the  blood  occurs,  carbonic 
anhydride  is  extricated  and  passes  off  with  the  expired  air,  and  at 
the  same  time  the  colour  of  the  blood  is  changed  from  a dusky 
purple  to  bright  crimson. 

All  bodies  may,  with  reference  to  combustion,  be  arranged 
under  one  of  three  classes.  The  first  class  consists  of  bodies  which, 
like  oxygen,  allow  other  substances  to  burn  in  them  freely,  but 
which  cannot  themselves,  in  ordinary  language,  be  set  on  fire : 
these  are  termed  supporters  of  combustion.  The  second  class  con- 
sists of  bodies  which,  like  charcoal,  actually  burn  when  sufficiently 


20 


VARIETIES  OF  OXIDES ACIDS BASES. 


heated  in  a gas  belonging  to  the  first  class : these  substances  are 
termed  conwustibles.  The  third  class  embraces  such  bodies  as 
will  neither  burn  themselves  nor  support  the  combustion  of 
others : they  may  be  made  red  hot,  but  do  not  burn  ; sand,  iron- 
rust,  and  earthy  bodies  in  general,  are  examples  of  this  kind; 
they  are  for  the  most  part  compounds  that  have  at  some  time  or 
other  been  produced  by  combustion  ; that  is,  they  are  bodies  that 
have  been  already  burned,  and  are  no  longer  fitted  to  undergo 
this  change. 

(337)  Varieties  of  Oxides, — The  compounds  which  oxygen 
forms  with  other  elements  are  in  chemical  language  termed  oxides^ 
and  a body  which  has  combined  with  oxygen  is  said  to  have 
become  oxidized.  The  number  and  variety  of  these  compounds 
are  veiy  great,  for  oxygen  is  the  most  widely  diffused  and  abun- 
dant of  the  elements.  It  constitutes  about  a fifth  in  bulk  of 
the  atmosphere  ; it  forms  eight-ninths  of  all  the  water  on  the 
globe,  and  it  is  not  less  extensively  met  with  amongst  the  solid 
constituents  of  the  earth  : chalk,  limestone,  and  marble — silica, 
in  all  its  varieties  of  sand,  flint,  quartz,  rock-crystal,  &c. — and  all 
the  various  kinds  of  clay,  each  contain  about  half  their  weight  of 
oxygen.  In  the  forms  of  animal  and  vegetable  life  it  is  also 
equally  generally  diffused  ; it  is  indeed  absolutely  essential  to  the 
maintenance  of  the  vital  functions  in  both  ; and  although  not 
the  only  body  which  is  fitted  to  support  combustion,  it  is,  from 
its  existence  in  the  atmospliere,  the  element  which,  in  the  vast 
majority  of  cases,  maintains  combustion  on  the  surface  of  our 
planet. 

Amongst  the  various  compounds  formed  by  oxygen,  it  is  re- 
markable that  there  exist  two  classes  which  are  in  chemical  pro- 
perties directly  opposed  to  each  other.  Many  substances,  like 
phosphorus,  by  their  combination  with  oxygen,  yield  a compound 
which  is  freely  soluble  in  water,  has  a sour,  burning  taste,  and 
turns  many  vegetable  blue  colours,  such  as  the  blue  of  an  infusion 
of  litmus  or  of  purple  cabbage,  to  a bright  red,  and  which,  in 
short,  possesses  the  characters  of  an  acid.  All  the  elements  which 
are  not  metallic,  with  the  exception  of  liydrogen  and  of  fluorine, 
form  with  oxygen  one  or  more  compounds,  which,  when  dissolved 
in  water,  are  acids,  and  in  many  cases  intensely  powerful  acids. 
Many  of  the  metals,  however,  by  their  union  with  oxygen,  give 
rise  to  bodies  of  an  opposite  kind,  which  have  been  termed  bases. 
Potassium,  for  example,  when  burned  in  oxygen,  furnishes  a white 
alkaline  substance,  which  is  dissolved  rapidly  by  water,  and  pro- 
duces a colourless  liquid,  of  a soapy,  disagreeable  taste,  and  a 
])eculiar  lixivial  smell : it  has  a caustic  action  on  the  skin,  restores 
the  blue  colour  to  litmus  which  has  been  reddened  by  an  acid, 
and  it  completely  neutralizes  the  strongest  acids.  Otlier  metals 
form  oxides  which,  though  not  soluble  in  water,  nevertheless  pre- 
serve their  basic  character,  and  neutralize  the  acids  perfectly. 
Perrons  oxide,  for  instance,  is  soluble  in  sulphuric  acid,  and  forms 
with  it  a cry stalliz able  salt,  whilst  water  is  set  free.  It  is  found 
that  when  an  element  combines  with  oxygen  to  form  an  acid,  it 


OZONE. 


21 


unites  with  a larger  number  of  atoms  of  oxygen  than  when  a base 
is  the  result  of  the  combination. 

Intermediate  between  the  acid  and  the  basic  oxides  is  a third 
class  of  oxides,  which  are  indisposed  to  enter  into  combination 
with  either  acids  or  bases.  The  black  oxide  of  manganese 
(MnO^),  or  (kfn0,Mn03),  the  magnetic  oxide  of  iron  (FeO, 
Fe^Og),  and  red  lead  (2  PbO,  PbO-2),may  be  mentioned  as  instances 
of  this  kind  ; such  oxides  are  often  produced  by  the  union  of  two 
otlier  oxides  with  each  other.  These  indifierent  oxides  are  some- 
times termed  saline  oxides,  from  their  analogy  to  salts  in  com- 
position (547  et  seq.). 

Independently  of  its  power  of  supporting  animal  life  and 
combustion,  oxygen  may  be  distinguished  by  direct  tests.  It  is 
insoluble  in  a solution  of  potash,  but  if  to  the  alkaline  liquid  a little 
pyi’ogallic  acid  be  added,  the  gas  is  rapidly  absorbed,  and  the  solu- 
tion becomes  of  an  intense  brown  colour.  A mixture  of  nitric 
oxide  with  any  gas  containing  uncombined  oxygen  immediately 
becomes  of  a reddish-brown  colour,  owing  to  the  formation  of 
red  fumes  of  peroxide  of  nitrogen  (367). 

(338)  Ozone. — When  a succession  of  electric  sparks  is  trans- 
mitted through  atmospheric  air  or  through  dry  oxygen,  a peculiar 
odour  is  perceived,  which  has  by  some  been  compared  to  that  of 
weak  chlorine.  To  the  body  which  produces  it  Schonbein  gave 
the  name  of  ozone^  (from  ojw,  to  emit  an  odour)  in  allusion  to  its 
strong  and  peculiar  odour.  Opinions  upon  the  cause  of  this 
odour  were  long  divided ; but  the  concurrent  observations  of 
several  accurate  experimentalists  seem  to  indicate  that  it  is  owing 
to  a modification  produced  in  oxygen  itself,  by  which  it  is  made 
to  assume  a more  active  condition.  One  of  the  easiest  methods 
of  exhibiting  the  production  of  ozone  consists  of  transmitting  a 
current  of  oxygen  through  a tube  into  which  a pair  of  platinum 
wires  is  sealed,  with  the  points  at  a little  distance  apart : on 
connecting  one  of  the  wires  with  the  prime  conductor  of  an  elec- 
trical machine  in  good  action,  whilst  the  other  wire  is  in  con- 
ducting communication  with  the  earth,  the  characteristic  odour  of 
ozone  is  immediately  developed  in  the  issuing  gas  ; but  notwith- 
standing the  powerful  odour  thus  produced,  a minute  portion  only 
of  the  oxygen  undergoes  this  change.  Andrews  and  Tait  {Phil. 
Trans.  1860)  have  shown  that  in  order  to  produce  the  maximum 
effect  in  electrifying  oxygen,  it  is  necessary  to  transmit  the  dis- 
charge silently.'^'  By  operating  in  sealed  tubes  upon  pure  and 
dry  oxygen,  they  succeeded,  when  great  care  was  taken  to  prevent 
the  transmission  of  sparks,  in  converting  a large  portion  of  the  gas 
into  ozone.  Ozone  is  much  denser  than  oxygen  itself;  by  a con- 
tinuous electrical  discharge  maintained  for  many  hours,  they 
effected  a contraction  in  bulk  of  the  ffas  amountiim  to  one-twelftli 

* Siemens  prepares  ozone  by  induction:  he  forms  a sort  of  Leyden  jar  by  coating 
the  interior  of  a long  tube  with  tinfoil ; over  this  tube  he  passes  a second  wider  tube 
also  coated  with  tinfoil,  but  on  its  outer  surface  ; between  the  two  tubes,  a current  of 
pure  dry  oxygen  is  then  transmitted,  which  becomes  electrified  by  induction,  on  con- 
necting the  inner  and  outer  coating  with  the  terminal  wires  of  an  induction-coil. 


22 


OZONE PKEPAKATION. 


of  the  entire  volume  operated  on  ; and  on  heating  the  gas  to  550° 
F.  the  ozone  disappeared,  whilst  the  oxygen  resumed  its  original 
volume.  The  passage  of  the  electric  sparh  likewise  immediately 
destroys  a large  proportion  of  the  ozone  which  had  been  previously 
produced. 

Ozone  may  also  be  obtained  without  the  aid  of  electricity. 
Ilouzeau  states  that  the  oxygen  evolved  from  peroxide  of  barium 
by  the  addition  of  oil  of  vitriol  contains  ozone ; it  has  a powerful 
odour,  and  he  found  that  it  oxidizes  ammonia,  and  kindles  the 
less  inflammable  variety  of  pliosphuretted  hydrogen  (454) ; after 
it  has  been  heated  it  no  longer  possesses  these  properties.  Later 
researches  have,  however,  rendered  it  probable  that  these  proper- 
ties are  due  to  the  formation  of  peroxide  of  hydrogen  in  small 
quantity,  and  to  its  suspension  in  the  oxygen  as  it  escapes.* 

If  a stick  of  clean  phosphorus,  moistened  with  a few  drops  of 
water,  be  placed  in  a bottle  of  atmospheric  air,  at  a temperature 
of  from  60°  to  70°,  the  slow  oxidation  of  the  phosphorus  is  attend- 
ed with  the  production  of  ozone  : in  an  hour  or  two  this  attains  its 
maximum.  If  the  phosphorus  be  not  then  removed,  the  ozone 
by  degrees  disappears,  owing  to  its  combination  wflth  the  phos- 
phorus. 'No  ozone  is  formed  if  the  air  be  perfectly  dry  ; and  dry 
oxygen  is  not  ozonized  by  phosphorus.  It  is  also  probable  that 
ozone  is  formed  in  other  slow  oxidations,  such  as  that  of  ether, 
and  of  oil  of  turpentine.  Schonbein  appears  to  have  proved  that 
in  all  such  cases  the  formation  of  ozone  is  accompanied  by  that 
of  peroxide  of  hydrogen  a fact  which  is  true  also  of  elec- 

trolytic ozone.f  Ozone,  as  obtained  by  any  of  these  processes,  is 
present  in  but  very  minute  quantity,  being  diluted  with  from  50 
to  200  times  its  volume  of  oxygen. 

When  diluted  sulphuric  acid,  or  a solution  of  the  sulphates, 
chromates,  phosphates,  and  several  other  salts  of  the  alkali-metals, 
is  decomposed  electrolytically  between  plates  of  platinum  or  gold 


* The  reader  is  referred  for  Schonbeiu’s  speculations  upon  the  existence  of  two 
opposite  forms  of  oxygen,  ozone  and  aatozone,  to  the  Phil.  Mag.  for  1858.  They  are 
ingenious,  but  although  the  existence  of  two  oppositely  polarized  forms  had  pre- 
viously been  rendered  probable  by  the  experiments  of  Brodie  and  others,  it  is  not  in 
accordance  with  analogy  that  ozone  should  be  the  isolated  form  of  one  of  these 
bodies.  A mixture  of  a solution  of  permanganate  of  potassium  with  one  of  peroxide 
of  hydrogen  evolves  oxygen,  whilst  hydrated  peroxide  of  manganese  is  precipitated ; 
and  in  like  manner  a solution  of  chromic  acid  acidulated  with  sulphuric  acid  gives 
off  oxygen  on  the  addition  of  peroxide  of  hydrogen,  whilst  green  sulphate  of  chrom- 
ium is  produced.  Hence  it  has  been  supposed  that  the  oxygen  in  the  permanganic 
or  chromic  acid  is  in  an  opposite  polar  condition  to  the  second  atom  of  oxygen  in  the 
peroxide  of  hydrogen ; the  tendency  to  union  between  these  two  supposed  oppositely 
polar  forms  of  oxygen  is  conceived  to  be  the  cause  of  the  decomposition,  and  the 
result  of  their  union  is  the  gaseous  oxygen  which  escapes.  (Brodie,  Phil.  Trans. 
1850  and  1862).  Yon  Bubo’s  experiments  tend  to  show  that  Schoiibein’s  so-called 
antozone  is  peroxide  of  hydrogen.  The  subjeet,  however,  still  needs  further  inves- 
tigation. 

f If  a clean  glass  rod  heated  to  about  500°  be  plunged  into  a jar  containing  a few 
drops  of  ether,  the  vapour  of  ether  undergoes  slow  oxidation,  ozone  seems  to  be 
formed:  the  vapours  turn  starch  moistened  with  iodide  of  potassium  blue;  and  the 
residual  ether  contains  peroxide  of  hydrogen,  and  if  agitated  with  a few  drops  of  a 
solution  of  acid  chromate  of  potassium,  acidulated  with  a little  sulphuric  acid,  a blue 
solution  of  perchromic  acid  in  the  ether  is  produced. 


OZONE PKOPEKTIES. 


23 


by  tbe  voltaic  battery,  the  oxygen  that  is  evolved  has  a powerful 
odour  of  ozone.  The  experiments  of  Andrews  {Phil.  Trans. 
1855  and  1860)  have  shown  the  identity  of  the  ozone  obtained  by 
the  electricity  of  the  machine,  with  that  produced  by  voltaic  action, 
as  well  as  with  that  obtained  by  the  oxidation  of  phosphorus  ; and 
these  conclusions  have  been  confirmed  by  Soret  and  by  Yon 
Babo  {Liebig’s  Annal.^  Stipplement-band.^  ii.  266),  in  opposition  to 
Baumert,  who  maintained  {Poggend.  Annal.  Ixxxix.  38)  that  elec- 
trolytic ozone  contains  a peculiar  peroxide  of  hydrogen,  as  Schon- 
bein  himself  at  one  time  supposed. 

Properties. — Ozone  is  insoluble  in  water,  and  in  solutions 
either  of  acids  or  alkalies,  but  is  absorbed  by  a solution  of  iodide 
of  potassium.  Air  charged  with  ozone  exerts  an  irritating  action 
upon  the  respiratory  organs.  Ozone  possesses  considerable  bleach- 
ing powers,  and  converts  blue  indigo  into  isatin : it  acts  rapidly 
as  a powerful  oxidizing  agent,  and  corrodes  organic  matters,  such 
as  the  cork  or  caoutchouc  used  in  connecting  the  different  parts 
of  the  apparatus  together : iron,  copper,  and  even  silver,  when 
moistened,  rapidly  absorb  it,  and  become  converted  on  their  sur- 
face into  oxides : silver  even  becomes  a peroxide,  though  this 
metal  does  not  enter  into  direct  combination  with  ordinary  oxy- 
gen either  when  moist  or  dry.  When  the  ozone  and  the  metals 
are  perfectly  dry,  little  or  no  absorption  of  ozone  occurs.  Dry 
mercury  as  well  as  dry  iodine,  however,  immediately  removes 
ozone.  It  is  remarkable  that  no  contraction  follows  the  absorp- 
tion of  ozone  by  these  or  by  any  other  agents  ; this  point  was 
carefully  and  minutely  observed  by  Andrews  and  Tait.  Hence  it 
seems  to  be  probable  that  the  ozone  is  resolved  into  a quantity  of 
ordinary  oxygen,  equal  in  bulk  to  itself,  which  is  liberated  at  the 
moment  that  another  portion  of  oxygen  enters  into  combination 
with  the  iodine  ; possibly  three  volumes  of  oxygen  become  con- 
densed into  two  ; one  volume  becoming  fixed,  whilst  two  volumes 
are  liberated  on  the  decomposition  of  ozone  by  a metal.  Ozone 
displaces  iodine  from  its  combination  with  the  metals,  setting  the 
iodine  at  liberty  ; indeed,  this  reaction  is  so  easily  produced,  that 
it  furnishes  the  readiest  and  most  delicate  method  of  detecting  the 
presence  of  traces  of  ozone  in  the  air ; a slip  of  paper  moistened 
with  starch  and  iodide  of  potassium,  and  inserted  into  a vessel  con- 
taining the  smallest  admixture  of  ozone,  becomes  blue  from  the 
action  of  the  libei*ated  iodine,  which  immediately  unites  with  the 
starch,  and  forms  the  blue  iodide  of  starch  which  is  so  character- 
istic of  iodine.  Indeed,  pure  oxygen  contained  in  a tube  inverted 
over  a solution  of  iodide  of  potassium  is  entirely  absorbed  by  the 
liquid,  if  the  gas  be  subjected  to  the  passage  of  a discharge  of  elec- 
tricity through  it  for  a sufficient  length  of  time,  hydrate  of  potash 
being  formed  by  the  absorption  of  oxygen,  wliile  iodine  is  set  free : 
(4KI -f  2ll20-f-*02=:4KII0-f-  2I2.)  If  the  experiment  be  prolonged, 
iodate  of  potassium,  peroxide  of  hydrogen  and  peroxide  of  potas- 
sium are  formed.  Paper  soaked  in  a solution  of  sulpliate  of  man- 
ganese (MnSO^)  likewise  shows  the  presence  of  ozone  by  becom- 
ing brown,  owing  to  the  manganese  in  the  sulphate  absorbing 


24 


NITROGEN. 


oxygen,  and  becoming  converted  into  the  insoluble  hydrated  per- 
oxide, whilst  sulphuric  acid  is  set  free.  If  the  paper  be  stained 
black  with  sulpliide  of  lead  (PbS),  this  stain  will  gradually  disap- 
pear ; both  the  sulphur  and  the  lead  will  absorb  the  ozone,  or 
active  oxygen,  and  a white  sulphate  of  lead  (PbSOJ  will  be 
formed.  One  of  the  most  singular  circumstances  connected  with 
ozone  is  the  efiect  of  heat  upon  it.  A temperature  not  much 
higher  than  that  of  boiling  water  is  sufScient  slowly  to  destroy  all 
its  active  character,  and  the  change  is  instantaneous  at  the  tem- 
perature of  570°.  By  placing  the  flame  of  a spirit-lamp  so  as  to 
heat  a part  of  the  tube  through  which  the  electrifled  oxygen 
escapes,  all  signs  of  ozone  disappear.  Ozonized  air  is  also  deozon- 
ized  by  transmission  over  cold  peroxide  of  manganese,  peroxide 
of  silver,  or  peroxide  of  lead. 

If  a piece  of  paper,  soaked  in  a mixture  of  starch  and  iodide 
of  potassium,  be  exposed  in  the  open  air  for  flve  or  ten  minutes, 
it  often  acquires  a blue  tint,  the  intensity  of  which  varies  on  dif- 
ferent days ; sometimes,  particularly  in  damp  or  foggy  weather, 
no  change  is  produced  by  such  exposure.  These  effects  are  seldom 
seen  in  towns,  but  generally  in  the  open  country,  or  on  the  sea- 
coast,  especially  when  the  ^vind  blows  off  the  sea.  They  are 
plausibly  supposed  to  be  owing  to  the  presence  of  traces  of  ozone 
in  the  atmosphere  ; and  theorist's  are  not  wanting  who  believe  they 
have  traced  the  prevalence  of  cholera  and  other  epidemics  to  the 
unusual  absence  of  ozone  in  the  air  during  lengthened  periods. 
Iodine  may,  however,  be  liberated  from  iodide  of  potassium  by 
nitrous  acid,  by  chlorine,  and  by  various  agents  besides  ozone,  so 
that  this  reaction,  although  a very  sensitive  one  for  ozone,  is  by  no 
means  characteristic  of  its  presence ; and  the  existence  of  traces 
of  ozone  in  the  atmosphere,  probable  though  it  is,  cannot  be  said 
to  have  been  unequivocally  proved.  Schdnbein,  in  order  to  obtain 
some  idea  of  the  proportion  of  the  agent  which  produces  the  effect, 
prepares  this  paper  of  a deflnite  strength,  by  dissolving  1 part  of 
pure  iodide  of  potassium  free  from  iodate  in  200  parts  of  distilled 
water,  which  is  thickened  by  heating  it  with  10  parts  of  white 
starch  : this  is  then  spread  upon  slips  of  unsized  paper,  which  are 
preserved  in  a stoppered  bottle  kept  in  the  dark. 

§ II.  UlTROGEN.*  11  = 14. 

Atomic  Yol.  n ; Theoretic  Sp.  Gr.^  0’9674  ; Observed 
Sp.  Gr.,  0*9713. 

(839)  It  has  already  been  stated  (334)  that  the  larger  propor- 
tion of  the  atmosphere  consists  of  a gaseous  body,  which  has  been 
named  nitrogen  (generator  of  nitre),  because  it  is  an  essential 
constituent  of  nitre : sometimes  the  name  of  azote  (from  a not, 

life,)  is  given  to  it,  because,  though  not  poisonous,  it  is  incapa- 
ble of  supporting  life.  This  element  was  discovered  by  Ruther- 
ford in  1772. 

* If  nitrogen  in  the  gaseous  state  be  regarded  as  (NN)  nitride  of  nitrogen^  its  mole- 
cular  volume  will  be  | 


PKEPAKATION  OF  NITKOGEN. 


25 


Properties. — ^I^itrogen  is  a colourless,  tasteless,  and  inodorous 
gas,  which  as  yet  has  resisted  every  effort  to  liquefy  it.  It  is 
somewhat  lighter  than  atmospheric  air ; calculating  from  Reg- 
nault’s  experiments,  100  cubic  inches  at  60°  F.,  Bar.  30°  in., 
weigh  30*119  grains.  Water  dissolves  not  more  than  of  its 
bulk  of  this  gas  at  ordinary  temperatures,  100  cubic  inches  of 
water  at  32°  absorbing  2*03  cubic  inches  of  nitrogen,  and  1*48 
cubic  inches  at  59°  (Bunsen).  Ho  two  substances  can  offer  a , 
more  striking  contrast  in  chemical  properties  than  oxygen  and 
nitrogen : the  one  the  most  energetic  of  the  elements,  the  other 
the  most  indifferent.  It  extinguishes  a taper  without  taking  fire 
itself ; an  animal  immersed  in  the  undiluted  gas  perishes  quickly 
for  want  of  oxygen,  but  it  is  not  directly  poisonous ; indeed,  it 
enters  as  a necessary  component  into  the  animal  frame,  and  with 
every  act  of  inspiration  it  finds  admission  into  the  lungs.  One 
very  important  purpose  that  it  fulfils  in  the  atmosphere  is  the 
dilution  of  the  oxygen,  which  is  rendered  thereby  less  stimulating 
to  the  living  system,  and  the  rapidity  of  ordinary  combustion  is 
likewise  thereby  moderated.  Hitrogen  is  one  of  the  most  exten- 
sively diffused  forms  of  matter,  as  must  be  evident  from  the  facts 
just  stated;  and  notwithstanding  its  apparent  indisposition  to 
enter  into  combination,  it  forms  a number  of  highly  interesting 
and  important  compounds.  For  example,  one  of  its  combinations 
with  oxygen,  when  dissolved  in  water,  forms  nitric  acid,  which 
exists  as  a natural  production  when  united  with  potassium  and 
sodium  in  the  nitrates  of  those  metals  : it  is  the  characteristic 
ingredient  in  ammonia ; and  though  it  occurs  in  but  small  quantity 
in  plants,  it  is  never  entirely  absent  from  them.  Hitrogen  also 
constitutes  an  essential  part  of  many  of  the  most  potent  and  valu- 
able medicines,  such  as  quinia  and  morphia,  as  well  as  of  some  of 
the  most  dangerous  poisons,  as  prussic  acid  and  strychnia.  It 
likewise  enters  largely  into  the  composition  of  many  animal  tis- 
sues. Organic  compounds  which  contain  nitrogen  are  frequently 
termed  azotised  substances. 

Preparation. — The  most  convenient  methods  of  obtaining 
nitrogen  are  based  upon  the  removal  of  oxygen  from  atmospheric 
air.  1. — The  simplest  plan  consists  in  placing  a few  fragments  of 
phosphorus,  dried  by  means  of  blotting-paper,  on  a porcelain  dish 
wliicli  is  floated  upon  the  surface  of  the  water  of  the  pneumatic 
trough  ; the  phosphorus  is  ignited  by  touching  it  with  a hot  wire, 
and  a glass  receiver  filled  with  air  is  then  inverted  over  it.  The 
phosphorus  burns  at  the  expense  of  the  oxygen  in  the  confined 
air,  and  being  partially  converted  into  vapour  by  the  heat  which 
attends  the  combustion,  is  diffused  through  the  gas,  and  thus 
quickly  searches  out  and  combines  with  every  portion  of  oxygen : 
when  cold,  the  nitrogen  may  be  decanted  into  another  jar  and 
examined.  Even  at  ordinary  temperatures,  a stick  of  phosphorus 
will,  if  introduced  into  a jar  of  air  which  is  standing  over  water, 
slowly  absorb  the  oxygen,  and  in  two  or  three  days  about  four- 
fifths  of  the  original  bulk  of  the  air,  consisting  of  nitrogen  nearly 
pure,  will  be  left. 


26 


COMPOSITION  OF  THE  ATMOSPHERE. 


2.  — The  removal  of  oxygen  from  the  air  may  also  be  effected 
slowly  in  various  ways.  Moistened  iron  filings  produce  a similar 
result,  the  metal  gradually  becoming  oxidized,  as  is  seen  by  the 
rusty  appearance  which  it  assumes.  Many  other  metals,  when 
moist,  moistened  lead  shavings,  for  example,  produce  a similar 
effect. 

3.  — Moistened  sulphides  of  the  alkaline  metals  likewise  absorb 
oxygen,  from  a confined  portion  of  air  very  rapidly  and  completely. 

4.  — When  larger  quantities  of  nitrogen  are  required,  metallic 
copper  may  be  employed  to  absorb  the  oxygen.  The  method  to 
be  adopted  in  this  case  is  exhibited  in  fig.  272.  c represents  a 


Fig.  212. 


long  straight  tube  of  hard  glass,  which  will  resist  a strong  heat 
without  fusion  : it  is  filled  with  metallic  copper  in  a finely  divided 
state ; for  this  purpose  the  metal  which  has  been  reduced  from 
the  powdered  oxide  by  means  of  hydrogen  ^as  is  well  adapted. 
The  tube  c rests  on  a sheet-iron  furnace,  d,  in  which  it  can  be 
surrounded  by  charcoal  and  raised  to  a red  heat ; ^ is  a bent  tube 
for  delivering  the  gas  into  a jar  over  water  or  mercury ; the  other 
extremity  of  the  tube  g is  connected  with  a bent  tube,  filled 
with  fragments  of  fused  caustic  potash ; and  the  air  which  sup- 
plies the  nitrogen  is  driven  from  the  gas-holder,  a,  over  the  ignited 
copper  in  a stream  which  is  easily  regulated  by  the  stopcock,  f. 
The  air  first  traverses  the  tube  which  contains  the  fused  potash, 
where  it  leaves  all  traces  of  carbonic  anhydride  and  moisture, 
and  it  then  passes  over  the  ignited  copper,  by  which  every  portion 
of  oxygen  is  completely  removed. 

5 "and  6. — Nitrogen  may  also  be  obtained  by  the  action  of 
chlorine  on  a solution  of  ammonia  (386),  and  it  is  furnished  in  a 
state  of  purity  by  heating  the  nitrite  of  ammonia  (369). 

§ III.  Composition  of  the  Atmosphere. 

(340)  If  a mixture  be  made  of  4 measures  of  nitrogen  and 
1 measure  of  oxygen  gas,  a candle  will  burn  in  it  as  in  atmo- 
spheric air ; it  may  be  breathed  as  air,  and  possesses  the  ordinary 
properties  of  the  air.  The  atmosphere  is,  in  short,  a mechanical 


COMPOSITION  OF  THE  ATMOSPHERE. 


27 


mixture  of  several  gases,  amongst  which  oxygen  and  nitrogen 
constitute  the  principal  portions:  these  gases,  notwithstanding 
their  difference  in  density,  are,  owing  to  the  principle  of  diffusion 
(67),  uniformly  mixed  with  each  other.  Chemical  operations  are 
continually  occurring  upon  the  earth’s  surface,  which  remove 
oxygen  and  add  a variety  of  other  gases,  amongst  which  carbonic 
anhydride  is  most  abundant.  Yet  so  beautifully  adjusted  is  the 
balance  of  chemical  actions  over  the  face  of  the  earth,  that  no 
perceptible  change  in  the  composition  of  the  atmosphere  has 
been  observed  since  accurate  experiments  on  the  subject  have  been 
practised. 

Air,  which  has  been  freed  from  carbonic  anhydride  and  aqueous 
vapour,  consists,  according  to  the  numerous  careful  analyses  of 
Dumas  and  Boussingault  {Ann.  de  Chimie^  III.  iii.  257),  on  an 
average  of  20*81  of  oxygen  by  measure,  and  79*19  of  nitrogen  in 
100-00  parts;  or  by  weight  of  23*01  of  oxygen,  and  76*99  of 
nitrogen.  These  experiments  were  performed  by  allowing  the  air 
to  stream  slowly  over  a weighed  quantity  of  heated  copper,  by 
which  the  oxygen  was  absorbed  (fig.  272)  whilst  the  nitrogen  was 
received  into  an  exliausted  fiask,  which  was  weighed  betore  the 
experiment  was  commenced  and  after  its  termination  ; the  quan- 
tity of  oxygen  was  found  by  the  gain  in  weight  experienced  by 
the  tube  containing  the  copper.  The  results  obtained  by  Beg- 
nault,  Brunner,  Yerver,  and  others,  by  different  methods  of 
analysis,  do  not  vary  more  than  -g-i-g-  from  the  quantity  of  oxygen 
just  mentioned.  Trifling  temporary  variations  no  doubt  occur 
from  local  causes ; but  the  air  brought  by  Gay-Lussac  from  an 
elevation  of  four  miles  above  the  surface  of  the  earth,  that  col- 
lected on  the  summit  of  the  Alps,  and  that  examined  both  in 
town  and  country  in  various  parts  of  the  globe,  presents  no  sensi- 
ble difference  from  the  mean  above  given.* 

* A portion  of  air  collected  by  Mr.  Welsh,  in  August,  1852,  at  an  elevation  of 
18,000  feet,  in  one  of  the  balloon  ascents  undertaken  by  him  and  Mr.  Green  under  the 
direction  of  the  Kew  Committee  of  the  British  Association,  contained  20-88  per  cent,  of 
oxygen  by  volume,  while  air  collected  at  the  surface  at  the  same  time  contained  20*92. 
The  air  was  collected  in  tubes  of  about  6 cubic  inches  in  capacity,  fitted  with  accurate 
stopcocks.  They  were  exhausted  previously  to  the  ascent,  and  were  fiUed  with  the 
air  for  examination  by  opening  the  stopcocks,  which  were  again  closed  as  soon  as  the 
charge  had  entered.  In  the  extensive  series  of  experiments  of  Regnault  (Aww.  de 
Chimie,  III.  xxxvi.,  385),  air  was  collected  at  different  points  of  the  earth’s  surface 
in  glass  tubes,  drawn  out  to  an  open  capillary  extremity  at  either  end,  fig.  213. 

When  a specimen  of  air  was  to  be  collected,  one  of  these  tubes  was  attached  by  a 
flexible  tube  to  a small  pair  of  bellows,  and  by  working  the  bellows  a few  times,  the 
tube  was  filled  with  air  of  the  locality.  The  capillary  tubes  were  then  drawn  off  and 
sealed,  as  at  a and  b,  by  momentary  contact  with  the  flame  of  a spirit-lamp,  and  the 
closed  ends  were  protected  from  injury  during  the  journey  by  small  caps  of  glass 
tube  fitted  with  corks.  The  analyses  of  the  air  thus  obtained  were  executed  by 
means  of  hydrogen,  in  a eudiometer  of  Regnault’s  contrivance.  The  same  apparatus 
was  used  by  myself  in  the  analyses  of  the  air  collected  by  Mr.  Welsh.  Frankland 
found  20-96  of  oxygen  in  air  collected  by  himself  from  the  summit  of  Mont  Blanc. 


28 


ESTIMATION  OF  AQUEOUS  VAPOUR  IN  THE  AER. 


100  cubic  indies  of  dry  air  weigh  at  60°  F.  and  30  inches  Bar., 
calculating  from  the  experiments 


of  Dumas  and  Boussingault 31*086  grs. 

of  Biot  and  Ai*ago 31*071:  ‘‘ 

of  Front 31*0117^' 

of  Fegnault 30*935  ‘‘ 


The  second  result  is  probably  the  most  accurate,  for  it  exactly 
corresponds  with  the  density  deduced  from  that  of  a mixture  ot* 
oxygen  and  nitrogen  in  the  proportions  in  which  they  occur  in 
the  atmosphere.  A cubic  foot  of  air,  according  to  this  result, 
weighs  536*96  grains  at  60°.  The  weight  of  a given  volume  of 
air  at  60°  F.,  under  a pressure  of  30  inches  Bar.,  is  therefore  only 
■g-^  of  that  of  an  equal  bulk  of  water  at  the  same  temperature. 
Owing  to  the  greater  solubility  of  oxygen  than  of  nitrogen,  rain 
water  and  melted  snow  always  contain  a larger  proportion  of 
oxygen  than  the  air  itself,  amounting  to  about  3i  per  cent,  of 
the  air  dissolved,  or  nearly  one  volume  of  oxygen  to  two  volumes 
of  nitrogen.  This  is  a circumstance  of  great  importance  to 
aquatic  animals,  and  one  which  could  occur  only  in  consecpience 
of  the  air  being  a mechanical  mixture  and  not  a chemical  com- 
pound of  the  two  gases  (64). 

In  addition  to  oxygen  and  nitrogen  the  atmosphere  contains  a 
certain  proportion  of  carbonic  anhydride,  a variable  but  minute 
trace  of  ammonia,  traces  of  nitric  acid,  and  of  some  compound 
of  carbon  and  hydi’ogen,  and  frequently  in  towns  a perceptible 
amount  either  of  sulphurous  anhydride  or  of  sulphuretted  hydro- 
gen. Aqueous  vapour  is  of  course  also  present  at  all  times, 
although  its  amount  is  liable  to  extensive  fluctuations. 

(341)  Estimation  of  Aqueous  Yajponr. — The  amount  of  aqueous 
vapour  at  any  spot  may  be  ascertained  by  means  of  the  hygrometer 

(194),  or  it  may 
be  determined  by 
a direct  experi- 
ment in  the  fol- 
lowing manner. 
A bent  tube,  6?, 
fig.  ■ 274,  filled 
with  pumice- 
stone,  moistened 
with  sulphm’ic 
acid,  is  connected 
with  a vessel,  e, 
of  knovm  capaci- 
ty ; suppose  it  be 
capable  of  con- 
taining 18  gallons 
of  water.  This 
vessel  having 
been  filled  with 
water,  is  allowed  to  empty  itself  slowly  by  opening  a stopcock, 


Fig.  274. 


ESTIMATION  OF  CARBONIC  ANHYDRIDE  IN  AIR. 


29 


which  terminates  in  a tube  bent  upwards  to  prevent  the  entrance 
of  air  at  the  bottom  ; a known  volume  of  air  is  thus  drawn 
through  the  tube  which  retains  all  the  moisture.  If  the 
weight  of  this  tube  be  determined  before  commencing  the  experi- 
ment, and  a second  time  after  it  is  completed,  the  increase  in 
weight  will  indicate  the  amount  of  moisture  in  the  bulk  of  air 
operated  upon.  The  temperature  is  ascertained  by  means  of  the 
thermometer,  and  the  atmospheric  pressure  is  obtained  by  an 
observation  of  the  barometer  at  the  time.  The  flow  of  water  by 
the  aspirator  is  rendered  uniform  during  the  whole  course  of  the 
experiment  by  making  the  tube  which  conveys  the  air  sufficiently 
long  to  reach  nearly  to  the  bottom  of  the  vessel,  as  shown  by  the 
dotted  line  which  passes  down  from  the  central  opening  at  the  top. 

(312)  Estimation  of  Carhonic  Anhydride. — The  quantity  of 
carbonic  anhydride  in  the  air  may  be  determined  in  the  course  of 
the  same  experiment.  If  the  bulbs  at  h be  filled  with  a strong 
solution  of  caustic  j^otasii  (sp.  gr.  1’25),  and  the  tube  with  frag- 
ments of  fused  potash,  the  gain  in  weight  experienced  by  the  tubes 
h and  c will  indicate  the  quantity  of  carbonic  anhydride  which 
has  been  absorbed  in  the  operation  ; the  bent  tube,  d^  is  filled  with 
pumice-stone  moistened  with  sulphuric  acid ; it  is  not  weighed, 
but  is  merely  interposed  as  a measure  of  precaution  between  the 
aspirator  e,  and  the  tube  (?,  to  prevent  any  accidental  trace  of 
moisture  from  passing  backwards  into  c.  The 
bulbs  seen  at  h are  to  be  filled  with  solution  of  Fig.  215. 

hydrate  of  potash  to  the  extent  shown  in  the 
enlarged  drawing,  fig.  275.  This  form  of  appa- 
ratus was  contrived  by  Liebig.  It  is  in  con- 
tinual requisition  in  the  laboratory,  for  the 
purpose  of  absorbing  gases  which  are  trans- 
mitted through  it ; by  placing  it  a little  on  one 
side,  the  gas  is  made  to  bubble  up  successively 
through  eacli  of  the  three  lower  bulbs,  besides 
being  brought  thoroughly  into  contact  with  the 
liquid  in  the  narrow  portions  of  tubing  which 
connect  the  different  bulbs  together.  This 
simple  contrivance  has  added  greatly  to  pre- 
cision in  experiments  of  this  kind.* 

The  proportion  of  carbonic  anhydride  in  the  atmosphere  varies 
from  3 to  6 parts  in  10,000  of  air.  De  Saussure  found  that 
within  these  limits  its  amount  is  lessened  after  rain,  owing  to  the 
solvent  action  of  the  descending  shower,  which  carries  a portion 
of  the  gas  with  it  to  the  earth.  It  increases  during  a frost,  and 

* Pettenkofer  estimates  the  quantity  of  carbonic  anhydride  in  air  by  agritating  a 
p^iven  volume  of  tlie  air  for  trial  with  a measured  amount  of  lime-water  of  known 
strength.  The  lime-water  used  for  this  purpose  is  graduated  by  the  alkalimetric 
method,  by  means  of  a standard  solution  of  oxalic  acid.  The  carbonic  anhydride 
neutralizes  and  precipitates  a certain  quantity  of  lime  in  the  form  of  chalk,  and  the 
quantity  of  lime  which  remains  in  the  solution  after  the  experiment  is  again  deter- 
mined by  the  solution  of  oxalic  acid.  The  difference  in  the  quantity  of  lime  before 
and  after  its  action  upon  the  air  enables  the  operator  to  calculate  the  proportion  of 
carbonic  anhydride  with  great  accuracy. 


30 


WATEE. 


diminishes  when  a thaw  sets  in.  During  the  night  it  increases, 
and  diminishes  again  after  sunrise.  It  is  less  in  amount  over 
large  bodies  of  water  than  over  large  tracts  of  land.  The  pro- 
portion of  carbonic  anhydride  is  less  liable  to  vary  on  elevated 
mountains,  where  it  is  generally  more  abundant  than  in  the  plains. 
It  is  also  more  abundant  in  densely  populated  districts  than  in 
the  open  country.  In  inhabited  dwellings,  and  in  rooms  for 
public  assemblies,  the  proportion  of  carbonic  anhydride  may,  how- 
ever, greatly  exceed  the  normal  amount. 

The  quantity  of  ammonia  and  nitric  acid  in  the  atmosphere  is 
materially  diminished  after  long-continued  and  heavy  rains.  Oc- 
casionally, from  local  and  accidental  circumstances,  other  gases 
and  vapours  are  also  met  with.  The  air  of  towns  contains  in 
addition  certain  organic  impurities  in  suspension.  Dr.  Angus 
Smith  has  attempted  to  estimate  their  amount  by  measuring  the 
quantity  of  a very  dilute  solution  of  permanganate  of  potassium 
of  known  strength  which  a given  bulk  of  air  will  deprive  of  colour. 
— {Q.  J.  Chem.  Soc.  xi.  217.)* 

The  average  composition  of  the  atmosphere  in  the  climate  of 
England  may  be  approximatively  stated  as  follows,  in  100  parts 
by  volume : — 

Avemge  Composition  of  the  Atmosphere. 


Oxygen 20‘61 

Nitrogen 7 7 '95 

Carbonic  anhydride *04: 

Aqueous  vapour 1 ’40 

Nitric  acid. ...  ) 

Ammonia V traces 


Carburetted  hydrogen, 
and  in  j Sulphuretted  hydrogen 
towns  { Sulphurous  anhydride. 


CHAPTEK  III. 

WATER. HYDROGEN. 

§ I.  Water.  = 18 ; Atomic  and  Mol.  Yol.  of  Yojpour  \ \ | ; 
or  HO  = 9 : Bjp.  Gr.  as  Yaponr  0-622,  as  Liquid  1*000, 

Ice  0-918. 

(343)  On  the  uses  of  water  it  is  almost  needless  to  enlarge,  for 
they  are  universally  felt  and  appreciated.  In  each  of  its  three 
physical  conditions,  the  blessings  whicli  it  confers  upon  man  are 
inestimable.  As  ice,  it  furnishes  in  northern  lands  for  months 
together,  a solid  bridge  of  communication  between  distant  places  : 

* If  air  which  has  been  scrupulously  freed  from  carbonic  anhydride  be  passed 
over  a column  of  pure  ignited  oxide  of  copper,  traces  of  carbonic  anhydride  are  always 
obtained,  owing  to  the  oxidation  of  some  combustible  compound  of  carbon.  In  the 
junctions  of  the  apparatus  employed  for  this  experiment  the  use  of  cork  and  caout- 
chouc must  be  avoided  (Karsten),  or  otherwise  the  carbonic  anhydride  might  be 
derived  from  them. 


GENERAL  PROPERTIES  OF  WATER. 


31 


in  the  liquid  condition,  it  is  absolutely  necessary  to  the  existence 
of  vegetable  and  animal  life ; in  this  shape,  too,  it  furnishes  to 
man  a continual  source  of  power  in  the  flow  of  streams  and  rivers  ; 
it  supplies  one  of  the  most  convenient  channels  of  communication 
between  places  widely  separated ; and  further,  it  is  the  storehouse 
of  countless  myriads  of  creatures  fitted  for  use  as  food : in  the 
state  of  vapour,  as  applied  in  the  steam-engine,  it  has  furnished  a 
power  which  has  in  later  years  done  more  than  any  other  physical 
agent  to  advance  civilization,  to  economize  time,  and  to  ameliorate 
the  social  condition  of  man.  In  each  and  all  of  these  points,  if 
rightly  considered,  we  must  perceive  the  entire  adaptation  of  this 
wonderful  compound  to  the  ends  which  it  was  designed  by  the 
Creator  to  fulfil. 

Glancing  at  the  physical  condition  of  our  planet,  we  cannot 
fail  to  be  impressed  with  the  important  effects  produced  by  the 
movements  of  water  at  periods  anterior  to  the  existence  of  man,  as 
well  as  in  more  recent  times.  To  such  causes  must  we  refer  the 
formation  of  sedimentary  rocks  and  their  arrangement  in  suc- 
cessive strata  upon  the  surface  of  the  earth  : even  now,  observation 
shows  that  denudation  is  proceeding  at  some  points,  elevation  and 
filling  up  of  hollows  at  others  ; whilst  the  accumulation  of  drift 
and  a variety  of  other  extensive  geological  changes  must  be  traced 
to  the  same  ever-acting  and  widely-operating  agency. 

It  may  further  be  observed  that  there  is  no  form  of  matter 
which  contributes  so  largely  as  water  to  the  beauty  and  variety  of 
the  globe  which  w^e  inhabit.  In  its  solid  state  we  are  familiar 
with  it  in  the  form  of  blocks  of  ice,  of  sleet  and  hail,  of  hoar-frost 
fringing  every  shrub  and  blade  of  grass,  or  of  snow  protecting  the 
tender  plant,  as  with  a fleecy  mantle,  from  the  piercing  frosts  of 
winter.  The  rare  but  splendid  spectacles  of  mock  suns,  or  par- 
helia, are  due  to  the  refractive  power  of  floating  spiculse  of  ice 
upon  the  sun’s  rays.  In  its  liquid  condition,  as  rain  or  dew,  it 
bathes  the  soil ; and  the  personal  experience  of  all  will  testify  to 
the  charm  which  the  waterfall,  the  rivulet,  the  stream,  or  the  lake, 
adds  to  the  beauty  of  the  landscape ; whilst  few  can  behold  un- 
moved the  unbounded  expanse  of  ocean,  which,  whether  motion- 
less, or  heaving  with  the  gently  undulating  tide,  or  when  lashed 
into  foam  by  the  storm  that  sweeps  over  its  surface,  seems  to 
remind  man  of  his  own  insignificance,  and  of  the  power  of  Him 
who  alone  can  lift  up  or  quell  its  roaring  waves.  In  vapour  how 
much  variety  is  added  to  the  view  by  the  mist  or  the  cloud,  which 
by  their  ever-changing  shadows  diversity,  at  every  moment,  the 
landscape  over  which  they  are  flitting ; wliilst  the  gorgeous  hues 
of  the  clouds  around  the  setting  sun,  and  the  glowing  tints  of  the 
rainbow,  are  due  to  the  refractive  action  of  water  and  watery 
vapour  upon  the  solar  rays. 

Properties. — At  the  ordinary  temperature  of  the  air,  water, 
when  free  from  admixture,  is  a clear,  colourless,  transparent  liquid, 
destitute  of  taste  or  smell.  At  temperatures  below  32°  it  freezes 
and  assumes  a variety  of  crystalline  forms  derived  from  the  rhom- 
bohedron  and  six-sided  prism.  Water  evaporates  at  all  tempera- 


32 


WATER  Ds  COMBINATION. 


tiires,  and  under  the  ordinary  pressure  of  the  atmosphere  it  boils 
at  about  212°.  Its  anomalous  expansion  by  heat  (ld3),  and  the 
important  purposes  thereby  attained  (151),  as  well  as  the  great 
dilatation  which  it  undergoes  on  fi-eezing  (76),  have  been  ah’eadj 
pointed  out.  Arago  and  Fresnel  have  shown,  that  notwithstand- 
ing the  gradual  dilatation  of  water  at  temperatures  below  39°,  its 
refractive  power  on  light  continues  to  increase  regularly,  as  though 
it  contracted.  Its  density  at  60°  is  taken  as  I'OOO,  and  it  forms 
the  standard  with  wliich,  in  this  country,  the  specific  gravities  of 
all  solids  and  liquids  are  compared.  A cubic  inch  of  water  at 
60°  F.  weighs  in  air  252-156  grains,  and  a cubic  foot  very  nearly 
1000  (more  exactly  997)  ounces  avoirdupois. 

To  the  chemist  water  is  invaluable  as  a solvent.  It  is  the  per- 
fection of  a neutral  substance ; and  it  enters  into  combination' 
most  extensively  both  with  acids  and  with  bases.  Experience  has 
shown  that  when  an  anhydride,  or  so-called  anhydrous  acid,  has 
once  been  allowed  to  combine  with  water,  the  entire  separation  of 
the  water  from  the  compound  is  often  impracticable,  unless  some 
powerful  base  be  presented  to  the  acid ; in  such  a case  the  base 
appears  to  displace  the  water,  and  its  expulsion  by  heat  is  then 
easily  effected.  Suppose,  for  example,  that  sulphuric  acid  has 
been  fi-eely  diluted  with  water  ; upon  the  application  of  heat  the 
water  at  first  passes  ofi‘  readily,  leaving  the  less  volatile  acid 
behind.  By  degrees,  however,  it  becomes  necessary  to  increase 
the  temperature  in  order  to  exyiel  the  water,  and  at  last  the  acid 
begins  to  evaporate  also,  and  finally  no  fm-ther  separation  can  be 
efiected,  because  when  the  temperature  rises  to  about  610°  F.  the 
entire  liquid  distils  over.  It  is  found  on  analysing  the  acid  when 
it  has  reached  this  point,  that  the  composition  of  the  liquid  may 
be  represented  by  the  formula  or  IIO,S03.  But  if  to  this 

concentrated  acid  a base,  such  as  oxide  of  lead,  be  added,  the  water 
is  easily  expelled,  and  anhydrous  sulphate  of  lead  is  obtained : — 

Pbe  + H.BO.^H.O-f  PbSe, : 

or  Pb0,  + H0,S03=ll0-f-Pb0,S03. 

Upon  the  older  and  still  current  ^dew  of  the  constitution  of  salts, 
which  regards  these  bodies  as  formed  by  the  union  of  an  anhydi-ide 
vdth  a base,  the  water  would  in  the  foregoing  instances  supply  the 
place  of  a base,  and  it  hence  has  been  termed  1)0810  water,  e.g.  \ — 

IIO,S03,  oil  of  vitriol. 

PbOjSOj,  sulphate  of  lead. 

Still  adopting  the  older  \dew,  it  has  been  supposed  in  a similar 
manner  that  water  combines  with  the  powerful  bases,  such  as 
potash  or  soda,  and  then  cannot  be  expelled  from  them  until  some 
acid  has  been  added.  Potash  in  the  form  in  which  it  is  obtained 
by  evaporating  down  its  aqueous  solution  and  heating  the  residue 
to  dull  redness,  contains  the  elements  of  one  equivalent  of  the  alkali 
and  one  of  water  (IvO,IIO)  : this  equivalent  of  water  cannot  be 
expelled  except  by  the  addition  of  an  acid,  such  as  sulphuric  acid  ; 
then  by  the  application  of  heat,  anhydi'ous  sulphate  of  potash  is 


I 


WATEK  IN  COMBINATION. 


33 


obtained.  In  sncli  a case  the  water  in  combination  with  the  base 
appears  to  perform  the  part  of  an  acid. 

The  foregoing  explanation  is  inadmissible  if  water  be  repre- 
sented as  consisting  of  H^O ; but  in  this  case  the  presence  of 
hydrogen  in  hydrate  of  potash  may  be  equally  well  accounted  for, 
if  it  be  supposed  that  caustic  potash  is  a compound  formed  upon 
the  same  plan  or  type  as  water,  but  that  it  contains  an  atom  of 
potassium  in  place  of  one  of  the  atoms  of  hydrogen  present  in 
the  molecule  of  water.  Further,  anhydrous  potash,  which  may 
be  formed  from  the  hydrate  of  tlie  alkali  by  heating  it  with 
potassium,  whilst  hydrogen  is  liberated,  is  viewed  as  containing 
two  atoms  of  potassium  in  place  of  the  two  atoms  of  hydrogen  in 
the  molecule  of  water.  The  relations  of  these  three  different  com- 
pounds may  be  thus  represented : — • 

Hydrate  of 

Water.  Potash. 

IfflO  ; Klie  ; KKO 

The  reaction  of  sulphuric  acid  upon  hydrate  of  potash  is  then 
a true  case  of  double  decomposition,  as  may  be  thus  repre- 
sented : — 


'otash. 


Acid. 


Water. 


2KHe  -f  211110  -I-  K,SO, 

the  two  atoms  of  potassium  of  the  base,  and  the  two  of  hydrogen 
in  the  acid,  changing  places  with  each  other,  whilst  sulphate  of 
potassium  and  water  are  each  formed  simultaneously. 

The  compounds  of  water  are  frequently  termed  hydrates. 
When  a body  is  described  as  being  entirely  free  from  water,  in 
combination,  it  is  commonly  said  to  be  anhydrous  (from  a not, 
water). 

Many  salts  in  crystallizing  unite  with  a definite  quantity  of 
water,  which  is  essential  to  the  form  of  the  salt,  but  which  may, 
by  the  application  of  a gentle  heat,  be  expelled  without  altering 
the  chemical  properties  of  the  saline  body.  In  this  case  the 
water  is  spoken  of  as  water  of  crystallization.  Many  salts  part 
with  such  water  by  mere  exposure  to  air.  Carbonate  of  sodium^, 
for  example,  crumbles  down  or  effloresces  to  a white  powder;  and 
the  same  thing  occurs  in  the  case  of  sulphate  of  sodium.^  The 
form  of  the  salt  depends  upon  the  quantity  of  this  water  of  crys- 
tallization. For  instance,  borax  is  always  found  to  crystallize 
with  10  atoms  of  water  (FTa^B^O^  . 10  II2O),  in  oblique  rect- 
angular prisms,  if  the  solution  of  the  salt  be  not  sufficiently 
concentrated  to  begin  to  crystallize  till  tlie  temperature  falls  to 
133°  F.  ; but  from  a more  concentrated  solution  borax  is  deposited 
in  regular  octohedra  with  only  5 atoms  of  water.  So,  again,  the 
sulphate  of  sodium  crystallizes,  under  ordinary  circumstances,  in 
oblique  four-sided  prisms  with  10  atoms  of  water  (N'a.^SO,  . 

* Other  salts,  on  the  coiitrarj,  absorb  moisture  from  the  atinosplmre,  and  become 
damp  or  even  liquefy  in  the  water  so  absorbed ; they  arc  then  said  to  deliquesce. 
Carbonate  of  potassium  and  chloride  of  calcium  offer  instances  of  this  kind. 

3 


34 


SEPARATION  OF  AIK  FROM  SOLUTION  IN  WATER. 


10  H^O) ; but  if  a solution  saturated  at  91°,  be  very  slowly  raised 
to  212°,  the  sulphate  of  sodium  is  deposited  in  rhombic  octohedra 
which  contain  no  water. 

(344)  Various  }dnds  of  Natural  Waters. — Owing  to  its  exten- 
sive solvent  powers,  water  is  never  met  with  naturally  in  a state 
of  purity.  Rain  Water collected  after  a long  continuance  of  wet 
weather,  approaches  nearest  to  it,  but  even  that  always  contains 
atmospheric  air,  and  the  gases  floating  in  the  air,  to  the  extent  of 
about  21  cubic  inches  of  air  in  100  of  water.* 

* The  quactity  of  air  which  is  contained  in  spring  or  other  water  can  be  readily 
ascertained  in  the  fohowing  manner.  A globular  flask,  a,  flg.  276,  capable  of  con- 
taining 14  or  16  ounces, 
such  as  is  used  for  taking 
the  density  of  vapours,  is 
fiUed  with  the  water  to  be 
examined,  and  connected 
by  a vulcanized  caoutchouc 
tube,  &,  to  a piece  of  baro- 
meter tube,  upon  which  is 
blown  a bulb,  c,  2 inches  or 
more  in  diameter.  This 
tube  is  bent  in  the  manner 
represented  in  the  figure; 
the  longer  limb  being  up- 
wards of  30  inches  in 
length,  and  terminating  be- 
low in  a recurved  extremity 
designed  to  deliver  the  gas 
disengaged  from  the  water, 
into  a graduated  jar,  d,  with 
an  expanded  funnel-shaped 
mouth,  which  is  supported 
in  a small  mercurial  bath. 
The  bulb,  c,  having  been 
about  half  filled  with  the 
water,  is  connected  with  the 
flask  by  the  caoutchouc 
tube,  which  is  firmly  se- 
cured at  both  ends  by  liga- 
tures. A small  wooden 
vice,  such  as  is  seen  at  /,  is 
made  use  of  to  compress 
the  vulcanized  tube  and  to 
cut  off  communication  be- 
tween the  flask  and  the  bulb,  c.  The  water  in  c is  now  made  to  boil  briskly  for  ten 
minutes  or  a quarter  of  an  hour,  until  all  the  air  is  expelled  from  the  tube,  the 
mouth  of  which  is  kept  just  below  the  surface  of  the  mercury.  When,  after  the 
boiling  has  been  continued  for  a few  minutes,  no  more  air  escapes  from  the  tube, 
the  jar,  d.  is  filled  with  mercury  and  placed  over  the  end  of  the  long  tube.  The  vice 
is  removed,  and  heat  applied  to  the  flask  ; the  water  speedily  begins  to  give  off  gas; 
and  the  quantity  increases  till  the  water  boils.  The  ebullition  must  be  continued 
steadily  for  a full  hour,  and  the  operation  terminated  by  a few  minutes’  brisk  boiling, 
by  which  the  delivery  tube  will  be  filled  with  steam,  and  all  the  air  will  be  driven  over 
into  the  jar.  One  object  of  the  globe,  c,  is  to  prevent  the  water  from  boiling  over  into  the 
jar,  d : a little  steam  always  condenses  in  the  jar  above  the  mercury,  but  this  is  a mat- 
ter of  small  consequence.  When  the  operation  has  terminated,  the  gas  is  allowed  to  cool, 
and  is  transferred  to  a tall  jar  of  water,  or  of  mercury,  where  its  bulk  can  be  measured. 

It  will  be  found  that  all  water,  including  even  that  which  has  been  recently  dis- 
tilled, contains  air.  For  example,  three  samples  of  water  twice  distilled  in  glass 
vessels,  were  submitted  to  experiment:  100  cub.  in.  of  the  first  specimen  contained 
l'85cub.  in.  of  air;  in  the  same  bulk  of  the  second  2T5,  and  the  third  specimen 
2 '38  cub.  in.  of  air  were  present ; the  oxygen  and  nitrogen  being  in  each  ease  almost 
exactly  in  the  proportion  of  1 measure  of  oxygen  to  2 measures  of  nitrogen. 


Fig.  276. 


MINERAL  WATERS RIVER  WATER. 


35 


Spring  Water ^ although  it  may  he  perfectly  transparent,  always 
contains  more  or  less  of  saline  matter  dissolved  in  it ; the  nature 
of  these  salts  will  of  course  vary  with  the  character  of  tlie  soil 
through  which  the  water  percolates.  The  most  usual  saline  impu- 
rities are  carbonate  of  calcium,  common  salt,  sulphate  of  calcium, 
and  sulphate  and  carbonate  of  magnesium.  The  waters  of  the 
New  Red  Sandstone  are  impregnated  to  a greater  or  less  extent 
with  sulphate  of  calcium.  Most  spring  waters  are  cliarged  with 
a notable  proportion  of  carbonic  acid,  wdiich  dissolves  a consider- 
able amount  of  carbonate  of  calcium  ; the  calcareous  springs  in 
the  chalk  districts  around  London  contain  from  18  to  20  grains 
of  chalk  per  gallon,  6 or  8 grains  of  which  become  separated 
by  exposure  of  the  water  to  the  atmosphere,  so  that  a running 
stream  will  seldom  contain  more  than  12  or  14  grains  of  chalk 
per  gallon  in  solution.  Waters  wLich  have  filtered  through 
a bed  of  chalk  also  often  contain  carbonate  of  sodium  in  consi- 
derable quantity,  as  is  the  case  with  the  deep-well  waters  of 
London. 

Mineral  Waters  are  waters  impregnated  with  a large  propor- 
tion of  any  one  of  the  above-named  salts,  or  with  some  substance 
not  so  commonly  met  with : such  waters  are  usually  reputed  to 
possess  medicinal  qualities,  wLich  vary  with  the  nature  of  the  salt 
in  solution.  Many  of  these  springs  are  of  a temperature  con- 
siderably higher  than  that  of  the  surface  of  the  earth  where  they 
make  their  appearance.  At  Carlsbad  and  Aix-la-Chapelle  this 
temperature  varies  from  160°  to  190°.  Such  hot  springs  either 
occur  in  the  vicinity  of  volcanoes,  in  which  case  they  generally 
abound  in  carbonic  acid,  as  well  as  in  common  salt  and  other  salts 
of  sodium  : or  they  spring  from  great  depths  in  the  rocks  of  the 
earliest  geological  periods,  and  contain  chlorides  of  calcium  and 
magnesium,  and  almost  always  traces  of  sulphuretted  hydrogen. 
(Berzelius.) 

Many  mineral  waters  contain  salts  of  iron  in  solution,  which 
impart  to  them  an  inky  taste  ; tliey  are  then  frequently  termed 
chalybeate  w^aters  ; some  of  the  Cheltenham  springs  are  of  this 
kind.  In  other  instances  carbonic  acid  is  very  abundant,  giving 
the  brisk  effervescent  character  noticed  in  Seltzer  water.  Less 
frequently,  as  in  the  Harrogate  water,  sulphuretted  hydrogen  is 
the  predominating  ingredient,  giving  the  nauseous  taste  and  smell 
to  such  sulphureons  waters.  In  other  instances  the  springs  are 
merely  saline^  and  contain  purgative  salts,  like  the  springs  at 
Epsom,  which  abound  in  sulphate  of  magnesium,  and  at  Chelten- 
ham, where  common  salt  and  sulphate  of  sodium  are  the  predo- 
minant constituents.  Many  of  these  saline  springs  also  contain 
small  quantities  of  iodine  and  bromine,  which  add  greatly  to  their 
therapeutic  activity. 

River  Water  is  less  fitted  for  drinking  than  ordinary  spring 
water,  although  it  often  contains  a smaller  amount  of  salts  ; for 
it  usually  holcls  in  solution  a much  larger  proportion  of  organic 
matter  of  vegetable  origin,  derived  from  the  extensive  surface  of 
country  which  has  been  drained  by  the  stream.  If  the  sewerage 


36  KIVER  WATER HARD  AHD  SOFT  WATER SEA  WATER. 

of  large  towns  situated  on  the  banks  be  allowed  to  pass  into  the 
stream,  it  is  of  course  still  less  lit  for  domestic  use.  Kunning 
water  is,  how’ever,  endowed  with  a self-purifjing  power  of  the 
liighest  importance ; the  continual  exposure  of  fresh  surfaces  to 
the  action  of  the  atmosphere  promotes  the  oxidation  of  the  organic 
matter,  and  if  the  stream  be  unpolluted  by  the  influx  of  the 
sewerage  of  a large  town,  this  process  is  generally  fully  adequate 
to  preserve  it  in  a wholesome  state.  River  water  almost  always 
requires  filtration  through  sand  before  it  is  fit  for  domestic  use  ; 
and  if  water- works  designed  to  supply  such  water  be  properly  con- 
structed, provision  is  made  for  this  hltration.  Suspended  matters, 
such  as  weeds,  fish-spawn,  leaves,  and  finely  divided  silt  or  mud, 
are  thus  removed ; but  vegetable  colouring  matter  in  solution, 
salts,  and  other  bodies,  when  once  they  are  dissolved,  cannot  be- 
arrested  by  such  a filter. 

In  the  gradual  percolation  of  water  through  the  porous  strata 
of  the  earth,  many  even  of  these  soluble  impurities  are  removed, 
particularly  those  of  organic  origin,  partly  by  adhesion  to  the 
surface  of  the  filtering  material,  but  chiefly  by  a slow  oxidation 
in  the  pores  of  the  soil. 

The  magnetic  oxide  of  iron,  indeed,  seems  to  exert  a peculiar 
influence  in  promoting  the  oxidation  of  organic  matter  contained 
in  water  which  is  allowed  to  percolate  through  it,  and  it  appears 
to  be  probable  that  this  action,  to  which  Mr.  Spencer  has  parti- 
cularly called  attention,  may  furnish  a valuable  auxiliary  to  the 
methods  of  filtration  at  present  in  use.  Filtration  through  beds 
of  iron  turnings  has  likewise  been  practised  in  some  cases  with 
advantages  of  a similar  description,  but  the  oxygen  is  in  this  case 
in  great  measure  absorbed  from  the  water  by  the  iron. 

The  presence  of  organic  matter  in  water  is  easily  ascertained 
by  the  reducing  influence  which  it  exerts  upon  chloride  of  silver 
or  of  gold,  or  upon  permanganate  of  potassium,  when  boiled  with 
them.  The  chloride  of  silver  becomes  purplish  : and  chloride  of 
gold  imparts  a brown  tint  to  the  water  under  such  circumstances, 
owing  to  the  precipitation  of  metallic  gold.  A very  dilute  solu- 
tion of  permanganate  of  potassium  is  rendered  colourless,  whilst  a 
brown  precipitate  of  hydrated  peroxide  of  manganese  is  formed. 

W ater  is  familiarly  spoken  of  as  hard  or  soft^  according  to  its 
action  on  soap.  Those  waters  wdiich  contain  compounds  of  cal- 
cium or  magnesium  occasion  a curdling  of  the  soap,  as  these 
bodies  produce  with  the  fatty  acid  contained  in  the  soap  a sub- 
stance not  soluble  in  water.  Soft  waters  do  not  contain  these 
salts,  and  dissolve  the  soap  without  difficulty.  Many  hard 
waters  become  softer  by  boiling ; in  such  cases  the  carbonic  acid 
is  expelled,  and  the  carbonate  and  part  of  the  sulphate  of  calcium 
which  were  held  in  solution  are  deposited,  and  cause  a fur  or 
incrustation  upon  the  inside  of  the  boiler  (655). 

Sea  Water  is  largely  impregnated  with  common  salt,  and  with 
chloride  of  magnesium,  to  which  it  owes  its  saline  bitter  taste.  It 
might  be  supposed  that  the  quantity  of  salts  which  it  contains  is 
continually  on  the  increase,  as  the  sea  is  the  receptacle  for  all  the 


SEA  WATER DISTILLED  WATER. 


37 


fixed  contents  of  the  river  water  which  is  discharged  into  the 
ocean,  since  pure  water  alone  evaporates  from  its  surface  ; hut  here 
also  there  is  a return  to  the  surface  of  the  soil  provided  for  in  the 
marine  plants,  the  fish,  and  their  representative  guano,  which  are 
perpetually  being  raised  from  its  depths  by  the  force  of  storms,  by 
predatory  birds,  and  by  the  industry  of  man.  The  specific  gravity 
of  sea  water  is  subject  to  trifling  variations,  according  to  the  part 
of  the  globe  from  which  it  is  taken.  The  waters  of  the  Baltic 
and  of  the  Black  Sea  are  less  salt  than  the  average,  while  those 
of  the  Mediterranean  are  more  so.  The  waters  of  the  Mediter- 
ranean in  the  Levant  are  more  salt  than  those  of  the  same  sea 
near  the  Straits  of  Gibraltar.  The  mean  specific  gravity  of  sea 
water  is  1’027,  and  the  quantity  of  salts  ranges  from  3*5  to  4 per 
cent.  According  to  Schweitzer  {Phil.  Mag.  1839,  vol  xv.  p.  58), 
the  water  of  the  British  Channel  is  composed  as  follows : — that 
of  the  Mediterranean,  analysed  by  Usiglio  {Ann.  de  Cliimie^  III. 
xxvii.  104),  will  be  seen  to  agree  very  closely  with  it  in  compo- 
sition : — 


British  Channel. 

Water 963 '743 7 2 

Chloride  of  sodium 28-05948 

Chloride  of  potassium 0-76552 

Chloride  of  magnesium 3 66658 

Bromide  of  magnesium 002929 

Sulphate  of  magnesium 2-29578 

Sulphate  of  calcium 1-40662 

Carbonate  of  calcium 0-O3301 

Iodine traces 

Ammonia traces 

Oxide  of  iron 


Mediterranean. 

962-345 

29-424 

0-505 

3-219 

0- 556 
2-477 

1- 357 
0-114 


0-003 


1000-00000 


1000-000 


Specific  gravity 


1027-4  at  60°  F. 


1025-8  at  70°  F. 


Minute  quantities  of  iron  and  phosphates  have  been  found  in  the 
waters  of  the  ocean,  but  nitrates  have  as  yet  eluded  the  most 
careful  observation. 

For  chemical  purposes  water  is  always  purified  by  distillation, 
which  may  be  effected  on  a small  scale  in  glass  retorts,  but  it  is 
generally  carried  on  in  a copper  still  provided  with  a pewter  or 
copper  worm.  Iron  pipes  may  also  be  safel}^  used  for  the  purpose 
of  condensation  ; but  lead  must  be  avoided.  The  still  should  not 
be  employed  for  any  other  purpose.  The  addition  of  lime  to  the 
water  before  submitting  it  to  distillation  is  useful,  as  it  retains  the 
excess  of  carbonic  acid,  and  also  traces  of  hydrochloric  acid,  which 
if  chloride  of  magnesium  be  present  are  apt  to  come  over,  owing 
to  the  decomposition  of  this  salt.  The  first  portions  of  water 
should  be  rejected,  because  they  usually  contain  traces  of  ammonia ; 
when  a few  drops  of  distilled  water  are  evaporated  upon  a slip  of 
glass,  no  stain  or  mark  should  be  left,  otherwise  some  saline  im- 
purity is  present. 

Water  was  long  supposed  to  be  an  elementary  substance. 
This,  however,  is  not  the  case  : it  is  a compound  of  oxygen  with 
hydrogen,  in  the  proportion  of  1 eguivaUnt  of  eacli,  or  two  atoms 
of  hydrogen  to  one  atom  of  oxygen;  its  symbol  is  tlierefore  II2O, 


38 


ANALYSIS  OF  WATER PREPARATION  OF  HYDROGEN. 


and  its  combining  number  18.  When  converted  into  vapour, 
18  grains  of  steam  occupy  twice  the  bulk  of  one  grain  of 
hydi’ogen  at  the  same  temperature  ; the  combining  volume  of 
aqueous  vapour  is  therefore  | | |,  if  the  combining  volume  of 


hydrogen  be  taken  as  fl. 

Its  composition  is  shown  m the  fol 

lowing  table : — 

Symb.  By 

weight. 

Dumas. 

By  vol.  Sp.  gr.  vap. 

Hydrogen 

H2  = 2 or  11-11 

11-12 

2 or  1-0  = 0-0692 

Oxygen 

e =16 

88-89 

88-88 

1 0-5  = 0.5528 

Water 

HaO  = 18 

100-00 

100-00 

2 1-0  = 0-6220 

§ II.  Hydrogen.  H ==  1. 

Sj).  Gr.  0-0692  ; Atomic  vol.  | | *. 

(345)  Preparation. — The  composition  of  water  may  be  deter- 
mined both  by  analysis  or  separation  of  its  constituents,  and  by 
synthesis  or  their  reunion  after  such  separation. 

1.  — An  elegant  mode  of  showing  the  composition  of  water  ana- 
lytically is  ahbrded  by  the  voltaic  battery.  A glass  vessel,  tig.  277, 
containing  two  platinum  plates,  a and  is  filled  with  water, 
slightly  acidulated  with  sulphuric  acid  to  improve  its  conducting 

power,  and  is  arranged  so  as  to  transmit 
the  current  of  a battery  consisting  of  three 
or  four  pairs  of  Grove’s  cells  (266).  Im- 
mediately that  the  two  platinum  plates  are 
connected  with  the  wires  of  the  battery, 
gas  rises  from  each  ; and  if  two  similar  jars 
be  filled  with  water  and  inverted  one  over 
each  plate,  the  volume  of  the  gas  which  rises 
from  the  platinode,  or  negative  plate,  J, 
will  be  found  to  be  exactly  double  of  tliat 
which  rises  from  the  zincode,  or  positive 
plate,  a : the  gas  in  the  tube  o will  sliow 
itself  to  be  oxygen  by  rekindling  a glowing 
match,  whilst  that  in  h extinguishes  flame, 
but  takes  fire  itself  when  a light  approaches 
it.  To  the  latter  gas  the  name  of  hydrogen 
(from  C5wp  water,  yswaoj  to  generate)  has  been  given.  Oxygen 
and  hydrogen  are  the  sole  ingredients  of  water,  and  by  their  union 
ill  the  proportion  of  two  measures  of  hydrogen  to  one  measure  of 
oxygen  this  liquid  is  reproduced. 

2.  — The  presence  of  hydrogen  and  oxygen  in  water  may  be 
shown  in  other  ways,  and  hydrogen  may  be  obtained  from  it  by 
chemical  means.  If  a piece  of  sodium  of  the  size  of  a pea  be 
wrapped  up  in  blotting  paper,  and  be  rapidly  introduced  beneath 
the  mouth  of  a strong  wide  tube,  10  or  12  inches  long,  filled  with 
water  and  inverted  in  the  pneumatic  trough,  bubbles  of  gas  will 
be  quickly  disengaged,  and  will  collect  on  the  upper  part  of  the 

* Free  hydrogen  is  now  commonly  regarded  as  (HH),  or  hydride  of  hydrogen,  with 
a molecular  volume  l ~|  \. 


Fig.  277. 

O H 


PKEPAIiATIOISr  OF  HYDROGEN. 


39 


tube.  On  inverting  the  tube  and  applying  a light,  the  gas  will 
take  tire  and  burn  with  flame  ; the  liquid  in  the  tube  will  be  found 
to  be  alkaline,  and  will  change  the  yellow  colour  of  turmeric  to 
brown  : soda  having  been  formed  by  the  combination  of  the  sodium 
with  oxygen  derived  from  water. 

3. — Hydrogen  may  be  also  obtained  by  the  action  of  water 
upon  iron  at  a high  temperature.  In  order  to  effect  this,  let  a piece 
of  iron  piping,  shown  at  a a,  fig.  278,  be  filled  with  iron  turnings. 


Fig.  278. 


and  heated  to  redness  in  a portable  furnace,  b ; and  let  a current 
of  steam  be  driven  through  the  tube  from  a small  boiler,  c,  attached 
to  one  extremity  of  the  pipe ; the  aqueous  vapour  in  its  passage 
will  be  decomposed,  the  oxygen  will  enter  into  combination  with 
the  heated  iron,  whilst  the  liberated  hydrogen  will  pass  on,  and 
may  be  collected  over  water  in  a jar,  d,  placed  over  the  mouth  of 
a bent  tube  attached  to  the  other  extremity  of  the  iron  pipe.  The 
decomposition  may  be  represented  in  symbols  as  follows : — 

3 Fed- 4 Il20=Fe0,  Fe^Og-f  4 H2. 

4.  — Deville  and  Debray  prepare  hydrogen  on  a large  scale 
nearly  pure,  by  transmitting  steam  over  charcoal,  or  coke  heated 
to  dull  redness.  Carbonic  anhydride  and  hydrogen  are  the  sole 
p'oducts  if  the  temperature  be  kept  sufficiently  low  : — 

2 H,o  + e 2 II,  F ee,. 

The  gas  is  purified  by  causing  it  to  traverse  an  apparatus  filled 
with  slaked  lime,  and  similar  to  that  known  as  tlie  dry  lime  puri- 
fier for  coal  gas.  If  the  temperature  be  allowed  to  rise  too  high, 
part  of  the  carbonic  anhydride  is  converted  into  carbonic  oxide 
(357),  and  this  gas  cannot  then  be  removed  from  the  mixture. 

5.  — It  may  also  be  obtained  by  heating  zinc  with  a solution  of 
hydrate  of  potash,  the  metal  combining  with  the  oxygen  of  the 
water,  or  displacing  the  hydrogen  contained  in  the  hydrate  of 


40 


PKOPERTIES  OF  HYDROGEN. 


potash,  whilst  the  hydrogen  is  liberated,  the  oxide  of  zinc  as  it  is 
formed  being  dissolved  by  the  alkaline  liquid — 

2 KHO  4-  Zn  becoming  K2^n02  + ; 

but  this  method  is  interesting  from  its  theoretical  bearings  rather 
than  from  any  practical  utility. 

6. — But  tlie  most  convenient  way  of  procuring  hydrogen  is  by 
the  action  of  diluted  sulphuric  acid  on  zinc.  The  zinc  may  be 
melted  in  an  iron  ladle,  and  poured  from  the  height  of  a few  feet 
into  a pail  of  cold  water,  by  which  means  it  is  granulated^  or  re- 
duced into  grains  or  flakes  : about  half  an  ounce  of  the  granulated 
zinc  is  introduced  into  a retort,  and  a diluted  acid,  prepared  by 
mixing  an  ounce  of  oil  of  vitriol  cautiously  with  6 ounces  of  cold 
water,  stirring  all  the  while,  is  poured  upon  the  zinc.  Hydrogen 
gas  is  soon  evolved  in  great  abundance : the  first  portions  of  gas 
which  are  contaminated  with  the  air  contained  in  the  retort,  must 
be  allowed  to  escape ; afterwards  the  gas  may  be  collected  in  the 
usual  way.  In  this  process  the  zinc  may  be  regarded  as  displac- 
ing the  hydrogen  of  the  acid,  and  forming  the  salt  called  sulphate 
of  zinc,  which  becomes  dissolved,  while  the  hydrogen  passes  ofi*  in 
the  gaseous  form.  The  change  may  be  illustrated  by  the  following 
equation : — 

-j-  Zn  = ZnSO^  + H^. 

An  ounce  of  zinc  is  sufficient  to  liberate  from  water  about  21- 
gallons  of  the  gas.  Scraps  of  iron  may  be  substituted  for  zinc  ; 
hut  in  this  case  the  gas  is  less  pure : it  has  a disagreeable  odour, 
due  to  the  presence  of  a peculiar  compound  of  hydrogen  and  car- 
bon, but  this  may  be  removed  by  allowing  the  gas  to  stream 
through  a tube  filled  with  fragments  of  wood  charcoal  (Stenhouse). 
The  gas  furnished  by  the  action  of  diluted  sulphuric  acid  on  zinc 
also  possesses  a peculiar  odour,  and  is  frequently  contaminated 
with  small  quantities  of  compounds  of  hydrogen  with  sulphur, 
arsenic,  and  carbon.  It  may  be  freed  from  these  impurities  by 
causing  it  to  pass  first  through  a strong  solutionr  of  potash,  and 
then  through  a solution  of  corrosive  sublimate,  or  of  nitrate  of 
silver. 

Properties. — Hydrogen  is  an  elementary  substance,  which  was 
discovered  by  Cavendish  in  1766,  and  was  called  by  him  inflam- 
mable air.  When  obtained  with  the  precautions  just  mentioned, 
it  is  a colourless,  transparent,  tasteless,  and  inodorous  gas.  Its 
refractive  power  upon  light  is  higher  than  that  of  any  other  gas, 
being  more  than  six  times  as  great  as  that  of  atmospheric  air  at 
the  same  temperature,  when  the  hydrogen  is  compressed  till  its 
weight  is  the  same  as  that  of  an  equal  bulk  of  air.  It  has  never 
been  liquefied,  and  is  even  less  soluble  in  water  than  nitrogen, 
100  cubic  inches  of  water,  according  to  Bunsen,  dissolving  1*93 
cubic  inches  of  hydrogen  at  all  temperatures  between  32°  and 
68°  F.  Hydrogen  is  the  lightest  form  of  matter  which  is  known  : 
its  weight  is  only  one-sixteenth  of  that  of  an  equal  bulk  of  oxygen, 
and  little  more  than  a fourteenth  of  that  of  air : 100  cubic  inches 
of  it  weigh  but  2T4  grains.  Owing  to  its  levity,  it  has  been 


GASEOUS  COMPOUNDS  OF  HYDROGEN. 


41 


extensively  used  for  aerostatic  purposes,  althougli  the  facility 
with  which  coal-gas  can  now  be  obtained  has  caused  this  latter, 
notwithstanding  its  much  greater  density,  to 
be  universally  substituted  for  hydrogen  in  fill- 
ing balloons.  A li^ht  bag  made  of  the  craw 
of  a turkey,  or  ot  collodion,  may  easily  be 
infiated  with  hydrogen,  and  will  ascend  rapid- 
ly, and  carry  with  it  a weight  of  several  grains. 

Owing  to  the  lightness  of  the  gas,  a jar  may 
be  easily  filled  with  it  by  displacement  without 
using  the  pneumatic  trough : — A tube,  8 or  10 
inches  long,  is  fixed  by  a cork,  in  the  manner 
shown  at  a,  fig.  279,  into  a three-necked  bottle 
containing  some  granulated  zinc  ; diluted  sul- 
phuric acid  is  introduced  through  the  funnel, 
and  the  gas,  after  the  atmospheric  air  in  the 
bottle  has  been  allowed  to  escape,  may  be  col- 
lected by  holding  a jar  over  the  tube,  as  at  b. 

The  hydrogen  will  be  retained  for  some  min-  ^ 
utes  even  if  the  jar  be  removed,  provided  that 
it  be  still  held  in  the  inverted  position ; while 
if  the  mouth  be  turned  upwards,  the  gas  will 
have  escaped  after  the  lapse  of  a few  seconds.  Pure  hydrogen, 
though  it  cannot  support  life,  is  not  poisonous,  and  when  mixed 
with  a certain  proportion  of  oxygen  it  has  been  breathed  for 
some  time  without  inconvenience ; but,  owing  to  its  rarity,  it 
renders  the  voice  temporarily  much  sharper  and  more  shrill  than 
usual. 

Hydrogen  has  a smaller  combining  number  than  any  other 
elementary  body,  and  it  has  hence  been  taken  as  the  unit  or 
standard  of  comparison,  both  for  atomic  weights  and  combining 
volume.  Its  proportional  number  is  therefore  unity,  or  1,  and  its 
combining  volume  1 or  | |'^. 


* The  proportions  in  which  the  different  elements  combine  with  hydrogen  to  form 
gaseous  compounds  afford  a well-marked  character  which  serves  as  a foundation  for 
grouping  the  different  elements  into  natural  families.  For  example,  in  the  table 
which  follows,  some  of  the  most  important  gaseous  compounds  of  the  different 
elements  with  hydrogen  are  enumerated : in  each  case  the  quantity  represented  by 
the  formula  given  indicates  two  volumes  of  the  gaseous  compound  (H  = 1 vol.  and 
HH  = 2 vols.). 

In  the  first  column  the  compounds  are  formed  by  the  union  of  one  atom  of  each 
compound.  The  metals  of  the  alkalies  and  one  or  two  others  displace  hydrogen  from 
its  compound  with  chlorine,  in  the  proportion  of  single  equivalents,  and  these  metals 
with  the  halogens  themselves  constitute  the  group  of  Monads. 

In  the  second  column  of  the  table  two  atoms  of  hydrogen  are  shown  in  combina- 
tion with  one  atom  of  certain  other  {dyad)  elements.  In  addition  to  the  non-metallic 
elements  which  thus  have  the  power  of  supplying  the  place  of  two  atoms  of  cldorine 
in  combining  with  hydrogen,  it  may  be  stated  that  the  metals  of  the  alkaline  earths 
and  the  ordinary  metals  which  form  basic  oxides,  displace  two  atoms  of  hydrogen, 
and  unite  with  two  atoms  of  chlorine  ; they  constitute  the  dyad  group  ot  metals. 

In  the  third  column  of  the  table  each  compound  given  contains  3 atoms  ot  h_ydro- 
gen  united  with  1 atom  of  some  other  {triad)  element.  These  also  have  their  repre- 
sentatives among  the  well-known  metals;  for  the  triads  embrace  gold,  aluminum, 
and  rhodium,  an  atom  of  each  of  which  unites  with  three  atoms  ot  chlorine,  and  is 
thus  equivalent  in  function  to  three  atoms  of  hydrogen. 


42 


cayexdish’s  eudiometek. 


Hydrogen  unites  directly  with  several  elements  if  heated  with 
them,  particularly  with  oxygen  and  with  chlorine.  If  heated 
with  sulphur,  with  bromine,  and  with  phosphorus,  it  also  combines 
with  them,  though  slowly  and  with  difficulty. 

(316)  Synthesis  of  ^Yater — Eudiometers. — Hydrogen  is  extreme- 
ly inflammable ; when  a lighted  taper  is  plunged  into  a jar  of  it, 
the  gas  takes  Are,  hut  the  taper  is  extinguished.  A jet  of  hydro- 
gen burns  with  a pale,  yellowish,  feebly  luminous  flame,  hut  gives 
out  great  heat.  If  the  gas  be  dried  by  causing  it  to  pass  through 
a tube  containing  chloride  of  calcium,  and  a cold  beU-jar  be  held 
over  the  burning  jet,  the  interior  of  the  glass  quickly  becomes 
bedewed  with  moisture,  owing  to  the  formation  of  water  by  the 
union  of  the  burning  hydi’ogen  with  the  oxygen  of  the  atmos- 
phere. Oxygen  and  hyffiogen  may  be  kept  in  a state  of  mixture 
at  the  ordinary  temperature  of  the  air  for  an  unlimited  period 
without  entering  into  combination ; but  the  passage  of  an  elec- 
tric spark,  the  application  of  a lighted  or  even  of  a glowing 
match,  and,  in  some  instances,  the  mere  contact  of  a cold  metallic 
substance,  such  as  platinum,  especially  if  the  metal  be  in  a flnely 
divided  state  (65),  is  sufficient  to  determine  their  immediate 
combination.  Sudden  compression  of  the  gases,  when  mixed, 
j^roduces  the  same  eflect  from  the  heat  evolved,  whilst  a still 
greater  amount  of  compression  if  it  be  gradually  applied,  even 
when  raised  till  it  is  equal  to  that  of  150  atmospheres,  fails  to 
produce  their  union. 

Cavendish,  in  his  inquiries  respecting  the  formation  of  water, 
effected  the  combination  of  the  two  gases  by  means  of  the  electric 
spark.  He  employed  for  this  purpose  a strong  glass  vessel,  a 
modiflcation  of  which  is  represented  at  a,  flg.  280.  Through  the 
upper  part  two  platinum  wires  are  inserted  to  within  the  eighth 


Compounds  of 
Monads. 

Compounds  of 
Dyads. 

Compounds  of 
Triads. 

Compounds  of 
Tetrads. 

Hydrochloric 

Acid. 

Water. 

Ammonia. 

Marsh  Gas. 

H Cl 

H2O 

H3N 

Hydrobromic 

Acid. 

Sulphuretted 

Hydrogen. 

Phosphuretted 

Hydrogen. 

Siliciuretted 

Hydrogen. 

H Br 

H2S 

H3P 

H^Si? 

Hydriodic 

Acid. 

Seleniuretted 

Hydrogen. 

Arseniuretted 

Hydrogen. 

"■  HI  ' 

HsSe 

H3AS 

Telluretted 

Hydrogen. 

Antimoniuretted 

Hydrogen. 

A 

H^Te 

H3Sb 

In  the  fourth  column  the  compounds  enumerated  contain  four  atoms  of  hydrogen 
in  combination  with  another  {tetrad)  element.  Among  the  metals,  platinum,  tin,  and 
a few  other  rarer  elements  discharge  the  functions  of  four  atoms  of  hydrogen,  each 
atom  of  the  metal  forming  a stable  compound  with  four  atoms  of  chlorine. 


SYNTHESIS  OF  WATEK EUDIOMETEKS. 


43 


of  an  incli  of  eacli  otlier.  The  vessel  can  be  closed  at  the  bottom 
by  a glass  stopcock,  c.  The  air  is  exhausted,  and  the  vessel 
screwed  upon  the  top  of  a jar,  b,  containing  a mixture  of  two 
measures  of  hydrogen  and  one  measure  of  oxygen : on  opening 
the  stopcocks  a portion  of  the  mixture  enters  the  vessel ; the 
cocks  are  then  closed ; and  an  electric  spark  passed  through  the 
mixture,  by  discharging  a small  Leyden  jar,  d,  through  the  pla- 
tinum wires,  <2,  5.*  A briglit  flash  is  seen  at  the  moment  of  the 
discharge,  and  the  gases  combine,  forming  steam,  which  becomes 
condensed  on  the  sides  of  the  glass : the  whole  of  the  two  gases, 
if  mixed  in  the  above 
proportions,  enter  into 
combination  with  each 
other.  On  again  open- 
ing the  stopcocks  a fresh 
quantity  of  the  gases  may 
be  admitted,  to  supply 
the  place  of  those  just 
condensed,  the  spark  may 
be  again  transmitted,  and 
the  process  may  be  re- 
peated till  the  whole  of 
the  gases  are  consumed, 
and  a considerable  quan- 
tity of  water  formed. 

The  uniformity  of  com- 
position, and  regularity 
of  proportion  in  which 
compounds  are  produced 
when  they  combine  che- 
mically, is  strikingly  illus- 
trated by  means  of  a mix- 
ture of  oxygen  and  hydro- 
gen gases.  The  two  gases 
may  be  mixed  in  any  arbitrary  proportion  in  a suitable  vessel, 
into  the  sides  of  which  two  platinum  wires  are  fused  for  the  pur- 
pose of  transmitting  the  electric  spark.  If  the  mixture  be  capa- 
ble of  exploding  at  all,  the  combination  will  be  found  to  have 
occurred  in  the  proportion  of  two  measures  of  hydrogen  to  one 
measure  of  oxygen,  no  matter  in  what  proportion  the  gases 
were  mingled.  If  oxygen  be  used  in  excess,  the  superfluous 
oxygen  will  be  found  remaining  uncombined ; and  if  hydrogen 
be  in  excess,  tlie  excess  of  hydrogen  will  be  left  unaltered  after 
the  transmission  of  the  spark. 

Upon  tliis  principle  a valuable  instrument,  the  Eudiometer^ 
is  constructed,  by  means  of  which  various  gaseous  mixtures  may 
be  analysed  with  great  exactness.  Many  diflerent  forms  of  this 
instrument  are  in  use.  One  of  the  simplest  and  most  convenient 

* The  discharge  from  the  secondary  current  of  a Ruhmkorff’s  coil  may  in  all  such 
cases  be  advantageously  substituted  for  the  spark  of  the  Leyden  jar. 


44 


SYNTHESIS  OF  WATER EUDIOMETERS. 


consists  of  a stout  siphon  tube,  fig.  281,  open  at  one  extremity  and 
closed  at  the  other.  Into  the  sides  of  the  tube,  near  the  sealed 
end,  two  platinum  wires,  <2,  J,  are  fused  for  the  purpose  of  trans- 
mitting an  electric  spark  through  the  cavity  of  the  tube.  The 
sealed  limb  is  accurately  graduated  to  hundredths  of  a cubic  inch, 
or  other  suitable  divisions.  Suppose  it  be  desired  to  ascertain  the 
proportion  of  oxygen  in  atmospheric  air ; the  instrument  is  first 
filled  with  mercury,  after  wdiich  a small  cpiantity  of  air  is  intro- 
duced : the  bulk  of  this  air  is  accurately  measured,  taking  care 
that  the  liquid  metal  stands  at  the  same  level  in  both  tubes.  A 
quantity  of  pure  hydrogen  about  equal  in  bulk  to  the  air  is  next 
introduced,  and  the  bulk  of  the  mixture  is  again  accurately 
measui’ed.  The  open  extremity  of  the  tube  is  now  closed  with 

the  finger,  below  which  a 
column  of  atmospheric  air 
is  safely  included ; this 
portion  of  air  acts  as  a 
spring  which  gradually 
checks  the  explosive  force, 
when  the  combination  is 
efiected  by  passing  a spark 
across  the  tube  by  means 
of  the  platinum  wires. 
The  mixture  is  then  ex- 
ploded by  the  discharge 
of  the  Leyden  jar.  The 
remaining  gas  now  occu- 
pies a smaller  volume,  owing  to  the  condensation  of  the  steam 
which  has  been  formed.  Mercury  is  therefore  again  poured  into 
the  open  limb,  until  it  stands  at  the  same  level  in  both  tubes,  and 
the  volume  of  the  gas  is  measured  a third  time.  One-third  of 
the  reduction  in  bulk  experienced  by  the  gas  will  represent  the 
entire  volume  of  oxygen  which  the  mixture  contained.  For 
accurate  experiments,  a very  complete  though  expensive  form  of 
eudiometer  upon  this  principle  has  been  contrived  by  Regnault. 
{Ann.  de  Chimie^  III.  xxvi.  333.) 

If  a mixture  of  oxygen  and  hydrogen  be  fired  in  the  air  in 
considerable  quantity,  as  when  a bladder-full  is  ignited, — or,  what 
is  still  better,  when  a quantity  of  soapsuds  is  blown  up  into  a 
lather  by  forcing  some  of  the  gaseous  mixture  out  of  a bladder 
through  a pipe  under  the  liquid, — a loud  and  sharp  report  attends 
the  combination  ; the  steam  which  is  formed  suddenly  expands 
from  the  high  temperature  attendant  on  the  combustion,  and 
immediately  afterwards  becomes  condensed  : great  dilatation  is 
first  produced,  followed  by  the  formation  of  a partial  vacuum  ; the 
surrounding  air  rushes  in  to  fill  the  void,  and  by  the  collision  of 
its  particles  produces  the  report.  If  the  hydrogen  be  mixed  with 
air,  a similar  but  feebler  explosion  occurs  when  a lighted  match 
is  applied  ; hence  it  is  especially  necessary  in  all  experiments  with 
hydrogen  to  allow  time  for  the  expulsion  of  the  atmospheric  air 
from  the  apparatus  before  setting  fire  to  the  issuing  jet.  The 


Fia.  281. 


SYNTHESIS  OF  WATER. 


45 


explosion  is  most  violent  when  2 measures  of  hydrogen  are  mixed 
Tvdth  5 of  air  : if  the  mixture  be  diluted  with  a large  excess  either 
of  hydrogen  or  of  air,  the  explosion  becomes  more  feeble  ; the 
heat  evolved  is  less  intense,  and  the  combustion  less  sudden,  until 
at  a certain  degree  of  dilution  no  explosion  follows  the  application 
of  flame,  but  the  mixture  burns  slowly  ; whilst,  if  still  more  diluted, 
it  takes  fire  only  just  at  the  spot  where  the  heat  is  applied,  but 
the  combustion  does  not  spread  through  the  mass. 

If  a long  tube,  open  at  both  ends,  be  held  over  a jet  of  burning 
hydrogen,  a rapid  current  is  produced  through  the  tube,  which 
occasions  a dickering  in  the  fiame,  attended  by  a series  of  small 
explosions  that  succeed  each  other  so  rapidly  and  at  such  regular 
intervals  as  to  give  rise  to  a musical  note,  the  pitch  and  quality 
of  which  varies  with  the  length,  thickness,  and  diameter  of  the 
tube. 

Pure  water  may  be  formed  in  considerable  quantities  by  a 
method  differing  from  those  hitherto  described ; the  operation  at 
the  same  time  furnishes  a means  of  ascertaining  accurately  the 
relative  weiglits  of  oxygen  and  hydrogen  which  enter  into  the  com- 
position of  water.  It  consists  in  transmitting  a current  of  liydrogen 
over  a weighed  quantity  of  oxide  of  copper  : at  a red  heat  hydrogen 
deprives  the  oxide  of  copper  of  its  oxygen,  and  forms  water ; by 
determining  the  \veight  of  the  water  thus  produced,  and  the  loss 
sustained  by  the  oxide  of  copper,  the  proportion  of  hydrogen  which 
has  combined  with  the  oxygen  can  be  ascertained.  The  appa- 
ratus required  for  the  purpose  is  represented  in  fig.  282.  A 


Fig.  282. 


quantity  of  oxide  of  copper  is  placed  in  the  globe,  f,  which  is 
constructed  of  glass  of  difficult  fusibility,  and  the  glohe  and  its 
contents  are  then  accurately  weighed.  A current  of  liydrogen, 
prepared  from  zinc  and  sulphuric  acid  in  the  bottle,  a,  is  alloweil 
to  bubble  up  through  a solution  of  hydrate  of  potasli,  n,  and  to 
traverse  three  bent  tidies  in  succession  ; the  first,  c,  is  filled  with 
fragments  of  pumice-stone  moistened  with  a solution  of  corrosive 
sublimate  (HgCl^) ; the  second,  d,  contains  fragments  of  fused 
caustic  potash  ; and  the  third,  e,  is  charged  with  jiumice  moistened 
with  oil  of  vitriol.  The  mercurial  salt  and  the  ]mtash  remove  the 
traces  of  arsenic,  sulphur,  and  carburetted  compounds,  which  the 


46 


SYNTHESIS  OF  WATEE OXYHYDROGEN  BLOWPIPE. 


gas  might  otherwise  carry  over,  and  the  oil  of  vitriol  absorbs  the 
last  traces  of  moisture.  Perfectly  pure  and  drj"  hydrogen  gas  is  thus 
delivered  in  the  globe,  f.  When  all  the  air  is  completely  displaced, 
heat  is  applied  to  the  globe ; the  oxide  of  copper  gives  up  its 
oxygen ; water  is  formed,  and  becomes  condensed  in  the  receiver, 
G,  as  well  as  in  the  attached  bent  tube,  h,  which  is  filled  with 
fragments  of  pumice  moistened  with  oil  of  vitriol : the  whole  of  the 
water  formed  is  by  this  means  arrested,  i is  a bulb  tube  contain- 
ing a little  oil  of  vitriol,  which  prevents  the  entrance  of  extraneous 
moisture,  and  by  its  motion  shows  the  progress  of  the  gas.  When 
the  globe,  f,  is  cold,  the  liydrogen  is  displaced  by  a current  of  air, 
and  on  weighing  the  globe  with  the  oxide  after  the  experiment 
lias  terminated,  the  loss  gives  the  quantity  of  oxygen  which  has 
combined  with  the  hydrogen  ; whilst  the  difference  between  the 
amount  of  oxygen  and  that  of  the  water  condensed  in  the  receiver, 
G,  and  tube  of  acid,  ii,  shows  the  quantity  of  hydrogen  that  has 
combined  with  it.  Two  grains  of  hydrogen  are  in  this  manner 
proved  to  require  exactly  16  grains  of  oxygen  for  their  conversion 
into  water.  (Dumas,  Annal.  de  Chimie^  III.  viii.  189.) 

Many  other  metallic  oxides  besides  oxide  of  copper,  when  heated 
in  a current  of  hydrogen,  part  with  their  oxygen,  and  are  brought 
back  to  the  metallic  condition.  If  tlie  bulb  be  weighed  first  when 
empty,  then  when  charged  with  oxide,  and  a third  time  after  the 
stream  of  gas  has  been  continued  till  all  formation  of  water  ceases, 
and  till  the  tube  has  become  cool,  the  loss  of  weight  sustained  by 
the  oxide  furnishes  the  proportion  of  oxygen  combined  with  the 
metal.  A true  and  very  accurate  analysis  of  the  oxide  will  thus 
have  been  effected : 79 '5  parts  of  oxide  of  copper  are  found  in 
this  way  to  contain  63*5  of  copper  and  16  of  oxygen. 

(347)  Hydrogen  in  the  act  of  combining  with  oxygen  emits  a 
very  intense  heat.  By  throwing  a jet  of  oxygen  into  a flame  of 
coal-gas  or  of  hydrogen,  or  still  better  by  introducing  a jet  of 
oxygen,  as  at  o,  fig.  283,  into  the  centre  of  a jet  connected  at  h 

with  a gas-holder  supplying  hydro- 
gen, so  that  the  two  gases  may 
become  mixed  just  before  they 
issue  from  the  common  orifice  of 
the  tube  <2,  a heat  may  be  obtain- 
ed which  can  scarcely  be  sur- 
passed by  chemical  means.  Some- 
times the  two  gases  are  mixed 
in  the  proportion  of  2 volumes  of 
hydrogen  to  1 volume  of  oxygen, 
and  introduced  into  a bladder  and 
burned  as  they  issue  through  a 
tube  of  particular  construction, 
known  as  Hemming’s  safety  jet. 
It  consists  of  a brass  tube,  about  6 
inches  long  and  two-thirds  of  an 
inch  in  diameter,  filled  with  pieces 
of  very  fine  brass  wire,  which  are  packed  closely  together,  and  then 


Fig.  283. 


drtjtvimond’s  light. 


47 


wedged  in  very  tiglitly  by  driving  a stout  conical  piece  of  wire  into 
the  axis  of  the' tube  (492).  This  tube  is  supplied  at  one  extremity 
with  a blowpipe  jet,  and  at  the  other  with  a screw  which  can  be 
connected  with  a stopcock  adjusted  to  the  neck  of  the  bladder.  The 
temperature  produced  by  burning  the  mixed  gases  from  such  a jet  is 
so  intense  that  thick  platinum  wire  is  melted  by  it  with  ease,  and 
is  partially  volatilized ; iron  and  steel  are  melted,  and  burn  with 
vivid  scintillations.  Rock  crystal  may  be  liquetied,  and  drawn 
out  into  threads  like  glass,  and  the  stem  of  a tobacco  pipe  may  be 
fused  into  an  enamel-like  bead.  When  the  oxyhydrogen  flame, 
which  is  but  very  feebly  luminous,  is  directed  upon  a small  cylin- 
der of  lime,  5,  this  earth  does  not  fuse,  but  it  becomes  white  hot, 
and  then  emits  a very  pirre  white  light  of  great  steadiness  and 
intensity,  which  may  be  maintained  for  hours,  if  care  be  taken  to 
expose  to  the  flame  fresh  surfaces  of  the  lime  by  causing  it  to 
revolve,  continually  but  very  slowly,  by  means  of  clockwork. 
This  object  may  be  obtained  less  perfectly  by  occasionally  turning 
the  pin,  <?,  which  supports  the  lime.  Without  this  precaution  a 
cavity  would  be  formed  opposite  to  the  jet,  from  volatilization  of 
a small  quantity  of  the  lime.  This  light  was  originally  proposed 
by  Lieut.  Drummond,  to  be  used  in  the  trigonometrical  survey  of 
Great  Britain,  and  it  is  astonisliing  at  what  distances  it  may  be 
seen  when  the  rays  are  concentrated  by  a parabolic  reflector.  On 
the  31st  December,  1845,  it  was  seen  across  the  Irish  Channel,  at 
half-past  3 p.m.  (during  daylight)  from  the  top  of  Slieve  Donard, 
in  Ireland,  by  an  observer  stationed  at  the  top  of  Snowdon, — an 
interval  of  108  miles  in  a direct  line ; and  it  has  more  than  once 
been  seen  at  a distance  of  112  miles. 

Water  is  formed  abundantly  whenever  combustible  bodies 
wliich  contain  hydrogen  are  burned  with  a free  supply  of  air. 
Wood,  tallow,  oil,  wax,  alcohol,  coal-gas,  and  most  of  our  ordinary 
combustibles  whicli  burn  with  flame,  in  this  manner  furnish  con- 
siderable quantities  of  water  in  the  act  of  burning. 

A striking  experiment  may  be  performed  with  hydrogen,  whicli 
shows  how  purely  conventional  are  the  terms  ‘ combustibles  ’ and 
‘ supporters  of  combustion.’  Let  a tall  bottle  with  a narrow  neck 
be  filled  with  hydrogen  gas ; through  a cork  which  passes  easily 
into  the  neck  of  the  bottle  fit  a jet  connected  with  a gas-holder 
containing  oxygen  ; place  the  bottle  mouth  downwards  and  set  fire 
to  the  hydrogen,  then  immediately  insert  the  cork  and  jet,  through 
which  a stream  of  oxygen  is  gently  issuing.  The  flame  will 
appear  to  attach  itself  to  the  oxygen  tube,  and  the  jet  of  oxygen 
will  be  burning  in  an  atmosphere  of  hydrogen.  Combustion,  in 
fact,  occurs  at  the  place  where  the  two  gases  first  come  into  con- 
tact. Suppose,  for  a moment,  that  the  earth’s  atmospliere  had 
contained  hydrogen  instead  of  oxygen ; oxygen  would  have 
appeared  to  us  in  the  light  of  a combustible  gas,  and  hydrogen  in 
that  of  a supporter  of  combustion. 


48 


CARBON. 


CHAPTER  lY. 

CARBON CARBONIC  ACID CARBONIC  OXIDE. 

§ I.  Carbonic  Anhydride  or  Carbonic  Acid.  -COj  =:  44. 
Atomic  and  Molecular  Volume^  \ \ | ; or  CO^  = 22 ; Observed 

Sjo.  Gr.  1-529  ; Theoretic  Sp.  Gr.,  1-5203. 

(348)  An  atmosphere  composed  only  of  oxygen,  nitrogen,  and 
steam,  though  perfectly  adapted  to  the  support  of  animal  life,  would 
he  unlit  to  sustain  vegetation.  Plants  require  for  their  growth 
and  development  a certain  portion  of  another  gas — carbonic  anhy- 
chlde.  Evidence  of  the  existence  of  this  body  in  the  air  (342)  is 
easily  obtained  by  exposing  a saucer  of  lime-water  to  the  atmos- 
phere : in  a few  minutes  its  surface  becomes  covered  with  a tliin 
pellicle,  which  if  disturbed  by  agitation  sinks  to  the  bottom.  The 
pellicle  is  renewed  after  each  agitation  until  the  wliole  of  tlie  lime 
contained  in  the  liquid  has  been  thus  rendered  insoluble.  This 
white  matter  is  chalk,  which  is  formed  by  the  union  of  carbonic 
anhydride  and  lime.  Such  compounds  of  carbonic  anhydride  with 
bases  are  termed  carbonates^  hence  chalk  is  chemically  termed 
carbonate  of  lime  or  carbonate  of  calcium.  When  the  chalk  thus 
obtained  is  heated  to  bright  redness  (which,  if  the  result  is  to  be 
accurately  examined,  must  be  effected  in  a platinum  tube),  car- 
bonic anhydride  is  expelled  as  a colourless  and  transparent  gas, 
while  pure  quick-lime  is  left  behind. 

Preparation. — In  actual  practice,  carbonic  anhydride  is  ob- 
tained by  a much  more  convenient  plan.  The  carbonic  being 
but  a feeble  acid,  it  is  expelled  from  its  compounds  b}’'  almost 
every  other  acid  which  is  freely  soluble  in  water ; it  is  therefore 
easily  separated  from  its  salts  by  the  addition  of  one  of  these 
acids.  Fragments  of  chalk,  or  marble,  which  is  a more  compact 
form  of  carbonate  of  calcium,  are  placed  in  a retort  or  gas-bottle, 
and  some  powerful  acid,  such  as  the  nitric  or  the  hydrochloric, 
diluted  with  8 or  10  times  its  bulk  of  water,  is  poured  upon  the 
chalk,  when  the  acid  radicle  exchanges  its  liydrogen  for  the  cal- 
cium and  produces  carbonic  acid  (H^-BOg),  which  immediately 
breaks  up  into  water  and  gaseous  carbonic  anhydride,  and  this  last 
escapes  with  a brisk  effervescence.  The  following  equation  shows 
the  nature  of  this  decomposition  when  chalk  and  hydrochloric  acid 
are  employed : — 

BaBOg  4-  2 HCl  = BaClg  -f  11^0  -f-  BB^, 
or  CaO,  COg  -h  HCl  = CaCl  + HO  -f  COg. 

Limestone,  Iceland  spar,  oyster-shells,  pearlash,  and  carbonate 
of  sodium,  all  yield  carbonic  anhydride  when  acted  on  by  a strong 
acid. 

Properties. — Under  the  ordinary  pressure  of  the  atmospliere 
carbonic  anhydride  is  a colourless,  transparent  gas,  with  a faintly 
acidulous  smell  and  taste  ; but  when  generated  in  a confined  space 
in  strong  vessels  it  becomes  condensed  to  a liquid  as  transparent 


CARBONIC  ANHYDRIDE. 


49 


and  colourless  as  water,  which,  according  to  Regnanlt,  boils  at 
— 109°.  At  32°  F.  it  requires  a pressure  of  38*5  atmospheres  to  re- 
tain it  in  the  liquid  state  (Faraday).  It  then  has  a specific  gravity 
of  0*83,  whilst  at  86°  the  specific  gravity  is  only  0‘60.  If  these 
data  be  correct,  the  liquid  expands  by  the  application  of  heat  four 
times  more  rapidly  than  air  (Thilorier) ; but  according  to  Andreeff 
{Liebig^ s Ann.  cx.  10)  the  expansion  of  the  liquid,  although 
greater  than  that  of  the  gas,  is  not  so  great  as  Thilorier  states. 
Andreeff  found  the  density  of  the  liquid  0'94T  at  32° ; 0*893  at 
50°  ; 0*86  at  60°  ; and  0*779  at  78°.  Liquefied  carbonic  anhy- 
dride does  not  mix  freely  with  water,  or  with  the  fixed  oils  ; but 
it  is  dissolved  in  all  proportions  by  alcohol,  ether,  oil  of  turpentine, 
naphtha,  and  bisulphide  of  carbon.  When  a stream  of  the 
liquefied  body  is  allowed  to  escape  into  the  air,  it  freezes  into  a 
snow-white  solid  (196) : and  if  a tube  containing  liquid  carbonic 
anhydride  be  plunged  into  a bath  of  the  solid  anhydride  mixed 
with  ether,  and  placed  in  the  vacuum  of  the  air-pump,  the  liquid 
in  the  tube  will  speedily  be  frozen  into  a clear,  transparent,  ice- 
like mass,  which  melts  at  — 70°  The  solidified  anhydride  is 
heavier  than  the  liquid  portion  in  which  it  is  being  formed. 

Gaseous  carbonic  anhydride  is  not  inflammable,  neither  will 
it  support  the  flame  of  burning  bodies : the  extinction  of  a taper 
is  one  of  the  means  frequently  resorted  to  for  detecting  its 
presence.  Many  other  gases,  however,  have  the  same  property ; 
some  additional  test,  therefore,  becomes  necessary.  Such  a test 
is  afforded  by  its  action  upon  lime-water,  which,  when  agitated 
with  the  gas,  is  immediately  rendered  milky  from  the  formation 
of  chalk ; a few  drops  of  any  strong  acid  dissolve  the  chalk  and 
restore  transparency  to  the  liquid ; an  excess  of  even  carbonic 
acid  has  the  same  effect. 

Carbonic  anhydride  in  its  concentrated  form  is  irrespirable,  for 
by  producing  spasm  of  the  glottis  it  is  prevented  from  entering  the 
lungs  ; when  diluted  with  air,  how- 
ever, it  may  be  breathed  without 
even  a suspicion  of  its  presence. 

If  the  proportion  exceed  3 or 
4 per  cent,  of  the  air  it  acts  as 
a narcotic  poison ; and  even  in 
much  smaller  quantities  its  de- 
pressing effects  are  very  injurious. 

The  ill  effects  experienced  in  crowd- 
ed and  ill- ventilated  rooms  are 
partly  due  to  the  presence  of 
this  gas  in  undue  quantity,'^  but 
partially  also  to  the  accumulation 
of  volatile  putrescible  organic 
particles  given  off  from  the  surface 
of  the  lungs  and  skin.  It  is  the 

* The  maximum  observed  by  Roscoe  in  his  experiments  on  the  atmosphere  of 
dwelling-houses,  was  0-33  per  cent.,  and  this  occurred  in  a crowded  school-room. — 
(^.  J.  Cliem.  Soc.  x.  265.) 

4 


Fig.  284 


50 


PKOPEKTIES  OF  CAEEOXIC  ACID. 


combination  of  these  circnmstances  which  renders  attention  to 
ventilation  a matter  of  such  high  importance. 

Gaseons  carbonic  anhydidde  is  more  than  half  as  heavj’  again  as 
atmospheric  air ; 100  cubic  inches  of  it  at  60°  F.  and  30  inches  Bar. 
weigh  47*303  grains;  from  its  density  it  may  easily  be  collected 
in  dry  vessels  by  displacement,  in  the  manner  represented  in  fig. 
284,  and  may  be  poured  from  one  vessel  into  another  like  water. 

Xo  definite  hydi’ated  carbonic  acid  is  known  ; the  anhydride, 
both  in  the  form  of  gas  and  in  its  denser  conditions  of  licpiid  and 
solid,  being,  as  its  name  indicates,  free  from  water ; but  it  appears 
convertible  into  a true  acid  by  solution  in  water 
pelding  H^GOg.  At  the  ordinary  temperature,  the  gas  is  soluble 
in  about  its  own  bulk  of  water ; and  its  solubility  increases  if  the 
pressure  be  increased ; * but  when  the  compression  is  suddenly 
removed,  the  gas  escapes  with  bri^k  efiervescence.  Advantage  is 
taken  of  this  circumstance  in  the  preparation  of  soda-water^  as 
it  is  called.  For  this  purpose  the  water,  which  may  or  may  not 
contain  soda  or  other  substances  in  solution,  is  mechanically 
charged  with  a large  quantity  of  carbonic  acid,  by  the  use  of  a 
condensing  syringe,  attached  to  a reservoir  filled  with  the  gas. 
The  excess  of  the  gas  thus  forced  into  the  liquid  occasions  the 
agreeable  briskness  and  pungency  so  much  prized  in  this  bev- 
erage. 

A solution  of  carbonic  acid  in  water  reddens  tincture  of  litmus ; 
but  the  red  colour  disappears  if  the  liquor  be  boiled  for  a few 
minutes,  ovfing  to  the  expulsion  of  the  gas.  The  aqueous  solu- 
tion of  the  acid  possesses  solvent  powers  which,  though  in  many 
instances  extremely  feeble,  are  yet  far  more  extensive  than  those 
of  pure  water.  By  the  continuous  action  of  water  charged  with 
carbonic  acid,  even  granite  and  the  hardest  rocks  are  disintegrat- 
ed, few  finely  diGded  minerals  being  able  to  resist  its  gradual 
and  long  continued  action.  The  proportion  of  gas  dissolved  is  in 
many  instances  very  minute,  but  as  few  natural  soimces  of  water 
exist  which  are  not  to  a greater  or  less  extent  impregnated  with 
carbonic  acid,  either  by  absorption  from  the  atmosphere  or  from 
the  soil,  the  solution,  insignificant  as  it  may  at  first  sight  appear,  is 
continually  proceeding,  and  in  the  lapse  of  time  it  efiects  changes 
of  great  importance  and  extent. 

The  briskness  of  spring  water,  and  the  preference  given  to  it 
as  a beverage,  is  partly  occasioned  by  the  carbonic  acid  which  it 
contains ; though  its  usual  coolness  and  the  abundance  of  atmo- 
spheric air  dissolved  in  it  are  still  more  important.  It  is  the 
absence  of  these  qualities  which  renders  boiled  or  distilled  water 
fiat  and  insipid. 

Carbonic  acid  was  originally  fixed  ah\  from  the  circum- 

stance of  its  haGng  been  discovered  by  Dr.  Black,  in  1757,  as  a 
solid  or  fixed  constituent  in  limestone,  and  from  its  becoming 
fixed  or  absorbed  by  solutions  of  the  pure  alkalies. 

* If  the  gas  be  simply  transmitted  through  the  water,  the  liquid  seldom  takes  up 
more  than  two-thirds  of  its  bulk. 


NATURAL  SOURCES  OF  CARBONIC  ACID. 


51 


(349)  Natural  Sources  of  Carhonic  Acid. — Besides  tlie  pro- 
cesses for  procuring  tlie  gas  already  described,  there  are  a variety 
of  cases  in  which  it  is  produced  on  a very  large  scale  in  nature. 

1.  — Bespiration  in  man  and  animals  is  always  attended  with 
the  formation  of  a large  proportion  of  the  gas.  This  fact  may 
be  easily  proved  by  forcing  air  from  the  lungs  by  means  of  a 
tube  through  lime-water,  which  will  speedily  become  milky  from 
the  deposition  of  carbonate  of  calcium.  The  proportion  of  car- 
bonic anhydride  in  respired  air  varies  from  3 to  4 per  cent.,  being 
usually  about  3|-  per  cent. 

2.  — Carbonic  acid  is  also  abundantly  formed  in  the  process  of 
fermentation,  and  is  the  cause  of  the  briskness  in  bottled  beer, 
champagne,  and  other  fermenting  liquors.  Many  accidents  have 
occurred  from  persons  incautiously  descending  into  an  empty 
fermenting  vat  before  the  gas  has  had  time  to  escape  and  mix 
with  the  air  : it  is  usual  to  facilitate  the  escape  of  the  dense  gas 
by  leaving  the  plug  at  the  bottom  of  the  vessel  open  for  some 
hours. 

3.  — ^In  the  operation  of  burning  lime  in  the  lime-kiln,  the 
heat  expels  from  the  limestone  the  carbonic  anh3'dride,  which 
escapes  in  large  volumes.  Manj^  a poor,  houseless  wanderer, 
tempted  by  the  warmth  of  the  kiln,  has  lain  down  in  the  stream 
of  air  proceeding  from  it,  and  has  slept  to  wake  no  more.  By 
the  operation  of  subterranean  heat  in  volcanic  districts  upon  lime- 
stone beneath  the  surface,  large  volumes  of  carbonic  anhydride  are 
continually  finding  their  wsij  into  the  atmosphere  ; immense  quan- 
tities are  discharged  from  open  craters  or  from  fissures  and  cavi- 
ties in  the  soil ; the  springs  in  such  districts  are  also  frequently 
liighly  charged  with  it,  and  the  gas  escapes  with  efiervescence  when 
they  reach  the  surface.  The  springs  of  Seltzer,  Pyrmont,  and 
Marienbad,  on  the  Continent,  and  of  Tunbridge,  in  our  own 
countiy,  exhibit  this  phenomenon. 

4.  — The  carbonic  acid  met  with  in  spring  water  is  in  many 
instances  derived  from  the  gradual  oxidation  of  the  vegetable  and 
other  organic  matter  which  it  holds  in  solution,  by  the  action  of 
the  oxygen  of  the  air  wliich  all  waters  naturally  contain.  The  lake 
waters  from  the  primitive  districts,  such  as  those  in  the  northern 
parts  of  Scotland,  leave  scarcely  any  residue  on  evaporation  except 
a little  organic  matter  ; they  are  very  free  from  carbonic  acid,  and 
the  bulk  of  oxygen  wliich  they  hold  in  solution  is  somewliat  more 
than  one-lialf  that  of  the  nitrogen.  If  such  waters  be  kept  in 
closed  vessels  for  a few  weeks  in  a warm  room,  the  oxygen  gradu- 
ally decreases,  and  in  its  place  a corresponding  volume  of  carbonic 
acid  is  found.  The  pure  water  of  Loch  Katrine,  for  example, 
when  first  collected  did  not  yield  more  than  0’06  cubic  inches  of 
carbonic  anhydride  per  gallon  ; but  the  quantity  of  this  gas  which 
the  same  sample  yielded  after  it  liad  been  kept  in  a closed 
vessel  for  some  weeks,  in  a warm  room,  rose  to  0*38  cubic  inches 
in  the  gallon,  whilst  the  oxygen  had  diminished  to  similar  extent. 
Spring  waters  which  rise  in  a sandy  district,  the  surface  of  which 
is  sparingly  clothed  with  vegetation,  and  from  which  conse- 


52 


ANALYSIS  OF  AIK  CONTAINING  CAKBONIC  ANIIYDKIDE. 


qiiently  they  can  take  np  but  little  organic  matter,  contain  but 
small  quantities,  often  mere  traces,  of  carbonic  acid ; whilst  the 
springs  of  highly  cultivated  districts,  such  as  those  which  rest 
more  or  less  directly  upon  the  chalk,  become  charged  with  organic 
matter,  which  gradually  undergoes  oxidation  in  the  soil,  and  the 
quantity  of  carbonic  acid  contained  in  such  waters  is  always  con- 
siderable, whilst  the  quantity  of  oxygen  which  they  hold  in  solu- 
tion is  proportionately  reduced.*  The  extent  to  which  this  change 
takes  place  in  river  water  is  very  remarkable.  It  is  well  exhibited 
in  the  case  of  the  Thames.  On  one  occasion,  some  samples  were 
taken  from  the  river  at  low  water  at  different  points  on  the  same 
day,  in  August,  1859  ; those  collected  above  the  metropolis  being 
nearly  free  from  contamination  with  sewerage  products,  whilst 
those  obtained  lower  down  were  extensively  impregnated  with 
them.  The  gases  were  expelled  from  each  sample  by  boiling, 
within  twenty-four  hours  from  the  time  of  its  collection,  and  the 

* The  analysis  of  these  gases  or  of  any  mixture  of  air  with  carbonic  anhydride, 
such,  for  example,  as  respired  air,  may  be  effected  with  sufficient  accuracy  for  most 
purposes  in  the  following  manner : — Supposing  that  the  gas  had  been  collected  over 
either  water  or  mercury,  it  becomes  necessary  to  transfer  a portion  of  it  from  the  jar 
in  which  it  has  been  collected  to  the  one  in  which  it  is  to  be  analysed,  A method  of 
effecting  this  is  shown  in  fig.  285.  Upon  the  board,  a c?,  is  fastened  a pipette, 
designed  for  effecting  this  transfer ; a is  a cylindrical  funnel  of  a capacity  of  about 
two  cubic  inches ; at  c is  a small  steel  stopcock,  or  a piece  of  vulcanized  caoutchouc 
tubing  compressed  by  a screw,  which  is  simpler  and  less  expensive ; by  either  of 
these  contrivances  the  contents  of  the  funnel  can  be  admitted  to  a vdde  thermometer- 
tube,  which  is  furnished  at  d.  Avith  a second  steel  stopcock  or  caoutchouc  tube  and 
screw  clamp ; 6 is  a bulb  of  the  capacity  of  one  cubic  inch,  or  rather  less  ; from  the 
upper  part  of  & proceeds  another  piece  of  thermometer-tube,  bent  as  shown  in  the  fig- 
ure, to  allow  of  its  introduction  into  the  gas-jar.  To  use  the  instrument,  the 
funnel,  a,  is  filled  with  mercury,  the  stopcocks  are  both  opened,  and  as  soon  as  the  air 
has  been  displaced  from  the  vertical  portion  of  the  fine  tube,  and  mercury  escapes 
through  c?,  the  stopcock,  d,  is  closed;  the  mercury  quickly  displaces  the  air  from  the 
rest  of  the  tube,  and  from  the  bulb  &,  and  as  soon  as  it  begins  to  fiow  out  at  the  open 
extremity  of  the  recurved  portion,  the  stopcock,  c,  is  closed.  The  instrument  being 
now  full  of  mercury  is  introduced  into  the  jar,  e,  of  the  gas  to  be  transferred,  and  its 
open  extremity  is  raised  above  the  level  of  the  water  in  the  jar,  e ; the  stopcock, 
is  then  opened,  and  whilst  the  mercury  runs  out  into  a vessel  placed  for  its  reception, 
the  gas  enters  from  e,  and  occupies  the  place  of  the  mercury  in  the  bulb,  h.  When 
a sufficient  quantity  has  been  admitted,  the  tube  is  depressed  below  the  level  of  the 
water  in  the  jar,  e ; the  stopcock,  c?,  is  closed,  and  the  pipette,  which  is  sealed  by  the 
admission  of  a little  water  into  the  capillary  tube,  is  withdrawn  from  the  jar,  /. 
The  gas  can  now  be  transferred  to  the  graduated  tube,  A,  standing  in  the  jar  of  mer- 
cury, g ; the  bent  limb  of  the  pipette  is  introduced  into  the  tube,  /i,  which  has  been 
previously  filled  with  mercury.  Fresh  mercury  is  poured  into  the  funnel,  a,  of  the 
pipette,  and  on  opening  the  stopcock,  c,  the  gas  is  expelled  into  the  tube,  h ; the  gas 
should  not  occupy  more  than  two-thirds  of  the  capacity  of  this  tube. 

The  proportions  of  carbonic  anhydride,  of  nitrogen,  and  of  oxygen  are  now  easily 
ascertained  in  the  following  manner : — The  bulk  of  the  gas  in  tube,  /i,  is  to  be  care- 
fully read  off,  care  being  taken  to  bring  the  mercury  to  the  same  level  within  and 
without  the  tube  ; the  temperature  and  the  pressure  being  observed  as  usual  Sup- 
posing that  it  has  thus  been  ascertained  that  a bulk  of  gas  of  about  two-thirds  of  a 
cubic  inch  is  to  be  subjected  to  the  analysis,  the  operator,  by  means  of  a glass 
syringe,  throws  up  ten  or  twelve  drops  of  a solution  of  caustic  potash  (sp.  gr.  1-4) 
into  the  tube.  The  glass  syringe  may  be  extemporaneously  prepared  from  a strong 
tube  which  is  softened  in  the  flame  of  a lamp,  drawn  off  and  recurved  at  one  end,  as 
shown  in  the  figure  at  i\  this  constitutes  the  body  of  the  syringe,  whilst  the  piston 
is  easily  formed  of  a piece  of  glass  rod,  provided  with  a plug  of  caoutchouc. 

The  operator  then  agitates  the  contents  of  the  tube  by  rapidly  thrusting  down  the 
tube  into  the  mercury,  and  withdrawing  it,  taking  care  to  keep  the  mouth  below  the 


SOrECES  OF  CAEBONIC  ANHYDEIDE. 


53 


results  obtained  are  given  in  tlie  following  table,  in  which  tliey 
are  contrasted  with  the  proportions  of  each  gas  furnished  by  a 
similar  experiment  upon  a sample  of  river  water  taken  above 
Teddington  Lock,  where  it  was  in  a pure  condition. 


Temp,  of  river,  71° 

Kingston. 

Hammersmith. 

Somerset 

House 

Greenwich. 

"Wool- 

wich. 

Ei-ith. 

Total  quantity  of  gas  in  ) 
cub.  in.  per  gallon  . j 

14*67 

(Not  deter-  1 

1 mined.  ) 

17*49 

19-77 

17*50 

20-64 

Carbonic  anhydride . . 

8*42 

j Not  deter-  ) 

1 mined,  j 

12-56 

15-42 

13-40 

15*80 

Oxygen  

Nitrogen 

2-07 

4-18 

1*16 

4-24 

0-43 

4-50 

0-07 

4-28 

0-07 

4-03 

0 52 
4-32 

Proportion  of  Oxygen  ), 
to  Nitrogen  . . . f 

1 : 2 

1 : 3-7 

1 : 10-5 

1 : 60 

1 :52 

1:8-1 

surface  of  the  mercury:  this  manoeuvre  is  several  times  repeated  in  quick  succes- 
sion; the  tube  is  again  left  at  rest  for  a minute  or  two,  and  the  absorption  is  noted 
by  a second  time  reading  off  the  volume  of  the  gas  at  the  proper  level.  The  difference 
indicates  the  amount  of  carbonic  anhydride. 

Fig.  285. 


In  order  to  aseertain  the  proportion  of  oxygen  in  the  remainder,  the  plan  recom- 
mended by  Liebig  is  the  simplest : — A solution  of  1 part  of  pyrogallio  acid  in  6 of 
water  is  prepared,  and  about  40  drops  of  the  solution  is  \)y  o.  fresh  syringe  injected  into 
the  tube  7i,  and  the  mixture  is  briskly  agitated  as  before ; the  solution  of  potash,  if 
oxygen  be  present,  becomes  of  an  intense  bistre  colour,  and  the  ox3''gen  is  quick  1}^  and 
completely  absorbed;  the  gas  is  measured  a third  time,  and  the  residue  is  estimated 
as  nitrogen  ; the  difference  between  the  second  and  third  readings  giving  the  volume 
of  oxygen.  A small  quantity  of  carbonic  oxide  amounting  to  between  2 and  3 per 
cent,  of  the  volume  of  the  oxygen  is  always  formed  in  this  operation. — (Crace  Calvert  ; 
Boussingault.) 


SOrKCES  OF  CAEBONIC  AXHYDEIDE. 


54 


From  these  experiments  it  will  be  seen  that  the  water  from 
Kingston  (above  Teddington)  is  thoroughly  aerated,  and  contains 
oxygen  in  the  proper  proportion  to  the  nitrogen,  which  when  in 
solution  is  as  1 to  2.  At  Hammersmith,  the  effect  of  the  organic 
impurities  in  abstracting  the  oxygen  begins  to  be  evident.  It  is 
much  more  marked  at  Somerset  House,  whilst  at  Greenwich, 
where  the  condition  of  the  river  at  low  water  is  about  at  the 
worst,  the  oxygen  has  nearly  disappeared.  At  Woolwich,  it  is 
nearly  as  bad,  but  by  the  time  Frith  is  reached  a great  improve- 
ment is  perceptible.  Had  the  experiments  been  continued  still 
lower  down  the  river,  the  proportion  of  oxygen  would  have  con- 
tinued to  increase,  owing  to  the  admixture  of  aerated  sea-water 
and  the  absorption  of  oxygen  due  to  the  successive  exposure  of 
the  water  to  the  air  in  its  onward  flow. 

5.  — Carbonic  anhydride  constitutes  what  is  termed  choke-dam^ 
by  miners,  and  it  often  occasions  much  loss  of  life  after  the  occur- 
rence of  an  explosion  of  carburetted  hydrogen,  or  fire-damp.  It 
frequently  also  accumulates  in  the  old  workings  of  mines,  and  in 
pits  or  wells.  Before  descending  into  them,  it  is  usual  to  lower  a 
lighted  candle  in  order  to  ascertain  whether  the  light  will  burn  ; 
if  it  does  so,  it  is  generally  considered  safe  to  venture  down. 
Instances,  however,  are  on  record  in  which  a candle  was  found 
burning  in  an  atmosphere  which,  nothwithstanding,  contained 
sufficient  carbonic  anhydride  to  cause  death.  When  it  is  neces- 
sary to  enter  into  an  atmosphere  considerably  charged  vflth  this 
gas,  Graham  suggests  as  a precaution  that  the  mouth  and  nostrils 
be  covered  with  a cloth  containing  a mixture  of  slaked  hme  and 
crystalhzed  sulphate  of  sodium.  Such  a mixture  is  porous  enough, 
in  a layer  of  an  inch  thick,  to  allow  the  passage  of  sufficient  air 
for  respiration,  whilst  the  moist  hme  completely  absorbs  the  car- 
bonic anhydride. 

6.  — There  is  also  another  mode  in  which  carbonic  anhydride 
is  very  largely  formed,  which,  independently  of  its  importance  as 
a source  of  the  gas,  is  interesting  as  throwing  light  upon  its 
chemical  nature.  Whenever  cliarcoal,  or  bodies  which,  like  wood, 
coal,  oil,  or  tallow,  contain  carbon,  are  burned  either  in  oxygen 
or  in  air,  carbonic  anhydride  is  obtained  abundantly ; if  the  gas, 
after  combustion  has  terminated,  be  agitated  with  hme-water,  this 
hquid  will  be  immediately  rendered  milky. 

Carbon  may  again  be  extracted  from  carbonic  anhydride.  If 
a small  piece  of  potassium,  heated  till  it  begins  to  burn  in  air,  be 
introduced  by  means  of  a platinum  spoon  into  a jar  of  gaseous 
carbonic  anhydride,  the  potassium  will  continue  to  burn  with 
great  brilliancy.  Potash  will  be  formed  at  the  e?vpense  of  the 
oxygen  which  the  gas  contains,  whilst  charcoal  is  liberated,  as 
may  be  seen  in  the  black  particles  which  are  suspended  in  the 
water  into  which  the  spoon  is  plunged  after  the  combustion  is 
complete.  Thus  carbonic  anhydride  is  shown,  both  synthetically 
and  analytically,  to  be  a compound  substance,  consisting  of  carbon 
and  oxygen,  and  its  composition  may  be  represented  as  fol- 
lows : 


GENERAL  PROPERTIES  OF  THE  CARBONATES. 


55 


Carbon 

Oxygen 

Carbonic 

anhydride 


il  11 

By  weifijht. 

12  or  27-28 

32  72  72 

Dumas. 

27-28 

72-72 

1 

h- < t— * 2- 

o o 

II  II 

Sp.  arr. 
0-4146 
1.1057 

002  = 

44 

100  00 

100-00 

2 1-0  = 

1-5203 

Carbonic  anhydride  is  not  decomposed  by  mere  elevation  of 
temperature,  but  if  a succession  of  electric  sparks  be  transmitted 
through  the  gas  it  is  partially  separated  into  carbonic  oxide,  and 
free  oxygen.  Sulphur,  chlorine,  and  the  halogens  may  be  heated 
with  the  gas  without  decomposing  it ; but  if  heated  with  hydrogen, 
water  and  carbonic  oxide  are  formed,  the  decomposition  bein^ 
represented  thus,  + Carbon,  and  many  ot 

the  metals,  such  as  iron  and  zinc,  also  remove  a portion  of  the 
oxyp’en  from  the  carbonic  anhydride,  and  convert  it  into  carbonic 
oxide  (357). 

Applications. — Sir  Goldsworthy  Gurney  has  turned  the  pro- 
perty of  extinguishing  flame  possessed  by  carbonic  anhydride  to 
an  important,  practical  account.  Coal  mines,  at  different  times 
and  from  various  causes,  are  liable  to  take  fire,  and  from  the  vast 
mass  of  heated  matter,  the  conflagration  not  unfrequently  resists 
all  the  ordinary  means  of  checking  its  ravages  ; many  acres  of 
subterranean  fire  are  thus  produced,  and  the  workings  are  of 
necessity  abandoned.  Sir  G.  Gurney,  in  such  cases,  closes  every 
opening  into  the  mine  but  two,  one  for  the  entrance,  the  other 
for  the  escape  of  the  gases,  and  then,  by  the  agency  of  the  steam 
jet,  pours  into  the  mine  a current  of  impure  carbonic  anhydride 
and  nitrogen,  obtained  by  forcing  a stream  of  air  through  a coke 
furnace  into  the  mine,  so  as  to  fill  the  entire  workings  with  the  gas ; 
he  has  thus  on  several  occasions  succeeded  at  a very  small  expense 
in  extinguishing  fires  which  have  raged  unsubdued  for  years.  A 
very  remarkable  case  of  this  kind  was  mentioned  in  the  Times  for 
May  22,  1851  : — The  ^ burning  waste  of  Clackmannan,’  situate 
about  seven  miles  from  Stirling,  had  been  for  30  years  on  fire. 
It  occurred  in  a seam  of  nine-foot  coal,  and  extended  over  an  area 
of  26  acres  ; yet  the  fire  was  successfully  extinguished : — about 
8,000,000  cubic  feet  of  gas  were  required  to  fill  the  mine,  and  a 
continuous  stream  of  impure  carbonic  anhydride  was  kept  up 
night  and  day  for  about  three  weeks.  The  difficulty  lay  not  so 
much  in  putting  out  the  fire,  as  in  cooling  down  the  ignited  mass 
so  that  it  should  not  again  burst  into  flame  on  readmitting  the 
air.  In  order  to  effect  the  necessary  reduction  of  the  tem])cra- 
ture,  water  was  blown  in  along  with  the  carbonic  anhydride  in 
the  form  of  a fine  spray  or  mist.  Subsequently,  cold  air  mixed 
with  the  spray  was  blown  in,  and  in  a month  from  the  com- 
mencement of  operations  the  fire  was  found  to  be  completely  ex- 
tinguislied. 

(350)  Carbonates. — Though  but  a feeble  acid,  the  radl(de  of 
carbonic  acid  unites  witli  the  metals  and  forms  a numerous  and 
important  class  of  salts,  which  have  till  lately  been  regai-ded  as 
monobasic ; in  which  case  (reverting  to  the  old  notation)  they 
would  contain  one  equivalent  of  the  anhydride  to  one  equivalent 


56 


GENERAL  PROPERTIES  OF  THE  aUiBONATES. 


of  the  base,  like  carbonate  of  potash  (KOjCO^).  But  in  the  case 
of  the  alkalies  a second  equivalent  of  the  anhydiide  may  be  com- 
bined with  the  metallic  oxide ; thus  with  potash  there  is  also  a 
bicarbonate  or  acid  carbonate  (KO,  HO,  2 CO2).  Ovdng  to  the 
existence  of  these  salts,  conjoined  with  a consideration  of  the 
properties  of  many  of  the  compounds  which  carbonic  anhydride 
forms  with  certain  organic  substances,  the  acid  is  now  very  gene- 
rally regarded  as  dibasic  (554),  in  which  case  its  formula  would 
be  double  of  that  formerly  adopted ; carbonate  of  calcimn  would 
then  be  represented  as  2 Ca0,C204,  or  HaHOg  ; carbonate  of 
potassium  as  2 1x0,020^,  or  Iv2€^3 ; and  bicarbonate  or  the  acid 
carbonate  of  potassium,  as  K0,II0,C204,  or  KHOOg.  The  for- 
mula of  all  the  carbonates  hitherto  regarded  as  neutral  would, 
upon  this  view,  be  doubled,  while  those  of  the  acid  carbonates  and 
some  of  the  double  carbonates  would  retain  their  former  value 
imchanged. 

The  carbonates,  with  the  exception  of  those  of  the  alkaline 
metals,  are  not  soluble  in  water  ; but  many  of  the  jiisoluble  car- 
bonates, and  in  particular  those  of  calcium,  magnesium,  barium, 
and  strontium,  may  be  dissolved  to  some  extent  by  water  charged 
with  carbonic  acid,  and  are  deposited  in  a crystalline  form  as  the 
gas  escapes  slowly  from  the  liquid.  All  the  carbonates  are  dis- 
solved with  effervescence  by  diluted  nitric  acid,  and  even  by 
acetic  acid : the  gas  which  comes  off  is  colourless,  and  renders 
lime-water  turbid ; it  possesses  the  properties  of  carbonic  anhy- 
dride, above  described.  Tlie  most  delicate  test  of  the  presence 
of  free  carbonic  acid  is  one  of  the  basic  salts  of  lead,  such  as  the 
subnitrate  or  the  subacetate,  a solution  of  whicli  is  instantly 
rendered  milky  by  the  action  of  the  acid  upon  it.  The  carbonates 
of  the  alkaline  metals,  when  in  solution,  are  also  decomposed  by 
acids,  with  effervescence  ; they  give  with  salts  of  calcium  a white 
precipitate,  which  is  immediately  redissolved  by  an  acid,  vdth  effer- 
vescence. All  the  carbonates,  with  the  exception  of  those  of  the 
alkaline  metals  and  barium,  are  decomposed  by  prolonged  ignition, 
the  salt  being  decomposed  into  the  anhych*ide  and  a metallic  oxide. 
The  carbonates  have  considerable  tendency  to  combine  witli  each 
other,  and  form  double  salts,  like  dolomite,  which  is  a double  car- 
bonate of  calcium  and  magnesium  (HgHa2O03).  Many  basic 
carbonates  are  also  known  ; they  are  often  hydrated  compounds 
— such,  for  example,  as  malachite  (■0uH202i'^^^^^3)- 

If  M and  M'  represent  the  atom  of  any  two  different  metallic 
monads,  such  as  potassium  and  sodium,  the  general  formulae  of 
the  carbonates  will  be  thus  indicated : — 

Hormal  salt,  M2-GO3 

Acid  salt,  MHe03 

Double  salt,  MM'OOg 

The  following  table  represents  the  composition  of  some  impor- 
tant carbonates : — 


CARBONATES CARBON. 


57 


Carbonate  of  potassium K26O3  • H2O 

Carbonate  of  sodium  Na2-G<:>3 . 10  H2O 

Acid  carb,  (bicarbonate)  of  potassium KHOO3 

Acid  carb.  (bicarbonate)  of  sodium  NaH-GOg 

Trona  (sesquicarb,  sodium) 2 ]Sra2G03,  H2OO3  • 3 H2O 

Sesquicarb.  of  ammonium 2 (H4]Sr)2  GG3,  G02 

Carbonate  of  barium BaGOs 

Carbonate  of  calcium GaGG3 

Carbonate  of  magnesium MgGG3 

Dolomite MgGa  2 GG3 

Baryto-calcite BaGa  2 G03 


Old  Notation. 

K0,C02  . HO 
NaO,  CO2.  10  HO 
KO,  HO,  2 CO2 
NaO,  HO,  2 CO2 
2 NaO,  HO  . 3 CO2 . 3 HO 
2 H4NO,  3 CO2 
BaO,  CO2 
CaO,  CO2 
MgO,  CO2 
MgO,  CaO,  2 CO2 
BaO,  CaO,  2 CO2 


Malachite Gu  GGs,  Gu  H2  G2 

Blue  carbonate  of  copper 2GUGG3,  GuHa  O2 


CuO,  CO2 . CuO,  HO 
2 (CuO,  CO2),  CuO,  HO 


§ 11.  Carbon.  0=12,  Gr  C=6. 

Sjp.  Gr.  as  diamond^  3'33  to  3*55  ; Theoretical  Density  of  its 
Yajyour^  0*4:146  ; Atomic  Vol.  \ | ] ? 

(351)  Carbon  is  an  elementary  body  of  the  greatest  impor- 
tance. It  is  found  nearly  in  a state  of  purity  in  the  diamond ; 
with  a larger  proportion  of  foreign  admixture  it  occurs  in  the  form 
of  graphite,  and  still  less  pure  in  the  abundant  deposits  of  pit  coal. 
It  is  also  met  with  in  enormous  quantities  in  combination,  under  a 
variety  of  forms.  Independently  of  the  quantity  of  it  which  exists 
difiused  through  tlie  atmosphere  in  the  state  of  carbonic  anhy- 
dride, it  is  a component  of  the  numerous  varieties  of  carbonate  of 
calcium  and  of  magnesium,  constituting  nearly  an  eighth  of  the 
entire  weight  of  the  former,  and  more  than  a seventh  of  that  of 
carbonate  of  magnesium.  It  is  the  characteristic  ingredient  of  all 
substances  which  are  termed  organic;  that  is,  of  substances 
which  are  produced  directly  or  indirectly  from  the  vegetable  or 
animal  creation.  The  solid  parts  of  plants,  shrubs,  and  trees  owe 
their  form  and  solidity  to  this  element,  which  is  mainly  supplied 
to  them  from  the  carbonic  anhydride  in  the  atmosphere.  This 
action  of  plants  upon  carbonic  anhydride  is  one  of  the  means 
ordained  for  preserving  uniformity  in  the  composition  of  the  air. 
The  quantities  of  carbonic  anhydride  poured  forth  from  the  bowels 
of  the  eartli,  and  derived  from  the  processes  of  respiration  and 
combustion,  and  from  numerous  other  less  apparent  sources,  would 
by  degrees  occasion  an  injurious  accumulation  of  the  gas,  but  for 
this  compensating  action.  In  solar  light  the  leaves  of  plants  de- 
compose both  carbonic  anhydride  and  water,  appropriating  the 
carbon  and  the  hydrogen  of  each  for  their  own  growth  and  nutri- 
tion, whilst  a large  proportion  of  the  oxygen  which  these  com- 
pounds contained  is  returned  into  tlie  air  in  the  gaseous  state. 
The  carbonic  anhydride  thus  poured  out  by  animals  as  a refuse 
and  poisonous  product,  supplies  food  and  substance  to  tlie  vege- 
table world,  which  in  its  turn  converts  the  carbon  into  a form 
suitable  for  the  maintenance  of  life  in  animals.  Eacli  great  divi- 
sion of  animated  nature  is  thus  seen  to  bo  essential  to  the  well- 
being and  even  to  the  support  of  the  other.  The  fuel  which  has 
been  burned  and  dissipated  in  vapour,  is  again  reduced  to  the 


58 


DIAMOND WHERE  FOUND MODE  OF  CUTTING. 


solid  state,  and  by  the  agency  of  vegetable  life,  it  is  once  more 
fitted  for  combustion.  Plants  are  in  fact  the  grand  agents  by 
which,  under  the  influence  of  the  chemical  action  of  the  sun’s 
rays,  deoxidation  is  effected,  while  animals  are  the  channels 
through  which  recombination  with  oxygen  is  unceasingly  pro- 
duced. 

(352)  Diamond^  Sp.  Gr.  from  3*33  to  3*55. — Carbon  is  found  in 
its  purest  state  in  the  diamond^  which  occurs  crystallized  in  forms 
belonging  to  the  regular  system.  The  crystals  are  generally  de- 
rivatives from  the  octohedron,  with  a cleavage  parallel  to  each  of 
the  planes  of  the  octohedron ; the  faces  are  often  convex,  and  the 
edges  are  generally  rounded,  or  lenticular^  as  they  are  termed,  in 
such  crystals.  Diamonds  usually  present  themselves  under  the 
appearance  of  semi-transparent  rounded  pebbles,  enclosed  in  a 
thin  brownish  opaque  crust.  The  gem,  when  freed  from  this  coat- 
ing, is  generally  colourless ; such  specimens  are  the  most  prized ; 
it  is,  however,  met  with  of  various  tints,  the  more  common  of 
which  are  yellow  and  different  shades  of  brown.  The  most  famous 
diamond  mines  are  those  of  Golconda  and  Bundelcund  in  India,  of 
Borneo,  and  of  the  Brazils.  The  origin  of  the  diamond  is  entirely 
unknown ; it  is  not  probable  that  it  has  been  formed  by  crystal- 
lization after  fusion,  since  intense  heat  reduces  the  diamond  to  the 
form  of  graphite.  The  circumstances  under  which  diamonds  are 
found  in  nature  afford  no  clue  to  the  process  of  their  formation. 
In  the  year  1827  a diamond  was  found  imbedded  in  a fine-grained 
quartzose  rock  [Itacolurmie)  in  Brazil,  but  with  few  exceptions  the 
gem  is  found  scantily  in  an  alluvial  matrix,  consisting  chiefly  of 
sandstone  and  rolled  quartz  pebbles,  from  which  the  diamonds  are 
extracted  by  washing  and  careful  sorting. 

Diamond  is  the  hardest  body  known,  crystallized  boron  ap- 
proaching it  most  nearly  in  this  respect : it  is  cut  and  polished  by 
employing  its  own  powder  for  the  purpose.  The  fine  diamond 
dust  used  for  this  object  is  mixed  with  a little  olive  oil,  and  spread 
over  a revolving  steel  plate,  and  the  diamond,  cemented  into  a 
suitable  support,  has  each  of  its  faces  in  turn  presented  to  the  flat 
face  of  the  disk.*  The  most  important  use  to  which  the  diamond 
is  applied  is  tlie  cutting  of  sheets  of  glass : only  the  natural  face 
of  the  crystal  can  be  employed  for  this  purpose,  crystals  with 
curved  faces  being  the  best ; they  are  set  in  a convenient  handle, 
and  a line  in  the  proper  direction  is  traced  with  the  diamond  across 
the  glass ; slight  pressure  on  each  side  of  the  cut  then  determines 

* The  Kohinoor  diamond,  which  was  cut  in  1852,  for  the  Queen,  was  imbedded  in 
a copper  vessel  of  about  the  size  of  a teacup,  into  which  it  was  cemented  with  a mix- 
ture of  equal  parts  of  tin  and  lead.  When  it  was  necessary  to  change  the  position  of 
the  gem,  the  solder  was  softened  by  immersing  the  cup,  with  the  diamond  imbedded, 
in  a charcoal  fire,  and  heating  the  metal  dll  it  assumed  a consistence  resembling  that 
of  wet  sand ; in  order  to  cool  the  diamond  more  quickly,  it  was  plunged  first  into  warm 
water  and  then  into  cold  water;  the  cutting  was  effected  by  means  of  a cast-iron 
wheel  revolving  on  a vertical  axis  about  2400  times  per  minute ; the  diamond  rested 
upon  the  upper  surface  of  the  wheel,  being  held  in  its  position  by  a kind  of  vice,  and 
the  pressure  against  the  revolving  disk  was  increased  or  diminished  by  adding  or  re- 
moving weights.  From  time  to  time  the  face  of  the  diamond  was  touched  with  a hair 
pencil  dipped  in  a cream  of  diamond  dust  and  oil 


GRAPHITE,  OK  PLITMBAGO. 


59 


the  fracture  in  the  right  direction.  A true  cut  is  effected  by  such 
a diamond  if  properly  used,  whilst  a diamond  with  angles  obtained 
l)y  cleavage  produces  only  a superficial  scratch  with  ragged  edges. 

The  diamond  has  a very  brilliant  lustre  and  a high  refracting 
power;  it  is  a non-conductor  of  electricity.  After  exposure  to 
sunshine,  many  specimens  emit  a feeble  phosphorescent  light, 
which  may  be  seen  in  a darkened  room.  In  vessels  from  which 
air  is  excluded,  it  may  be  heated  intensely  without  change.  If  it 
be  suspended  in  a cage  of  platinum  wire,  heated  to  bright  redness, 
and  plunged  into  oxygen  gas,  it  will  burn  with  a steady  red  light, 
and  with  the  production  of  pure  carbonic  anhydride.  The  dia- 
mond, however,  is  not  perfectly  pure  carbon : it  always  leaves  a 
minute  yellowish  ash,  which  has  been  found  to  contain  silica  and 
oxide  of  iron.  This  ash  has  generally  the  form  of  a cellular  net- 
work, and  may  perhaps,  at  some  future  time,  assist  in  determining 
the  origin  of  tliis  valuable  gem.  'No  heat  hitherto  applied  suffices 
for  the  fusion  or  volatilization  of  the  diamond,  or  indeed  of  carbon 
in  any  of  its  forms,  though  in  the  intense  heat  of  the  voltaic  arc, 
it  appears  to  be  mechanically  transported  from  one  electrode  to 
the  other  (355).  When  the  diamond  is  introduced  into  the  flame 
of  the  voltaic  arc,  it  undergoes  a remarkable  change ; as  soon  as 
it  becomes  white  hot  it  begins  to  swell  up,  loses  its  transparency, 
suddenly  acquires  the  power  of  conducting  electricity,  becomes 
specifically  lighter,  and  is  converted  into  a black  opaque  mass, 
resembling  coke.  The  density  of  a diamond  thus  altered  was 
2‘6778,  while  in  its  crystalline  condition  it  was  3'336  (Jacquelain, 
Ann.  de  Cliimie.^  III.  xx.  467).  The  heat  of  the  oxyhydrogen  jet 
was  found  to  be  insufficient  to  produce  this  change. 

(353)  Graphite^  or  Plumbago  {Sp.  Gr.  from  2'35  to  2T5),  is  a 
second  form  in  which  carbon  occurs  native.  Its  once  celebrated 
mine  at  Borrowdale  is  now  nearly  exhausted.  It  is  also  found  in 
Ceylon,  and  in  several  parts  of  the  United  States,  always  in  rocks 
belonging  to  the  earliest  formation.  It  has  also  been  found  abun- 
dantly in  the  Batougal  mountains,  near  the  frontier  of  China,  in 
South  Siberia.  The  Borrowdale  graphite  occurs  in  clay-slate ; 
in  other  localities  it  is  imbedded  in  gneiss,  mica-slate,  or  granular 
limestone.  Graphite  occurs  either  massive  or  in  six-sided  crys- 
talline plates  belonging  to  the  rhombohedral  system.  Carbon,  in 
the  two  forms  of  diamond  and  plumbago,  offers  an  excellent 
instance  of  dimorphism  ; the  properties  which  it  displays  in  these 
two  states  are  as  widely  different  as  those  of  any  two  dissimilar 
elements.  Graphite  has  a metallic,  leaden-grey  lustre,  whence 
its  familiar  name  of  hlach-lead.  It  is  very  friable,  and  conse- 
quently feels  unctuous  to  the  touch,  and  leaves  traces  on  paper 
upon  which  it  is  rubbed.  The  particles  of  which  it  is  composed 
are,  however,  extremely  hard,  and  they  rapidly  wear  out  the  saws 
employed  to  cut  it.  It  a])pears  to  exist  in  two  distinct  modifica- 
tions, one  of  which,  like  the  Borrowdale  graphite,  is  fine-grained 
and  amorphous ; the  other,  like  the  Ceylon  variety,  is  composed 
of  small  flat  plates,  united  by  a cementing  material ; this  form  of 
graphite  generally  occurs  in  a matrix  of  quartz  (Brodie).  Graphite 


60 


OXIDIZED  PKODECTS  FROM  GRAPHITE. 


is  an  excellent  conductor  of  electricity.  It  is  never  met  with  in  a 
state  free  from  foreign  admixtime ; when  hnnied  in  oxygen  it  leaves 
from  2 to  5 per  cent,  of  ash,  which  generally  contains  quartz,  and 
oxides  of  manganese  and  iron ; these  bodies,  however,  are  merely 
accidental  impurities.  The  fine-grained  amoq^hous  graphite  is 
highly  prized  for  the  manufacture  of  ‘ lead  pencils  ’ : where  pieces 
of  sufficient  size  can  be  obtained  they  are  sawn  into  thin  slices,  and 
these  again  into  small  rectangular  prisms,  which  are  placed  in  cedar 
wood  for  use.  It  has  been  found  that  the  smallest  fragments,  if  of 
good  quality,  and  the  fine  powder  (which  was  formerly  consolidat- 
ed by  melting  it  with  a minute  quantity  of  sulphur,  and  was  used 
for  the  coarser  kinds  of  pencils)  may  be  again  reduced  into  coherent 
plates  by  subjecting  it  to  enormous  pressure,  and  may  thus  be  fitted 
for  the  manufacture  of  the  best  pencils.  Black-lead  is  extensively 
used  for  lubricating  machinery,  and  as  it  is  quite  unaltered  by 
exposure  to  the  weather,  it  forms  a serviceable  coating  to  protect 
coarse  iron  work  fi’om  rust.  An  application  of  graphite  which  is 
of  some  importance  to  the  chemist,  is  its  use  in  the  manufacture 
of  what  are  termed  black-lead  crucibles,  or  blue-pots ; the  clay 
employed  in  making  them  is  mixed  with  a coarse  kind  of  gra- 
pliite ; the  pots  made  from  this  mixture  are  much  less  hkely  to 
crack  when  heated  than  if  made  of  fire-clay  only. 

Brodie  (Ann.  de  Chimie^  III.  xlv.  351)  has  described  a method 
of  obtaining  graphite  in  a state  of  piiilty,  and  in  a very  finely 
divided  form.  It  consists  in  mixing  coarsely-powdered  graphite 
with  a fomteenth  of  its  weight  of  chlorate  of  potassium ; the 
mixture  is  introduced  into  an  iron  pot,  and  difiiised  thi’ough  a 
quantity  of  concentrated  sidphuric  acid,  equal  to  twice  the  weight 
of  the  graphite  employed.  The  mixture  is  heated  over  a steam 
bath  so  long  as  any  peroxide  of  chlorine  is  disengaged  ; it  is  then 
allowed  to  cool,  thrown  into  water,  and  washed  thoroughly.  If 
graphite  which  has  been  subjected  to  this  treatment  and  diled,  be 
heated  to  redness,  it  gives  off  gas,  increases  greatly  in  bulk,  and 
becomes  reduced  to  an  exceedingly  fine  powder.  In  cases  in 
which  the  graphite  was  originally  mixed  with  silica,  this  impurity 
may  be  got  rid  of  by  adding  a small  quantity  of  fiuoride  of  sodium 
to  the  mixture  of  graphite  with  chlorate  of  potassium  and  sulphu- 
ric acid ; the  silica  is  then  expelled  in  the  form  of  fiuoride  of 
silicon. 

It  appears  that  during  this  treatment  the  graphite  becomes 
oxidized ; and  that  a new  compound  of  carbon,  hycfrogen,  and 
oxygen  is  formed,  whicli  enters  into  combination  with  the  sul- 
phmlc  acid,*  and  this  compound  is  decomposed  by  ignition. 

* This  oxidized  substance  may  be  obtained  in  a state  of  purity  by  the  following 
process  {Q.  J Chem.  Soc.  xii.  261); — IMix  intimately  1 part  of  finely  powdered  Ceylon 
graphite  with  three  parts  of  chlorate  of  potassium,  and  add  sufficient  of  the  strongest 
nitric  acid  to  render  the  mixture  fluid ; after  whicli  expose  it  for  three  or  four  days 
to  the  heat  of  140°  on  a water  bath.  Exposure  of  the  mixture  to  the  direct  rays  of 
the  sun  abridges  the  time  required.  The  residue  must  be  washed  \Nnth  water  freely, 
dried,  and  subjected  four  or  five  times  to  the  same  treatment. 

Graphic  Acid  (€11,11405),  as  this  compound  is  termed  by  Brodie,  forms  yellow  silky 
plates,  which  are  insoluble  in  water  and  in  acids.  It  is  slowly  attacked  by  ammonia 


PIT  COAL CONSUMPTION  OF  SMOKE. 


61 


The  graphitic  modification  of  carbon  may  be  obtained  artifi- 
cially by  several  processes.  When  cast  iron  is  melted  in  contact 
with  an  excess  of  charcoal,  it  takes  np  a considerable  quantity  of 
it,  and  if  the  iron  be  allowed  to  cool  slowly,  the  carbon  crystallizes 
out  in  the  six-sided  plates  peculiar  to  graphite.  In  the  manu- 
facture of  coal-gas,  those  parts  of  the  retort  which  are  exposed  to 
the  highest  temperature,  partially  decompose  the  gas  as  it  escapes  ; 
a part  of  the  carbon  which  it  held  in  combination  is  deposited, 
and  by  degrees  a layer  of  very  pure  dense  carbon  is  formed,  pos- 
sessed of  a lustre  reseml^ling  that  of  a metal.  The  density  and 
appearance  of  this  mass  vary  according  to  the  temperature,  and 
the  gaseous  pressure  to  which  it  has  been  subjected. 

Pit  coal  is  a substance  originally  of  vegetable  origin,  which 
has  become  altered  in  appearance  and  composition  by  the  combined 
action  of  heat  and  moisture  under  great  pressure.  The  composi- 
tion of  coal  varies  considerably  according  to  the  extent  to  which 
these  decomposing  actions  have  advanced  : the  different  varieties 
of  coal  will  be  noticed  hereafter,  but  in  all  cases  it  consists,  like 
vegetable  matter  in  general,  of  carbon,  hydrogen,  and  oxygen, 
with  a small  proportion  of  nitrogen ; and  in  addition,  it  contains 
a variable  quantity  of  saline  and  earthy  substances,  which  always 
exist  in  the  juices  of  plants,  besides  a variable  amount  of  iron 
pyrites  or  bisulphide  of  iron.  These  saline  matters  are  left,  when 
the  coal  is  burnt  in  an  open  fire-place,  and  constitute  the  ashes ; 
whilst  the  carbon  and  hydrogen  are  entirely  converted  into  car- 
bonic anhydride  and  water,  if  an  adequate  supply  of  oxygen  from 
the  air  be  furnished  ; but  the  burning  of  coal,  even  in  an  open  fire, 
is  never  complete,  so  that  it  gives  on*  a quantity  of  gaseous  and 
tarry  matters,  holding  finely  divided  carbon  or  soot  in  suspension.'^ 

and  by  potash,  the  ammonia  gradually  combining  with  it,  forming  a gelatinous  body 
susceptible  of  decomposition  by  acids,  which  occasion  the  separation  of  a white  gela- 
tinous mass. 

When  graphic  acid  is  exposed  to  a temperature  of  between  500°  and  600°,  it 
undergoes  decomposition  with  almost  explosive  violence,  with  evolution  of  heat  and 
light,  giving  off  gas,  and  producing  an  exceedingly  bulky,  flocculent,  sooty-looking 
substance  which  still  retains  both  carbon  and  hydrogen.  If,  in  order  to  regulate  the 
heat  applied,  the  graphic  acid  be  placed  in  paraffin  oil,  and  the  temperature  be  grad- 
ually raised  to  520°,  the  hydrocarbon  becomes  of  a deep  red  colour,  and  the  acid 
gives  off  water  and  carbonic  acid,  leaving  a substance  of  graphitoid  appearance,  con- 
sisting of  O22II2O4 ; if  this  new  body  be  further  heated  in  an  atmosphere  of  nitrogen, 
water  and  carbonic  oxide  escape,  leaving  a residue  containing  <76eH40ii.  Even  if 
heated  to  redness  in  nitrogen,  it  retains  a portion  of  oxygen  and  hydrogen,  giving  olf 
water,  carbonic  anhydride,  and  carbonic  oxide. 

Brodie  considers  that  in  these  compounds  the  graphite  retains  its  allotropic  state, 
which  he  terms  Graphon^  and  that  it  possesses  in  this  form  a combining  number  of 
33,  with  the  symbol  Gr.  If  this  be  so,  graphic  acid  -01111405  might  be  represented 
as  Gr4H405,  the  first  residue  022II2O4  as  Gri,H204,  and  the  second  Ocellil^n,  as 
Gr24HjOii ; graphic  acid  being  regarded  by  Brodie  as  analogous  to  the  hydrated  oxide 
of  silicon  81311405  discovered  by  Wohler  and  Buff  (471a). 

* Consumption  of  Smoke. — When  a quantity  of  fresh  coal  is  thrown  upon  a hot 
fire,  the  coal  immediately  begins  to  undergo  decomposition : various  compounds  of 
carbon  with  hydrogen  being  abundantly  extricated  in  the  form  of  gas  or  vapour : a 
portion  of  these  immediately  takes  fire  and  burns  with  a bright,  luminous  fiamo,  but 
a large  proportion  of  these  hydrocarbons,  on  coming  into  contact  with  the  glowing 
embers,  is  further  more  or  less  completely  decomposed,  the  carbon  and  hydrogen  ex- 
periencing a separation  from  each  other ; the  hydrogen,  which  is  the  more  combusti- 


COMErSTIOX  OF  SMOKE. 


G2 


'Wlien  the  coal  is  heated  in  long  closed  iron  cylinders,  so  construct- 
ed as  to  exclude  atmospheric  air,  hut  to  allow  free  escape  for  vola- 
tile matters,  a large  quantity  of  gaseous  substances,  containino;  the 
oxygen,  hydrogen,  and  nitrogen,  with  a part  of  the  carbon  ot  the 
coal,  passes  off,  while  the  greater  proportion  of  the  carbon  remains 
behind,  and  constitutes  col:e^  which  is  the  only  one  of  the  pro- 
ducts that  will  be  noticed  at  present.  Coke  is,  chemically,  the 
same  substance  as  the  graphite  deposited  from  the  gas,  but  in  a 
less  pure  form,  owing  to  the  earthy  matters  which  are  mixed  with 
it.  As  a fuel  coke  is  often  to  be  preferred  to  coal,  since  it  biums 
without  emitting  any  visible  smoke ; it  has  also  the  advantage  of 
not  swelling  or  caking  together  when  lieated,  and  thus  the  danger 
of  choking  the  draught  is  avoided.  The  higher  the  temperature 
to  which  coke  is  exposed  during  its  manufacture,  the  more  dense 

ble  element,  becomes  burned,  or,  if  the  supply  of  oxygen  be  inadequate,  it  passes  off 
in  the  gaseous  form,  whilst  the  carbon,  o\\'iug  to  the  minute  state  of  subdivision  of 
its  particles,  is  carried  up  the  chimney  suspended  in  the  current  of  heated  gases.  By 
proper  care,  the  volumes  of  black  smoke  ordinarily  poured  forth  from  the  chimneys 
of  our  houses  and  factories,  may,  however,  be  prevented,  and  the  annoyance  due  "to 
this  contamination  of  the  atmosphere  in  our  large  towns  to  a great  extent  obviated ; 
whilst  a considerable  saving  of  fuel  may  at  the  same  time  be  effected. 

The  principles  involved  in  the  prevention  of  smoke  are — 1st,  the  sujiply  of  fuel  in 
small  quantity  at  a time,  taking  care  to  maintain  a strong,  steady  lire,  in  order  that 
the  gases  may  be  burned  as  fast  as  they  are  generated;  and,  2nd,  the  supply  of  an 
adequate  quantity  of  atmospheric  air.  The  latter  condition  is  not  so  easily  accom- 
plished in  the  furnaces  of  the  manufacturer  as  might  be  sujDposed.  The  regulated 
supply  of  fuel  in  small  quantities  may  obviously  be  ensured  by  due  care  on  the  part 
of  the  stoker,  but  it  requires  more  labour  and  attention  than  is  usually  bestowed  by 
him.  Various  contrivances  have  been  from  time  to  time  invented  for  effecting  the 
prevention  of  smoke,  one  class  of  these  having  for  their  object  the  regnilar  supply  of 
fuel  by  mechanical  means,  as  is  proposed  by  Juckes’s  apparatus,  the  essential  points 
of  which  are  shown  in  section  in  fig.  286. 

Fig.  286. 


The  fire-bars,  b b,  in  this  case  consist  of  a series  of  endless  chains,  which  are  car- 
ried very  slowly  forward  by  machinery  connected  with  the  toothed  wheels  w w.  A 
continuous  but  very  gradual  supply  of  fuel  is  furnished  from  the  hopper,  h,  in  front 
of  the  furnace,  and  the  amount  of  coal  thus  admitted  is  regulated  by  raising  or  lower- 
ing the  door  d.  This  apparatus  fulfils  its  object  well,  but  the  wear  and  tear  of  the 
fire-bars  is  considerable, 


PREPAKATION  OF  COKE. 


63 


does  it  become,  and  the  better  is  it  fitted  for  producing  a steady 
and  intense  heat,  when  burned  as  fuel ; though  unless  the  supply 
of  air  be  tolerably  abundant,  it  burns  less  freely  in  this  dense  con- 
dition than  when  less  compact.  In  order  to  furnish  a coke  suited 
for  the  use  of  locomotive  engines,  it  is  customary  to  construct  coke 
ovens,  which  are  usually  built  of  brick,  and  lined  with  fire-bricks, 
the  walls  being  from  2 to  3 feet  in  thickness,  to  economize  heat : 
and  this  object  is  further  effected  by  building  several  ovens  toge- 
ther in  one  continuous  piece  of  masonry.  One  of  these  ovens,  12 
feet  in  internal  diameter  and  4 feet  in  height,  will  convert  3|-  tons 
of  coal  into  coke  in  forty-eight  hours.  The  oven  has  a sliding  door 
in  front,  for  the  purpose  of  introducing  and  withdrawing  the 
charge,  and  for  regulating  the  admission  of  air,  which  plays  over 
the  surface  of  the  heap  and  burns  off*  the  volatile  matters,  which 
escape  by  a short  chimney.  The  combustion  proceeds  gradually, 
from  above  downwards : in  about  forty  hours  after  commencing 
the  operation,  the  door  is  completely  closed,  and  the  furnace  left 
for  five  or  six  hours ; at  the  end  of  that  time  the  coke  is  with- 
drawn, and  quenched  with  water.  A bituminous  coal,  like  the 
Newcastle  coal,  furnishes  in  this  way  a very  dense  lustrous  coke, 
which  splits  into  long  columnar  masses  or  prisms,  as  the  tempera- 
ture in  the  oven  gradually  falls  when  the  door  is  closed.  A fresh 
charge  is  introduced  into  the  oven  whilst  its  walls  still  remain  red 
hot.  The  coke  is  never  melted  in  this  operation,  and  the  appear- 
ances of  fusion  which  it  frequently  exhibits  are  due  to  the  lique- 
faction, by  heat,  of  the  bituminous  portions  of  the  coal,  before  they 

In  another  class  of  smoke-burning  contrivances,  the  object  is  to  burn  the  smoke 
which  is  formed  in  small  quantity,  by  supplying  air  at  a high  temperature,  to  the 
unburnt  gases  as  they  escape  from  the  fire-place.  Fig.  287  represents  in  section 
the  plan  adopted  by  Mr.  F.  C.  Hills  for  attaining  this  object. 

Fig.  287. 


The  coal  is  thrown  into  the  fire  by  hand,  but  in  moderate  quantities  at  a time,  the 
fire-door,  a,  being  perforated  for  the  admission  of  air.  The  fire-bars,  b b,  are  tubular 
and  allow  the  passage  of  air  into  the  channel,  C,  which  opens  into  tlie  chimney  just 
behind  the  bridge,  e,  of  the  fire-grate ; the  air  becomes  heated  as  it  passes  through 
the  tubular  bars,  and,  if  the  quantity  thus  admitted  is  not  sutlicient  to  complete  the 
combustion  of  the  unburned  gaseous  products  as  they  escape,  more  air  can  be  supplied 
from  below  by  raising  the  damper,  d. 


64 


MAxrrAcmiE  of  wood  charcoal. 


have  Hndergone  carbonization.  A very  pure  form  of  carbon  ig 
frequently  observed  in  the  tissnres  of  the  mass,  in  the  form  of 
black  fibres,  closely  resembling  horsehair  in  appearance. 

Coke  may  also  be  prepared,  though  with  less  advantage,  by  a 
smothered  combustion  of  the  coal  in  heaps,  in  a manner  similar 
to  that  practised  in  making  charcoal.  Coke  is  subject  to  great 
variation  in  appearance  and  bulk,  this  variation  depending  on  the 
kind  of  coal  emploj^ed  in  producing  it : it  is,  however,  nearly 
always  more  bulky  than  the  coal  that  yields  it. 

(354)  Charcoal : Amorphous  Carhoii. — Carbon  also  exists  in 
a third  form,  distinct  from  that  of  graphite,  and  in  this  state  it  is 
amorphous,  or  entirely  destitute  of  crystalline  structure.  Lamp- 
hlack  is  a variety  of  this  kind  of  charcoal ; it  is  largely  manufac- 
tured by  heating,  in  an  iron  pot,  vegetable  matters  rich  in  carbon, 
such  as  resin  or  tar ; the  vapours  thus  disengaged  are  kindled,  and 
burned  in  a current  of  air  insufficient  for  their  complete  combus- 
tion ; t]ie  hydrogen  which  these  bodies  contain,  being  the  more 
inflammable  ingredient,  burns  off  first,  leaving  the  carbon  in  the 
form  of  a very  finely  divided  powder,  such  as  that  which  consti- 
tutes the  visible  portion  of  smoke.  The  smoky  products  of  this 
imperfect  combustion  are  made  to  pass  through  a large  chamber, 
the  walls  of  which  are  covered  with  coarse  cloth,  and  here  the  lamp- 
black is  deposited.  Lampblack  always  retains  a portion  of  some 
incompletely  burned  compounds  of  carbon  and  hydrogen.  The 
purest  form  in  which  finely  divided  carbon  can  be  obtained  for 
chemical  purposes  is  furnished  by  passing  the  vapour  of  oil  of 
turpentine  or  of  ether  slowly  through  tubes  maintained  at  a full 
red  heat ; a fine  powder  of  charcoal  is  deposited  within  them ; but 
this,  also,  even  if  again  heated  intensely  in  closed  vessels,  always 
retains  traces  of  hydrogen. 

Tinder  is  another  variety  of  carbon  in  the  amorphous  or  non- 
crystalline form  ; but  the  most  important  variety  is  Wood  Char- 
coal^ which  is  largely  manufactured  by  heating  billets  of  wood  to 
dull  redness  in  cast-iron  cylinders,  set  in  the  furnace  either  verti- 
cally or  horizontally,  and  j^i’O'dded  with  a tightly  fitting  lid  at 
one  end.  The  best  plan  consists  in  enclosing  the  wood  to  be 
charred  in  a second  lighter  case,  which  can  be  easily  introduced 
into  and  withdrawn  from  the  fixed  cylinder,  which  is  set  in  ma- 
sonry, and  protected  from  the  direct  action  of  the  flame  by  a 
casing  of  fire-brick.  From  this  kind  of  iron  retort  proceeds  a 
tube  connected  with  a condensing  apparatus,  where  the  liquid 
products  of  the  decomposition  may  be  arrested,  whilst  the  uncon- 
densible gases  pass  on,  and  are  directed  into  the  fire-place,  where 
they  are  consumed.  After  the  heat  has  been  continued  for  four 
or  five  hours,  the  end  of  the  outer  cylinder  is  removed,  the  inner 
case  with  its  charge  is  withdrawn,  and  the  whole,  whilst  still  red 
hot,  plunged  into  an  extinguisher  or  iron  case,  provided  with  a 
tightly  fitting  lid,  which  protects  it  from  the  action  of  the  air ; in 
this  condition  it  is  left  to  cool  gradually. 

In  countries  where  wood  is  abundant,  the  charcoal  is  manu- 
factured by  a much  ruder  method.  A plot  of  ground  is  levelled 


PEEPAEATION  OF  WOOD  CHAECOAL. 


65 


in  or  near  the  forest,  a stake  is  driven  into  the  ground,  and  a 
quantity  of  brushwood  having  been  placed  around  its  base,  logs 
of  wood  are  piled  up  regularly  round  the  stake  so  as  to  form  a 
mound,  which  is  partially  covered  up  with  powdered  charcoal, 
leaves,  turf,  and  earth;  the  heap  is  then  fired  by  introducing 
lighted  fagots  into  an  aperture  left  at  the  base  of  the  mound  for 
this  purpose : large  quantities  of  moisture  are  presently  exhaled, 
and  when  the  whole  mass  is  thoroughly  ignited,  it  is  still  more 
closely  covered  up  from  the  air,  the  workmen  regulating  the 
admission  of  air  as  circumstances  require ; it  is  then  allowed  to 
burn  out.  When  quite  cold,  the  earth  employed  to  stifle  the 
combustion  is  removed,  and  the  charcoal  is  fit  for  use.  The  com- 
bustion of  one  part  of  the  wood  is  thus  employed  as  a source  of 
heat  for  charring  the  rest.  Charcoal  prepared  in  this  manner  is, 
for  the  purposes  of  fuel,  preferable  to  that  made  in  cylinders  ; it  is 
denser  and  is  more  completely  deprived  of  volatile  matters,  because 
the  heat  to  which  it  is  exposed  is  much  more  intense,  and  is  con- 
tinued for  a much  longer  period.  If  the  diameter  of  the  heap  be 
30  feet  or  more,  the  operation  is  not  complete  in  less  than  a month. 
A slow  combustion  is  found  to  yield  more  charcoal  than  one  which 
is  rapidly  effected.  The  resulting  charcoal  retains  the  form  of 
the  wood,  but  it  is  much  reduced  in  size,  generally  not  amounting 
to  more  than  three-fourths  of  the  bulk  of  the  wood,  and  never 
exceeding  one-fourth  of  its  weight. 

Experience  shows  it  to  be  much  more  economical  to  employ 
dry  wood  in  the  preparation  of  charcoal  than  wood  in  its  green 
condition.  Karsten  found  that  100  parts  of  recently  felled  wood, 
by  drying  at  212°,  lost  57  parts ; by  raising  the  temperature  to 
302°  the  loss  upon  the  original  weight  amounted  to  not  less  than 
67  parts ; and  the  33  parts  of  dry  residue  when  charred  left  25 
parts  of  charcoal ; but  100  parts  of  the  same  wood,  if  charred 
without  any  preliminary  drying,  left  only  11  parts  of  charcoal. 
This  remarkable  difference  in  produce  depends  upon  the  decom- 
posing action  of  charcoal  at  a high  temperature  upon  water,  in 
consequence  of  which  much  of  the  carbon  escapes  in  the  gaseous 
state  in  the  form  of  carbonic  oxide,  whilst  the  hydrogen  of  the 
water  also  passes  off  as  gas. 

The  object  of  preparing  charcoal  as  a fuel  is  to  get  rid  of  mois- 
ture and  volatile  matters,  which,  at  the  moment  of  their  formation, 
greatly  reduce  the  temperature  of  the  burning  mass,  owing  to  the 
large  quantity  of  heat  which  they  carry  off*  in  the  latent  state. 
Charcoal  also  contains  in  the  same  bulk  a larger  amount  of  carbon 
than  the  wood  which  furnished  it,  and  by  supplying  a more  com- 
pact fuel  concentrates  into  a smaller  space  the  heat  which  it  emits, 
a condition  which,  in  metallurgical  operations  demanding  a high 
temperature,  is  often  of  the  greatest  importance. 

In  the  economy  of  material  to  be  used  as  a combustible  it  is 
not  sufficient  to  consider  simply  the  absolute  amount  of  heat  which 
a given  weight  of  the  fuel  emits  whilst  burning.  The  radiating 
power  of  a solid  mass  of  fuel  is  much  higher  than  that  of  a gaseous 
combustible,  but  the  temperature  of  flame  is  very  high.  A fuel 
5 


66 


YAEIETIES  OF  CHAECOAL. 


which  burns  with  flame  is  therefore  necessary  where  it  is  needful 
to  communicate  an  elevated  temperature  to  objects  at  a distance 
from  the  flre-grate,  or  to  raise  large  masses  to  a uniform  tempera- 
ture. Wood  and  bituminous  coals  are,  consequently,  particularly 
useful  in  the  glass  furnace  and  in  the  porcelain  kiln ; whilst  in 
heating  boilers,  and  objects  in  which  direct  radiation  can  act  with 
its  full  effect,  coke,  anthracite,  and  coal  which  burns  with  but 
little  flame,  are  especially  valuable.  In  an  ordinary  open  Are, 
these  flameless  fuels  are  also  the  most  useful,  as  the  heat  is  thrown 
off  by  them  into  the  room  most  completely,  instead  of  being  car- 
ried up  the  chimney  with  the  gaseous  products. 

Charcoal  never  consists  solely  of  pure  carbon.  According  to 
the  experiments  of  Yiolette,  100  parts  of  black  alder  {Bourdaine) 
wood,  charred  at  the  following  temperatures,  gave  amounts  of 
charcoal  progressively  diminishing ; but  the  per-centage  of  carbon 
in  the  residual  charcoal  was  found  to  increase,  as  shown  in  the 
table. 


Temperature  of 
charring, 

Per-centage  of 
charcoal. 

Per-centage  of  carbon 
in  charcoal. 

480° 

50 

65 

570° 

33 

73 

750° 

20 

80 

2730° 

15 

96 

A peculiar  kind  of  charcoal,  but  imperfectly  burned,  and  of  a 
reddish-brown  colour,  termed  by  the  French  charbon  roux^  is  oc- 
casionally prepared  for  the  manufacture  of  the  gunpowder  used  for 
sporting  purposes.  Powder  made  with  this  charcoal  absorbs  mois- 
ture more  rapidly  than  ordinary  gunpowder.  Charbon  ronx  is 
procured  by  forcing  steam,  under  a pressure  of  about  two  atmo- 
spheres, through  a coil  of  heated  pipe,  and  directing  this  super- 
heated steam,  at  about  510°,  into  the  iron  cylinder  containing  the 
wood  : in  a few  hours  the  charring  of  the  wood  is  effected.  The 
following  is  stated  by  Pegnault  to  be  its  average  composition  in 
100  parts : — 


Carbon 

. 71-42 

Hydrogen  . 

4-85 

Oxygen  and  Hitrogen  . 

. 22-91 

Ash  .... 

0-82 

Animal  Charcoal^  or  ivory  black,  is  prepared  by  heating 
bones  in  cylinders  in  a manner  similar  to  that  employed  for  wood 
charcoal. 

(355)  General  Properties  of  Carbon. — Carbon  in  all  the  forms 
above  mentioned  is  chemically  the  same.  At  atmospheric  tempe- 
ratures it  is  one  of  those  substances  in  which  chemical  attraction 
exhibits  least  activity ; consequently  a superflcial  charring  is  fre- 
quently resorted  to  with  a view  to  protect  wood  from  decay,  as  in 
the  case  of  piles  which  are  driven  into  mud  or  into  the  beds  of 


POWER  OF  CHARCOAL  TO  PROMOTE  OXroATIOH. 


67 


rivers,  to  serve  as  foundations.  For  the  same  reason  it  is  a com- 
mon practice  to  char  the  interior  of  tubs  and  casks  destined  to 
hold  liquids.  Lampblack  furnishes  the  most  indestructible  of 
black  pigments,  and  has  long  been  employed  on  this  account  as 
the  basis  of  printing  ink.  The  diamond  is  a non-conductor  of 
electricity  ; in  its  other  forms  carbon  is  an  excellent  conductor, 
ranking  next  to  the  metals  in  this  respect.  In  a state  of  tine 
subdivision  it  is  a bad  conductor  of  heat,  but  its  conducting  power 
increases  with  its  density.  Finely  divided  charcoal  is  usually 
stated  to  have  strong  antiseptic  powers.  It  certainly  has  a re- 
markable action  upon  putrescible  substances  ; but  Stenhouse  has 
shown  that  this  action  consists  in  a rapid  process  of  oxidation 
dependent  upon  the  power  which  charcoal,  when  in  a finely  divid- 
ed state,  possesses  of  condensing  oxygen.  The  offensive  effluvia 
from  animal  matter  in  an  advanced  state  of  putrefaction  disappear 
when  the  putrefying  substance  is  covered  with  a layer  of  charcoal ; 
it  continues  to  decay,  but  without  emitting  any  odour,  till  at 
length  all  the  carbon  is  dissipated  as  carbonic  anhydride,  the 
hydrogen  as  water,  and  the  nitrogen  remains  as  nitric  acid.  The 
remarkable  power  possessed  by  charcoal  of  absorbing  various 
bodies,  particularly  colouring  matters  and  many  bitter  principles, 
when  in  a finely  divided  state  (54),  as  well  as  its  property  of  con- 
densing a large  proportion  of  gaseous  matters  within  its  pores  (65), 
has  been  already  mentioned.  So  rapid  is  this  action,  that  Sten- 
house has  proposed  to  use  a respirator  filled  with  charcoal,  to  pro- 
tect the  mouth  and  nostrils  in  an  infected  atmosphere  ; and  the 
employment  of  trays  of  powdered  wood  charcoal  in  dissecting- 
rooms,  in  the  wards  of  hospitals,  and  in  situations  where  putrescent 
animal  matter  is  present,  is  found  to  exert  a most  beneficial  influ- 
ence in  sweetening  the  atmosphere  by  absorbing  and  decomposing 
the  offensive  gases.  These  properties  render  charcoal  a valuable 
material  in  the  construction  of  filters,  not  only  for  decolorizing 
purposes,  but  likewise  for  assisting  in  purifying  water  for  domestic 
use.  It  is  now  also  employed  most  suGcessfully  to  prevent  the 
escape  of  noxious  vapours  at  the  ventilating  openings  of  the  sewers, 
as  it  allows  the  free  passage  of  air,  but  condenses  the  offensive 
effluvia  in  its  pores,  where  they  are  destroyed  by  a process  of 
oxidation.  It  will  continue  active  for  years  if  kept  dry. 

Carbon  is  usually  regarded  as  neither  fusible  nor  volatile ; but 
in  the  course  of  some  experiments  with  a voltaic  battery  of  intense 
energy,  consisting  of  600  cells  of  Bunsen’s  construction,  connected 
so  as  to  form  a battery  of  100  pairs  of  6 cells  each,  Despretz  found 
on  operating  upon  carbon  points  in  an  exhausted  receiver,  that  the 
vessel  became  filled  with  a dark  cloud,  which  was  deposited  upon 
the  sides  of  the  glass  as  a black  crystalline  powder  ; and  by  ex- 
posing charcoal  obtained  from  pure  sugar,  or  from  essence  of  tur- 
pentine, to  the  action  of  the  battery  in  a small  crucible  of  ])iire 
charcoal  connected  with  the  positive  electrode,  the  whole  of  the 
charcoal  powder  became  cemented  into  a coherent  mass  which 
appeared  to  have  been  fused,  and  which  exhibited  the  properties 
of  graphite. 


68 


SYNTHESIS  OF  CARBONIC  ANHYDRIDE. 


At  high  temperatures  carbon  combines  rapidly  with  oxygen, 
and  will  remove  it  from  a great  number  of  its  compounds,  espe- 
cially from  the  oxides  of  the  metals  ; hence  the  various  forms  of 
carbon  are  very  extensively  employed  in  the  reduction  of  these 
substances  to  the  metallic  condition.  The  deoxidizing  power  of 
carbon  is  sometimes  exerted  at  the  ordinary  temperature  of  the 
air.  Schonbein  found  that  ferric  salts  may  be  reduced  to  the 
condition  of  ferrous  salts,  by  simply  agitating  their  solutions  with 
charcoal  powder,  and  the  mercuric  are,  in  like  manner,  converted 
into  mercurous  salts.  Charcoal  decomposes  steam  at  a red  heat ; 
hydrogen  is  liberated,  and  a mixture  of  carbonic  oxide  and  car- 
bonic anhydride  is  formed. 

It  was  long  supposed  that  sulphur  is  the  only  non-metallic 
element  besides  oxygen  with  which  carbon  can  be  made  to  unite 
directly,  and  a high  temperature  is  required  in  this  case  also  to 
effect  the  combination.  The  experiments  of  Berthelot  have  proved 
that  by  igniting  charcoal  uitensely  by  means  of  the  voltaic  arc 
in  a current  of  pure  hydrogen,  a particular  hydrocarbon,  acetylene, 
is  formed. 

The  compounds  of  carbon  with  the  metals  are  termed  carbu- 
rets or  carbides. 

(356)  Synthesis  of  Carbonic  Anhydride. — Since  a knowledge 
of  the  composition  of  carbonic  anliydride  is  a fundamental  datum 
for  the  analysis  of  organic  compounds,  the  proportion  in  which 
oxygen  comhines  with  carbon  to  produce  carbonic  anhydride  has 
lieen  determined  with  the  greatest . care,  by  the  combustion  of 
weighed  quantities  of  diamond,  of  graphite,  and  of  charcoal,  in  a 
stream  of  diy  oxygen.  The  apparatus  employed  for  this  purpose 
is  indicated  in  fig.  288.  a represents  a gas-holder  filled  with 


Fig.  288. 


oxygen ; b a tube  containing  fragments  of  caustic  potash,  or 
pumice-stone  moistened  with  sulphuric  acid,  for  removing  all 
traces  of  moisture  from  the  oxygen  \ c d ^ tube  of  hard  glass 
traversing  the  sheet-iron  furnace,  e.  At  c is  a platinum  tray  con- 
taining the  weighed  portion  of  diamond  or  graphite  ; the  front  of 
the  tube  d is  occupied  by  a column  of  oxide  of  copper,  the  object 


CARBONIC  OXIDE. 


69 


of  which  is  to  oxidize  completely  any  trace  of  carbonic  oxide 
which  might  be  formed.  The  apparatus  is  tilled  with  dry  oxygen 
by  opening  the  stopcock  of  the  gas-holder,  a,  to  a regulated  dis- 
tance, and  the  fore-part  of  the  tube,  is  brought  to  a red  heat 
by  means  of  heated  charcoal ; the  heat  is  then  applied  to  the  spot, 
c,  where  the  carbon  lies.  The  carbon  burns  and  becomes  con- 
verted into  carbonic  anhydride,  which  traverses  the  column  of 
heated  oxide  of  copper;  r is  a weighed  tube,  tilled  with  chloride 
of  calcium,  which,  if  water  were  present,  would  be  found  to 
increase  in  weight,  but  in  which  no  deposit  of  moisture  is  formed 
if  the  experiment  be  properly  conducted.  The  carbonic  anhy- 
dride passes  on,  and  is  absorbed  by  a strong  solution  of  potash 
which  is  contained  in  the  bulbs  of  the  Liebig’s  apparatus,  shown 
at  G.  The  excess  of  oxygen  absorbs  moisture  as  it  passes 
through  this  liquid,  but  before  it  is  allowed  to  escape  into  the 
air  it  is  rendered  perfectly  dry  by  causing  it  to  pass  through 
an  additional  tube,  n,  filled  with  fragments  of  caustic  potash. 
The  increase  in  w^eight  acquired  by  the  tubes  g and  h furnishes 
the  weight  of  the  carbonic  anhydride  corresponding  to  the  quan- 
tity of  carbon  consumed,  and  the  quantity  of  carbon  burned 
is  ascertained  by  weighing  the  platinum  tray  and  its  con- 
tents after  the  experiment  has  terminated.  By  experiments 
conducted  upon  this  principle  it  has  been  determined  that  12 
parts  of  carbon  require  for  conversion  into  carbonic  anhydride 
exactly  32  parts  of  oxygen  (Dumas  and  Stas ; Ann.  de  Chimie.^ 
III.  i.  5). 

Diamond,  graphite,  and  charcoal  are  thus  shown  to  be  chemi- 
cally the  same  substance,  though  they  differ  entirely  in  pro- 
perties; these  three  conditions  being  allotropic  modifications 
of  carbon  (87),  the  difierences  in  properties  arising  not  from 
difierences  in  their  chemical  nature,  but  in  their  molecular 
arrangement. 

If  a piece  of  pure  carbon  be  burned  in  a jar  of  oxygen  over 
mercury,  it  will  be  found  after  the  combustion  is  over,  and  the 
gas  lias  cooled  to  the  initial  temperature  of  the  oxygen,  that  its 
volume  has  undergone  no  permanent  change : the  bulk  of  the 
oxygen,  therefore,  is  not  altered  by  this  combination  ; the  car- 
bonic anhydride  which  is  formed  occupies  precisely  the  same 
space  as  the  oxygen  which  produced  it. 

(357)  Carbonic  Oxide  : (CO  = 28) ; Sj).  Gr.  0-967  ; Atomic 
and  Mol.  Vol.  \ \ |. — It  has  been  stated  that  carbonic  anhydride 
is  wholly  deprived  of  its  oxygen  when  heated  with  potassium  ; 
but  if  some  metal,  such  as  zinc  or  iron,  which  has  a less  powerful 
attraction  for  oxygen,  be  substituted  for  the  potassium,  the  car- 
bonic anhydride  will  only  be  partially  deoxidized ; the  metal  will 
deprive  it  of  exactly  half  the  oxygen  which  it  contains,  and  a new 
gaseous  body,  termed  carbonic  oxide^  will  be  produced.  The 
bulk  of  this  new  gas  is  exactly  equal  to  that  of  the  carbonic 
anhydride  that  furnished  it.  Carbonic  oxide,  mixed  with  free 
hydrogen,  is  also  obtained  abundantly  when  steam  is  transmitted 
over  charcoal  heated  to  bright  redness. 


70 


PEEPAKATION  OF  CAEBONIC  OXIDE. 


Preparation. — 1.  Carbonic  oxide  may  be  conveniently  pre- 
pared by  mixing  powdered  chalk  with  an  equal  weight  of  iron  or 
zinc  filings,  and  exposing  the  mixture  to  a red  heat  in  a gun- 
barrel.  The  chalk  when  ignited  gives  olf  carbonic  anhydride, 
which  in  contact  with  the  heated  metal  is  decomposed ; oxide  of 
iron  or  of  zinc  is  formed,  quick-lime  remains  in  the  retort  mixed 
with  the  metallic  oxide,  and  the  carbonic  oxide  gas  after  being 
washed  with  water  containing  slaked  lime  in  suspension,  with  a 
view  to  absorb  any  undecomposed  carbonic  anhydride,  may  be 
collected  over  water,  in  which  it  is  but  slightly  soluble.  T^ese 
chemical  chano;es  mav  be  represented  in  the  following  manner ; 
eae03  + Zn=feaO  -f  ZnO  -f  OO. 

2.  — Carbonic  oxide  is  often  produced  abundantly  in  the  ordi- 

nary process  of  combustion  in  stoves  and  furnaces : this  mode  of 
its  formation  is  important,  for  it  exercises  a material  influence 
upon  the  economy  of  combustion,  inasmuch  as  all  the  carbonic 
oxide  thus  carried  off  unburnt  represents  so  much  fuel  wasted ; 
while  in  many  metallurgic  operations  the  carbonic  oxide  so  pro- 
duced plays  a conspicuous  part  in  the  reduction  of  the  ore  to  the 
metallic  state,  the  oxides  of  iron,  lead,  copper  and  many  other 
metals,  being  reduced  when  heated  with  it,  whilst  carbonic  anhy- 
dride is  formed.  It  is  owing  to  the  production  of  carbonic  oxide 
that  anthracite  can  be  employed  in  roasting  the  copper  ores  at 
Swansea,  flame  being  essential  to  the  due  performance  of  the 
process  (869).  The  formation  of  carbonic  oxide  in  an  open  fire 
which  is  burning  steadily  without  emitting  smoke  is  often  evi- 
denced by  the  flickering  blue  flame  seen  playing  over  the  glowing 
embers.  In  this  case  carbonic  anhydride  is  first  fonned  at  the 
bottom  of  the  grate,  from  the  free  access  of  air  to  this  part  of  the 
burning  fuel ; but  the  carbonic  anhydi’ide  as  it  traverses  the  red- 
hot  coke  enters  into  combination  with  an  additional  quantity  of 
carbon,  and  the  anhydride,  by  losing  half  its  oxygen,  is  converted 
into  its  own  bulk  of  carbonic  oxide : at  the  same  time  the  carbon 
of  the  heated  fuel  which  has  entered  into  combination  with  this 
removed  oxygen  furnishes  anotlier  equal  quantity  of  the  same  gas : 
the  heated  carbonic  oxide  takes  fire  as  soon  as  it  mixes  with  the 
air  which  passes  over  the  upper  surface  of  the  fire.  The  reaction 
between  the  hot  carbon  and  carbonic  anhydride  may  be  thus 
represented : + 0 = 2 OO. 

3.  — If  one  of  the  formiates  be  treated  with  oil  of  vitriol,  pure 
carbonic  oxide  is  obtained  ; for  instance  : — 

2 isaOiie,+ii,so,=2  oo+]sxse,+2H3e. 

4.  — Carbonic  oxide  may  also  be  formed  in  several  other  ways. 
Half  an  ounce  of  the  yellow  prussiate  of  potash,  if  heated  in  a 
retort  with  4 or  5 ounces  of  oil  of  vitriol,  yields  more  than  a gallon 
of  the  pure  gas  (Fownes).  Care  is  requisite  in  applying  the  heat, 
because  when  the  temperature  rises  to  a certain  point  the  extrica- 
tion of  the  gas  takes  place  with  tumultuous  rapidity.  The  reac- 
tion is  in  this  case  of  a complicated  nature,  but  is  expressed  by 
the  annexed  symbols  : — 


PEOPERTIES  AND  COMPOSITION  OF  CAEBONIC  OXIDE.  T1 

Ferrocy.  potass.  "Water.  Sulphuric  acid. 

Carb.  oxide.  Sulph.  potassium.  Sulph.  iron.  Sulph.  ammonium. 

fe^+  + F^e~+  3 

5. — Another  method  by  which  carbonic  oxide  may  be  obtained 
with  facility  consists  in  heating  oxalic  acid  with  5 or  6 times  its 
weight  of  oil  of  vitriol.  The  oxalic  acid  is  thns  deprived  of  water, 
and  is  resolved  into  a gaseous  mixture  consisting  of  equal  meas- 
lu’es  of  carbonic  anhydride  and  carbonic  oxide : by  allowing  the 
mixed  gases  to  pass  through  a vessel  filled  with  a solution  of 
potash,  or  Avith  milk  of  lime,  the  carbonic  anhydride  is  absorbed, 
and  the  carbonic  oxide  may  be  collected  in  a state  of  purity. 
The  decomposition  may  be  thus  explained : — 

Oxalic  acid.  Water.  Carb.  oxide.  Carb.  anhydride. 

A convenient  mode  of  washing  the  gas  is  shown  at  b,  fig.  289 ; 


Fig.  289. 


the  bent  tube  is  connected  to  the  neck  of  the  retort,  a,  and  passes 
to  the  bottom  of  a wider  tube,  c,  open  both  at  top  and  bottom, 
Avhich  passes  into  the  Avashing  bottle,  d : a moveable  gas-tight 
joint,  Avhich  can  be  mounted  or  dismounted  in  a moment,  is  thus 
obtained. 

Properties. — Carbonic  oxide  is  a transparent  colourless  gas, 
with  a faint  oppressive  odour.  It  is  much  lighter  than  carbonic 
acid,  having  a specific  gravity  of  0*967  (Wrede).  All  attempts 
at  its  liquefaction  have  as  yet  been  unsuccessful.  It  is  but  very 
sparingly  soluble  in  water,  100  parts  of  this  liquid  dissolving  3*28 


COMPOrXDS  OF  CAEBOX  WITH  OXTGEX. 


parts  at  32°,  and  2'd3  at  59°  (Bunsen).  When  respired,  even 
though  largely  diluted  with  air,  it  acts  as  a direct  poison,  produc- 
ing a peculiar  sensation  of  oppression  and  tightness  of  the  head. 
It  does  not  support  combustion,  but  burns  itself  with  a beautifid 
pale  blue  light,  producing  by  its  combination  with  ox^^gen  carbonic 
anhych’ide  only.  A solution  of  subchloiide  of  copper  in  hydi*o- 
chloric  acid,  or  of  a cupreous  salt  dissolyed  in  ammonia,  gradually 
absorbs  carbonic  oxide  if  agitated  with  it.  The  solution  of  this 
compound  is  not  decomposed  by  dilution,  but  if  the  liquid  be 
boiled  most  of  the  gas  is  expelled  imaltered.  The  compound 
with  subchloride  of  copper  crystalhzes  in  fatty-looking  scales, 
consisting  of  (COCu'Cl  . II,-0-),  but  by  exposm-e  to  air  it  is 
quickly  decomposed.  Carbonic  oxide  is  absorbed  by  potassium 
if  the  metal  be  heated  to  about  176°  in  the  gas,  and  according  to 
Brodie,  the  combination  occurs  in  the  proportion  shown  by  the 
foiTQula,  -COK.  This  property  is  sometimes  employed  for  sepa- 
rating carbonic  oxide  from  its  mixture  with  other  inflammable 
gases  in  the  process  of  analysing  mixtures  of  such  gases. 

Carbonic  oxide  has  been  supposed  to  form  the  radicle  of  a 
numerous  series  of  compounds ; it  exen  enters  directly  into  com- 
bination with  hycbate  of  potash  when  heated  with  it,  conxerting 
it  into  formiate  of  potassium  : IvH0-|-'C0=K€^H02  (Berthelot). 

Cornjposition. — The  chemical  composition  of  carbonic  oxide 
may  be  ascertained  in  the  following  manner : — Introduce  into  the 
bent  eudiometer  (flg.  2S1)  a certain  measure,  say  20  parts,  of  car- 
bonic oxide,  then  add  20  measm’es  of  pure  oxygen ; pass  the  elec- 
tric spark  with  the  precautions  abeady  described : the  10  measm-es 
of  gas  will  become  diminished  to  30  measures.  If  a little  solution 
of  potash  be  introduced,  20  measures  of  the  residual  gas  will  disap- 
pear, leaxing  10  measures  of  unaltered  oxygen : the  20  measures 
of  gas  absorbed  are  carbonic  anhydride.  Xow  carbonic  anhy chide 
contains  its  own  bulk  of  oxygen,  but  the  20  measures  of  carbonic 
oxide  haxe  required  only  10  measm-es,  or  half  their  bulk,  of  oxygen 
to  conxert  them  into  the  anhydride.  Carbonic  oxide  therefore 
must  haxe  contained  the  other  10  measures  of  oxygen ; in  other 
words,  half  its  bulk  of  oxygen.  But  the  specihc  gravity  of 
cai-bonic  oxide  is  0-9671;  deduct  from  this 

0'552S=half  the  speciflc  graxity  of  oxygen 

0-1116 ; this  remainder  is  the  weight  of  the 
carbon  combined  with  0-5528  of  oxygen. 

Aow  0-5528  : 0-1116  ::  16  : 12.  The  proportion  by  weight  of 
oxA'gen  to  carbon  in  carbonic  oxide  is  therefore  as  16  to  12,  or 
1 atom  of  each,  and  its  composition  may  be  thus  represented : — 


Carbon, 

Oxygen, 


By  weisht. 

e = 12  or  42  80 
O = 16  57-14 


Bv  volume.  Sp.  Gr. 
2 or  1-0?=  0-4146 
1 0-5  = 0-5528 


Carb.  oxide,  00  = 28  100  00  2 1-0  0-9674 


Carbonic  oxide  and  carbonic  anhydi-ide,  widely  as  they  difier 


PRODUCTION  OF  NITRIC  ACID. 


7S 


in  properties,  consist,  it  is  evident,  of  the  same  elements ; but  the 
proportions  of  the  two  elements  differ  in  the  two  cases.  Carbonic 
oxide  is  the  compound  of  carbon  that  contains  the  smallest  pro- 
portion of  oxygen,  the  relative  composition  of  the  two  bodies 
being : — 

C.  O.  Carbon.  Oxygen. 

Carbonic  oxide  OO  = 28  or  12  + 16  = 42-86  + 57-14 

Carbonic  anhydride  OO2  = 44  12  + 32  = 27*28  -t-  72*72 

v / 

- In  loo  parts. 


CHAPTEK  Y. 

COMPOUNDS  OF  NITROGEN  WITH  OXYGEN  AND  WITH  HYDROGEN. 

§ I.  Compounds  of  ^Nitrogen  with  Oxygen. 

(358)  The  attraction  of  nitrogen  for  oxygen  is  much  feebler 
than  that  of  either  carbon  or  hydrogen  for  oxygen,  so  that  it  is 
not  easy  to  procure  their  direct  union, — especially  as  the  tempera- 
ture emitted  by  the  nitrogen  and  oxygen  in  the  act  of  combina- 
tion is  comparatively  low.  hlitrogen,  notwithstanding,  forms  with 
oxygen  five  distinct  compounds,  containing,  respectively,  1,  2,  3, 
4,  and  5 atoms  of  oxygen  with  2 atoms  of  nitrogen.  They  may 
all  be  obtained  free  from  water. 

These  compounds  have  been  named 

By  weight.  In  100  parts. 


N.  o.  Nitrogen.  Oxygen.  Mol.  vol. 

Nitrous  oxide NaO  = 44  or  28  + 16  63-64  + 36-36  (m 

Nitric  oxide NO  = 30  14  + 16  46*67  + 53*33  | | | 

Nitrous  anhydride N2O3  = 76  28  + 48  36*85  -|-  63*15 

Peroxide  of  nitrogen N2O4  = 92  28  -l-  64  30*44  + 69*56  I I 

Nitric  anhydride N2O.5  = 108  28  + 80  25*93  + 74*07 


(359)  h^’iTRic  Acid;  HKO3,  or  IIO,K05  = 63:  jSp.  Gr.  of 
Liquid^  1*517 ; Boiling-jpt.  184°. — The  most  important  of  the 
compounds  of  oxygen  with  nitrogen  is  that  which  when  in  com- 
bination with  water  was  formerly  called  aquafortis^  and  is  now 
designated  nitric  acid.  It  was  known  to  the  alchemists,  but  its 
true  composition  was  first  determined  by  Cavendish  in  1785. 
When  nitrogen  is  mixed  with  12  or  14  times  its  bulk  of  hydrogen, 
and  a jet  of  the  mixed  gas  is  allowed  to  burn  in  air  or  in  oxygen, 
the  water  which  is  formed  has  a sour  taste  and  an  acid  reaction, 
owing  to  the  simultaneous  formation  of  a small  quaritity  of  nitric 
acid.  In  this  case  the  nitrogen  burns  by  the  aid  of  the  heat 
developed  during  the  combustion  of  the  hydrogen,  and  the  oxidized 
compound  combines  at  once  with  the  water  formed,  which  much 
increases  its  chemical  stability.  It  was,  indeed,  owing  to  the  acci- 
dental production  of  nitric  acid  in  the  course  of  his  experiments 
on  the  formation  of  water  by  the  combustion  of  hydrogen,  that 


74 


NITEIC  ACID YTS,  PEEPAEATION. 


Cayendish  was  induced  to  institute  the  train  of  researches  which 
terminated  in  this  important  discovery. 

If  two  volumes  of  nitrogen  be  mixed  with  5 volumes  of  oxygen, 
and  introduced  into  the  bent  eudiometer  (tig.  281)  and  the  tube 
be  tilled  up  with  an  infusion  of  blue  litmus  in  distilled  water,  a 
series  of  electric  sparks  may  be  transmitted  through  the  mixture 
by  means  of  a Euhmkortf ’s  coil : under  these  circumstances  the 
two  gases  will  combine  slowly,  and  the  litmus  will  be  reddened. 
The  heat  of  the  spark  determines  the  combination  of  the  gases 
just  at  the  spot  through  which  it  passes,  but  the  action  does  not 
extend  further.  In  like  manner,  if  a number  of  sparks  be  passed 
from  the  electrical  machine,  between  two  metallic  points,  over 
moistened  litmus-paper,  in  air,  a red  spot  will  be  produced  upon 
the  paper,  owing  to  the  formation  of  nitric  acid  in  minute  quan- 
tity by  the  combination  of  oxygen  with  nitrogen  in  presence  of 
aqueous  vapour  in  the  air.  During  stormy  weather,  and  indeed 
whenever  a flash  of  lightning  passes  through  a moist  atmos- 
phere, the  same  compound  is  produced  in  appreciable  quantity. 
Indeed,  it  is  rare  to  meet  with  rain  water  in  which  traces  of 
nitrate  of  ammonium  may  not  be  detected,  if  the  experiment  is 
made  with  accuracy.  Ammonia  likewise  yields  nitric  acid  under 
certain  circumstances  by  slow  oxidation  (369). 

This  oxide  of  nitrogen  also  occurs  in  combination  with  potas- 
sium or  sodium,  in  the  form  of  an  efflorescence  on  the  soil,  espe- 
cially in  tropical  climates,  as  in  some  parts  of  India  and  Peru. 
The  compound  formed  with  potassium  constitutes  the  nitre  or 
saltpetre  of  commerce.  The  nitrates  of  the  alkaline  metals  are 
often  present  in  the  water  of  wells  in  towns  or  in  the  vicinity  of 
cemeteries,  the  nitric  acid  being  in  these  cases  produced  by  the  oxi- 
dation of  azotized  animal  matters,  as  they  undergo  decomposition 
during  the  percolation  of  their  aqueous  solution  through  the  soil. 

Prejparation. — It  is  from  one  of  the  nitrates  that  the  acid  is 
always  obtained  for  chemical  purposes.  When  nitrate  of  potas- 
sium is  heated  with  a powerful  acid,  such  as  the  sulphuric,  mutual 
decomposition  occurs.  The  potassium  and  hydrogen  change 
places,  forming  sulphate  of  potassium  and  nitrate  of  hydrogen,  or 
nitric  acid.  The  sulphate  of  potassium  remains  in  the  retort, 
whilst  the  more  volatile  nitric  acid  distils  over,  and  may  be  con- 
densed in  the  usual  manner.  The  method  of  procuring  nitric  acid 
offers  a good  example  of  the  general  principle  upon  which  acids 
which  admit  of  being  distilled  without  experiencing  decomposition 
are  obtained  from  their  salts.  In  preparing  nitric  acid  on  the 
small  scale,  equal  weights  of  nitre  and  oil  of  vitriol  are  placed  in 
a glass  retort,  and  the  distillation  is  proceeded  with  in  the  manner 
shown  in  flgs.  136  and  137,  Part  I.  p.  307. 

During  the  distillation  red  fumes  appear  in  the  retort,  arising 
from  a partial  decomposition  of  the  acid,  and  a formation  of  some 
of  the  lower  oxides  of  nitrogen,  whilst  a yellowish  corrosive  liquid 
is  condensed  in  the  receiver : this  liquid  is  concentrated  nitric 
acid  (IINO3)  j fumes  strongly  in  the  air,  and  emits  a powerful 
irritating  acid  odour. 


NITRIC  ACID MODES  OF  PREPARATION. 


75 


On  the  large  scale,  iron  retorts,  fig.  290,  coated  with  fire-clay 
on  the  inside  of  the  upper  part,  where  they  are  exposed  to  the  acid 
vapours,  are  employed  for  the  distillation,  and  nitrate  of  sodium 
is  substituted  for  nitrate  of  potassium,  as  it  is  a cheaper  salt,  and 
likewise  yields  9 per  cent,  more  nitric  acid  than  nitrate  of  potas- 


sium. The  cylinders,  or  retorts  are  arranged  in  pairs  in  a furnace, 
so  that  each  fire  heats  two  cylinders,  as  shown  in  the  section,  1. 
The  cylinders  are  supplied  with  a moveable  lid,  <?,  c?,  at  each  end. 
The  nitrate  is  introduced  into  the  retort,  a,  through  the  opening 
at  c,  which  is  closed  during  the  distillation  by  a stone  lid,  fitted 
accurately  to  the  aperture  ; and  the  oil  of  vitriol  is  added  by  a 
funnel  at  after  the  retort  is  closed.  As  soon  as  the  acid  is 
introduced,  the  funnel  is  withdrawn,  and  the  opening  at  e is  closed 
with  a plug.  The  nitric  acid  as  it  distils  over  passes  through  the 
pipe  and  is  condensed  in  a series  of  stoneware  bottles,  the  first 
of  which  is  seen  at  b.  The  acid  which  is  collected  in  the  first 
receiver  is  always  contaminated  wnth  sulphuric  acid,  and  that  in 
the  last  is  rather  dilute,  as  water  is  placed  in  it  to  condense  the 
nitrous  fumes. 

Upon  the  large  scale  it  is  customary  to  employ  a proportion 
of  sulphuric  acid  smaller  than  that  used  when  the  distillation  is 
performed  in  glass  vessels,  for  it  is  quite  possible  to  effect  a com- 
plete decomposition  of  the  nitrate  by  heating  it  with  one-half  its 
weight  of  oil  of  vitriol.  Under  these  circumstances,  however,  a 
higher  temperature  is  needed  to  expel  the  last  portions  of  acid,  and 
a considerable  quantity  of  the  nitric  acid  is  thereby  decomposed 
and  wasted.  The  residue  in  the  retort,  wUen  the  smaller  quan- 
tity of  sulphuric  acid  is  used,  is  much  less  soluble  in  water,  and 
consequently  is  much  more  difficult  of  removal : but  in  the  iron 
cylinder  of  the  manufacturer  this  is  of  no  moment,  because  the 
saline  mass  can  easily  be  detached  by  the  use  of  iron  tools  when 
the  distillation  is  at  an  end. 

The  cause  of  these  differences  in  the  result  of  the  processes 
adopted  on  the  large  and  small  scale  lies  in  the  fact  that  sul- 
phuric acid  by  its  reaction  upon  potash  gives  rise  to  two  different 
sulphates,  one  of  which  contains  twice  as  much  potassium  as  the 


76 


IsTTEIC  ACID PKEPAEATIOX PEOPEETIES. 


other ; the  acid  sulphate  consisting  of  KHSO^,  while  the  neutral 
sulphate  contains 

When  nitre  and  sulphuric  acid  are  mixed  in  the  proportion  of 
equal  weights,  the  acid  sulphate  of  potassium  is  obtained,  and 
nitric  acid  distils  readily ; the  change  is  represented  in  the  follow- 
ing equation  : — 


or 


Nitre. 

KNO3  + 
KO.XOs  + 


Sulphuric 

acid. 

2 (HO^SOa) 


Nitric 

acid. 

HNO3 

HO^XOs 


+ 

+ 


Acid  sulphate  of 
potassium. 

^ * ^ 

KHSO4 

KO,HO,  2 SO3 ; 


but  if  the  nitrate  be  mixed  with  sulphuric  acid,  in  the  proportion 
of  2 equivalents  of  each,  the  decomposition  takes  place  in  two 
successive  stages ; in  the  first  of  these,  half  the  nitre  only  is 
decomposed,  and  a gentle  heat  only  is  needed  for  the  distillation 
of  the  nitric  acid  so  produced.  The  following  equation  may  be 
employed  to  represent  this  part  of  the  change  : — 


Nitre. 


Sulphuric 

acid. 


Nitre. 


Acid  sulphate  of 
potassium. 


2 Kxe3-f  H.,se,  = KXO3  + Hxe3  -p  khso. 


As  soon  as  the  first  half  of  the  nitric  acid  has  passed  over,  the 
temperature  begins  to  rise,  and  the  acid  sulphate  of  potassium 
reacts  on  the  undecomposed  nitre ; the  second  half  of  the  nitric 
acid  is  liberated,  but  at  the  same  time  is  partially  decomposed, 
particularly  towards  the  end  of  the  operation  : the  whole  of  the 
potassium  remains  in  the  retort  in  the  form  of  the  sparingly  solu- 
ble neutral  sulphate.  This  second  stage  of  the  decomposition  is 
exliibited  in  the  subjoined  equation  : — 

Acid  sulphate  of  Nitric  Sulphate 

Nitre.  potassium.  acid.  of  potassium. 

KXO3  -f-  KHSO4  = HXO3  -p  K2SO4 

Nitric  Acid  (monohydrate),  HAO3 ; or  H0,K03 : Sp.  gr.  of 
liquid^  1’51T,  at  69°  ; Ijoiling-pt.  184°  : Comp,  in  100  parts, 
N2O3,  85‘72 ; HjO,  14'28. — The  acid  which  is  obtained  by  the 
foregoing  process  is  of  a yellowish  or  red  colour,  owing  to  the 
presence  of  some  of  the  lower  oxides  of  nitrogen  ; these  may,  if 
necessary,  be  got  rid  of  by  mixing  the  acid  with  an  equal  bulk  of 
oil  of  vitriol,  and  submitting  the  mixture  to  distillation.  If  the 
first  portions  be  collected,  and  gently  warmed  while  a current  of 
dry  air  is  sent  through  the  acid,  sheltered  from  strong  davlight, 
the  acid  may  be  obtained  as  colourless  as  water,  and  quife  tree 
from  the  lower  oxides  of  nitrogen.  It  is,  however,  so  unstable  in 
this  concentrated  form  that  it  cannot  be  redistilled  alone  without 
experiencing  partial  decomposition.  When  exposed  to  the  sun’s 
light  a similar  effect  is  produced  ; oxygen  gas  is  evolved,  and  the 
acid  becomes  coloured  owing  to  tlie  formation  of  lower  oxides  of 
nitrogen.  AYhen  pure,  nitric  acid  is  a colourless,  limpid,  fuming, 
powerfully  corrosive  liquid,  which  freezes  at  about  — 40°.  It 
begins  to  boil  at  184°,  but  the  temperature  rises  gradually,  owing 
to  the  decomposition  of  the  liquid ; oxygen  and  nitrous  fumes  are 


NITRIC  AGED MODES  OF  DECOMPOSITION. 


77 


evolved ; the  boiling-point  continnes  to  rise  slowly  till  it  reaches 
250°,  at  which  point  the  acid  in  the  retort  has  a composition 
approaching  to  (2  3 H^O),  and  distils  unchanged. 

Owing  to  the  facility  with  which  the  acid  parts  with  oxygen,  it 
is  continually  employed  as  an  oxidizing  agent.  If  it  be  dropped 
into  hot  finely  powdered  charcoal,  the  charcoal  burns  vividly ; if 
it  be  mixed  with  a little  oil  of  vitriol,  and  poured  into  oil  of  tur- 
pentine, the  mixture  bursts  into  flame.  Sulphur,  phosphorus,  and 
iodine  are  oxidized  by  it,  the  phosphorus  almost  with  explosive 
violence.  ISTitric  acid  is  one  of  the  most  corrosive  substances 
known.  It  rapidly  destroys  all  animal  textures,  and  if  somewhat 
diluted  stains  the  skin,  wool,  feathers,  and  all  albuminous  bodies 
of  a bright  yellow  colour.  The  acid  in  a somewhat  diluted  state 
is,  indeed,  often  used  to  impart  a permanent  yellow  dye  to  woollen 
and  silken  goods.  Nitric  acid  acts  violently  upon  tin  or  iron 
filings,  especially  if  they  be  previously  moistened  with  a few 
drops  of  water  ; and  indeed  it  attacks  most  of  the  metals  except 
gold,  platinum,  rhodium,  and  iridium : but  it  is  most  active  upon 
them  when  diluted  to  a specific  gravity  of  from  1*35  to  1*25. 
The  action  of  nitric  acid  upon  the  metals  varies  with  its  tempera- 
ture and  degree  of  dilution.  The  pure  concentrated  acid,  IINOg, 
is  in  fact  without  action  upon  tin,  iron,  bismuth,  and  many  other 
metals  at  ordinary  temperatures.  The  presence  of  nitrous  acid 
in  the  nitric  acid  greatly  increases  its  oxidizing  power,  for  owing 
to  the  instability  of  nitrous  acid  this  compound  parts  with  its 
oxygen  very  readily.  At  a temperature  of  0°  the  acid,  whether 
concentrated  or  dilute,  is  without  action  on  copper,  but  it  dissolves 
zinc  rapidly. 

(360)  Action  of  Acids  on  Metals. — The  chemical  action  of  nitric 
acid  upon  the  metals  is  a process  of  considerable  importance,  but 
in  order  to  study  with  advantage  the  eftects  to  which  it  gives  rise 
it  will  be  useful  to  consider  the  action  of  acids  upon  the  metals 
from  a general  point  of  view.  It  has  already  been  stated  that  the 
metals  unite  directly  with  many  of  the  non-metallic  elements,  such 
as  chlorine,  oxygen,  and  sulphur.  Antimony,  for  example,  will  take 
fire  spontaneously  if  allowed  to  fall  in  fine  powder  into  chlorine. 
Iron  will  burn  in  oxygen  if  first  heated  to  the  point  of  ignition ; 
and  copper  turnings,  if  mixed  with  powdered  sulphur,  will,  on  the 
application  of  heat,  combine  with  the  sulphur,  and  will  emit  during 
the  action  a vivid  light.  The  metallic  oxides,  when  presented  to 
the  acids,  become  quickly  dissolved ; oxide  of  copper  is  brought 
into  solution  by  diluted  sulphuric  acid,  oxide  of  zinc  quickly  disap- 
pears when  agitated  with  hydrochloric  acid,  and  oxide  of  lead  is 
rapidly  dissolved  by  acetic  acid. 

But  a metal  will  not  unite  directly  with  an  anhydride.  Union 
between  a metallic  oxide  and  an  anhydride  may,  however,  occur, 
though,  even  then,  the  action  is  much  favoured  by  tlie  presence 
of  water.  Sulphuric  anhydride,  for  instance,  does  not  act  upon 
iron,  but  the  anhydride  is  immediately  absorbed  by  caustic  potash, 
KIIO  -f-  SO3  becoming  KHSO-^ ; and  in  like  manner,  carbonic 
anhydride  is  rapidly  absorbed  by  slaked  lime. 


78 


NITEIC  ACID ACTION  OF  ACIDS  UPON  METALS. 


When  the  metals  are  presented  to  the  acids  other  phenomena 
are  observed  ; a brisk  action  frequently  takes  place,  accompanied 
by  the  evolution  of  a gas,  and  it  is  very  often  stated  that  the 
metal  first  becomes  oxidized,  and  is  then  dissolved  by  the  acid. 

It  is  not,  however,  necessary  to  assume  that  the  metal  always 
undergoes  oxidation  as  a preliminary  step,  for  it  may  be  supposed 
that  the  metal  simply  displaces  the  hydrogen  of  the  acid.  When, 
for  example,  zinc  is  placed  in  diluted  sulphuric  acid,  the  metal  is 
dissolved  with  rapidity,  whilst  hydrogen  escapes  in  the  gaseous 
form ; + Zn  yielding  ZnSO-^  + H2.  A similar  result  is 

obtained  when  iron  or  tin  is  dissolved  in  hydrochloric  acid,  ferrous 
or  stannous  chloride  being  produced,  whilst  hydrogen  is  given 
off,  the  reaction  in  the  case  of  iron  being : 2 HCl  + Fe  = FeCl2 
+ When  an  oxide  is  employed  instead  of  a metal,  the 
hydrogen,  instead  of  escaping  as  gas,  is  eliminated  in  the  form  of 
w^ater  ; for  instance,  in  the  action  of  oxide  of  zinc  upon  sulphuric 
acid,  the  change  may  be  represented  as  ZnO  + = ZnSr0^ 

+ H2O ; and  again  with  oxide  of  copper  and  hydrochloric  acid. 
One  + 2 HCl  = -GUCI2  + 1120. 

The  ordinary  action  of  metals  upon  sulphuric  acid,  in  which  the 
components  of  the  acid  are  united  by  powerful  chemical  ties,  is,  as 
we  have  just  seen,  comparatively  simple  ; but  where  the  elements 
of  the  acid  are  but  feebly  held  together,  as  is  the  case  with  nitric 
acid,  the  reactions  are  often  more  complicated.  AYhen,  for  example, 
silver  or  copper  is  dissolved  in  nitric  acid,  hydrogen  may  as  before 
be  displaced  from  the  acid  by  the  metal  which  becomes  dissolved ; 
but  owing  to  the  facility  with  which  nitric  acid  parts  with  its 
oxygen  no  hydrogen  is  set  free— for  at  the  moment  of  its  liberation 
it  becomes  oxidized  at  the  expense  of  the  elements  of  the  nitric 
acid — one  of  the  lower  oxides  of  the  nitrogen  is  formed,  and  occa- 
sions the  disengagement  of  ruddy  fumes  instead  of  the  colourless 
and  infiammable  hydrogen.  In  many  instances  it  is  probable 
that  the  radicle  of  the  acid  itself  is  deoxidized  by  the  direct 
action  of  the  metal,  the  oxide  of  the  metal  then  forming  a salt 
with  the  undecomposed  portion  of  acid  by  double  decomposition, 
as  already  explained  where  an  oxide  acts  upon  an  acid  : — for 
example,  when  metallic  silver  acts  upon  heated  nitric  acid,  a por- 
tion of  the  acid  furnishes  oxygen,  disengaging  nitric  oxide,  whilst 
the  freshly  formed  oxide  of  silver  reacts  upon  another  portion  of  the 
acid,  Ag20-  4-  2 HHO3  yielding  H2O  + 2 AgHOg.  The  exact 
nature  of  the  decomposition,  however,  varies  in  different  cases ; sil- 
ver wdien  allowed  to  become  dissolved  slowly  in  the  cold  in  an  excess 
of  diluted  nitric  acid  produces  nitrous  acid  (HH O2)  which  remains 
in  solution  : 2 Ag  + 3 HAO3  giving  2 AgN03  -}-  H2O  -t-  IIXOj, 
and  the  metal  is  dissolved  wfithout  evolution  of  gas  ; a similar 
effect  is  also  produced  by  palladium.  With  metals  which  attack 
the  acid  more  vigorously,  such  as  copper  or  mercury,  nitric  acid 
of  moderate  concentration  (sp.  gr.  1*25  to  1*3)  disengages  nitric 
oxide  in  large  quantity : for  example,  3 -Bu  8 TtHOg  yields 
2 HO  -f  3 (On  2 HO3)  + 4 IlgO  ; but  if  the  acid  be  more  highly 
concentrated  (sp.  gr.  1*42),  peroxide  of  nitrogen  is  disengaged 


NITRIC  ANHYDRIDE,  OR  ANHYDROUS  NITRIC  ACID.  79 

abundantly  ; On  + 4 HlSTOg  yielding  On  2 + 2 + 2 H^O. 

And  when  the  decomposition  occurs  at  a high  temperature,  free 
nitrogen  is  usually  disengaged  in  considerable  quantity,  the  acid 
undergoing  complete  deoxidation.  If  the  metal  has  a still  more 
energetic  action,  as  zinc,  for  example,  the  acid  when  dilute  yields 
nitrous  oxide  amongst  its  gaseous  products  ; 5 Zn  + 10  IIIIO3  = 
+ 4 (Zn  2 NOs)  4-  4 H^O.  When  zinc  or  tin  is  used  with 
a stronger  acid,  ammonia  is  amongst  the  products  ; for  instance, 
4 Zn  + 9 HbTOg  = 4 (Zn  2 + 3 +H3II,  the  ammonia 

combining  with  the  excess  of  acid  employed. 

(361)  Hydrates  of  Nitric  Acid. — It  is  doubtful  whether  any 
definite  hydrates  of  the  acid  HllOg  really  exist.  When  concen- 
trated nitric  acid  is  exposed  to  the  air  it  absorbs  moisture,  and  if 
70  parts  of  the  concentrated  acid  be  mixed  with  30  of  water  it 
emits  a sensible  amount  of  heat.  Many  chemists  believe  that  a 
hydrate  of  nitric  acid  of  considerable  stability  is  formed  under 
these  circumstances,  and  that  it  has  a composition  represented  by 
the  formula  (2  3 This  hydrate  would  contain  60 

per  cent,  of  the  anhydride  and  40  of  water : such  an  acid 
has  a sp.  gr.  of  1*424;  it  boils  at  250°,  and  may  be  distilled 
under  ordinary  pressures  apparently  unaltered.  A weaker  acid 
when  heated  parts  with  its  water  till  it  arrives  at  this  density, 
and  a stronger  acid,  when  distilled,  also  loses  acid  until  reduced 
to  this  point,  the  liquid  in  the  retort  eventually,  in  both  cases, 
acquiring  a density  of  1*424.  This  apparent  stability  does  not 
seem  to  be  due,  however,  to  the  existence  of  any  true  hydrate, 
but  to  the  particular  relation  of  the  density  of  the  vapour  of 
nitric  acid  to  that  of  water  under  a pressure  of  30  inches  of 
mercury ; for  by  conducting  the  distillation  at  reduced  pressures, 
Koscoe  found  that  the  density  of  the  acid  in  the  retort  has  no 
real  fixed  point,  and  that  an  acid  may  be  thus  obtained  which 
does  not  correspond  in  composition  to  any  definite  hydrate,  but 
that  the  proportion  of  water  varies  with  the  pressure  under  which 
the  boiling  takes  place. 

The  table  on  the  following  page  indicates  the  per-centage  of 
nitric  anhydride,  often  called,  dry  nitric  acid,  contained  in 

aqueous  solutions  of  nitric  acid  of  various  specific  gravities. 

(362  Nitric  Anhydride^  or  Anhydrous  Nitric  Acid  (UgO^). 
Fusing  jpt.  85° ; Boiling  pt.  113°. — This  substance  is  a very 
unstable  compound,  which  may  be  obtained  in  the  form  of  per- 
fectly transparent,  brilliant,  colourless  crystals,  derived  from  the 
right  rhombic  prism  ; they  melt  at  85°  and  boil  at  113°  : at  about 
the  temperature  last-named  the  compound  begins  to  undergo 
decomposition.  Sometimes  the  crystals,  even  if  kept  in  sealed 
tubes,  become  decomposed  at  the  ordinary  atmospheric  tempera- 
ture, and  the  tube  bursts  with  a dangerous  explosion  from  the 
pressure  exerted  by  the  liberated  gases.  The  crystals  are  dis- 
solved rapidly  by  water,  emitting  much  heat,  and  producing 
ordinary  hydrated  nitric  acid. 

In  order  to  procure  the  anhydride,  a uniform  current  of  per- 
fectly dry  chlorine  gas  is  transmitted  very  slowly  over  crystals  of 


80 


NITRIC  ACm COIVIMON  IMPURITIES. 


Strength  of  Nitric  Acid  (Tire). 


Specific 

gravity. 

N2O5  in  100  1 

parts  by  weight. ' 

Specific 

gravity. 

N2O5  in  100 
parts  by  weight. 

1-5000 

79-700 

1-2887 

39-053 

1-4940 

77-303 

1-2705 

36-662 

1-4850 

74-918 

1-2523 

34-271 

1-4760 

72-527 

1-2341 

31-880 

1-4670 

70-136 

1-2148 

29-489 

1-4570 

67-745 

1-1958 

27-098 

1-4460 

65-354 

1-1770 

24-707 

1-4346 

62-963 

1-1587 

22-316 

1-4228 

60-572 

1-1403 

19-925 

1-4107 

58-181 

1 1227 

17-534 

1-3978 

55-790 

1-1051 

15-143 

1-3833 

53-399 

1-0878 

12-752 

1 3681 

51-068 

1-0708 

10-361 

1-3529 

48-617 

1-0540 

7-970 

1-3376 

46-226 

1-0375 

5-579 

1-3216 

43-835 

1-0212 

3-188 

1-3056 

41-444 

1-0053 

0-797 

well-dried  nitrate  of  silver : the  salt  is  at  first  heated  to  about 
200°  till  the  decomposition  has  commenced,  and  the  temperature 
is  then  lowered  to  about  150°.  The  operation  is  one  of  consider- 
able delicacy,  and  requires  attention  to  a number  of  minute  pre- 
cautions, for  the  details  of  which  the  reader  is  referred  to  De\dlle’s 
paper  {^Ann,  de  Cliimie^  III.  xxviii.  241).  The  chlorine  displaces 
the  nitric  acid  radicle  from  the  nitrate  of  silver  ; chloride  of  silver 
is  formed,  and  the  radicle  breaks  up  into  nitric  anhydilde  whilst 
oxygen  escapes.  By  surrounding  the  receiver  with  a freezing 
mixture,  the  nitric  anhydi’ide  is  condensed  in  crystals.  ■ The 
decomposition  may  be  represented  in  the  following  manner, 
though  it  is  probably  not  quite  so  simple*  : — 

Nitrate  of  silver.  Chlor.  silver.  Nitric  anhydride. 

4 AgXe3  -I-  2 Cl,  give  4 AgCl  4-  O,  -f  2 

Deville  ascertained  the  composition  of  nitric  anhydride  by 
estimating  the  quantity  of  nitrogen  which  a given  weight  of  the 
compound  furnished  after  the  oxygen  had  been  removed  from  it  by 
transmitting  its  vapours  over  finely  divided  metallic  copper,  which, 
at  a high  temperature,  combines  rapidly  with  the  oxygen.  100 
parts  by  weight  of  the  anhydride  were  thus  found  to  contain  25-9 
of  nitrogen  ; the  deficiency,  T4T,  is  oxygen  : or  28  parts  of  nitro- 
gen are  united  with  80  of  oxygen. 

(363)  Common  Impurities  of  the  Acid. — The  nitric  acid  of 
commerce  is  liable  to  be  contaminated  with  a variety  of  foreign 
matters,  of  which  sulphuric  acid,  chlorine,  potash,  and  oxide  of 
iron  are  the  most  frequent.  Its  usual  yellow  or  red  colour  is 
owing  to  the  presence  of  some  of  the  lower  oxides  of  nitrogen. 


* Possibly  a nitric  oxychloride  is  formed  first,  thus : — 2 AgNOs  -h  2 Cla  = 2 AgCl 
-t-  2 NOaCl  4-  Oa,  and  then  this  nitric  oxychloride  decomposes  a second  atom  of  nitrate 
of  sfiver;  AgNOg -f-NOaCl  = AgCHNaOs. 


NITRATES. 


81 


If  pure,  it  leaves  no  fixed  residue  when  evaporated  on  a slip  of 
glass,  and  gives  no  precipitate  when,  after  dilution  with  three  or 
four  times  its  bulk  of  w^ater,  it  is  tested  for  sulphuric  acid  with 
nitrate  of  barium,  and  for  chlorine  wfith  nitrate  of  silver.  By 
distilling  it  a second  time,  it  may  readily  be  obtained  of  specific 
gravity  1*1:2,  and  free  from  all  impurities  except  the  lower  oxides 
of  nitrogen.  If  chlorine  be  present,  nitrate  of  silver  may  be 
added  so  long  as  the  silver  salt  occasions  a precipitate,  or  a silver 
coin  may  be  dissolved  in  the  acid ; after  which  tiie  rectification 
may  be  proceeded  with.  The  lower  oxides  of  nitrogen  may  be 
removed  by  diluting  the  acid  with*  w^ater  till  of  a sp.  gr.  not 
exceeding  1*12,  and  then  distilling  with  2 or  3 per  cent,  of  the 
acid  chromate  of  potassium. 

Nity^ates. — i^itric  acid  is  monobasic ; that  is  to  say,  each  atom 
of  acid  requires  one  atom  of  a monad  metal  like  potassium  to  neu- 
tralize it ; the  salts  which  it  forms  are  termed  nitrates.  Their  gene- 
ral formula  is  M'llOg.  These  salts  may  be  procured  without 
difficulty  by  dissolving  either  the  metal  itself,  or  its  oxide,  or  its 
carbonate,  in  nitric  acid  more  or  less  diluted.  Many  of  the  nitrates, 
including  those  of  potassium,  sodium,  ammonium,  barium,  lead, 
and  silver,  are  anhydrous.  Others  combine  with  6 atoms  of  water 
of  crystallization ; among  these  are  the  salts  of  magnesium 
(Mg  2 N03 . 6 H^O),  zinc,  nickel,  cobalt,  iron,  and  co|)per ; 
whilst  in  others  the  proportion  of  the  water  is  difterent,  nitrate  of 
calcium  retaining  4 I120-,  and  nitrate  of  strontium  5 II^O.  If  crys- 
tallized at  a high  temperature,  nitrate  of  copper  retains  only 
3 II20',  and  nitrate  of  strontium  may  be  obtained  in  the  anhydrous 
form.  ISTo  acid  nitrates  are  known  to  exist,  but  several  basic 
nitrates  may  be  procured ; that  is  to  say,  salts  may  be  formed 
Avhich  contain  more  than  one  equivalent  of  base  for  each  equiva- 
lent of  acid  : such,  for  instance,  as  basic  nitrate  of  copper,  (Ou  2 
^03 . 3 Oueil^O.) 

The  following  table  gives  the  composition  of  some  of  the  nitrates : 


Nitrate  of  potassium  . 

“ sodium 

“ ammonium  . 

“ barium 

“ strontium  . 

“ calcium 

“ magnesium  . 

“ zinc 

“ iron  . 

“ copper 

“ lead 

“ silver  . 

Mercurous  nitrate 
Basic  nitrate  of  lead 
Basic  nitrate  of  copper 
Basic  mercurous  nitrate 


KNOg 
NaNOg 
n4N  NOg 
Ba  2 NOa 

Sr  2 NO3  . 5 H2O 
Ba  2 N03 . 4 H2O 
Mg  2 N03  . 6 H20 
Zn  2 N03  . 6 H30 
Fe  2 N03  . 6 H20 
0u  2 N03  . 6 H20 
Pb  2 N03 

AgN03 

. BgN03  . H20 
Pb  2 N03,  Pbll202 
0u  2 N03,  3 0ull202 
3HgN03  . HgII0 


KO,  NO5 
NaO,  NO, 

H4NO,  NO5 
BaO,  NO5 

SrO,  NO5  . 5 HO 
CaO,  NO,  . 4 HO 
MgO,  NO5  . 6 HO 
ZnO,  NO5  . 6 HO 
FeO,  NO5  . 6 HO 
CuO,  NO5  . 6 HO 
PbO,  NO5 
Ago,  NO5 
HgoO,  NO5  . HO 
2 Pb  0,  NO5  . HO 
4 CuO,  NO,  . 3 HO 
4 Hg.^O,  3 NOfl  . HO 


Most  of  the  nitrates  fuse  readily  when  lieated  : at  an  elevated 
temperature  they  are  all  decomposed.  At  first,  from  tlie  nitrates 
of  the  alkalies,  oxygen  nearly  pure  escapes,  and  nitrite  is  formed  : 
afterwards  the  nitrite  undergoes  deconqmsition,  a mixture  of 
oxygen  and  nitrogen  passing  ofi*,  and  in  most  cases  the  pure  oxide 


82 


DETECTION  OF  NITEIC  ACID. 


of  the  metal  is  left.  TThen  thrown  on  glowing  coals,  the  nitrates 
are  decomposed  with  scintillation  : if  paper  be  moistened  ^vith  the 
solution  of  any  nitrate,  allowed  to  diy,  and  then  burned,  the 
smouldering  combustion  characteristic  of  touch-paper  will  be  pro- 
duced. This  property  is,  however,  also  exhibited  by  the  salts  of 
some  other  acids,  of  which  the  chloric  is  the  most  important. 

All  the  nitrates,  when  heated  with  sulphuric  acid,  evolve  nitric 
acid ; but  there  is  no  ready  method  of  precipitating  nitric  acid 
from  its  solutions,  since  all  its  compounds  are  dissolved  by  water 
more  or  less  freely.  Various  indirect  methods  have  been  proposed 
for  ascertaining  its  presence.^  One  of  the  best  of  these  consists 
in  neutralizing  the  solution,  if  acid,  with  potash,  and  evaporating 
nearly  to  dryness  : then  adding  a few  copper  clippings,  and  heating 
the  mixture  with  a little  oil  of  vitriol : the  copper  decomposes  the 
nitric  acid  if  present,  and  characteristic  red  fumes  of  peroxide  of 
nitrogen  show  themselves.  A quantity  of  these  fumes,  too  small 
to  be  fusible,  may  be  rendered  evident  by  suspending  in  the  vessel 
a piece  of  paper  moistened  with  a mixture  of  starch  and  solution 
of  iodide  of  potassium,  which  will  become  blue  from  liberated 
iodine.  A still  smaller  quantity  of  the  acid  may  be.  detected  by 
mixing  a small  quantity  of  a concentrated  solution  of  green 
sulphate  of  iron  with  the  liquor  to  be  tested,  and  allo">ving  the  oil 
of  Vtriol  to  flow  gradually  into  the  solution  so  as  to  form  a dis- 
tinct stratum  below  it.  In  this  case  the  characteristic  action 
consists  in  the  formation  at  the  line  of  contact  between  the  two 
liquids,  of  a brownish-red  solution,  the  colour  of  which  disappears 
on  boiling ; the  coloration  depends  upon  the  cu’cumstance  that 
the  nitric  oxide  which  is  formed  bv  the  deoxidizino:  action  of  one 

* The  accurate  quantitative  determination  of  nitric  acid  when  mixed  with  other 
acids  is  a matter  of  considerable  difficulty.  One  method  consists  in  the  conversion 
of  the  acid  into  ammonia,  and  the  subsequent  determination  of  the  amount  of  ammo- 
nia found  (369).  Another,  which,  when  the  quantity  of  nitric  acid  is  very  small, 
furnishes  excellent  results,  is  that  proposed  by  Pugh  {Q.  J.  Chem.  Soc.  xii.  35).  It  is 
based  upon  the  determination  of  the  amount  of  stannous  chloride  which  is  converted 
into  stannic  chloride  when  the  solution  is  heated  with  nitric  acid  in  presence  of  an 
excess  of  hydrocliloric  acid.  A certain  quantity  of  the  concentrated  solution  con- 
taining the  nitric  acid  to  be  determined  is  introduced  into  a strong  tube,  and  a known 
volume  of  a solution  of  stannous  chloride  in  a large  excess  of  hydrochloric  acid  is 
added,  the  strength  of  the  tin  solution  having  been  ascertained  by  the  use  of  a 
standard  solution  of  the  acid  chromate  of  potassium.  Care  is  taken  to  employ  an 
excess  of  the  tin  solution.  A fragment  of  marble  is  dropped  into  the  tube  so  as  to 
produce  a quantity  of  carbonic  anhydride  sufficient  to  displace  the  atmospheric  air. 
The  tube  is  then  carefully  sealed  and  exposed  for  about  a quarter  of  an  hour  to  a 
temperature  of  340°.  It  is  allowed  to  cool,  and  the  contents  of  the  tube  are  next 
transferred  to  a glass  and  diluted  with  three  or  four  ounces  of  water ; a few  drops  of 
a weak  solution  of  iodide  of  potassium  and  starch  are  then  added,  and  the  amount 
of  tin  still  remaining  in  the  form  of  stannous  salt  is  determined  by  the  addition  of  a 
graduated  solution  of  the  acid  chromate  of  potassium,  until  the  liquid  becomes  blue 
from  the  liberation  of  iodine.  The  reaction  upon  wliich  this  process  depends  may 
be  thus  expressed : — 

HXO3  + 4 SnCls  4-  9 HQ  = H^XCl  -I-  4 SnCb  + 3 HaO ; 

the  nitrogen  of  the  nitric  acid  being  wholly  converted  into  ammonia  during  the  opera- 
tion : the  difference  between  the  amount  of  the  acid  chromate  originally  required  to 
peroxidize  the  quantity  of  tin  solution  employed,  and  that  actually  consumed  after  the 
experiment  is  over,  yielding  the  data  for  fixing  the  quantity  of  nitric  acid : 393-3  grs. 
of  the  acid  chromate  of  potassium  represent  63  of  nitric  acid  (HXO3),  or  54  of  N3O5. 


NITROUS  OXIDE PREPARATION. 


83 


portion  of  tlie  iron  salt,  becomes  dissolved  with  the  distinctive 
brown  colour,  in  the  solution  of  the  unoxidized  part  of  the  ferrous 
salt;  the  deoxidation  of  the  nitric  acid  which  occurs  may  be 
represented  in  the  following  equation  : — 

Ferrous  Sulpli.  Nitric  Ferric  Nitric 

sulphate.  ac.d.  acid.  sulphate.  oxide.  Water. 

+ 3 H2Se4  + 2 HNOg  = 3 S^)  + 2 NO  + 4 H^O 

If  a few  drops  of  hydrochloric  acid  be  added  to  a solution 
which  contains  free  nitric  acid,  or  a nitrate  in  solution,  the  liquid 
acquires  the  power  of  dissolving  gold  leaf.  This  effect,  however, 
is  produced  by  hydrochloric  acid  in  solutions  of  the  chlorates, 
bromates,  and  iodates ; but  the  presence  of  these  salts  may  be 
detected  by  other  characters  (382,  392,  397). 

(364)  Nitrous  Oxide,  Protoxide  of  Nitrogen  : NaO  = 44. 
Mol.  Vol.  I I |:  orNO  = 22.  Theoreiic  Sp.  Gr.  1-5238  ; Observed 
/Sp.  Gr.  1-527. — Preparation. — 1.  If  a mixture  of  equal  parts  of 
nitric  and  sulphuric  acid,  diluted  with  8 or  10  parts  of  water,  be 
digested  on  metallic  zinc,  the  metal  displaces  hydrogen,  which  at 
the  moment  of  its  liberation  deoxidizes  the  nitric  acid,  and  a colour- 
less gas  is  slowly  given  off,  composed  of  2 atoms  of  nitrogen  united 
with  1 of  oxygen. 

2.  — But  to  obtain  the  gas  in  a pure  state  it  is  far  better  to  heat 
nitrate  of  ammonium  (H^NNOg,  the  salt  furnished  by  neutraliz- 
ing pure  nitric  acid  with  carbonate  of  ammonium)  in  a glass 
retort ; the  salt  quickly  melts,  and  at  a temperature  of  between 
400°  and  500°  apparently  begins  to  boil,  but  in  reality  it  is  under- 
going decomposition,  by  which  it  is  entirely  resolved  into  the 
gaseous  nitrous  oxide  and  steam.  The  temperature  must  be 
carefully  watched,  and  not  be  allowed  to  rise  so  high  as  to  occa- 
sion the  production  of  white  vapours  in  the  retort,  because  the 
decomposition  is  then  apt  to  occur  with  explosive  violence.  The 
reaction  maybe  explained  as  follows  : Ammonium  is  a compound 
of  nitrogen  with  hydrogen ; when  the  nitrate  of  ammonium  is 

Jieated,  the  hydrogen  of  the  ammonium  combines  with  part  of  the 
oxygen  of  the  nitric  acid,  forming  water,  wdiilst  the  nitrogen  of 
the  ammonium  at  the  same  time  becomes  oxidized  at  the  expense 
of  another  part  of  the  oxygen  of  the  nitric  acid.  The  result  is 
that  tlie  whole  of  the  nitrogen,  both  of  the  nitric  acid  and  of  the 
ammonia,  is  liberated  in  the  form  of  nitrous  oxide ; H^N  NO3 
becoming  2 II^O  -h  N^O.  An  ounce  of  the  salt  furnishes  about 
500  cubic  inches  of  the  gas. 

3.  — L.  Smith  adopts  a modification  of  the  foregoing  process  for 
preparing  the  gas : he  decomposes  sal  ammoniac  by  means  of 
nitric  acid  (of  sp.  gr.  1-20)  at  a gentle  heat.  The  gas  which  is 
obtained  in  this  manner  is  not  ])ure,  but  is  contaminated  w-ith 
small  quantities  of  chlorine  and  of  nitrogen  ; the  chlorine  may  be 
removed  by  allowing  the  gas  to  bubble  up  tlirougli  a solution  of 
])otash.  Advantage  may  sometimes  be  taken  of  this  action 
of  nitric  acid  on  sal  ammoniac  to  destroy  an  excess  of  muriate  of 
ammonia  in  solution  in  the  course  of  an  analysis. 


84 


PKOPERTIES  AXD  CO^VIPOSITION  OF  NITROUS  OXIDE. 


Properties. — ^Nitrous  oxide  is  a transparent,  colourless  gas, 
with  a faint  sweetish  smell  and  taste : 100  cubic  inches  of  water 
at  32°  dissolve  130  cubic  inches  of  the  gas ; at  59°,  77  cubic  inches  ; 
and  at  75°,  only  60  cubic  inches  (Bunsen).  Owing  to  this  con- 
siderable diminution  in  solnhility  with  the  rise  of  temperature, 
it  should  he  collected  over  warm  water.  Under  a pressure  of  50 
atmospheres  at  45°,  it  is  reducible  to  a colourless  liquid,  of  sp.  gr. 
at  45°,  of  0‘908.  It  boils  at  about  — 126°  (Eegnault),  and  may 
he  frozen  into  a transparent  solid  at  about  — 150°.  When  the 
liquid  nitrous  oxide  was  mixed  with  bisulphide  of  carbon  and 
exposed  to  evaporation  in  xacuo.,  Uatterer  obtained  a reduction 
of  temperature  wiiich  he  estimated  at  220°  F. ; this  is  a lower 
point  than  has  hitherto  been  attained  by  any  other  means.  The 
gaseous  nitrous  oxide  lias  a specific  gravity  of  1'527,  which  coin- 
cides with  that  of  carbonic  anhydride.  This  gas  possesses  the 
qualities  neither  of  an  acid  nor  of  an  alkali.  It  supports  the 
combustion  of  many  bodies  with  a brilliancy  resembling  that 
which  they  exhibit  when  burned  in  oxygen.  It  is,  however,  at 
once  distinguished  from  oxygen  by  its  considerable  solubility  in 
water.  A glowing  match  bursts  into  fiame  when  plunged  into 
nitrous  oxide : sulphur  when  kindled  burns  in  it  with  a pale  rose- 
coloured  flame. 

Soon  after  the  discovery  of  the  nitrous  oxide,  Davy  ascertained 
that  it  may  be  respired  for  a few  minutes  : it  then  produces  a sin- 
gular species  of  transient  intoxication,  attended  in  many  instances 
with  an  irresistible  propensity  to  muscular  exertion,  and  often  to 
uncontrollable  laughter ; hence  the  gas  has  acquired  the  popular 
name  of  laughmg-gas. 

Composition. — If  nitrous  oxide  be  passed  repeatedly  through 
a porcelain  tube  heated  to  briglit  redness,  the  gas  is  decomposed 
into  a mixture  of  oxygen  and  nitrogen,  2 volumes  becoming 
expanded  permanently  into  the  space  of  3 volumes.  An  easy 
method  of  analysing  the  nitrous  oxide  consists  in  mixing  it  with 
hydrogen,  and  passing  an  electric  spark  through  the  mixture.  If 
4 measures  of  nitrous  oxide  be  mixed  with  an  excess  of  hydi’ogen 
gas,  say  with  6 measures  of  hydrogen,  in  the  bent  eudiometer 
(fig.  281),  10  measures  of  mixed  gas  will  be  produced  ; and  on 
transmitting  the  electric  spark,  inflammation  will  occur ; steam 
will  be  formed  by  the  oxidation  of  the  hydrogen,  and  will  be 
immediately  condensed ; the  10  measures  will  thus  be  reduced 
to  6 : but  the  quantity  of  oxygen  contained  in  the  nitrous  oxide 
cannot  be  at  once  inferred  from  this  change  of  bulk : before  this 
can  be  done,  it  is  needful  to  ascertain  how  much  hydrogen  is  left 
in  the  mixture.  This  may  be  efiected  by  mixing  the  6 remaining 
measures  with  two  measures  of  oxygen,  thus  making  8 measures, 
and  again  transmitting  the  electric  spark.  Steam  will  again  be 
formed,  and  immediately  condensed : the  8 measures  of  the  mix- 
ture will  now  be  reduced  to  5 ; 3 measures  of  the  gas  will  there- 
fore have  disappeared,  two-thirds  of  which,  or  2 measures,  are 
hydrogen : 1 measure  of  the  gas  now  left  must  consequently  be 
oxygen  which  was  added  in  excess,  and  the  remaining  4 measures 


PKEPAKATION  OF  NITRIC  OXIDE. 


85 


are  nitrogen.  Of  tlie  6 measures  of  hydrogen  originally  added, 
4 have  therefore  combined  with  oxygen  derived  from  the  nitrous 
oxide  ; and  since  4 measures  of  hydrogen  require  two  measures  of 
oxygen  for  conversion  into  water,  the  4 measures  of  the  nitrous 
oxide  must  have  contained  two  measures  of  oxygen.  It  appears, 
also,  that  nitrous  oxide  contains  its  own  bulk  of  nitrogen,  since 
the  4 measurps  of  the  gas  originally  employed  furnish  4 measures 
of  nitrogen  ; this  nitrogen  is  moreover  so  combined  with  2 mea- 
sures of  oxygen,  that  the  6 measures  of  the  two  gases  when  united 
are  condensed  into  the  space  of  4 measures,  or  into  two-thirds 
of  the  bulk  which  they  occupied  when  separate.  The  specific 
gravity  of  the  gas  shows  that  this  conclusion  is  correct,  for  100 
cubic  inches  are  found  by  experiment  to  weigh  between  47  and 
48  grains,  and  by  calculation  we  find  that  such  should  be  the 
case,  for — 

Grains.  By  vol.  Sp  frr. 

100  cub.  in.  of  nitrogen  weigh 30T2  or  1*0  = 0-971 

50  cub.  in.  of  oxygen  weigh 17’10  0*5  = 0-5528 


They  give  100  cub.  in.  of  nitrous  oxide,  1417-22  i.q  _ 1*5238 
and  weigh ) 

The  proportion  of  nitrogen  contained  in  the  gas  may  also  be 
ascertained  by  means  of  potassium  ; for  if  potassium  be  heated  in 
nitrous  oxide,  it  burns  vividly,  and  is  converted  into  potash,  leav- 
ing a volume  of  nitrogen  equal  to  that  of  the  gas  employed.  The 
composition  of  this  gas  may  therefore  be  thus  represented  : — 

By  weight. 

Nitrogen N2  = 28  or  63-64  2 vols. 

Oxygen O ==  16  36-36  1 vol. 


Nitrous  oxide.  .N2O  = 44  100-000  2 vols. 

(365)  Nitric  Oxide  ; Nitrosyl ; Deutoxide^  or  Binoxide^  of 
Nitrogen^  (NO  or  NO^  = 30)^'  ; Gr.  1-039;  Atomic  Vol.  \ | |. 
— Preparation. — 1.  If  nitric  acid  be  diluted  with  twice  its  bulk 
of  water,  so  as  to  reduce  it  to  a specific  gravity  of  about  1*2,  and 
be  poured  upon  copper  clippings  or  metallic  mercury  placed  in  a 
retort,  brisk  action  speedily  occurs ; a gentle  heat,  if  necessary, 
may  be  applied  until  it  commences  ; the  retort  becomes  filled  with 
red  fumes,  and  a gas  is  disengaged,  which  if  collected  over  water 
will  be  found  to  be  colourless ; 1 ounce  of  copper  by  solution  in 
about  4 ounces  of  the  diluted  acid  would  yield  nearly  420  cubic 
inches  of  nitric  oxide.  If  the  heat  be  too  high  the  gas  is  apt  to 
be  contaminated  with  nitrogen.  During  tliis  decomposition  the 
metal  displaces  hydrogen  from  one  portion  of  tlie  acid  and  forms 
a nitrate,  which  is  dissolved,  whilst  the  liydrogen,  in  the  moment 
of  its  liberation,  decomposes  another  portion  of  tlie  acid,  water  is 
formed,  and  nitric  oxide  liberated.  Tlie  following  equation 
shows  the  reaction  which  occurs  between  3 atoms  of  cojiper  and 

* The  vapour  density  of  this  compound  is  anomalous,  NO  yielding  2 volumes 
(II  = 1 vol.)  instead  of  N2O2  as  would  be  requisite  if  the  compound  followed  the 
usual  law. 


86 


COMPOSITION  AND  PEOPEKTIE3  OF  NITEIC  OXIDE. 


8 of  nitric  acid,  resulting  in  the  formation  of  2 atoms  of  nitric 
oxide  and  3 atoms  of  nitrate  of  copper : — 

Copper.  Nitric  acid.  Nitrate  of  copper.  Nitric  oxide.  Water. 

3 Ou  + 8 IIXO3  =r  3 ("Bu  2 XO3)  + 2 XO  + 4 

2. — The  nitric  oxide  may  also  he  obtained  perfectly  pure  by 
digesting  hydrochloric  acid  with  iron  filings  till  it  will  dissolve  no 
more,  decanting  the  clear  liquid,  and  adding  to  it  its  own  bulk  of 
hydrochloric  acid  : on  placing  the  solution  in  a retort,  and  adding 
nitrate  of  potassium,  the  nitric  oxide  is  immediately  evolved  in 
large  quantity  (Pelouze).  The  reaction  is  not  so  simple  as  in  the 
preceding  case  ; it  is  represented  as  follows  : — 

Ferrous  Hydrochlor.  Nitrate  of  Ferric  Chloride  of  Nitric 

chloride.  acid.  potassium.  chloride.  Water.  potassium.  oxide. 

6 FbCIo  + 8 iilCl  + 2 ^iv6  3 FgoCIb  “!■  4.  H2^  F 2 KCl  + 2 NO. 

A simple  modification  of  this  method  consists  in  placing  in  a 
retort  1 ounce  of  commercial  nitre,  8 ounces  of  ferrous  sulphate, 
and  pouring  upon  them  half  a pint  of  diluted  sulphuric  acid  (1 
oimce  of  acid  to  3 ounces  of  water).  Such  a mixtm-e  will  give 
nearly  400  cubic  inches  of  pure  nitric  oxide. 

Coinposition. — The  composition  of  nitric  oxide  cannot  be 
ascertained  by  detonation  with  hycbogen  ; for  equal  volumes  of 
hydrogen  and  nitric  oxide  burn  quietly  with  a green  fiame  on 
the  approach  of  a burning  body.  Davy  analysed  nitric  oxide  by 
heating  charcoal  strongly  in  it ; 2 volumes  of  the  gas  by  this 
treatment  furnish  1 volume  of  nitrogen,  and  1 volume  of  car- 
bonic anhydride  : but  carbonic  anhydride  contains  its  own  volume 
of  oxygen  ; nitric  oxide  must  therefore  have  consisted  of  1 volume 
of  nitrogen  united  without  condensation  with  1 volume  of  oxygen. 
The  density  of  the  gas  confirms  the  correctness  of  this  result,  for 
by  experiment  100  cubic  inches  weigh  rather  more  than  32  grains, 
and  by  calculation, 

Grs.  By  voL  Sp.  sr. 


50  cubic  inches  of  nitrogen  weigh 15‘06  or  0'5  = G'486 

50  cubic  inches  of  oxygen IT'IO  0 5 = 0-552 

100  cubic  inches  of  nitric  oxide 32-16  I'O  = 1-033 


Potassium  burns  when  heated  in  the  gas,  potash  being  produced. 
If  the  experiment  be  conducted  in  such  a manner  as  to  allow  the 
residual  gas  to  be  measured  after  the  combustion  is  over,  2 volumes 
of  the  nitric  oxide  will  be  found  to  leave  1 volume  of  nitrogen. 
A similar  result  is  obtained  when  tin  is  heated  in  the  gas  ; conse- 
quently its  composition  may  be  thus  represented  : — 


By  weight. 

Nitrogen N = 14  or  46-67  1 vol. 

Oxygen O = 16  53-33  1 vol. 


Nitric  oxide N0  = 30  100-00  2 vols. 

Properties. — Xitric  oxide  has  a strong  disagreeable  odour, 
and  cannot  be  respired.  It  has  hitherto  resisted  all  attempts  to 


NITKOTJS  ANHYDEIDE PEEPAEATION. 


87 


liquefy  it.  Water  does  not  dissolve  more  than  •gV  of  its  bulk  of 
this  gas.  Nitric  oxide  is  the  most  stable  of  the  oxides  of  nitrogen  ; 
it  may  even  be  exposed  to  a red  heat  without  undergoing  decom- 
position, but  a succession  of  electric  sparks  converts  it,  if  it  be 
moist,  into  a mixture  of  nitrogen  and  nitric  acid  ; and  if  digested 
upon  moistened  iron  filings,  or  a moist  sulphide  of  one  of  tlie 
alkaline  metals,  it  is  slowly  converted  into  nitrous  oxide.  Many 
burning  bodies,  such,  for  instance,  as  a lighted  taper,  or  phospho- 
rus just  kindled,  are  extinguished  when  plunged  into  the  gas  ; but 
a decomposition  of  the  gas  will  be  effected  if  the  phosphorus  be 
burning  vigorously,  and  it  will  deflagrate  with  a brilliancy  equal 
to  that  produced  by  its  combustion  in  oxygen. 

Nitric  oxide  is  completely  absorbed  by  a solution  of  ferrous 
sulphate,  with  which  it  forms  a deep  reddish-brown  liquid.  All 
the  ferrous  salts  exert  a similar  action,  and,  according  to  Peligot, 
2 atoms  of  the  salt  of  iron  absorb  1 atom  of  nitric  oxide,  the  solu- 
tion in  the  case  of  the  sulphate  containing  (2  PeSO^,  NO.)  The 
deep  colour  of  the  liquid  thus  formed  is  employed,  as  has  already 
been  mentioned  (363),  for  the  purpose  of  ascertaining  the  presence 
of  nitric  acid  in  solution.  This  liquid  absorbs  oxygen  rapidly 
from  the  air  or  from  gaseous  mixtures ; when  heated,  most  of  the 
nitric  oxide  is  expelled  from  it  unchanged.  Solutions  of  stannous 
and  mercurous  salts  also  absorb  nitric  oxide,  but  they  undergo 
change,  and  the  gas  cannot  again  be  expelled  from  them  by  heat. 
Nitric  acid  likewise  absorbs  the  gas  rapidly  : if  the  acid  be  con- 
centrated, the  solution  becomes  reddish  brown ; if  more  diluted, 
it  is  green ; if  still  weaker,  the  solution  is  blue,  but  if  diluted 
below  a specific  gravity  of  1T5,  little  of  the  gas  is  absorbed,  and 
tlie  acid  remains  colourless. 

The  nitric  oxide  is  neither  acid  nor  alkaline  in  its  characters. 
It  has,  however,  a very  powerful  attraction  for  oxygen,  and  to  this 
circumstance  is  owing  one  of  the  most  characteristic  properties  of 
the  gas.  When  mixed  with  oxygen,  or  with  any  gas  containing 
uncombined  oxygen,  dense  red  fumes  are  produced.  These  red 
fumes  are  freely  soluble  in  water,  and  furnish  an  acid  liquid. 
Formerly  tliis  circumstance  was  employed  to  determine  the  quan- 
tity of  oxygen  in  mixture  with  other  gases ; but  the  method  is 
now  abandoned,  as  the  absorption  is  not  uniform,  owing  to  the 
formation  in  uncertain  quantity  of  a mixture  of  the  soluble  oxides 
of  nitrogen.  It  may,  however,  be  used  with  advantage  as  a qua- 
litative test  to  demonstrate  the  existence  of  uncombined  oxygen 
in  a gaseous  mixture.  Nitric  oxide  also  unites  with  half  its  v^olume 
of  chlorine  when  the  two  gases  are  mixed,  and  chloronitrous  gas 
NOCl  is  formed  (377). 

(366)  Nitrous  Anhydride  (N^Og  = 76,  or  NO3  = 38  ; formerly 
known  as  llyponitrous  Acid). — Preparation. — 1.  l>y  mixing  in 
an  exhausted  flask  4 volumes  of  nitric  oxide  with  1 volume  of 
oxygen,  both  in  a perfectly  dry  state,  brownish-red  fumes  of 
nitrous  anhydride  are  formed,  which  at  a temperature  of  0°  F. 
become  condensed  into  a blue  very  volatile  liquid,  which  emits  a 
red  vapour. 


88 


NITEOUS  AGED NITEITES. 


2. — j^itrons  anhydride  may  also  be  obtained  nearly  in  a state 
of  purity,  by  heating  in  a capacious  retort  1 part  of  starch  with 
8 parts  of  nitric  acid  of  sp.  gr.  1*25  : it  may  be  dried  by  passing 
it  over  chloride  of  calcium,  and  may  then  be  liquefied  by  trans- 
mission through  a TJ-shaped  tube  surrounded  by  a mixture  of  ice 
and  salt. 

Properties. — A small  quantity  of  water  converts  the  anhydride 
into  nitrous  acid,  but  a larger  quantity  quickly  decomposes  it 
into  nitric  acid  and  nitric  oxide  : hence  the  presence  of  a small 
quantity  of  water  converts  the  blue  into  a dark  green  liquid,  but 
a larger  quantity  decomposes  it  with  etfervescence  : nitric  acid  is 
formed,  and  nitric  oxide  escapes.  This  last  reaction  may  be  thus 
represented : -f  3 IST^Og  give  2HAO3  + 4 NO. 

Though  in  its  uncombined  form  nitrous  anhydride  is  decom- 
posed by  water  with  such  facility,  yet  its  radicle  forms  permanent 
compounds  with  the  metals  of  the  alkalies  : these  salts  are  called 
nitrites.  Their  general  formula  is  M'NOj.  If  nitric  oxide  be 
placed  over  a solution  of  caustic  potash,  and  small  quantities  of 
oxygen  be  added,  nitrite  of  potassium  is  produced  in  the  liquid 
and  if  nitre,  or  nitrate  of  sodium,  be  heated  to  redness  until  the 
gas  which  is  evolved  begins  to  contain  nitrogen,  the  residue  will 
be  found  to  be  composed  chiefly  of  nitrite  of  potassimn  or  sodium.* 
These  nitrites  are  soluble  in  alcohol,  and  may  thus  be  separated 
from  the  corresponding  nitrates,  which  are  insoluble.  The  nitrites 
of  potassium  and  sodium,  and  the  monobasic  nitrites  of  silver  and 
lead,  are  anhydrous.  A considerable  number  of  double  nitrites 
of  potassium  may  be  formed.  Lang  has,  for  instance,  among 
others,  described  the  following  : — 

Nitrite  of  potassium 2 KN02 . H2O 

“ “ and  barium .. . 2 KN'02,  Ba  2 NO2  • H2  0' 

“ “ and  zinc 2 KNO2,  2 . HiO 

“ “ “q2KKe,,BalI0.,^e,. 

If  the  nitrite  either  of  potassium  or  of  sodium  be  dissolved  in 
water,  and  nitrate  of  silver  be  added,  a sparingly  soluble  nitrite 
of  silver  is  precipitated  : by  dissolving  this  precipitate  in  hot 
water,  it  is  obtained  pure  in  crystals  as  the  liquid  cools.  The 
addition  of  cold  diluted  sulphuric  acid  to  a solution  of  a nitrite 
decomposes  the  salt,  and  the  liquid  then  becomes  of  a brownish- 
red  colour  on  adding  a solution  of  ferrous  sulphate.  The  nitrites 
may  thus  be  distinguished  from  the  nitrates,  since  the  latter  do 
not  change  coloim  when  similarly  treated,  unless  heat  be  applied. 
Acid  solutions  of  the  nitrites  destroy  the  blue  colour  of  indigo  at 
ordinary  temperatures ; they  bleach  the  permanganate  of  potas- 
sium, and  slowly  reduce  acid  chromate  of  potassium  to  a green 
salt  of  chromium.  The  terchloride  of  gold  is  reducible  to  the 
metallic  form  by  these  salts,  and  mercurous  salts  give  a grey  pre- 
cipitate of  reduced  mercury.  A very  minute  trace  of  any  nitrite 

* Scbonbein  has  shown  that  the  solutions  of  the  nitrates  of  the  alkali  metals,  as 
well  as  some  other  nitrates,  may  be  reduced  slowly  to  nitrites  by  stirring  or  agitation 
with  a rod  of  zinc  or  of  cadmium,  the  reduction  being  accelerated  by  heat. 


NITROUS  ACID PEROXIDE  OF  NITROGEN. 


89 


may  be  detected  by  mixing  a dilute  solution  of  iodide  of  potassium, 
free  from  iodate,  with  starch  and  a little  diluted  hydrochloric  acid 
(sp.  gr.  1*006) ; the  liquid  to  be  tested,  after  being  acidulated  with 
hydrochloric  acid,  is  then  to  be  added  to  the  test  mixture,  wdien 
the  blue  colour  of  iodide  of  starch  will  appear,  even  when  only 
traces  of  a nitrite  are  present. 

The  presence  of  nitrites  in  the  well  waters  of  towns  is  of  com- 
mon occurrence,  probably  owing  to  the  oxidation  of  ammonia. 
I^itrous  acid  is  formed  from  ammonia,  when  the  latter  is  in  con- 
tact with  atmospheric  air  in  the  presence  of  platinum  black,  or  of 
a coil  of  heated  platinum  wire  ; if  a coil  of  red-hot  platinum  wire 
be  held  in  a jar  of  air  moistened  with  a few  drops  of  a strong 
solution  of  ammonium,  white  fumes  of  nitrite  of  ammonium  will 
be  formed.  The  contact  of  metallic  copper  is  still  more  eliectual 
in  promoting  the  formation  of  nitrous  acid  from  ammonia,  when 
free  oxygen  is  present ; if  a small  quantity  of  pulverulent  copper 
be  shaken  up  in  a bottle  of  air,  with  a few  drops  of  a solution  of 
ammonia,  the  oxygen  will  be  absorbed  in  a few  minutes,  and 
nitrous  acid  will  be  found  in  the  liquid.  Even  bright  slips  of 
copper  effect  a similar  oxidation  of  tlie  ammonia,  whilst  oxide 
of  copper  is  formed  simultaneously.  The  cause  of  these  pheno- 
mena is  obscure  ; they  belong  to  the  class  of  actions  commonly 
known  as  catalytic.  According  to  Schdnbein,  the  white  fumes 
produced  during  the  spontaneous  oxidation  of  phosphorus  in  air 
consist,  not  of  phosphorous  anhydride,  but  of  nitrite  of  ammonium, 
formed  by  the  action  of  the  ozone  upon  moist  air. 

(367)  Peroxide  of  ISTitrogen  : IIijiyonitriG  acid  (formerly 
called  Nitrous  acid),  ^2^4  = ^2,  or  ==  46  ; Meltin,g-iyt.  16°, 
Peligot;  10°,  Miiller:  Boiling-gjt.  71°. — Preparation. — 1.  The  red 
fumes  which  appear  on  mixing  nitric  oxide  with  atmospheric  air 
consist  mainly  of  peroxide  of  nitrogen.  The  peroxide  may  be 
procured  in  prismatic  crystals  by  passing  2 volumes  of  nitric 
oxide  and  1 of  oxygen,  both  perfectly  dry,  into  tubes  previously 
dried  with  scrupulous  care,  and  cooled  down  by  a mixture  of  ice 
and  salt.  (Peligot,  Ann.  de  Chimie.^  III.  ii.  61.)  Tliese  crystals 
melt  at  10°  F.  ; at  the  ordinary  temperature  of  the  air  they  form 
an  orange-coloured  liquid,  which  boils  at  71°,  and  produces  a deep 
brownish-red  vapour.  It  is  remarkable  that  after  this  compound 
has  once  been  melted  it  does  not  freeze  even  at  0°,  This  sub- 
stance is  decomposed  by  *water  with  singular  facility  ; a minute 
trace  of  water  is  sufficient  to  prevent  the  formation  of  the  crystal- 
line compound,  occasioning  in  its  stead  the  production  of  a green 
liquid  (])robably  17203,N20„Il20),  similar  to  tliat  obtained  by  the 
distillation  of  nitrate  of  lead.  The  peroxide  of  nitrogen  was  long 
considered  to  possess  acid  properties,  and  hence  was  termed  nitrous 
acid.  It,  however,  does  not  form  specific  salts,  but  is  immediately 
decomposed  by  bases  into  a nitrate  and  nitrite  : — 

^2^4  + 2 KIIO,  yielding  KNO,  + KNO^  IIjO. 

P>ut  when  the  liquid  peroxide  is  digested  on  a metal,  such  as 
potassium,  lead,  or  mercury,  nitrate  of  the  metal  is  formed,  and 


90 


PEROXIDE  OF  XITEOGEX. 


Fig.  291. 


nitric  oxide  is  expelled ; with  potassium  for  instance,  K -!- 
= KXO3  -f  nitrite  is  formed  under  these  cii’cmn 

stances. 

2. — If  nitrate  of  lead  he  dried,  and  heated  strongly  in  a small 
glass  retort,  it  is  decomposed ; deep  red  fmnes,  consisting  ot  a 
mixture  of  peroxide  of  nitrogen  and  free  oxy2:en  are  produced, 
and  oxide  of  lead  is  left : 2 (Pb  2 XO3)  = 2 Pb^  + 2 -h 
If  the  red  vapour  be  made  to  pass  thi’ough  a bent  tube  siuTOunded 

by  ice  and  salt,  as  shown 
in  fig.  291,  the  peroxide 
is  condensed  to  a liquid 
which  is  green,  owing  to 
the  presence  of  a little 
moistui’e.  Towards  the 
latter  part  of  the  distil- 
lation the  anhydi’ous 
peroxide  comes  over, 
and  if  the  receiver  be 
changed,  it  may  be  ob- 
tained in  crystals.  The 
liquid  peroxide  is  nearly 
colomdess  at  0°  : it  be- 
comes yellow  at  11°  F., 
and  at  ordinaiy  temper- 
atm’es  is  red.  It  has  a 
specific  gravity  of  1 '151, 
boils  at  82°,  and  fr’eezes 
at  — 10°.  It  emits  a 
dense  brownish-red  vapour,  winch  becomes  deeper  In  tint  as  the 
temperature  rises,  till  at  100°  it  is  almost  opaque. 

Playfaii*  and  IT anklvn  have  shown  it  to  be  probable  that  at 
low  temperatimes  the  compound  has  the  formula  but  that 

as  the  temperatm'e  rises  it  assumes  the  constitution  [MiiUer 

{Lieb.  Ann.  cxxil.  15)  finds  the  sp.  gr.  of  the  vapour,  at  82°,  to  be 
2'70  ; = I ^ I theoretically  would  give  3'18  ; whilst  at  170° 

the  sp.  gravity  of  the  vapour  is  only  1'81 ; and  Mitscherlich,  at 
some  temperature,  probably  higher,  but  not  stated,  found  it  as 
low  as  1'71 ; the  calculated  density  for  the  formula  XO3  = | I | 
is  1'591. 

This  wIQ  be  seen  by  the  folio wmg  table : — 


By  weight  Bv  volume. 

Nitrogen X = 14  or  30-44  1 or  0-5  = 0-4S6  ' or  Xa  2 or  I'O  = 0-9T2 

Oxygen 0^=  32  69-56  2 1 0 = MOo  | 04  4 2-0=2-211 

Peroxide  of ) ^ 100*00  2 1*0  1-591  Xa04  2 1*0  3-183 

nitrogen  ) I 

This  vapour  has  a pecuhar,  suffocating  odour.  It  supports  the 
combustion  of  a taper,  and  of  many  burning  bodies  ; potassium 
takes  fire  m it  spontaneously.  If  water  be  added  gradually  to  the 
hquid  peroxide,  it  passes  through  various  tints,  becoming  succes- 
sively orange,  yellow,  green,  blue,  and  finally  colourless,  an  efier- 


COMPOUNDS  OF  NITKOGEN  WITH  HYDKOGEN. 


91 


vescence  being  occasioned  during  the  whole  time  from  tlie  escape 
of  nitric  oxide,  finally  nitric  acid  in  abundance  is  formed  in  the 
liquid  ; -j-  3 NO2  = ^ HNO3.  The  nitric  oxide,  on 

mixing  with  the  oxygen  of  the  air,  reproduces  the  peroxide  of 
nitrogen  as  usual.  The  different  tints  assumed  by  the  liquid  during 
dilution  appear  to  be  owing  to  the  solution  of  the  nitric  oxide  in 
varying^proportion  in  the  nitric  acid  produced  by  the  decomposi- 
tion. JPeroxide  of  nitrogen  combines  directly  with  hydrochloric 
acid,  and  forms  several  chlorinated  compounds  (STY).  It  also  is 
absorbed  by  concentrated  sulphuric  acid,  and  forms  a crystalline 
compound  with  it  (2  H2S04,N20-4S0-g)  (412). 

Peroxide  of  nitrogen  may  be  distinguished  from  nitrous  acid 
by  its  power  of  imparting  to  a neutral  solution  of  sulphocyanide 
of  potassium  a red  tint  closely  resembling  that  produced  in  the 
same  reagent  by  the  persalts  of  iron  ; in  a few  minutes,  however, 
the  decomposition  proceeds  further,  and  the  liquid  becomes  colour- 
less (Hadow). 

(368)  The  important  influence  of  proportion  upon  the  products 
of  chemical  combination  is  exhibited  in  a striking  light  by  these 
compounds  of  nitrogen  with  oxygen.  The  same  elements,  accord- 
ing to  the  quantities  in  which  they  are  united,  may,  as  in  nitric 
acid,  produce  one  of  the  most  corrosive  compounds  in  the  range 
of  chemistry  ; or  may  give  rise,  as  in  the  case  of  the  nitrous  oxide, 
to  a stimulating  and  intoxicating  gas,  which  may  be  breathed  with 
impunity ; while  the  intermediate  combinations  exhibit  properties 
entirely  different  from  either.  A broad  distinction  may  also  be 
easily  traced  between  the  results  of  mixture  and  those  of  true 
chemical  union.  The  properties  of  the  atmosphere  are  the  results 
of  simple  admixture  : the  chemical  qualities  of  oxygen  appearing 
to  be  simply  diluted  by  its  apparently  inert  companion,  nitrogen 

^ (just  as  the  sweetness  of  sugar  is  reduced  by  the  addition  of 
water) ; whilst  each  one  of  the  true  combinations  of  nitrogen 
with  oxygen  exhibits  characters  distinct  from  those  of  either  of  its 
components. 

§ II. — Compounds  of  JTitkogen  with  Hydkogen. 

Ammonia,  Volatile  Alkali^  or  Spirit  of  Hartshorn  (Hghl  = IT). 
Melting-pt.  — 103°  ; Boiling-pt.  — 3T°  ; Theoretic  Sp.  Gr.  0*5896 ; 

Observed  Sp.  Gr.  0*59  ; Atomic  and  Mol.  Yol.  | | |. 

(369)  This  important  compound  has  received  the  name  of 
ammonia,  from  the  circumstance  of  its  having  been  obtained  from 
a salt  first  procured  in  Libya,  near  the  temple  of  Jupiter  Ammon, 
and  hence  termed  sal  ammoniac.  Nitrogen  and  hydrogen  do  not 
combine  directly  with  each  other ; nevertheless,  their  indirect 
combination  is  a circumstance  of  continual  occurrence.  The 
spontaneous  decomposition  of  moist  animal  matters,  which  contain 
both  hydrogen  and  nitrogen,  and  almost  every  process  of  oxida- 
tion in  the  presence  of  moisture,  is  attended  with  tlic  formation  of 
ammonia.  The  hydrogen,  at  the  moment  of  its  liberation  from 


92 


SOUKCES  OF  AMMONIA. 


tlie  water  by  deoxidation,  appears  to  enter  into  combination  with 
tlie  nitrogen  of  the  atmosphere,  which,  to  a small  extent,  is  held 
in  solution,  and  thus  ammonia  is  formed.  If  a current  of  nitric 
oxide  be  transmitted  over  a mixture  of  hydrate  of  potash  and 
slaked  lime,  nitrates  of  potassium  and  calcium  are  formed,  while 
ammonia  is  generated.  Moistened  iron  filings,  if  exposed  to  the 
air,  become  rusty,  and  the  oxidized  compound  retains  a small 
quantity  of  ammonia.  The  deoxidation  of  dilute  nitric  acid  by 
the  metals  also  frequently  gives  rise  to  the  production  of  ammonia  ; 
both  nitrogen  and  hydrogen  are  liberated  simultaneously,  a part 
of  the  water  undergoing  deoxidation  at  the  same  time  that  the 
acid  is  decomposed.  Tin,  zinc,  and  iron  exhibit  this  effect  in  a 
marked  degree  (p.  78). 

This  reaction  has  been  used  as  a means  of  estimating  the 
quantity  of  nitric  acid  in  solutions ; for  by  dissolving  zinc  very 
slowdy  in  diluted  hydrochloric  acid,  and  adding  the  nitric  solution 
in  small  quantities  at  a time,  the  whole  of  the  nitric  acid  is  con- 
verted into  ammonia.  (ISTesbit,  Q.  J.  Chem.  Soc.  i.  681.)  Har- 
court  has  improved  upon  this  method  («/.  Chem.  Soc.  1862,  xv.  381) ; 
he  distils  the  concentrated  liquid  with  caustic  potash  and  a mixtm’e 
of  granulated  zinc  and  iron  turnings,  and  receives  the  distillate  con- 
tainincr  the  ammonia  into  a known  weis'ht  of  a standard  solution 
of  sulphuric  acid.  'When  a mixture  of  2 volumes  of  nitric  oxide 
and  5 of  hydrogen  is  transmitted  over  spongy  platinum  or  plati- 
nized asbestos  gently  heated,  water  and  ammonia  are  produced. 
Iladow  has  also  observed  the  formation  of  ammonia  when  nitrous 
acid  or  peroxide  of  nitrogen  is  reduced  by  transmitting  either  of 
them  through  a solution  of  sulphide  of  potassium  and  hydrogen 
(KHS)  or  through  one  of  ferrous  acetate. 

Ammonia  exists  in  minute  quantity  in  the  atmosphere.*  It  is 
also  found  in  clayey  and  in  peaty  soils,  both  of  which  absorb  it 
freely.  AYhen  azotised  matters  are  heated  with  the  hydi’ated 


* According  to  the  elaborate  researches  of  Ville,  which  appear  to  have  been  con- 
ducted with  every  precaution  to  ensure  accuracy,  10,000,000,000  parts  of  air  contained 
on  the  average,  in  the  year  1851,  237  parts  by  weight  of  ammonia,  and  in  1852,  210 
parts.  This  amounts  to  about  one  volume  of  ammonia  in  twenty-''  ght  million  volumes 
of  air : other  experimenters  make  the  quantity  considerably  higher.  The  proportion 
of  ammonia  contained  in  rain  water  is  liable  to  considerable  variation:  m 1,000,000 
parts  of  rain  water  collected  in  Paris  during  the  last  five  months  of  1851,  Barral 
found  3'49  parts;  Boussingault,  at  Liebfraunberg,  in  1852,  found  only  0-744  parts; 
and  Lawes  and  Gilbert,  at  Rothamstead,  in  1853  and  1854,  found  the  average  amount 
from  Mardi  to  August  to  be  1-142,  from  September  to  February,  0 927  parts:  the 
average  of  the  two  last  determinations  would  give  about  1 grain  of  ammonia  in  14 
gallons  of  rain  water.  Boussingault  has  corroborated  Barral’s  results  by  experiments 
upon  the  rain  collected  in  Paris ; indeed  it  is  not  surprising  that  in  a populous  city, 
crowded  with  animal  life,  and  with  the  exuviae  of  animals,  the  proportion  of  ammonia 
in  its  atmosphere  should  be  much  higher  than  in  the  surrounding  districts.  It 
appears,  also,  that  a larger  quantity  of  ammonia  is  always  contained  in  the  water  that 
is  collected  at  the  commencement  of  a shower  than  at  the  end  of  it,  and  more  after  a 
drought  than  after  a period  of  rainy  weather.  In  the  water  of  dews  and  fogs,  also, 
the  amount  of  ammonia  was  found  to  be  much  higher  than  in  rain  water.  The  pro- 
portion of  ammonia  in  water  derived  from  the  atmosphere  is,  in  short,  greater,  the 
smaller  the  faU,  a circumstance  which  is  easily  accounted  for  by  the  high  solubility 
of  the  gas  in  water.  The  atmospheric  supply  of  ammonia  is  intimately  connected  with 
the  storing  of  nitrogen  in  plants. 


PKEPAKATION  AND  PROPERTIES  OF  AlkEVIONIACAL  GAS. 


93 


alkalies,  they  are  decomposed,  and  the  whole  of  the  nitrogen, 
unless  present  in  the  form  of  nitrate  or  cyanide,  is  disengaged  as 
ammonia  ; upon  this  fact  is  based  the  method  of  determining  the 
amount  of  nitrogen  in  organic  compounds.  For  the  purposes  of 
manufacture  ammonia  is,  however,  always  procured  by  the  distil- 
lation, in  closed  vessels,  of  organic  matters  containing  nitrogen. 
During  the  distillation  of  bones,  and  of  animal  refuse  generally, 
ammonia  in  considerable  quantity  is  formed,  and  condensed  along 
with  the  foetid  products  of  the  operation.  But  the  principal  part 
of  the  ammonia  used  in  this  country  is  obtained  from  the  refuse 
products  of  the  distillation  of  coal  for  the  manufacture  of  gas. 
Amongst  these  products  are  water,  and  a considerable  quantity  of 
carbonate  and  sulphide  of  ammonium  ; the  ammoniacal  salts  be- 
come dissolved  in  the  water,  and  constitute  the  ammoniacal  liquor 
of  the  gas-works  ; this  liquor  is  saturated  subsequently  with  sul- 
phuric or  with  hydrochloric  acid,  and  thus  the  sulphate  or  muriate 
of  ammonia  of  commerce  is  procured  (61Y). 

Preparation. — If  equal  weights  of  quicklime  and  either  of  the 
salts  last  named  be  separately  powdered  and  intimately  mixed, 
the  powder,  on  being  transferred  to  a retort  and  gently  heated, 
gives  off  abundance  of  pure  ammonia,  as  a transparent,  colourless 
gas,  of  the  peculiar,  pungent  odour  of  smelling  salts.  An  ounce 
of  muriate  of  ammonia,  if  fully  decomposed,  would  yield  about 
380  cubic  inches  of  the  gas.  The  lime  combines  with  the  acid 
and  sets  the  ammonia  at  liberty;  the  result  when  muriate  of 
ammonia  is  used  admitting  of  representation  as  follows  : — 


Fig.  292. 


Lime.  Mur.  ammonia.  Chloride  calcium.  Ammonia.  Water. 

OaO  + 2~H]ia  = -^Cl,  + 2 + H^. 

Properties. — Ammonia  produces  a flow  of  tears  from  the  eyes  ; 
it  has  an  acrid  taste,  and,  when  breathed  in  a concentrated  form,  is 
fatal  to  life,  from  its  irritating  effects  on  the  lungs.  In  a more  dilu- 
ted form  it  is  a highly  valuable  stimulant.  Ammonia  does  not  sup- 
port the  flame  of  burning  bod- 
ies, but  is  feebly  combustible  ; 
a jet  of  the  gas  directed  across 
the  stream  of  hot  air  issuing 
from  a lighted  argand  lamp, 
burns  with  a very  pale  green 
flame.  If  the  gas  be  mingled 
with  an  equal  bulk  of  oxygen, 
the  mixture  may  be  detonated 
liy  means  of  the  electric  spark  ; 
water,  nitrogen,  and  traces  of 
nitric  acid  are  formed.  If  a 
mixture  of  ammonia  and  air 
or  oxygen  be  passed  over  spon- 
gy platinum,  water  and  nitric 
acid  are  amongst  the  products. 

Ammonia  is  extremely  soluble  in  water,  and  must  therefore  be 


94: 


PROPERTIES  OF  A^IMOXIA. 


collected  either  over  mercury,  or  by  displacement,  in  the  man- 
ner &ho^vn  in  tig.  292.  The  latter  mode  of  collecting  it  may  easily 
be  effected,  as  the  gas  has  little  more  than  half  the  density  of 
atmospheric  air,  its  sp.  gr.  being  only  0‘59.  Ammonia  has  a pow- 
erful alkaline  reaction,  and  turns  turmeric  paper  brown.  A"hen 
collected  by  displacement,  the  gas  must  be  allowed  to  pass  into 
the  bottle  until  a piece  of  dry  turmeric  paper  held  to  the  mouth 
of  the  bottle  is  immediately  turned  brovm  ; the  tube  is  then 
withdrawn,  and  the  stopper,  slightly  greased,  is  inserted. 

Ammonia  neutralizes  the  most  powerful  acids,  and  forms  a 
very  important  class  of  salts.  Any  volatile  or  gaseous  acid 
brought  into  an  atmosphere  containing  ammonia,  produces  a 
white  cloud,  owing  to  the  formation  of  a solid  salt.  The  property 
is  often  employed  to  detect  small  quantities  of  ammonia ; slaked 
lime  or  hydrate  of  potash  is  mixed  with  the  solution  suspected  to 
contain  ammonia,  and  the  whole  gently  warmed  in  a tube ; a rod 
moistened  with  hydrochloric  acid  diluted  vdth  half  its  bulk  of 
water  is  then  placed  in  the  upper  part  of  the  tube  or  vessel,  and 
if  ammonia  be  present,  white  fumes  appear,  even  when  the  quan- 
tity of  ammonia  is  too  small  to  be  distinguished  by  the  smell. 
When  ammoniacal  gas  is  required  in  a state  free  from  moisture  it 
must  be  transmitted  over  quicklime,  not  over  chloride  of  calcimn  ; 
for  this  salt,  as  well  as  many  other  saline  compounds,  absorbs 
ammonia  and  forms  with  it  a definite  compound  (622). 

Ammoniacal  gas  may  be  liquefied  by  exposure  to  a cold  of 
— 4:0°  F.,  or  still  more  readily  by  generating  it  under  the  pressiu’e 
of  its  own  atmosphere.  The  easiest  method  is  the  following : — 
Chloride  of  silver  in  powder  is  exposed  to  a cmTent  of  dry  ammo- 
niacal gas ; the  ammonia  is  rapidly  absorbed,  and  the  chloride 
increases  in  weight  more  than  one-third.  This  substance  is  placed 
in  one  limb  of  a strong  tube  bent  to  an  obtuse  angle,  and  then 
hermetically  sealed ; on  applying  heat  to  the  chloride,  and  cooling 
the  other  end  of  the  tube  with  a freezing  mixture,  the  ammonia 
is  condensed  as  a colourless  liquid,  which  boils  at  —3 7° *3  (Feg- 
nault),  exerts  a pressure  of  6-9  atmospheres  at  60°,  and  has  a 
specific  gravity  of  0-731  at  60°  (Faraday;  or  0-614:,  Andreeff). 
By  a cold  of  —103°  it  is  frozen  to  a white,  translucent,  crystalline 
solid,  which  is  denser  than  the  liquid.  The  chloride  of  silver 
re-absorbs  the  liquefied  ammonia  at  ordinary  temperatm-es,  and 
slowly  reproduces  the  original  compound.- 

Composition. — The  composition  of  ammonia  may  be  ascer- 
tained as  follows : — If  the  dry  gas  be  subjected  to  a succession  of 
electric  sparks,  by  the  aid  of  Buhmkorff's  coil,  or  if  it  be  passed 
slowly  through  a porcelain  tube  containing  iron  or  copper  tm-n- 
ings,  heated  to  bright  redness,  the  gas  is  decomposed ; it  becomes 
dilated  to  double  its  volume : 2 volumes  of  ammonia  become  4 ; 
and  the  gas  produced  may  be  shown,  by  detonating  a portion  of 
it  with  oxygen,  to  consist  of  a mixture  of  1 volume  of  nitrogen 
with  3 volumes  of  hydrogen.  If,  after  mixing  8 measures  in  the 
bent  eudiometer  with  1 of  oxygen,  so  as  to  make  12  measures  in 
the  whole,  the  electric  spark  be  transmitted,  3 measures  will  be 


COMPOSITION  AND  SOLUTION  OF  AMMONIA. 


95 


left,  owing  to  the  formation  of  steam  and  its  subsequent  conden- 
sation. Since  in  the  formation  of  water  2 measures  of  hydrogen 
combine  with  1 measure  of  oxygen,  one-third  of  the  volume  of 
gas  which  has  disappeared,  or  3 measures,  will  be  oxygen,  and 
two-thirds,  or  6 measures,  will  be  hydrogen.  On  agitating  the 
residual  gas  with  a solution  of  hydrate  of  potash,  no  change  of 
bulk  will  occur,  consequently  no  carbonic  anhydride  can  have 
been  formed ; but  on  the  addition  of  pyrogallic  acid  {n,ote^  p.  53) 
to  the  gas  while  still  in  contact  with  the  alkaline  liquid,  the 
excess  of  oxygen  will  be  absorbed.  This  wdll  amount  to  1 meas- 
ure, whilst  2 measures  of  nitrogen  remain  unacted  upon ; 2 
measures  of  nitrogen  must  therefore  have  been  present  in  the 
ammonia  in  combination  with  the  6 of  hydrogen  which  have 
become  condensed  as  steam ; consequently,  since  the  ammonia 
doubles  its  volume  when  decomposed  by  heat,  the  4 volumes  of 
ammonia  must  have  been  formed  by  6 volumes  of  hydrogen  and 
2 of  nitrogen,  condensed  into  half  their  bulk.  The  composition 
of  ammonia  may  therefore  be  thus  represented  : — 

By  weight.  By  vol.  Sp.  gr. 

Hydrogen  H3  = 3 or  17*65  3 or  1*5  = 0*1036 

Nitrogen  N = 14  82*35  1 0*5  = 0*4860 

Ammonia  H3N  17  100*00  2 1*0  0*5896 

Other  striking  proofs  of  the  composition  of  ammonia  are 
afforded  by  the  action  of  heat  upon  some  of  its  salts.  The 
decomposition  of  nitrate  of  ammonium  offers  one  of  these  : by  the 
action  of  lieat,  as  already  explained  (364),  the  nitrate  of  ammo- 
nium (K^NNO^)  is  decomposed  into  water  and  nitrous  oxide, 
2 H^O  + 'Nfi- ; the  4 atoms  of  hydrogen  in  the  ammonia  com- 
bining wdth  2 of  oxygen  in  the  nitric  acid  radicle,  and  leaving  the 
nitrogen  of  the  ammonia  to  combine  with  nitric  oxide  derived 
from  the  nitric  acid.  If  a solution  of  the  nitrite  of  ammonium 
be  heated,  the  salt  is  decomposed,  water  and  pure  nitrogen  are 
liberated:  the  result  may  be  thus  represented,  II^NNO^  = 
2 II^O  + : the  hydrogen  of  the  ammonium  is  in  this  case 
exactly  sufficient  to  combine  with  the  oxygen  of  the  nitrous  acid 
radicle,  forming  water : this  is  an  excellent  mode  of  obtaining 
pure  nitrogen."^  Chlorine  also  decomposes  ammonia  at  ordinary 
temperatures,  and  liberates  nitrogen  gas.  Under  certain  circum- 
stances it  produces  the  detonating  compound  known  as  chloride 
of  nitrogen  (386).  Bromine  and  iodine  likewise  decompose  ammo- 
nia, and  form  similar  detonating  compounds,  without  producing 
any  liberation  of  nitrogen. 

370)  Solution  of  Ammonia. — A solution  of  ammonia  in  water 

* When  nitrogen  is  to  be  procured  in  this  way,  the  most  convenient  method 
consists  in  preparing  nitrite  of  potassium  by  saturating  a solution  of  hydrate  of 
potash,  of  sp.  gr.  1*38,  with  nitrous  acid  disengaged  by  acting  upon  starch  with 
nitric  acid  of  sp.  gr.  1*25.  This  solution,  if  it  be  left  slightly  alkaline,  may  be  pre- 
served without  alteration.  When  it  is  wanted  for  the  preparation  of  nitrogen,  the 
liquid  is  to  be  mixed  with  three  times  its  bulk  of  a saturated  solution  of  sal  ammo- 
niac, and  gently  heated  in  a small  retort : nitrogen  is  evolved  abundantly,  and  with 
great  regularity  (Coreuwinder). 


96 


SOLUTIOX  OF  AMMONIA. 


is  a reagent  continnallY  required  in  tlie  laboratory.  "When  am- 
moniacai  gas  is  passed  into  water  it  is  rapidly  absorbed,  with 
considerable  extrication  of  heat ; at  a temperature  of  32°,  Cariiis 
found  that  water  takes  up  about  1050  times  its  volume  of  the 
gas  ; at  59°,  727  times  its  volume  ; and  at  78°,  586  times  its 
volume  : water  saturated  with  ammonia  at  60°  contains  more 
than  one-third  of  its  weight  of  the  gas,  increasing  in  bulk  nearly 
one-half,  and  becoming  specifically  lighter.  The  follovdng  table 
indicates  the  strength  of  solutions  of  pure  ammonia  of  dilferent 
specific  gra^fities : — 


Strength  of  Solutions  of  Ammonia  at  57°  F.  {Cariiis.) 


Ammonia 
in  100 
parts  by 
weight. 

Specific 

gravity. 

[ Ammonia 

1 in  100 
: parts  by 
weight. 

1 

Specific  j 
gravity.  1 

i ; 

1 Ammonia 
in  100 
parts  by 
weight. 

1 : 

j Specific  i 
j gravity. 

Ammonia 
in  100 
parts  by 
weight. 

Specific 

gravity. 

36 

; 0-8844 

27 

0-9052  i 

18 

1 0-9314  ; 

9 

0-9631 

35 

0-8864 

26 

0-9078  1 

17 

0-9347 

1 8 

0-9670 

34 

0-8885 

25 

0-9106 

16 

0-9380 

7 

0-9709 

33 

0-8907 

24 

0-9133 

15 

0-9414  ! 

1 8 

0-9749 

32 

0-8929 

23 

0-9162 

14 

0-9449  ! 

I 5 

0-9790 

31 

0-8953 

22 

0-9191 

13 

0-9484  i 

4 

0-9831 

30 

0-8976 

21 

0-9221 

12 

0-9520  ! 

3 

0-9873 

29 

0-9001 

20 

0-9251 

11 

0-9556  ! 

9 

0-9915 

28 

0-9026 

19 

0-9283 

10 

0-9593  ! 

1 

0-9959 

Solution  of  ammonia  is  colourless  and  intensely  alkaline ; it 
has  an  acrid,  caustic  taste,  and  blistei's  the  skin  if  applied  to  it  in 
a concentrated  form;  it  freezes  at  about  —10°  F.,  yielding  a gela- 
tinous mass,  destitute  of  odour.  Simple  exposime  of  the  solution 
at  ordinary  temperatures  to  the  air  is  attended  with  an  escape  of 
the  gas,  which  occasions  the  pungent  smell  of  the  liquid.  By 
heat  the  ammonia  is  ex|3elled  rapidly,  with  the  appearance  of 
ebullition,  thereby  furnishing  a ready  extempore  method  of  pro- 
curing the  gas.  By  heating  the  liquid  for  some  time,  the  whole 
of  the  ammonia  may  be  cbiven  off',  so  that  nothing  but  water  is 
left  in  the  retort. 

Solution  of  ammonia  is  prepared  on  the  large  scale  by  mixing 
together  in  a capacious  retort  equal  weights  of  well-burned  quick- 
lime and  sal  ammoniac ; the  lime  is  slaked  and  made  into  a paste 
with  water  before  mixture.  The  retort  is  then  connected  with  a 
series  of  bottles  similar  to  those  used  for  condensing  nitric  acid. 
If  the  operation  be  conducted  on  the  small  scale  in  the  laboratory, 
the  arrangement  shown  in  fig.  293  may  be  adopted.  The  three- 
necked bottles,  B,  c,  D,  E,  are  known  by  tlie  name  of  "Woulfe’s 
bottles ; in  the  globe,  a,  a small  quantity  of  water  is  placed,  to 
retain  any  solid  particles  which  may  be  mechanically  carried  over 
by  the  gas ; in  the  first  bottle,  b (which  may  be  kept  cool  by 
immersion  in  cold  water),  a quantity  of  water  equal  in  weight  to 
that  of  the  sal  ammoniac  used  is  introduced,  taking  care  that  it 
shall  not  fill  more  than  half  the  capacity  of  the  bottle,  whilst  the 
second  contains  water  to  condense  any  gas  that  may  escape 
through  the  first.  Each  bottle  is  provided  with  a safety  tube 


WOULFE’s  bottles AMLOOGEN. 


97 


open  at  both  ends,  so  that  if  the  gas  were  absorbed  in  b,  for 
example,  more  rapidly  than  it  was  supplied,  instead  of  the  liquid 
being  driven  back  from  the  bottle,  c,  air  would  enter  by  the  safety 
tube,  and  the  equilibrium  would  be  restored.  The  tube  which 
delivers  the  gas  passes  down  through  the  safety  tube,  and  projects 


Fig.  293. 


a little  beyond  its  lower  opening,  so  that  the  gas  rises  in  bubbles 
through  the  liquid  .and  collects  in  the  bottle;  an  air-tight  joint, 
which  can  be  mounted  and  dismounted  immediately,  is  thus 
obtained. 

Solution  of  ammonia,  if  pure,  should,  when  evaporated,  leave 
no  solid  residue ; the  presence  of  carbonic  acid  may  be  detected 
by  lime-water,  which  it  renders  milky ; that  of  chlorine  by  acidu- 
lating slightly  with  pure  nitric  acid,  and  adding  nitrate  of  silver, 
when  it  gives  a white  cloud ; that  of  sulphuric  acid  by  a white 
precipitate  with  nitrate  of  barium  after  dilution  and  saturation 
with  nitric  acid ; that  of  lime  by  a white  precipitate  on  adding 
oxalate  of  ammonium ; and  that  of  copper  or  lead  derived  from 
the  apparatus,  by  a black  or  brown  precipitate  or  cloud  with  sul- 
phuretted hydrogen.  Lead  in  small  quantity  is  a very  frequent 
impurity  in  the  commercial  solution ; it  is  usually  derived  from 
the  action  of  the  ammonia  on  the  flint-glass  bottles  in  which  it  is- 
often  improperly  kept. 

Alcohol  also  dissolves  ammonia  in  abundance. 

The  salts  of  ammonia  will  be  described  with  those  of  the- 
other  alkalies. 

(371)  Amidogen  (ITjK^lG). — Ammonia  is  the  only  compound 
of  hydrogen  and  nitrogen  that  has  been  obtained  in  the  isolated 
form.  IVlien,  however,  potassium  is  heated  gently  in  perfectly 
dry  ammoniacal  gas,  the  ammonia  disappears,  half  its  volume  of 
hydrogen  is  liberated,  and  a fusible,  olive-green  compound  is 
formed,  consisting  of  KH,N.  The  ammonia  is  decom]>osed  by  tlie 
potassium  in  the  following  manner : 2 Ilghf  -f  becomes 
2 KlIjN  -f  II^.  The  compound  II^hT  has  received  the  name  of 
7 


98 


AI^IMONIUM THE  HALOGENS. 


amidogen^  and  is  supposed  by  some  chemists  to  be  capable  of 
existing  in  combination  with  several  metals  and  with  a variety  of 
bodies  derived  from  the  organic  kingdom,  though  late  researches 
have  rendered  it  more  probable  that  all  these  bodies  are  to  be 
regarded  as  substitution-products  formed  upon  the  type  of  ammonia. 
Compounds  of  this  class  have  received  the  name  of  amides  / they 
will  be  more  conveniently  examined  hereafter. 

Ammonium  (H^IST^IS). — This  compound,  as  is  the  case  with 
amidogen,  has  not  been  obtained  in  a separate  form.  All  the^ 
usual  so-called  salts  of  ammonia,  however,  appear  to  contain  it. 
Nitrate  of  ammonium,  for  example,  consists  not  simply  of  HgN, 
NOg,  but  of  Il3N,HO,NO„  that  is,  it,  in  addition,  contains  the 
elements  of  water,  which  cannot  be  expelled  by  heat  without  the 
entire  decomposition  of  the  salt ; this  nitrate  is  therefore  looked 
upon  as  a nitrate  of  ammonium,  H4N0,N05,  or  Sal 

ammoniac  is  on  this  view  regarded  as  chloride  of  ammonium 
N,C1.  The  full  discussion  of  the  grounds  upon  which  this  theory 
rests  will  be  best  postponed  till  we  enter  upon  a description  of  the 
salts  of  ammonia  (610  et  seg.). 


CHAPTEE  YI.  • 

THE  HALOGENS. 

(372)  Befoke  proceeding  to  notice  some  other  compounds  of 
the  four  elements  already  described,  it  will  be  desirable  to 
examine  the  other  non-metallic  simple  substances.  We  pass  on, 
therefore,  to  a group  of  four  closely  allied  bodies,  viz.,  chlorine, 
bromine,  iodine,  and  fluorine.  These  elements  are  characterized 
by  the  powerful  activity  of  their  chemical  attraction  for  other 
substances  at  the  ordinary  temperature  of  the  air;  and  conse- 
quently none  of  them  are  found  in  an  uncombined  state.  They 
form  with  the  metals  compounds  analogous  to  sea  salt,  and  have 
been  termed  halogens^  or  salt-producers  (from  aX^,  sea  salt). 

§ I.  Chlokine  : Cl=35’5  ; Theoretic  Sp.  Gr.  2*453/  Observed 
Sjp.  Gr.  2*47  / Atomic  Yol.  [ |.* 

(373)  Chloeine,  the  most  important  member  of  the  group  of 
halogens,  was  discovered  by  Scheele  in  1774.  It  is  abundantly 
met  with  in  combination  with  sodium,  with  which  it  constitutes 
ordinary  table  salt.  This  necessary  of  life  occurs  plentifully  in 

* Many  chemists  regard  pure  chlorine  as  chloride  of  chlorine,  and  consequently 
its  molecular  volume  would  be  (ClCl)  = 2 vols.  or  frl  |.  The  molecular  volume 
of  all  the  halogens  in  their  free  state  will  be  2,  if  that  of  chlorine  be  so  regarded  ; 
the  free  substances  being  viewed  respectively  as  chloride  of  chlorine,  bromide  of 
bromine,  iodide  of  iodine. 


PKOPERTIES  OF  CHLOKINE BLEACHING  ACTION. 


99 


beds  in  various  parts  of  the  world,  and  is  tlie  most  abundant  of 
the  saline  bodies  contained  in  tlie  waters  of  the  ocean.  It 
contains  rather  more  than  60  per  cent,  of  chlorine. 

Properties. — Chlorine  is  a transparent  gas  of  a greenish-yellow 
colour  (whence  the  name  is  derived,  from  green,)  and  of 

a powerful  suffocating  odour,  producing,  if  breathed,  even  when 
largely  diluted  with  air,  distressing  irritation  of  the  air  passages, 
attended  with  coughing.  It  is  much  heavier  than  air,  100  cubic 
inches  weighing  between  77  and  78  grains.  Under  a pressure  of 
4 atmospheres  at  60°,  it  is  condensed  to  a yellow,  limpid  liquid,  of 
sp.  gr.  about  1’33  ; it  does  not  conduct  electricity,  and  remains 
unfrozen  even  at  the  cold  of  — 220°.  Chlorine  is  soluble  in 
about  half  its  bulk  of  cold  water ; this  solution,  which  is  readily 
formed  by  agitating  the  gas  and  water  together,  has  the  colour, 
odour,  and  astringent  taste  of  the  gas.  According  to  Schdnfeld, 
water  at  50°  dissolves  2*585  times  its  bulk  of  the  gas ; at  59°, 
2*368,  and  at  104°,  1-365  times  its  bulk.  Chlorine,  in  consequence 
of  this  solubility,  cannot  be  advantageously  collected  over  cold 
water.  Mercury  is  acted  upon  by  the  gas  with  great  rapidity. 
It  is  necessary,  therefore,  either  to  use  warm  water  in  the 
pneumatic  trough,  or  to  receive  the  gas  by  the  process  of 
displacement  in  dry  bottles.  With  water,  chlorine  forms  a 
definite  hydrate  (Cl,  5 142^),  which  crystallizes  at  32°  ; if 
it  be  enclosed  in  hermetically  sealed  tubes,  it  furnishes  a ready 
method  of  obtaining  liquefied  chlorine,  since  it  is  easily 
decomposed  by  a gentle  heat  into  water  and  free  chlorine ; 
the  latter  amounts  to  about  one-fourth  of  the  volume  of  the 
liquid. 

Chlorine  is  not  combustible,  and  it  does  not  combine  directly 
Avith  oxygen.  A taper  burns  in  it  with  a reddish,  smoky  fiame, 
the  hydrogen  of  the  combustible  vapour  of  the  wax  combining 
with  the  chlorine,  whilst  part  of  the  carbon,  for  which  its  chemi- 
cal attraction  is  but  small,  is  deposited.  Many  bodies,  however, 
take  fire  spontaneously  when  introduced  into  chlorine  ; this  is 
the  case  with  phosphorus  : many  of  the  metals  in  a finely  divided 
state  do  the  same  ; among  them  are  copper  leaf,  finely  powdered 
antimony  and  arsenicum.  A great  number  of  organic  substances 
rich  in  hydrogen  are  decomposed  by  chlorine,  sometimes  with  such 
rapidity  as  to  inflame  them  ; a bit  of  paper  dipped  into  oil  of  tur- 
pentine and  plunged  into  the  gas  bursts  into  flame,  and  deposits 
an  abundance  of  a black  carbonaceous  compound. 

The  action  of  chlorine  upon  bodies  containing  hydrogen  is 
often  of  a very  peculiar  kind.  It  combines  with  part  of  the 
hydrogen  and  withdraws  it  from  the  comliination ; each  atom  of 
hydrogen  uniting  witli  an  equivalent  of  chlorine,  and  forming  a 
powerful  acid,  the  hydrochloric  (IICl) ; whilst  at  tlie  same  time 
for  each  atom  of  hydrogen  so  withdrawn  from  the  original  com- 
pound, an  equivalent  oi  chlorine  is  substituted.  It  is  in  this  way 
that  chlorine  exerts  those  bleaching  powers  which  have  rendered 
so  essential  a service  to  the  calico-printer  and  the  paper-maker. 
Most  of  the  vegetable  colouring  matters  contain  hydrogen,  and 


100 


MAXTTACrrKE  OF  CHLOEIXE. 


are  decomposed  by  chlorine,  whilst  colourless,  or  nearly  colour- 
less, compoimds  containing  chlorine  are  formed  instead  of  the 
coloirred  compounds  with  hydrogen.  If  a solution  of  chlorine  be 
mixed  with  some  of  the  bine  hqnid  formed  by  dissolving  indigo 
in  sulphuric  acid,  or  with  ordinary  wilting  ink,  or  with  tincture 
of  litmus,  the  colom’  will  in  each  case  be  immediately  and  almost 
completely  discharged,  and  it  cannot  be  subsequently  restored. 

Another  property  of  chlorine  of  great  value  is  its  disinfecting 
power, — by  which  is  meant  its  power  of  destroying  noxious 
vapoius  and  miasmata ; with  this  wew  it  is  frequently  employed  for 
fmnio’ating  buildings  after  the  occiurence  of  contagions  diseases. 

Preparation. — 1.  Chlorine  may  be  easily  prepared  from  a mix- 
ture of  lO-J  parts  by  weight  of  oil  of  vitriol,  previously  diluted  with 
7 parts  of  water,  and  allowed  to  cool,  and  ^ parts  of  pounded 
chloride  of  sodium  mixed  intimately  with  3 parts  of  finely  pul- 
verized black  oxide  of  manganese.  The  decomposition  may  be 
represented  as  follows  : — 


Oxide  Chlor.  Sulph. 

mang.  sodium.  Sulph.  acid.  mangan.  Sulphate  of  sodium.  Water.  Chlorine. 


MnOg  + 2 NaCl  + 3 H2SO4  = + 2 XaHSO-4  + 2 H2O  + CU* 


The  gas  comes  ofiT  slowly  in  the  cold,  but  freely  on  the  application 
of  a gentle  heat.  A little  hydrocliloric  acid  is  always  formed  in 
tlie  reaction  ; this  acid  is  easily  removed  from  the  chlorine  by 
allowing  the  gas  to  bubble  up  through  a vessel  containing  water, 
in  the  manner  shown  in  fig.  289,  where  a similar  apparatus  is 
employed  for  carbonic  oxide. 

2. — The  preparation  of  chlorine  is  practised  on  an  enormous 
scale  in  the  manufacture  of  bleaching  powder,  or  cldoride  of  lime. 
It  is  generally  prepared  in  capacious  stills,  suflicientlv  large  to 
hold  200  gallons  of  liquid ; these  are  usually  made  of  Yorkshire 
flags  clamped  together  with  ironwork,  and  the  joints  rendered 
tight  by  vulcanized  caoutchouc.  Tlie  lower  part  of  these  stills  is 
enclosed  in  a case  through  which  a current  of  steam  is  transmitted. 
Hydrochloric  acid  in  solution,  of  specific  graHty  from  1‘160  to 
IT 70  (which  is  obtained  as  a waste  product  in  the  manufacture 
of  carbonate  of  sodium  from  sea  salt),  is  run  throusch  a curved 
funnel  into  the  stills,  which  are  charged  with  oxide  ot  manganese 
in  small  lumps.  Chloride  of  manganese  is  formed,  and  free  chlo- 
rine is  liberated  in  abundance  ; the  reaction  is  illustrated  by  the 
following  symbols  : — 

Oxide  mangan.  Hydrochlor.  acid.  Chlor.  mangan.  Water.  Chlorine. 

MnO,  + 4HC1  = HnCl,  -f  2 H,e  + Cl,. 

This  process  may  also  often  be  resorted  to  on  the  small  scale  in 
the  laboratory  with  advantage.  Three  oimces  of  powdered  oxide 
of  manganese  ^rith  half  a pint  of  the  commercial  mmlatic  acid 
diluted  with  3 oimces  of  water,  will  yield  between  3 and  4 gallons 
of  the  gas.  Care  must  be  taken  not  to  use  an  acid  more  dilute 
than  1T5  in  the  preparation  of  the  gas  ; since,  owing  to  a neglect 


CHLOEIBES. 


101 


of  this  precaution,  explosions  have  in  some  instances  occurred  in 
operating  on  the  large  scale : hypochlorous  acid,  or  one  of  the 
lower  explosive  oxides  of  chlorine,  was  probably  formed  in  these 
cases. 

Uses. — Besides  the  application  of  chlorine  on  the  large  scale 
in  bleaching,  it  is  frequently  employed  for  disinfecting  purposes. 
In  the  laboratory  it  is  in  continual  requisition  as  an  oxidizing 
agent : owing  to  its  attraction  for  hydrogen  it  readily  decomposes 
water,  and  liberates  oxygen,  which  at  the  moment  that  it  is  set 
free  enters  readily  into  comlDination.  The  preparation  of  chlorate 
of  potassium  (382),  of  ferric  acid  (159),  and  of  the  peroxides  of 
cobalt  and  nickel  (720,  730),  afford  illustrations  of  this  mode  of 
employing  it ; and,  in  researches  upon  the  nature  of  many  com- 
pounds furnished  by  organic  chemistry,  it  often,  as  in  the  series 
of  compounds  obtained  from  Dutch  liquid  (488),  is  used  as  a 
means  of  throwing  light  upon  their  molecular  constitution. 

Chlorides. — Chlorine  combines  with  all  the  non-metallic  ele- 
ments, and  forms  with  many  of  them  compounds  of  great  impor- 
tance ; it  also  enters  into  combination  with  all  the  metals,  and  it 
combines  directly  with  a large  number  of  them,  wdth  the  usual 
phenomena  of  combustion ; the  compounds  which  it  forms  are 
termed  chlorides.  With  the  exception  of  the  chlorides  of  silver 
and  the  lower  chlorides  of  mercury  and  copper,  they  are  all  more 
or  less  soluble  in  water.  The  lower  chlorides  of  gold  and  plati- 
num and  chloride  of  lead  are  sparingly  soluble,  especially  the 
former  two.  It  frequently  happens  that  chlorine  combines  wdth 
the  same  metal  in  more  proportions  than  one  : for  example,  with 
iron,  ferrous  chloride  (BeCl2)  and  ferric  chloride  (Pe^Clg)  may  be 
formed ; with  platinum  the  compound  (PtCl2)  platinous  chloride, 
known  as  the  protochloride,  and  a second,  platinic  chloride  (PtCl^), 
usually  distinguished  as  the  bichloride,  may  be  obtained ; and 
generally,  for  each  basic  oxide  of  the  metal,  a corresponding 
chloride  exists  (538). 

Chlorine  when  in  solution  in  the  uncombined  form  is  easily 
recognised  by  its  odour  and  its  bleaching  properties.  Both  when 
free,  and  when  combined  with  a metal,  it  gives,  on  the  addition 
of  a solution  of  nitrate  of  silver,  a curdy,  flocculent,  white  precipi- 
tate which  changes  to  violet  on  exposure  to  light : this  white  pre- 
cipitate consists  of  chloride  of  silver,  and  is  easily  re-dissolved  by 
adding  a small  quantity  of  solution  of  ammonia,  but  it  is  insoluble 
in  nitric  acid.  When  free  chlorine  acts  upon  nitrate  of  silver, 
a small  quantity  of  chlorate  is  formed  wdth  the  chloride  : 
Cl«  -f  6 Ag]Sre3  H-  3 1120  = 5 AcrCl  -f  AgC103  -f  6 111703. 

(374)  IIydkochlorio  Acid  : Muriatic  Acid  (IICl  = 3(1 -5) ; 
Theoretic  Bp.  Gr.  1’2610;  Observed^  1'2474;  Atomic  and  Mol. 
^ ol.  I I |. — The  most  important  of  the  compounds  wdiich  chlo- 
rine forms  wdth  the  non-metallic  elements  is  that  obtained  by 
its  combination  with  hydrogen.  The  twm  gases  may  be  mixed  in 
equal  volumes,  and  they  will  remain  wdthont  action  upon  each 
other,  if  kept  in  the  dark  ; but  the  moment  that  they  are  lu’onght 
into  direct  sunlight  they  unite  wdth  a powerful  explosion,  and  a 


102 


HYDEOCHLOEIC  ACID. 


colourless,  intensely  acid  gas  is  tlie  product.  In  diffused  daylight 
the  combination  takes  place  gradually ; but  the  application  of  a 
lighted  match,  or  the  passage  of  the  electric  spark  through  the 
mixture,  instantly  determines  its  explosion.  One  volume  of 
chlorine  unites  thus  with  one  volume  of  liydrogen,  producing  2 
volumes  of  hydrochloric  acid ; no  condensation  therefore  occurs 
in  the  act  of  union.  The  composition  of  hydrochloric  acid  is  con- 
sequently the  following : — 


By  wetght.  By  vol.  Sp.  gr. 

Chlorine Cl  = 35-5  or  97'26  1 or  0-5  = 1-2265 

Hydrogen H = DO  2-74  1 0-5  = 0.0345 


Hydrochloric  acid HCl  = 36  5 100-00  2 1-0  = 1-2610 

So  powerful  is  the  attraction  of  chlorine  for  hydrogen,  that  if 
either  a solution  of  chlorine  in  water,  or  the  gas  itself  in  a moist 
state,  be  exposed  to  the  sun’s  rays,  water  is  decomposed,  hydro- 
chloric acid  is  formed,  and  the  oxygen  of  the  water  is  liberated : 
in  the  dark,  however,  chlorine  has  no  power  to  decompose  water. 

If  moist  chlorine  be  transmitted  through  a red-hot  porcelain 
tube,  hydrochloric  acid  is  formed,  and  oxygen  is  set  free  ; though, 
on  the  other  hand,  when  hydrochloric  acid  gas  is  mixed  with  air 
and  transmitted  through  an  ignited  porcelain  tube,  chlorine  is 
liberated  and  water  is  produced. 

The  composition  of  hydrochloric  acid  may  be  analytically 
determined  by  heating  sodium  in  a measured  volume  of  the  gas. 
The  metal  burns  vividly,  and  liberates  a quantity  of  hydrogen 
equal  in  bulk  to  that  of  half  the  gas  employed  ; common  salt  is 
formed  at  the  same  time.  Analogous  results  are  obtained  if  iron 
or  tin  be  substituted  for  sodium  ; chloride  of  iron  or  of  tin  being 
formed,  whilst  hydrogen  is  set  at  liberty. 

The  presence  both  of  hydrogen  and  of  chlorine  in  the  acid 
gas  is  easily  shown  by  the  following  experiment  (Graham)  : — A 
quantity  of  hydrochloric  acid  is  liberated  from  fused  chloride  of 
sodium  by  oil  of  vitriol,  contained  in  the  retort,  tig.  291,  and 


Fig.  294. 


is  dried,  by  being  passed  tlirough  a tube,  Z>,  tilled  witli  chloride  of 
calcium  : this  tube  is  connected  by  vulcanized  caoutchouc,  c,  with 
a tube  upon  which  two  bulbs  have  been  blown : in  the  tirst  of 
these,  some  pounded  anhydrous  black  oxide  of  manganese  is 


PEOPEETIES  AND  SOLUTION  OF  HYDEOCHLOEIC  ACID.  103 


placed : a piece  of  litmus-paper  inserted  in  the  bottle,  f \ which 
receives  the  escaping  gas,  is  quickly  reddened.  On  applying  heat 
to  the  bulb,  containing  the  oxide,  chloride  of  manganese  is 
produced,  and  not  being  volatile,  it  remains  in  the  bulb,  whilst 
water  is  formed  and  becomes  condensed  in  the  second  bulb,  e ; in 
the  meantime  free  chlorine  passes  on  into  the  bottle,  /*,  showing 
itself  by  its  peculiar  colour  and  its  bleaching  effect  upon  the 
litmus-paper.  The  reaction  has  already  been  explained,  and  may 
be  represented  by  the  following  symbols : 4 HCl  -f  MnO-2  = 
2 H,e  -f  MnCl,  -4-  Cl,. 

Preparation. — Hydrochloric  acid  gas  is  easily  procured  by  in- 
troducing fragments  of  common  salt  (which  has  been  fused  in  a 
crucible  at  a red  heat  and  allowed  to  cool)  into  a glass  retort,  and 
pouring  over  it  twice  its  weight  of  oil  of  vitriol.  Abundance  of 
hydrochloric  acid  gas  escapes ; it  must  be  collected  either  over 
mercury  or  by  displacement  of  the  air  from  dry  bottles.  An 
ounce  of  salt  yields  about  350  cubic  inches  of  the  gas.  In  this 
case  the  hydrogen  of  the  oil  of  vitriol  is  transferred  to  the  chlorine 
of  the  common  salt,  whilst  the  radicle  of  the  acid  combines  with 
the  sodium  and  forms  acid  sulphate  of  sodium,  as  is  shown  in  the 
following  equation : — 

Chloride  of  Oil  of  Hydrochlor.  Acid  sulph. 

sodium.  vitriol.  acid.  sodium. 

5^01  4-  HCl  + HaHSe,. 

Properties. — Hydrochloric  acid  is  a colourless  gas,  of  a peculiar, 
pungent  odour,  and  an  intensely  acid  taste ; it  irritates  the  eyes, 
and  if  breathed  even  when  largely  diluted  produces  coughing.  It 
is  also  very  injurious  to  vegetation,  causing  the  leaves  to  shrivel 
and  turn  brown.  It  is  heavier  than  air ; 100  cubic  inches  at  60° 
and  30  inches  Bar.  weighing  39*64  grains.  Under  a pressure  of 
40  atmospheres  at  50°  it  is  condensed  to  a colourless  liquid  of  sp. 
gr.  1*27,  which  dissolves  bitumen  ; it  has  never  been  frozen  ; the 
refracting  power  of  this  liquid  is  less  than  that  of  water.  Hydro- 
chloric acid  gas  is  incombustible,  and  extinguishes  burning  bodies. 
It  reddens  dry  litmus-paper ; when  allowed  to  escape  into  the  air 
it  produces  white  fumes  by  condensing  the  atmospheric  moisture, 
and  forming  witli  it  a body  less  volatile  than  pure  water.  It  is 
instantly  absorbed  by  water:  a lump  of  ice  liquefies  in  a jar  of 
the  gas,  and  absorbs  it  in  a moment. 

(375)  Solution  of  Hydrochloric  Acid. — The  solution  of  hydro- 
chloric acid  in  water  is  an  indispensable  requisite  in  the  labora- 
tory. It  is  easily  prepared  for  use  by  placing  in  a capacious 
retort  3 parts  of  fused  chloride  of  sodium  in  fragments,  and  intro- 
ducing gradually,  through  a bent  funnel,  5 parts  of  oil  of  vitriol. 
If  pounded  salt  be  used,  the  action  of  the  acid  is  apt  to  be  too 
rapid.  The  retort  is  connected  with  a series  of  Woulfe’s  bottles  ; 
in  the  first  a small  quantity  of  water  is  placed  to  detain  any  im- 
purities which  might  be  carried  over  mechanically  witli  tlie  gas ; 
the  second  bottle  may  contain  4 parts  of  water,  and  sliould  be 
immersed  in  a vessel  of  cold  water,  as  the  condensation  of  tlie  gas 


104 


SOLUTION  OF  HYDROCHLOKIC  ACID. 


is  attended  with  a great  disengagement  of  heat.  On  applying  a 
gentle  heat  to  the  retort  the  acid  comes  over  and  is  condensed ; 
an  easily  soluble  acid  sulphate  of  sodium  remains  in  the  retort,  as 
explained  above.  For  manufacturing  purposes  the  decomposition 
is  effected  in  iron  cylinders,  hke  those  employed  in  the  prepara- 
tion of  nitric  acid,  and  only  one-half  the  quantity  of  sulphuric  acid 
prescribed  above  is  used;  2 F’aCl  -f-  H^SO^  = 2 HCl  + FTa^SO^. 
The  acid  in  this  case  is  in  the  proportion  of  one  equivalent  to 
each  equivalent  of  salt,  neutral  sulphate  of  sodium  remaining  in 
the  cylinder,  whilst  the  acid  is  condensed  in  a series  of  salt -glazed 
stoneware  jars,  arranged  as  Woulfe’s  bottles.  Hydrochloric  acid 
is  largely  employed  in  the  arts,  particularly  in  the  preparation  of 
chlorine  as  a preliminary  to  the  manufacture  of  chloride  of  hme 
and  chlorate  of  potassium.  It  is  also  largely  used  as  a solvent  for 
tin  by  the  dyer  and  calico-printer,  as  well  as  in  the  manufacture 
of  sal  ammoniac. 

W ater  at  40°  absorbs  nearly  its  own  weight,  or  about  480  times 
its  hulk  of  hydrochloric  acid  gas,  increasing  in  volume  about  one- 
third,  and  acquiring  a density  of  1'2109.  It  forms  a colourless, 
fuming  liquid,  which,  by  a slight  elevation  of  temperature,  parts 
with  the  gas  abundantly  ; at  this  strength  it  contains  nearly  43 
per  cent,  of  acid,  which  is  about  the  proportion  indicated  by  the 
formula  (HCl.  3 HjO). 

If  the  strong  acid  be  placed  in  a retort,  and  distilled,  it  loses 
hydrochloric  acid,  until  the  liquid  which  remains  has  a density  of 
ITOO  at  60°  ; at  this  point  it  distils  unchanged.  A weaker  acid 
if  distilled  parts  with  its  water  freely,  until  it  acquires  the  density 
of  ITOO,  and  then  it  likewise  distils  unchanged,  at  a temperature 
of  233°.  Such  an  acid  contains  about  20  per  cent,  of  hydro- 
chloric acid,  and  corresponds  in  composition  with  the  formula 
(HCl . 8 H^O).*  Common  hydrochloric  acid  may  therefore  easily 
be  purified  by  dilution  till  it  has  a sp.  gr.  of  IT,  and  then  distill- 
ing, f Bineau,  by  concentration  of  the  acid  at  the  ordinary  tem- 
perature of  the  air  in  vacuo  over  sulphuric  acid,  obtained  a hydrate 
(HCl . 6 HjO)  of  sp.  gr.  1T28,  containing  25  per  cent,  of  the 
anhydrous  acid.  According  to  this  observer  (Ann.  de  Chimie.^ 
III.  vii.  259),  the  vapour  of  the  acid,  sp.  gr.  ITO,  has  a density 


* Eoscoe  and  Dittmar  {Q.  J.  Chem.  Soc.  xii.  128)  by  varying  the  pressure  under 
which  the  distillation  is  effected,  have,  however,  shown  that  this  apparent  constancy 
of  composition  is  really  an  accidental  circumstance,  and  that  there  is  no  definite 
hydrate  of  this  acid ; but  that  for  every  pressure  an  aqueous  solution  exists,  which, 
when  distilled  under  that  pressure,  possesses  a fixed  composition  and  fixed  boiling- 
point,  For  example,  when  distilled  under  a pressure  of  2 inches  of  mercury,  the  dis- 
tillate contained  23'2  per  cent,  of  hydrochloric  acid ; distilled  under  15  inches,  the 
per-centage  of  acid  was  21-3,  corresponding  to  the  formula  (2  HCl  . 15  H2O);  whilst 
under  a pressure  of  30  inches  the  per-centage  of  acid  was  reduced  to  20'24  (HCl . 8 H2O) ; 
if  distilled  under  a pressure  of  60  inches,  the  amount  of  acid  fell  to  19*0  ; and  under 
90  inches  as  low  as  18’2  of  HCl  per  cent. ; the  composition  of  the  liquid  in  the  last 
case  corresponding  nearly  to  (HCl , 9 H2O).  Water  at  32°,  according  to  these  obser- 
vations, dissolves  0*825  of  its  weight  of  hydrochloric  acid  gas,  under  a pressure  of  30 
inches  of  mercury ; and  at  60°  it  dissolves  0‘745  of  its  weight. 

■f  Chlorine,  however,  as  well  as  chloride  of  arsenic  and  sulphurous  acid,  passes 
over  with  the  distillate,  if  present. 


STKENGTH  OF  SOLUTIONS  OF  HYDEOCHLOEIC  AGED.  105 

of  0'69,  1 volume  of  tlie  acid  and  8 volumes  of  aqueous  vapour 
being  united  without  condensation. 

Commercial  hydrochloric  acid  is  liable  to  be  contaminated 
with  iron,  which  gives  it  a yellow  colour ; and  with  the  chlorides 
of  sodium  and  arsenic,  the  latter  derived  from  the  sulphuric  acid 
employed  in  its  preparation.  Sulphuric  and  sulphurous  acids  and 
free  chlorine  are  also  often  present  in  it.  If  pure,  the  acid  should 
leave  no  residue  when  evaporated  ; on  saturating  it  with  ammonia 
it  should  give  no  precipitate  of  oxide  of  iron  ; sulphuretted  hydro- 
gen should  produce  no  turbidity  in  it,  which  would  be  the  case  if 
arsenic,  free  chlorine,  or  sulphurous  acid  were  present ; and  on 
dilution  with  three  or  four  times  its  bulk  of  water,  no  white  cloud 
of  sulphate  of  barium  should  be  produced  by  the  addition  of 
chloride  of  barium.  Traces  of  sulphurous  acid  are  also  easily 
detected  by  Lowenthal’s  test,  which  consists  in  the  addition  of  a 
mixture  of  perchloride  of  iron  and  ferricyanide  of  potassium  : if 
sulphurous  acid  be  present,  Prussian  blue  is  formed  by  the  reduc- 
ing action  of  the  acid  on  the  mixture. 

The  following  table  contains  the  amount  by  weight  of  hydro- 
chloric acid  in  100  parts  of  solutions  of  the  acid  of  the  various 
densities  therein  enumerated,  at  a temperature  of  77°  : — 


Strength  of  Hydrochloric  Acid.  (H.  Davy.) 


Specific 

gravity. 

Hydrochloric 
acid  in  100  parts. 

Specific 

gravity. 

Hydrochloric 
acid  in  lOO  parts. 

1*21 

42*43 

1*10 

20-20 

1-20 

40-40 

1-09 

18-18 

1T9 

38-38 

1*08 

16-16 

1*18 

36-36 

1-07 

14  14 

1*17 

34-34 

1*06 

12*12 

1-16 

32-32 

1-05 

10*10 

1-15 

30  30 

1-04 

8-08 

1*14 

28*28 

1*03 

6-06 

1-13 

26*26 

1-02 

4*04 

1-12 

24-24 

1-01 

2-02 

1-11 

22-22 

A solution  of  hydrochloric  acid  is  decomposed  by  all  the 
metals  which  decompose  water  at  a red  heat : the  metal  is  dis- 
solved, and  hydrogen  gas  is  set  free,  just  as  when  iron  or  zinc  is 
acted  upon  by  diluted  sulphuric  acid  : for  example  ; 2 HCl  + Zii 

= Znci,  -h  ir,. 

(376)  Action  of  Hydrochloric  Acid  on  Metallic  Oxides. — The 
action  of  hydrochloric  acid  upon  the  oxides  of  the  metals  is  pecu- 
liar. Protoxides  are  dissolved  by  the  acid,  and  appear  to  combine 
with  it ; but  on  evaporating  the  liquid,  a compound  is  ol)tained  in 
which  neither  hydrochloric  acid  nor  the  metallic  oxide  is  present, 
and  which  contains  neither  hydrogen  nor  oxygen  ; doidde  decom- 
position ensues.  AVhen  tlie  oxide  of  a uni-equivalent  metal,  siicli 
as  thallium,  or  when  hydrate  of  soda,  for  exain[)le,  combines  with 
hydrochloric  acid,  the  hydrogen  of  the  acid  is  exactly  sufficient 
by  combination  with  the  oxygen  of  the  oxide  to  form  water,  which 


106  ACTION  OF  HTDEOCHLOKIC  ACID  ON  METALLIC  OXIDES. 


remains  in  the  solution,  or  else  evaporates  on  the  application  of 
heat,  Avhilst  the  metal  and  the  chlorine  nnite  du’ectlj  with  each 
other,  as  is  shown  bj  the  following  symbols : — 


Hydrochloric 

acid. 


2 HCl  }deld  2 TlCl 


Water. 

+ 

Water. 

KaHO  + HCl  yield  HaCl  + HA 


Hydrochlor. 

acid. 


Chloride 
of  sodium. 


When  the  oxide  of  a bi-equivalent  metal  is  employed,  the 
reaction  is  similar,  but  two  atoms  of  hydi’ochloric  acid  are  con- 
cerned : — 


Baryta. 


Hydrochlor.  acid.  Chlor.  barium. 


Water. 


BaO  -b  2HC1  = fiaCl,  -f  HA 
But  though  the  metal  may  exist  in  solution  in  the  form  of  chloride, 
this  circumstance  does  not  prevent  its  precipitation  in  the  form  of 
oxide,  when  a strong  base,  such  as  hydrate  of  potash,  is  added  to 
a solution  which  contains  the  chloride  of  the  metal  in  question, 
provided  that  the  metal  be  capable  of  forming  an  oxide  insoluble 
in  water.  For  example,  if  to  a solution  of  chloride  of  copper  a 
solution  of  hydrate  of  potash  be  added,  the  potassium  and  copper 
change  places,  chloride  of  potassium  is  formed,  wliilst  the  hydi’ated 
oxide  of  copper  is  precipitated.  It  is,  in  fact,  an  ordinary  in- 
stance of  double  decomposition  : — 

Chloride  Hydrate  of  Chloride  of  Hydrated  oxide 

of  copper.  potash.  potassium.  of  copper. 

-f  2^^He  = Tm  + , 


A reaction  not  less  instructive  occurs  when  oxides  containing 
a larger  proportion  of  oxygen  than  the  protoxides  are  treated  with 
hydi’ochloric  acid.  When,  for  instance,  1 atom  of  sesquioxide  of 
iron  (FeAa)  is  subjected  to  its  influence,  6 atoms  of  hydrochloric 
acid  are  decomposed,  3 atoms  of  water  are  formed,  and  an  atom 
of  perchloride  of  iron  is  obtained  in  solution  : — 

Hydrochlor.  Sesquiox.  Perchlor. 

acid.  of  iron.  Water.  of  iron. 


6 HCl  + Fe A give  3 HA  + 

It  sometimes  happens  that  no  chloride  corresponding  to  the 
oxide  exists.  There  is,  for  example,  no  stable  perchloride  of  man- 
ganese : in  this  case  1 atom  of  the  bin  oxide  of  manganese  decom- 
poses 4 atoms  of  hydrochloric  acid ; 2 atoms  of  ’water  and  1 atom 
of  chloride  of  manganese  are  formed,  wdiilst  2 atoms  of  chlorine 
are  liberated*  this  being,  in  fact,  the  usual  mode  of  obtaining 
chlorine  gas : — 

Oxide  of  Hydrochloric  Chloride  of 

manganese.  acid.  manganese.  Water.  Chlorine. 


MnO„  -f 


4 HCl  give  HnCl, 


+ 


2 HA  + 


Cl, 


NITRO-MUEIATIC  ACID. 


107 


The  presence  of  hydrochloric  acid  and  of  the  soluble  chlorides 
in  solution  is  indicated  by  the  formation  of  a white,  insoluble, 
curdy  precipitate  of  chloride  of  silver,  when  a solution  of  nitrate 
of  silver  is  added  to  the  liquid;  bTaCl  -h  AgbTOg  becoming 
AgCl  + Nal^Og.  This  precipitate  is  soluble  in  ammonia,  but  in- 
soluble in  nitric  acid.  Mercurous  nitrate  also  gives  a white  pre- 
cipitate of  mercurous  chloride  (calomel)  in  solutions  of  metallic 
chlorides:  Hgl^Og-f-lSTaCl^hTaNOg  + HgCl.  The  precipitate  is 
soluble  in  chlorine  water,  insoluble  in  diluted  nitric  acid,  and  is 
imuiediately  blackened  by  ammonia. 

(377)  Aqua  Regia  : Nitro-Muriajtio  Acid. — The  name  of 
aqua  regia  was  given  by  the  alchemists  to  a mixture  of  nitric  with 
hydrochloric  acid,  from  the  power  that  it  possesses  of  dissolving 
gold,  the  Mdng  of  metals.’  Both  platinum  and  gold  are  insolu- 
ble in  either  acid  separately ; but  when  the  two  acids  are  mixed, 
they  decompose  each  other ; free  chlorine,  and  abundant  ruddy 
fumes,  long  mistaken  for  peroxide  of  nitrogen,  being  liberated : 
the  chlorine  in  the  moment  of  its  extrication  acts  upon  the  metals 
and  dissolves  them.  The  nature  of  the  reaction  and  the  true 
composition  of  these  fumes  were  first  correctly  ascertained  by 
Gay-Lussac ; the  investigation  formed  indeed  one  of  the  last  scien- 
tific labours  of  this  distinguished  chemist  {Ann.  de  Chimie.^ 
III.  xxiii.  203). 

ddoro-Nitric  Gas  (HOClg  orNOgClg);  Boiling-jpoint,!^''. — 
If  a mixture  of  I part  of  concentrated  nitric  acid  and  3 parts  of 
hydrochloric  acid  be  placed  in  a fiask  and  subjected  to  a gentle 
heat  in  the  water  bath,  a,  fig.  295,  red  fumes  pass  ofi*  in  abundance. 


Fig.  295. 


These  vapours,  if  transmitted  through  a bottle,  n,  which  may  be 
cooled  by  immersion  in  melting  ice,  deposit  a little  volatilized 
hydi’ochloric  acid  and  water,  but  the  red  fumes  pass  on,  and  may 


lOS 


CHLOEO-XTTPJC  GAS CHLOROXITEOUS  GAS. 


be  condensed  as  a heavy  red  liquid  in  the  tube  receiver,  c,  which 
is  plunged  into  a mixtui-e  of  ice  and  salt,  while  free  chlorine  es- 
capes fr’om  the  open  extremity  of  the  tube,  c,  and  appears  in  the 
bottle,  D.  The  liquid  may  be  preserved  by  sealing  up  the  tine 
tubes  on  either  side  by  means  of  the  blowpipe,  the  object  of 
di’awing  out  the  extremities  of  the  tube,  c,  is  to  protect  the  corks 
through  which  they  pass  from  the  corrosive  action  of  the  chloro- 
nitrous  vapour.  If  it  be  desired  to  collect  the  compound  for 
analysis,  a bent  tube  fiUed  with  chloride  of  calcium  may  be  inter- 
posed between  b and  c,  to  absorb  all  traces  of  moistm’e.  In  this 
reaction  2 atoms  of  nitric  acid  decompose  6 of  hydi’ochloric  acid, 
producing  2 of  the  red  compound  (XOCl,)  (which  may  be  termed 
cldoro-n  itric  gas),  I atoms  of  water,  and  2 of  fr’ee  chloiine : — 

Hydrochlor.  Chloro-nitric 

Xitricacid.  ’ acid.  gas.  Water.  Chlorine. 

2 11X03  -f  6 HCl  = 2 XOCI3  + 


Chloro-nitric  gas  may  be  regai'ded  as  peroxide  of  nitrogen,  in 
which  2 atoms  of  chlorine  have  taken  the  place  of  1 atom  of 
oxygen.  At  aU  temperatures  above  19°  it  is  a gas  of  a deep 
lemon-yellow  colom*,  with  the  suffocating  odour  of  aqua  regia.  It 
may  be  condensed  by  transmitting  it  through  a tube  suiTounded 
by  a fr-eezing  mixture  of  ice  and  salt,  when  it  fonns  a transparent, 
red,  fummg  hqiiid.  IXater  decomposes  the  compound  imme- 
diately, appearmg  to  dissolve  it : but  the  solution  contains  hydi'O- 
chloric  acid  and  the  elements  of  peroxide  of  nitrogen : 

Chloro-nitric  Peroxide  of  Hydroclor, 

gas.  W ater.  nitrogen.  ' acid. 

xeci,  -f-  H,e  give  xe^  -f  2 hci. 


A similar  decomposition  ensues  when  it  is  mixed  with  an  alkaline 
base,  for  it  does  not  fonn  salts.  The  gas  cannot  be  confined  over 
mercmw,  since  it  attacks  the  metal  instantly,  fomiing  calomel  and 
liberating  nitric  oxide  : — 

Chloro-nitric 

gas.  Mercury.  Calomel  Xitric  oxide. 

XOCl,  + 2 Hg  give  2 HgCl  -f  XO. 

CTdo'ro-Xit/'ous  fXOCl) ; Uteoretic  Sp.  6^/’.  2 ‘265  ; Atomic 
Yol.  i , ;. — When  chloiine  is  mixed  with  nitric  oxide  in  the 
gaseous  state,  they  combine  and  yield  a dense  orange-colom-ed 
gas ; 2 volumes  of  nitric  oxide  and  1 of  chlorine  produce  2 vol- 
umes of  the  new  compound.  It  cannot  be  formed  over  mercury, 
as  it  is  immediately  decomposed  by  this  metal.  At  a tempera- 
ture of  0°  it  is  reduced  to  a red  hquid  resembhng  the  chloro-nitric 
compound  in  odour  and  aspect,  and  which  boils  at  about  32°, 
Aqua  regia,  under  certain  circumstances,  may  produce  both 
chloro-nitric"^and  chloro-nitrous  gas,  just  as  the  nitric  oxide  may, 
according  to  the  circumstances  under  which  it  is  mixed  "with 
oxygen,  form  nitrous  anhydride,  or  peroxide  of  nitrogen.  In  the 


OXIDES  OF  CHLOKINE HYPOCIILOKOUS  ANHYDKIDE. 


109 


early  stages  of  tlie  decomposition  of  aqua  regia,  the  product  is 
nearly  pure  chloro-nitric  gas  (NOC\),  but  as  the  decomposition 
advances,  the  quantity  of  chloro-nitrous  gas  (NOCl)  increases. 
ISTeither  of  these  chlorinated  compounds  exerts  any  solvent  action 
upon  gold  or  platinum.  By  the  action  of  dry  hydrochloric  acid 
gas  upon  anhydrous  peroxide  of  nitrogen,  a third  chlorinated 
compound,  NO2CI  (sp.  gr.  of  liquid  1*32  ; of  vapour  2*63),  appears 
to  be  formed,  mixed  with  other  bodies. 

Aqua  regia  is  largely  employed  as  an  oxidizing  agent ; by  its 
action  perchlorides  of  the  metals  are  formed  in  solution,  and  when 
the  liquid  is  decomposed  by  an  alkali,  the  oxide  of  the  metal 
corresponding  in  composition  to  the  perchloride  is  precipitated. 
By  boiling  the  solutions  of  the  metals  in  aqua  regia  with  an  excess 
of  hydrochloric  acid,  the  whole  of  the  nitric  acid  may  be  decom- 
posed and  expelled,  and  a pure  solution  of  the  metallic  chlorides 
with  excess  of  hydrochloric  acid  will  be  formed. 

Oxides  of  Chlorine. 

(378)  The  attraction  of  chlorine  for  oxygen  is  so  feeble  that 
the  two  elements  do  not  enter  directly  into  combination  with  each 
other.  Several  compounds  of  oxygen  and  chlorine  may,  however, 
be  obtained  by  indirect  'methods.  Three  of  these  oxides  may  be 
obtained  in  the  isolated  form ; they  are  the  following : — 

In  100  parte. 

Mol.  vol.  , * » 

^ Cl.  O. 

Hypochlorous  anhydride CbO  = 81  [HZl  81*60  + 18*40 

Chlorous  anhydride CI2O3  = 11*9  f | ']~|  59*66  + 40*34 

Peroxide  of  chlorine C102  = 61*5  [JD  ^^*59  + 47*41 

Four  monobasic  oxidized  acids  of  chlorine  may  also  be  ob- 
tained, viz. : — 

Hypochlorous  acid HCIO  = 52*5 

Chlorous  acid HC102  = 68*5 

Chloric  acid HC103  = 84*5 

Perchloric  acid HC104  = 100*5 

Millon’s  experiments  have  rendered  it  probable  that  other 
oxidized  compounds  also  exist,  the  result  of  the  combination  of 
some  of  those  already  mentioned  witli  chloric  and  perchloric 
anhydrides. 

(379)  Hypochlorous  Anhydride (Cl^O  = 87) ; Mol.  Yol.  | | |; 
Theoretic  Sp.  Gr.  3 *005  ; Observed  2 '977  ; Boiling-pt.  about  68°, 
or  CIO =43 '5. — If  chlorine  in  a perfectly  dry  state  be  passed 
slowly  through  a tube,  d,  fig.  296,  filled  wdth  well-dried  oxide  of 
mercury  obtained  by  precipitation  from  a solution  of  corrosive 
sublimate  by  means  of  hydrate  of  potash,  immediate  action  com- 
mences, and  a gas  is  produced  which  may  be  condensed  into  a 
liquid  by  surrounding  the  receiver,  e,  with  a mixture  of  ice  and 
salt.  The  chlorine  is  prepared  in  the  flask,  a,  washed  with  water 
in  the  bottle,  n,  and  dried  by  allowing  it  to  traverse  the  bent  tube, 
c,  which  is  filled  with  pumice-stone  moistened  with  oil  of  vitriol. 

The  reaction  between  the  chlorine  and  oxide  of  mercury  ap- 


110 


HTPOCHLOEOrS  ACID. 


pears  to  be  of  a simple  nature.  2 atoms  of  chlorine  displace  1 , 
atom  of  oxygen  from  the  mercury,  and  this  oxygen  at  the  moment 

Fig.  296. 


of  its  liberation  unites  ’^ith  two  other  atoms  of  chlorine  to  form 
h}y>ochlorous  anhydride : — 

Oxide  mere.  Chlorine.  Chlor.  mere.  Hypochlor.  anhyd. 

+ Ta,  = H^i,  + CIA 

^'pochlorous  anhydride  is  thus  procured  as  a deep  red  liquid, 
which  emits  a vapour  of  a deeper  colour  than  that  of  chlorine, 
with  a peculiar  suffocating  chlorous  smell.  This  vapour  is  re- 
markable for  the  ease  with  which  it  is  decomposed,  the  warmth 
of  the  hand  causing  its  separation  into  chlorine  and  oxygen  with 
explosion  ; 2 volumes  of  the  anhydride  in  this  way  produce  a 
mixture  composed  of  2 volumes  of  chlorine  and  1 volume  of  oxy- 
gen. The  composition  of  tlie  gas  is  therefore  as  follows  : — 


Chlorine 

Bv  weight. 
= 'il'or  81-6 

By  volume. 

2 or  1-0  = 

Sp.  ST. 

2-453 

Oxygen 

= 16 

18-4 

1 0-5  = 

0-552 

Hypochlorous  j 
anhydride  \ 

ci^e 

= 87 

100-0 

2 1-0  = 

3-005 

Hypochlorous  Acid  (HCIO  or  II0,C10=:52‘5). — TTater  dis- 
solves about  200  times  its  bulk  of  gaseous  h}q30chlorous  anhy- 
dride, and  forms  with  it  a pale  yellow  solution,  which  has  an  acrid, 
but  not  sour  taste.  In  a concentrated  form  this  solution  is  very 
unstable ; it  acts  as  a powerful  oxidizing  agent ; but  is  rapidly 
decomposed  when  exposed  to  the  light,  bubbles  of  chlorine  escap- 
ing from  it,  whilst  chloric  acid  is  formed.  Charcoal,  iodine,  sul- 
phur, selenium,  phosphorus,  arsenicum,  and  finely  powdered  an- 


HYPOCHLOROrS  ACID. 


Ill 


timony,  decompose  a solution  of  liypoclilorous  acid  rapidly,  and 
are  converted  by  it  respectively  into  carbonic,  iodic,  sulpliuric, 
selenic,  phosphoric,  arsenic,  and  antimonic  acids : if  the  solution 
be  concentrated  the  action  is  sometimes  attended  with  explosion. 
Iron  filings  are  also  immediately  oxidized  with  evolution  of 
chlorine.  Silver  is  converted  into  chloride  whilst  oxygen  is  liber- 
ated, and  copper  and  mercury  combine  with  both  the  oxygen  and 
the  chlorine,  furnishing  oxychlorides.  The  contact  of  chloride  of 
silver  with  the  solution  of  the  acid  also  decomposes  the  latter, 
causing  the  separation  of  both  oxygen  arid  chlorine  in  the  gase- 
ous form,  whilst  the  metallic  chloride  appears  to  have  undergone 
no  alteration.  Hypochlorous  acid  attacks  the  skin  and  turns  it 
brown  ; but  its  most  important  property  is  its  bleaching  power, 
which,  according  to  the  experiments  of  Gay-Lussac,  is  twice  as 
great  as  that  of  the  chlorine  which  it  contains.  When  hypochlo- 
rous acid  or  any  of  its  salts  is  heated  with  hydrochloric  acid  in 
excess,  an  atom  of  each  acid  is  decomposed,  water  is  formed,  and 
2 atoms  of  chlorine  are  liberated;  HCl  + HClO^H^O-fCl^.  If  a 
fragment  of  sal  ammoniac  be  suspended  in  a solution  of  hypochlo- 
rous acid,  oily-looking  drops  of  the  explosive  compound  known 
as  chloride  of  nitrogen  (386)  are  formed. 

Hypochlorous  acid  by  its  action  upon  the  alkalies  and  earths, 
furnishes  salts  termed  hypochlorites.  These  compounds  are  de- 
composed even  by  feeble  acids,  such  as  the  carbonic ; and  the 
hypochlorous  acid  thus  liberated,  shows  its  usual  bleaching  action 
on  vegetable  colours.  The  solutions  of  these  salts  are  decomposed 
by  gently  heating  them,  and  they  become  converted  into  a mix- 
ture of  chloride  and  chlorate  : thus — 

Hypochlorite  Ch'oride  of  Chlorate  of 

of  potassium.  potassium.  potassium. 

3 KCie  become  2 KCl  + KCie3. 

This  change  is  retarded  by  the  addition  of  an  excess  of  caustic 
alkali. 

When  chlorine  acts  upon  the  oxides  of  metals  which  have 
but  a feeble  attraction  for  oxygen,  these  bases  are  often 
completely  decomposed.  In  consequence  of  this  reaction,  a weak 
solution  of  hypochlorous  acid  is  easily  prepared  by  agitating  1 
part  of  the  red  oxide  of  mercury  with  12  parts  of  water  in 
a large  bottle  of  chlorine  gas,  care  being  taken  tliat  the 
oxide  of  mercury  is  in  slight  excess.  The  chlorine  is  rapidly 
absorbed  ; part  of  the  oxide  of  mercury  is  decomposed  by 
the  chlorine,  and  the  chloride  of  mercury  thus  produced  unites 
with  a portion  of  unchanged  oxide  of  mercury,  forming  a brown 
insoluble  oxychloride  of  that  metal  ; the  solution  on  being 
decanted  is  found  to  contain  hypochlorous  acid.  The  reaction 
may  be  represented  as  follows ; — 

Water.  Oxide  of  mercury.  Chlorine.  Oxychloride  of  mercury.  Hypochlor.  acid. 

lie  + 2 Hge,HgCi/  + 2 iicie. 


112 


BLEACHING  COMPOUNDS. 


(380)  Bleaching  Compounds. — If  the  base  upon  which  chlorine 
is  made  to  act  be  a powerful  one,  such  as  an  alkah  or  alkaline 
earth,  the  gas  is  absorbed,  and  a peculiar  compound  possessed  of 
bleaching  properties  is  produced.  It  is  in  this  way  that  the 
bleaching  compounds  so  extensively  used  in  the  arts  under  the 
names  of  chloride  of  hme,  chloride  of  potash,  and  chloride  of 
soda,  are  prepared. 

Of  these  bleaching  compounds  the  chloride  of  hme  is  the 
most  important.  It  is  prepared  by  slaking  well-burnt  lime, 
and  exposing  it  to  the  action  of  chlorine  gas  in  layers  of  2 or 
3 inches  m thickness,  upon  perforated  shelves  in  chambers 
made  of  lead,  or  of  Yorkshue  flagstones.  The  chlorine  must  be 
admitted  gradually,  in  order  to  prevent  too  rapid  a rise  of 
temperature  consequent  upon  a quick  absorption  of  the  gas.  If 
the  heat  be  aUowed  to  rise  beyond  100°  or  110°  F.,  a quantity  of 
chloride  and  chlorate  of  calcium  is  formed,  the  reaction  being 
similar  to  that  which  occurs  during  the  preparation  of  chlorate  ot 
potassium  (382).  Slaked  hme  (-GaH^Oj)  may  in  this  operation  be 
made  to  take  up  about  half  its  weight  of  chlorine  ; but  it  is  not 
possible  to  combine  hydrate  of  hme  in  the  form  of  powder  with 
an  entire  equivalent  of  chlorine  so  as  to  form  the  compound 
GaOCl^ : the  product  always  contains  a considerable  excess 
of  uncombined  hme.*  Many  chemists  consider  both  this  com- 
pound and  the  corresponding  compounds  with  potash  and  soda  to 
be  h}q)Ochlorites  of  the  metals  which  enter  into  their  formation : 
in  this  case  they  must  be  double  salts  of  the  hypochlorite  and 
chloride  of  the  metal.  This,  however,  is  more  than  questionable ; 


Hydrate  of  lime. 


Chlorine. 


Chloride 
of  calcium. 


Hypochlorite 
of  calcium. 


2 Gall202  -f  2 Clj  = GaClg  -f  Ga  2 CIO 


W ater. 

+ 


* A few  years  ago.  Mr.  Dunlop,  of  the  St.  Rollox  "Works,  Glasgow,  introduced 
a method  of  preparing  chlorine  for  the  manufacture  of  bleaching  powder,  by 
decomposing  a mixture  of  common  salt  and  nitrate  of  sodium  with  sulphuric  acid. 
In  this  operation  chlorine  and  nitrous  acid  are  evolved,  whilst  sulphate  of  sodium  is 
produced;  the  reaction  may  be  traced  by  the  equations  following: — 


Nitrous 

Chlor.  sod.  Nitrate  of  sodium.  Sulph.  acid.  Sulphate  of  sodium.  Chlorine,  anhydride.  Water. 

4XaS  + \ Xa^’^  -H  TbUSoT = T^a^S^  -f  Vo?  + + Th^. 

The  mixed  gases  are  made  to  pass  through  a vessel  containing  oil  of  vitriol,  by 
which  the  nitrous  acid  is  rapidly  absorbed,  whilst  the  chlorine  passes  on  to  the  lime. 
A current  of  air  is  made  to  act  on  the  nitrous  sulphuric  acid,  by  which  the  nitrous 
acid  becomes  converted  into  nitric  acid,  owing  to  the  absorption  of  oxygen ; and  the 
mixed  acids  being  made  to  act  upon  fresh  chloride  of  sodium,  without  the  addition 
of  nitre,  give  rise  to  a similar  succession  of  decompositions : — 


Nitrous 

Sulph.  acid.  Nitric  acid.  Chloride  of  sodium.  Sulph.  sodium.  Chlorine.  anh3'dride.  Water. 

' + 2 HXGa  + 4 NaCl  = 2 + +^Th?0. 

The  nitrous  sulphuric  acid  may  also  be  at  once  made  use  of  in  the  leaden  chambers 
in  the  manufacture  of  oil  of  vitriol  (413). 


CHLOKEDE  OF  LIME ITS  APPLICATION. 


113 


they  are  probably  direct  combinations  of  chlorine  with  the 
oxides.  If  the  compound  be  supposed  to  be  a pure  chloride  of 
lime  or  oxychloride  of  calcium,  the  reaction  is  simply  an 
absorption  of  chlorine,  by  which  the  compound  OaOCl^  is  formed  ; 
but  if  it  be  supposed  that  a hypochlorite  is  produced,  the  following 
decomposition  must  occur  : — 

Chloride  Hypochlorite 

Hydrate  of  lime.  Chlorine.  of  calcium.  of  calcium.  Water. 

2 OaHA'  + 4-  ba  2^  Clo'  + 

Chloride  of  calcium  is  deliquescent,  and  is  soluble  in  alcohol ; but 
bleaching  powder,  when  properly  made,  is  not  deliquescent,  and 
yields  scarcely  any  chloride  of  calcium  to  alcohol. 

Chloride  of  lime  emits  the  peculiar  odour  of  hypochlorous 
acid  when  exposed  to  the  air  ; under  these  circumstances, 
however,  it  gradually  absorbs  carbonic  anhydride,  and  exhales, 
not  hypochlorous  acid,  but  chlorine, — a circumstance  which  causes 
it  to  be  frequently  used  as  a disinfecting  agent.  Cloths  dipped  in 
an  aqueous  solution  of  the  chloride,  when  hung  up  in  the  room  to 
be  fumigated,  continue  for  many  hours  to  emit  chlorine  gradually, 
but  in  quantities  too  small  to  be  injurious  to  the  inmates.  Com- 
mercial chloride  of  lime  is  only  partially  soluble  in  water,  and 
leaves  a large  residue  of  hydrate  of  lime.  An  excess  of  any  acid 
when  poured  upon  the  powder  causes  a free  evolution  of  chlorine  ; 
but  if  the  aqueous  solution  be  mixed  with  half  the  quantity  of 
sulphuric  acid  required  to  neutralize  the  lime,  hy[)ochlorous  acid 
may  be  distilled  off  and  condensed  in  a diluted  form  in  a suitable 
receiver.  The  reaction  which  occurs  may  be  thus  represented : — 

Chloride  Hypochlo- 

Chloride  of  lime.  Sulph.  acid.  Sulph.  calcium.  of  calcium.  rous  acid. 

2 OaOCll  -f  yield  + OaCl,  -f 

Chloride  of  lime  is  consumed  in  vast  quantities  in  the  bleach- 
ing of  calicoes  and  other  woven  goods.  The  calico  is  well  washed, 
and  boiled  successively  with  lime-water,  with  much  diluted  sulphu- 
ric acid,  and  with  a weak  solution  of  caustic  soda,  in  order  to  remove 
the  weaver’s  dressing,  and  greasy  and  resinous  matters  : it  is  then 
well  washed  and  digested  in  a solution  of  chloride  of  lime,  con- 
taining 2 or  2-|-  per  cent,  of  bleaching  powder.  The  bleaching 
effect  of  this  solution  is  not,  however,  rendered  apparent  till  the 
goods  are  immersed  in  very  dilute  sulphuric  acid,  which  decom- 
poses the  chloride  of  lime  immediately,  and  by  liberating  chlorine 
witliin  the  fibres  of  the  cloth  itself,  rapidly  removes  the  colour. 
Still,  however,  it  is  not  perfectly  white.  The  calico  is  tlierefore 
washed,  and  a second  time  subjected  to  the  action  of  alkali,  to 
remove  the  colouring  matter  now  rendered  soluble  in  it  by  the 
action  of  the  chlorine  ; again  it  is  passed  through  a weaker  solu- 
tion of  chloride  of  lime,  and  then  through  dilute  acid ; finally  it 
is  thoroughly  washed  in  a copious  stream  of  water,  in  order  to 
remove  the  last  traces  of  sulphuric  acid,  which  would  otherwise 
destroy  the  fibre. 


llrt  ESmiATIOX  OF  THE  BLEACHING  POWER  OF  CHLORIDE  OF  LDIE. 


(3S1)  Estimation  of  the  Bleaching  Power  of  Chlonde  of  Lime. 
— The  commercial  value  of  bleaching  powder  depends  upon  the 
quantity  of  chlorine  which  can  be  liberated  from  it  by  the  addition 
of  an  acid  ; for  it  is  this  portion  of  its  chlorine  only  which  is  avail- 
able for  bleaching  pm-poses.  Gay-Lussac  proposed  to  estimate 
the  bleaching  power  by  measurement  of  the  bulk  of  a solution  of 
indigo  of  known  strength  which  a given  weight  of  the  chlonde  is 
able  to  deprive  of  its  blue  colour ; and  subsequently  he  determined 
the  amoimt  of  available  chlorine  by  the  quantity  of  a standard 
solution  of  arsenious  acid  which  could  be  converted  by  a known 
weight  of  the  bleaching  powder  into  arsenic  acid. 

A still  more  convenient  plan  has  been  described  by  Graham. 
It  depends  upon  the  determination  of  the  quantity  of  a fenous 
salt  which  a given  weight  of  bleaching  powder  in  the  presence  of 
an  excess  of  acid  can  convert  into  a ferric  salt  : if  ferrous  sulphate 
be  used,  2 atoms  of  chlorine  are  required  for  the  conversion  of 
2 atoms  of  that  salt  into  1 atom  of  ferric  sulphate  ; the  chlorine 
decomposing  water  and  becoming  hydrochloric  acid,  as  is  shown 
in  the  following  equation  : — 

2 FeSO,  -f-  2 H,Se,  -h  GaOCl,  = Fe,  3 SO,  -f  2 HCl 

-r  GaSO^  -f  HjO. 


Fig.  297. 


Seventy-eight  grains  of  crystallized  green  sulphate  of  iron  require 
10  grains  of  chlorine  for  its  conversion  into  the  ferric  sulphate. 
In  making  an  experiment  upon  the  value  of  a bleaching  powder, 
78  grains  of  clean  dry  crystals  of  the  green  sulphate  are  dissolved 
in  about  two  ounces  of  water,  and  acidulated  with  sulphuric  or 
hydrochloric  acid  ; 50  grains  of  the  bleaching  powder  are  rubbed 
up  in  a mortar  with  2 ounces  of  warm  water, 
and  transferred  to  a burette  or  tall  narrow  tube 
(fig.  297),  capable  of  holding  1000  grains  of 
water,  and  graduated  into  100  equal  parts  from 
above  downwards.  The  mortar  is  washed  with 
a little  more  water,  and  the  washings  added  to 
the  liquid  in  the  burette,  which  is  filled  up 
exactly  to  0°.  The  openings  at  top  are  closed 
with  the  finger  and  thumb,  and  the  contents 
of  the  vessel  are  mixed  thoroughly  by  agitation. 
The  solution  of  chloride  of  lime  is  "then  added 
gradually  to  the  sulphate  of  iron  (constantly 
stirring  the  mixtm-e),  until  the  whole  of  the 
ferrous  salt  is  converted  into  ferric  salt.  The  progress  of  the 
oxidation  is  ascertained  by  means  of  a solution  of  the  red  prussiate 
of  potash,  which  strikes  a deep  blue  with  the  liquid  if  it  contain 
any  unchanged  ferrous  sulphate.  Several  drops  of  this  liquid  are 
spotted  over  a white  plate,  and  after  each  addition  of  the  chloride 
of  lime  to  the  solution  of  sulphate,  a drop  of  the  iron  solution  is 
mixed  with  one  of  these,  and  the  addition  of  the  chloride  is  con- 
tinued so  long  as  the  blue  colour  appeal’s.  The  stronger  the 
bleaching  powder,  the  fewer  will  be  the  number  of  divisions 
required  to  be  pom*ed  from  the  burette.  This  number  of  divisions 


CHLOEIMETRY CHLORIC  ACH). 


115 


divided  by  2 will  indicate  the  number  of  grains  of  bleaching 
po-wder  which  contain  10  grains  of  available  chlorine.  The 
strength  of  the  powder  is  therefore  obtained  by  the  following  pro- 
portion, in  which  m represents  the  number  of  measures  poured 
from  the  burette  : — 

^ ; 10  : : 100  : x (the  number  of  grains  of  chlorine  in  100  grains 
of  the  powder) ; or 

The  process  of  converting  a lower  oxide  of  a metal  into  one 
of  its  higher  oxides,  by  means  of  chloride  of  lime,  admits  of  being 
frequently  employed ; indeed,  a solution  of  chloride  of  lime,  when 
mixed  with  hydrochloric  acid,  furnishes  a powerful  oxidizing 
agent.  Peroxide  of  bismuth,  of  cobalt,  of  nickel,  and  of  lead, 
may  be  obtained  readily  by  adding  a neutral  solution  of  chloride 
of  lime  to  neutral  solutions  of  the  salts  of  these  metals  and  heat- 
ing the  liquid. 

(382)  Chloric  Acid  (IICIO3,  or  110,0105  = 84*5). — Chloric 
anhydride  has  not  been  isolated,  but  if  a current  of  chlorine  gas 
be  caused  to  pass  through  a solution  of  caustic  potash,  it  is  rap- 
idly absorbed,  even  when  transmitted  in  a continuous  stream,  and 
a bleaching  liquid  is  formed,  which,  on  the  application  of  heat, 
loses  its  bleaching  properties,  and  is  gradually  converted  into  a 
mixture  of  chloride  and  chlorate  of  potassium ; 6 atoms  of  chlorine 
and  6 of  hydrate  of  potush  furnishing  5 of  chloride  of  potassium 
and  1 atom  of  the  chlorate,  whilst  water  is  liberated — 

3 CI3+6  iaie=5  Kci4-Kcie3-i-3  H,e. 

The  chlorate  of  potassium  being  sparingly  soluble  is  freed  fi’om 
the  chloride  by  two  or  three  crystallizations.  In  order  to  obtain 
chloric  acid,  the  chlorate  is  decomposed  by  the  addition  of  hydro- 
tluosilicic  acid,  which  forms  an  insoluble  compound  with  the 
potassium,  and  chloric  acid  is  liberated — 

2 KCie3-f  H3SiF5=2  HCie3  + K3Si  F^. 

The  acid  solution  may  be  poured  off  from  the  precipitate,  and 
concentrated  by  evaporation  over  the  water-bath  at  a heat  not 
exceeding  100°  F.,  till  it  forms  a syimpy  liquid  of  a faint  chlorous 
smell,  and  a powerfully  acid  taste.  It  is  instantly  decomposed 
by  contact  with  organic  matter,  and  in  its  concentrated  form  it 
chars  and  even  sets  tire  to  paper.  By  a temperature  a little  above 
100°  the  acid  is  decomposed  into  oxygen  gas,  clilorine,  and  })er- 
chloric  acid;  8 110103,  yielding  411010,-1-2  II^O 3 O,, -h  2 01.,. 
In  diffused  daylight,  it  gradually  undergoes  spontaneous  decom- 
position. On  one  occasion  a small  specimen  whicli  I had  sealed 
up  in  a glass  tube  was  placed  aside  upon  a shelf;  but  in  a few 
weeks,  although  left  untouched,  the  tube  exploded  in  consequence 
of  the  expansive  force  of  the  liberated  gases. 

The  metallic  salts  of  chloric  acid  require  a liigher  temperature 
for  their  decomposition  than  the  acid  itself.  The  action  of  heat 
upon  chlorate  of  potassium  has  already  been  meHtioned  as  afford- 


116 


CHLOKATES PERCHLOKIC  ACID. 


ing  a verv  convenient  source  of  pure  oxygen  (335),  This  salt, 
when  heated  to  a point  a little  short  of  redness,  fuses  and  is  con- 
verted into  chloride  of  potassium  and  oxygen  gas ; 2 KCIO3  be- 
coming 2 KCI  + 3O2. 

This  decomposition  also  furnishes  data  for  ascertaining  the 
composition  of  chloric  acid  ; for  if  a given  weight  of  the  chlorate 
he  calcined  with  suitable  precaution,  the  loss  indicates  the  entire 
(Quantity  of  oxygen  which  it  contained.  The  proportions  of  chlo- 
rine and  of  potassium  in  chloride  of  potassium  being  known,  the 
composition  of  chloric  acid  is  readily  calculated. 

Chlorates. — The  salts  of  chloric  acid,  or  the  chlorates.,  are 
monobasic,  with  the  general  formula  M'ClOg.  All  of  them  are 
decomposed  by  heat ; oxygen  is  expelled,  and  generally  a chloride 
of  the  metal  is  left  behind : the  chloride  can  be  detected  in  the 
residue  by  nitrate  of  silver.  The  chlorates  produce  scintillation 
when  thrown  upon  ignited  charcoal ; and  when  heated  with  com- 
bustible substances,  such  as  phosphorus  or  sulpliur,  they  explode 
violently.  It  generally  happens  that  mere  friction  with  these 
bodies  is  sufficient  to  cause  a powerful  detonation  : for  example, 
if  half  a grain  of  sulphur  be  triturated  in  a mortar  with  2 or  3 
grains  of  chlorate  of  potassium,  the  friction  is  attended  with  a 
series  of  small  explosions.  '^Yhen  a fragment  of  a chlorate  is 
placed  in  a di’op  of  oil  of  vitriol,  a yellow  colour  is  produced,  and 
the  peculiar  odour  of  peroxide  of  chlorine  is  evolved.  Xitric  acid 
decomposes  the  chlorates  with  formation  of  a nitrate  and  per- 
chlorate of  the  metal,  while  free  chlorine  and  oxvgen  escape  ; 

8 Kcie3+ d Hxe3=d  Kcie.-f  2 ci^-p  3 e,+2  Hje+i  ksb,. 

Hydi’ochloric  acid  liberates  euchlorine  (p.  120).  Xany  of  the 
chlorates  are  deliquescent ; they  are  all  soluble  in  water ; but 
mercurous  chlorate  is  least  so  ; their  solutions  are  not  precipitated 
by  nitrate  of  silver  ; many  of  them  also  are  soluble  in  alcohol. 
Paper  soaked  in  a solution  of  a chlorate,  and  allowed  to  dry,  ac- 
quires the  property  of  smouldering  when  kindled,  and  burns  in 
the  same  manner  as  touch-paper.  The  chlorates  when  in  solution, 
even  in  small  quantity,  may  readily  be  distinguished  from  the 
nitrates,  by  adding  first  a few  drops  of  a solution  of  indigo,  and 
then  a solution  of  sulphurous  acid ; the  blue  colour  immediately 
disappears  even  without  the  application  of  heat,  but  it  remains 
unaltered  when  nitrates  only  are  present.  The  chlorates  of  potas- 
sium, sodium,  and  silver  are  anhydrous  ; that  of  bariiun  contains 
1 atom  of  water,  and  that  of  strontium  6 atoms  of  water. 

Chlorate  of  potassium,  when  in  solution,  often  afibrds  a con- 
venient method  of  converting  the  metallic  protoxides  into  perox- 
ides ; since  by  the  addition  of  hydrochloric  acid  to  the  solution, 
chloric  acid  is  set  at  liberty  and  exerts  its  oxidizing  power.  Iron, 
for  example,  when  it  exists  in  a solution  as  a ferrous  salt,  is  thus 
readily  converted  into  a ferric  salt  when  the  liquid  is  boiled. 

(383)  Pekchlokic  Acid  (IICIO,,  or  II0,C10,  = 100*5). — 
Perchloric  anliydride  is  unknown.  If  instead  of  heating  the 
chlorate  of  potassium  to  complete  decomposition,  the  temperatui'e 
be  moderated  and  the  process  stopped  when  one-third  of  the  total 


PERCHLORIC  ACID. 


117 


quantity  of  oxygen  lias  been  expelled,  tlie  mass  will  have  assumed 
a pasty  condition,  and  will  be  found  to  contain  a compound  of 
chlorine  with  a still  higher  proportion  of  oxygen,  to  which  the 
name  of  perchloric  acid  has  been  given  ; this  compound  remains 
in  combination  with  a portion  of  the  potassium.  The  reaction 
appears  to  consist  in  the  resolution  of  2 atoms  of  the  chlorate  into 
1 atom  of  perchlorate  (KCIO^)  and  1 of  chlorite  of  potassium 
(KCIO2) ; this  latter  salt  being  unable  to  exist  at  so  high  a tem- 
perature, is  immediately  converted  into  oxygen  gas  and  chloride 
of  potassium,  as  follows  : — 


Chlorate  of 
potassium. 


Chlorite  of 
potassium. 


Perchlorate  of 
potassium. 


Chlorite  of 
potassium. 


Chloride  of 
potassium. 


Oxygen. 


2 KCie3  = KCie,  -f  KCie„  and  KCIO,  = KCl  + O,. 


By  crystallization  the  perchlorate  of  potassium  is  readily  separated 
from  the  more  soluble  chloride.  The  perchlorate  is  freely  dissolved 
by  boiling  water,  but  as  the  salt  is  much  less  soluble  at  ordinary 
temperatures,  it  crystallizes  from  the  solution  as  it  cools,  and  is 
deposited  in  octohedra.  At  a red  heat  the  perchlorate  is  itself 
resolved  into  oxygen  and  chloride  of  potassium. 

One  method  of  obtaining  perchloric  acid  in  the  form  of  hydrate 
consists  in  distilling  the  perchlorate  of  potassium  with  four  times 
its  weight  of  oil  of  vitriol : if  the  receiver  be  kept  cool,  the  first 
portions  that  distil  over  crystallize  in  long  silky  deliquescent 
needles  consisting  of  (IIC104,H20) : a large  proportion  of  the 
acid,  however,  is  decomposed  into  chlorine  and  oxygen  gases. 
According  to  Boscoe,  the  best  method  of  preparing  perchloric 
acid  consists  in  boiling  down  a solution  of  chloric  acid  obtained 
by  the  action  of  hydrofluosilicic  acid  upon  chlorate  of  potassium. 
Lower  oxides  of  chlorine  escape,  and  an  impure  solution  of  per- 
chloric acid  is  left,  which  is  purified  by  distillation,  when  a heavy, 
colourless,  thick  oily  liquid  passes  over.  If  this  be  heated  it  gives 
off*  dense  white  'fumes.  By  distilling  this  liquid  with  four  times 
its  volume  of  oil  of  vitriol,  a yellow  mobile  fluid  consisting  of  pure 
perchloric  acid  (IICIO-^)  first  comes  over.  This  is  followed  by  a 
thick  oily  liquid,  which  is  a hydrate  (containing  65*8  per  cent,  of 
the  anhydride),  of  the  form  (IICIO^,  2 II2O).  If  this  be  mixed 
with  tlie  pure  acid  IICIO^  in  equivalent  proportions,  it  forms  the 
white  fusible  crystalline  substance  (IIC104,Il20)  already  described. 
This  crystallizable  hydrate,  when  heated  to  230°,  is  decomposed 
into  the  pure  acid  (IICIO^)  which  distils  over,  whilst  the  oily 
hydrate  remains  in  the  i-etort,  and  does  not  distil  over  till  the 
temperature  is  raised  to  397°. 

Perchloric  Acid  (IICIO, ; Sp.  Gr.  of  liquid  1'782)  is  a colour- 
less volatile  liquid,  which  soon  becomes  yellow,  owing  to  libera- 
tion of  one  of  the  oxides  of  chlorine.  It  remains  li(piid  at  a 
temperature  of  — 31°.  It  is  one  of  the  most  powerful  oxidizing 
agents  known ; a drop  of  it  brought  into  contact  witli  cliarcoal, 
with  paper,  or  almost  any  organic  substance,  iinniediatelv  produces 
combustion  with  an  explosive  violence  falling  but  little  short  of 
that  of  the  so-called  chloride  of  nitrogen.  It  })roduces  frightful 


118 


CHLOEOUS  AIN^HYDKIDE. 


burns  if  allo'sved  to  fall  upon  the  skin.  It  cannot  be  redistilled 
without  experiencing  decomposition,  generally  attended  with  ex- 
plosion. If  sealed  up  in  tubes  it  gradually  undergoes  spontaneous 
decomposition,  and  the  tubes  burst  with  ex^^losion.  With  water 
it  combines  with  evolution  of  great  heat,  and  if  the  proportion  of 
water  be  not  too  large  it  reproduces  the  white  crystals  of  Serullas 
(HCIO^H^O).  Diluted  perchloric  acid  is  of  a purely  sour  taste, 
and  does  not  destroy  vegetable  colours  ; in  this  form,  indeed,  it  is 
the  most  stable  of  all  the  oxides  of  chlorine.  It  will  even  dissolve 
iron  and  zinc  with  evolution  of  hydrogen  gas. 

Perchloric  acid  forms  the  salts  known  as  perchlorates^  with  the 
general  formula  M'CIO^ : they  in  general  are  deliquescent.  Hone 
of  them  are  insoluble,  though  the  perchlorate  of  potassium  requires 
upwards  of  150  times  its  weight  of  cold  water  for  solution : the 
salts  of  this  acid  with  sodium,  barium,  and  silver,  are  soluble  in 
alcohol.  All  the  perchlorates  are  decomposed  by  heat,  with  evo- 
lution of  oxygen  and  formation  of  a chloride,  but  they  may  be 
distinguished  from  the  chlorates  by  not  yielding  a yellow  gas  when 
moistened  with  oil  of  wtriol. 

(384)  Chlorous  Anhydride  (Cl^Og^llO)  ; Sp.  Gr.  2'646,  Mol. 
Yol.  I I I I ; or  CIO3  = 59 ’5. — This  substance  may  be  obtained 
in  the  form  of  a gas  of  a deep  yellowish-green  colour ; it  is  not 
liquefied  by  exposure  to  a temperature  of  — 4°  F.  Chlorous  an- 
hydride is  a dangerous  compound  to  prepare,  as  exposure  to  a 
temperature  not  much  exceeding  130°  F.  is  sufficient  to  decom- 
pose it  with  a powerful  explosion.  Contact  with  most  combusti- 
ble non-metallic  elements,  such  as  sulphur,  selenium,  tellurium, 
and  phosphorus,  decomposes  the  gas  with  explosion ; arsenicum 
has  a similar  effect.  Most  of  the  metals — including  copper,  lead, 
tin,  zinc,  and  iron — are  without  action  upon  it,  but  mercury  ab- 
sorbs it  completely.  A solution  of  the  acid  (HCIO^  = 68*5), 
however,  oxidizes  all  these  metals,  and  they  commonly  yield  a 
mixture  of  chlorate  and  chloride,  especially  if  the  acid  be  in  excess ; 
for  instance,  2 Zn  -f  4 IICIO^  = ZnCl^  + 2 ClOg  + 2 H^O. 

The  composition  of  chlorous  anhydride  is  the  following,  and 
its  combining  volume  is  anomalous,  as  appears  from  the  experi- 
ments of  Millon,  confirmed  by  those  of  Schiel,  the  molecule  occu- 
pying 3 volumes  instead  of  2 : — 

By  weight.  Millon.  By  voL  Sp.  gr. 

Chlorine  . .Clo  = 11  or  59-66  60-15  2 or  0-66  1-635 

Oxygen  . .O3  = 48  40-34  39-85  3 1-00  DIOS 


Chlorous  \ 
anhydride  j 


ClaOa  = 119  100  00 


100-00  3 1-00  2-140 


This  gas  is  soluble  in  about  one-sixth  of  its  bulk  of  water,  and  the 
solution,  even  when  diluted  very  largely,  has  a bright  yellow 
colour.  The  compound  is  prepared  by  deoxidizing  chloric  acid ; 
this  object  is  effected  b,y  means  of  arsenious  acid,  when  the  gas  is 
required  in  a state  of  purity.  Three  parts  of  arsenious  anh}t.h’ide 
(white  arsenic)  and  4 of  chlorate  of  potassium  are  rubbed  up  into 
a paste  with  water,  and  16  parts  of  pure  nitric  acid,  of  sp.  gr,  1'24, 


PEROXIDE  OF  CHLORINE. 


119 


are  added ; the  whole  is  placed  in  a small  flask,  which  is  filled 
lip  to  the  neck  with  the  mixture,  and  a very  gentle  heat  is  applied 
by  means  of  a water-bath  (Millon,  Ann.  de  Chimie^  III.  vii.  822). 
The  gas  must  be  collected  by  displacement  in  dry  bottles,  as  it  is 
rapidly  decomposed  by  mercury.  In  this  operation  the  arsenious 
acid  becomes  oxidized  at  the  expense  of  the  nitric  acid ; nitrous 
acid  is  formed,  and  this  in  turn  is  reconverted  into  nitric  acid  by 
decomposing  the  liberated  chloric  acid  : for  example — 

Arsenious  Nitric  Arsenic  Nitrous 

acid.  acid.  acid.  acid. 

H^A^3  + HJSre,  = H,Ase,  + ; and 


Nitrous 

acid. 


Chlorate 
of  potassium. 


Nitrate  of 
potassium. 


Chlorous 

anhydride. 


Water. 


2 ime,  -f  2 Kcie3  = 2 kno,  -f  ci a = ha. 


Tartaric  acid  may  be  substituted  for  arsenious  anhydride  in 
this  operation,  but  the  gas  is  then  mixed  with  carbonic  anhydride. 

Chlorous  acid  (HCIA)  possesses  considerable  bleaching  power ; 
it  acts  slowly  upon  bases,  and  forms  monobasic  salts,  termed 
chlorites.,  with  the  general  formula  M'CA.  Chlorite  of  potassium 
(KCIO2)  is  deliquescent : if  its  solution  be  slowly  evaporated  to 
dryness,  it  is  converted  into  a mixture  of  chloride  and  chlorate  of 
the  metal,  in  equivalent  proportions.  The  chlorites  of  sodium, 
barium,  and  strontium  are  also  deliquescent.  The  chlorites  are 
decomposed  by  the  feeblest  acids,  such  even  as  carbonic  acid. 
Hitrate  of  lead  produces  a sulphur-yellow  scaly  precipitate  in 
their  solutions,  owing  to  the  formation  of  a chlorite  of  lead  (Pb 
2 CIO2).  Chlorite  of  silver  is  also  yellowish  and  insoluble. 

The  chlorites  may  be  distinguished  from  the  hypochlorites  by 
the  addition  of  a mixture  of  arsenious  anhydride  with  nitric  acid, 
wdiich  does  not  destroy  the  bleaching  power  of  the  chlorites,  whilst 
it  destroys  that  of  the  hypochlorites.  Their  solutions  deoxidize 
an  acidulated  solution  of  permanganate  of  potassium. 

(385)  Peroxide  of  Chlorine  (CA,  or  C104=67-5) ; Theoretic 
Sp.  Gr.  2-331,  Observed  2*3227 ; Boiling-pt.  68°  ; 3fol.  Voh  | | |. 
— This  compound  is  gaseous  at  ordinary  temperatures,  but  by 
slight  pressure,  or  by  exposure  to  a cold  of  — 1°  F.,  it  is  reducible 
to  a red  liquid,  which,  according  to  Millon,  is  liable  to  explode  as 
powerfully  as  chloride  of  nitrogen.  The  gas  is  of  a colour  still 
deeper  than  that  of  chlorous  anhydride,  and  has  a similar  but 
less  irritating  odour.  It  may  be  preserved  unaltered  in  the  dark, 
but  is  gradually  decomposed  in  the  sunlight  into  its  component 
gases.  Water  dissolves  about  20  times  its  bulk  of  the  c:as,  and 
ibrms  a yellow  solution,  which  bleaches  powerfully.  I'lie  gas 
requires  great  care  in  its  preparation,  as  a temperature  of  140°  or 
145°  determines  its  explosion ; 2 volumes  of  this  gas  furnish  a 
mixture  of  2 volumes  of  oxygen  and  1 of  chlorine,  its  composition 
being  represented  on  the  following  page. 

Peroxide  of  chlorine  may  be  thus  obtained : — F used  chlorate 
of  potassium  is  broken  into  coarse  fragments,  and  treated  with 


120 


PEROXIDE  OF  CHLORINE. 


By  weight. 

Chlorine  Cl  = 35-5  or  52*59 
Oxygen  02  = 32*0  47*41 


By  vol.  Sp.  gr. 

1 or  0*5  = 1 226 

2 1*0  = 1-105 


Peroxide  of ) 
chlorine  ) 


cie2 


67*5  100*00 


2 1*0  2*331 


two-thirds  of  its  weight  of  oil  of  vitriol,  the  action  being  favonred 
by  a very  gentle  heat.  The  reaction  may  be  represented  by  the 
following  equation : — 


Chlorate  of 
potassium. 


3 KCIO3 


4- 


Sulphuric 

acid. 


2 H2S04 


Perox.  of 
chlorine. 


= 2 C102  + 


Perchlor. 

potassium. 

KC104  + 


Acid  sulph. 
potassium. 


Water. 


2KHS04  -I-  H20. 


This  peroxide  may  also  be  procured  mixed  with  carbonic  anhy- 
dride, by  mixing  chlorate  of  potassium  and  crystallized  oxalic 
acid,  both  finely  powdered  separately,  and  gently  heating  to  150° 
(Calvert). 

Peroxide  of  chlorine  acts  rapidly  upon  mercury,  and  must 
therefore  be  collected  by  displacement.  Mere  contact  with  many 
combustible  matters  at  once  determines  its  explosion.  Place,  for 
instance,  4 or  5 grains  of  chlorate  of  potassium  at  the  bottom  of  a 
tall  glass,  and  pom^  upon  it  a little  water ; 
then  having  placed  the  glass  in  a deep 
plate  (fig.  298),  add  a piece  of  phosphorus 
of  about  the  size  of  a pea,  and  by  means  of 
a long  funnel  pour  slowly  in  about  a tea- 
spoonful of  oil  of  vitriol ; flashes  of  a beau- 
tiful green  light,  attended  with  a crack- 
ling noise,  will  be  immediately  produced. 
If  loaf  sugar  and  chlorate  of  potassium  be 
separately  powdered,  and  mixed  in  equal 
proportions  with  each  other  on  a sheet  of 
paper,  by  means  of  a spatula,  the  addition 
of  a drop  of  'sulphuric  acid  will  liberate 
peroxide  of  chlorine,  which  will  be  decom- 
posed by  the  combustible  matter,  and  sufficient  heat  will  be 
emitted  to  cause  the  mass  to  burst  into  flame,  and  to  deflagrate 
with  great  brilliancy.  Peroxide  of  chlorine  is  not  possessed  of 
acid  properties ; alkaline  solutions,  however,  absorb  it  rapidly,  but 
when  evaporated,  they  yield  a mixture  of  chlorite  and  chlorate  of 
the  metal : — 

Perox.  chlorine  of  Chlorite  of  Chlorate  of  ^ 

perox.  cnionne.  potash.  potassium.  potassium.  vvater. 

2^,  + 2 Klie  = KCl^  + KCie3  -f  HA 

Other  oxides  of  chlorine  have  been  obtained ; they  have  a 
composition  which  may  be  explained  by  considering  them  as 
compounds  of  chlorous  anhydride  with  chloric  or  with  perchloric 
anhydride ; they,  however,  present  but  few  points  of  interest. 
Davy’s  eiichlorine^  which  is  evolved  on  gently  heating  a chlorate 
with  hydrochloric  acid,  is  a yellow  explosive  gas,  consisting  of  a 


Fia.  298. 


CHLOKIDE  OF  NITROGEFT. 


121 


mixture  of  chlorine  with  one  of  these  compound  oxides,  the 
chloro-chloTic  acid  (2  Cl206,Cl203 ; Millon). 

(38^)  Chlokide  of  Nitrogen  (HCl2N,Cl3N  ?) ; Sp.  Gr.  of 
Liquid^  1-653. — The  attraction  existing  between  chlorine  and 
nitrogen  is  very  feeble ; the  compound  commonly  known  by  the 
name  of  chloride  of  nitrogen  is  always  obtained  by  indirect 
means. 

If  a current  of  ammoniacal  gas  be  directed  into  a bottle  of 
gaseous  chlorine  it  will  take  fire  spontaneonsly,  burning  with  a 
green  fiame,  whilst  hydrochloric  acid  is  formed,  and  nitrogen  is 
set  free  ; dense  white  fumes  being  generated  by  the  union  of  the 
hydi*ochloric  acid  with  undecomposed  ammonia.  By  modifying 
the  experiment,  the  reaction  may  be  employed  as  a means  of 
obtaining  nitrogen  gas,  for  when  a stream  of  chlorine  gas  is 
transmitted  through  a solution  of  ammonia,  the  hydrochloric  acid 
as  fast  as  it  is  formed  combines  with  undecomposed  ammonia,  and 
nitrogen  is  liberated : if  the  solution  be  concentrated,  each  bubble 
of  chlorine  produces  a fiash  of  light.  One  atom  of  ammonia, 
when  decomposed  by  3 atoms  of  chlorine,  yields  1 atom  of  nitro- 
gen ; 2 H3N  -f-  3 CI2,  becoming  6 HCl  + The  nitrogen  is  apt 
to  be  mixed  with  a variable  quantity  of  oxygen,  a little  water 
being  also  decomposed  at  the  same  time.  (A.  Anderson.) 

But  if  instead  of  acting  on  a solution  of  free  ammonia,  a bottle 
of  chlorine  perfectly  clear  from  greasy  matter  be  inverted  over 
a leaden  dish  containing  a solution  of  1 part  of  sal  ammoniac 
(H4NCI),  in  12  parts  ot  water,  drops  of  a yellow  oily-looking 
liquid  gradually  collect  on  the  surface  of  the  liquid  and  fall  to 
the  bottom,  whilst  the  chlorine  slowly  disappears : this  liquid  is 
the  substance  known  as  chloride  of  nitrogen.  A safer  method  of 
obtaining  this  body  consists  in  suspending  a fragment  of  sal  am- 
moniac (say  20  or  30  grains)  in  a solution  of  hypochlorous  acid ; 
oily  drops  of  the  so-called  chloride  of  nitrogen  are  gradually 
formed,  and  sink  in  the  liquid  as  the  salt  is  dissolved.  The  new 
body  remains  liquid  at  — 16°,  but  is  very  volatile,  and  possesses  a 
peculiar  penetrating  odour.  It  is  one  of  the  most  dangerous  com- 
pounds known,  for  it  explodes  with  tremendous  violence  when 
heated  to  between  200°  and  212°  F.,  emitting  a flash  of  light 
when  the  detonation  occurs.  The  explosion  is  so  sudden  that  it 
invariably  breaks  any  glass  or  porcelain  vessel  in  which  it  may  be 
contained : hence  a leaden  saucer  is  used  in  preparing  the  com- 
pound. The  liquid  chloride  also  explodes  violently  at  ordinary 
temperatures  when  brought  into  contact  with  many  inflammable 
substances,  such  as  oil  of  turpentine,  ])hosphorus,  and  the  fixed 
oils.  The  alkalies  likewise  cause  its  immediate  ex])losion.  On 
the  other  hand,  it  does  not  explode  when  touched  with  the  resins, 
the  strong  acids,  with  metallic  bodies  in  general,  or  with  sugar. 

Little  or  nothing  is  known  of  the  cause  of  these  remarkable 
reactions,  or  of  the  light  and  heat  emitted  when  the  chloride 
explodes  by  slightly  elevating  its  temperature  ; in  this  case  and  in 
the  analogous  instances  of  the  explosion  of  the  oxides  of  chlorine, 
light  is  emitted,  not  during  the  act  of  combination,  as  is  usual, 


122 


CHLOEEDES  OF  CAEBON. 


but  during  the  expansion  and  sudden  separation  of  the  two 
gaseous  elements. 

The  analysis  of  this  body  is  attended  with  great  difficulty ; 
indeed,  considerable  doubt  exists  as  to  its  true  composition.  It 
is  highly  probable  that  it  is  not  simply  a chloride  of  nitrogen,  but 
a combination  of  chlorine,  nitrogen,  and  hydrogen  (HCl2K,Cl3lI), 
somewhat  analogous  to  the  corresponding  explosive  compound 
which  may  be  formed  with  iodine  (400). 

(387)  Chloeides  of  Caebon.^' — Chlorine  does  not  unite  directly 
with  carbon,  but  Faraday  succeeded  in  procuring  several  compounds 
between  these  elements  by  the  decomposition  of  Dutch  liquid, 
a combination  of  carbon  and  hydrogen  with  chlorine,  obtained 
under  circumstances  which  will  be  explained  when  treating  of 
olefiant  gas  (488). 

Acetylene  Chloride  (formerly  Suhchloride)  of  Carhon  (OaCl^) 
forms  fine  silky  crystals,  which  may  be  sublimed  in  closed  vessels 
without  change  ; it  is  soluble  in  ether.  This  substance  is  obtained 
by  decomposing  the  ethylene-chloride  of  carbon  (-02014)  by  causing 
it  to  pass  several  times  through  a tube  heated  to  bright  redness. 
If  heated  in  air  on  platinum  foil,  it  burns  with  a red  smoky  flame. 

Ethylene  Chloride  (formerly  Protochloride)  of  Carbon  (02CI4) ; 
S'p.  Gr.  of  Liquid^  1-552;  of  Vajpour^  5*82;  Mol.  Vol.  [ J |; 
Boiling-pt.  248°. — This  compound  was  procured  by  Faraday  from 
the  solid  chloride  (02Cle)  by  subliming  it  repeatedly  through  a 
tube  filled  with  fragments  of  glass  heated  to  redness.  It  is  a 
transparent  colourless  liquid,  with  an  aromatic  odour. 

Faradafs  Chloride  (formerly  Sesguichloride)  of  Carbon 
(02C16) ; 8p.  Gr.  of  Solid.,  2-0;  of  Vapour.,  8-157  : Mol.Yol.\  \ |; 
Melting-pt.  320° ; Boiling-pt.  360°. — This  chloride  was  originally 
procured  by  the  action  of  chlorine  upon  Dutch  liquid  (488)  (Fara- 
day) ; but  it  has  since  been  obtained  by  the  action  of  chlorine 
upon  a variety  of  derivatives  from  the  alcohol  series.  It  is  a vola- 
tile crystalline  solid,  with  an  aromatic  odour  resembling  that  of 
camphor.  It  is  soluble  in  alcohol,  in  ether,  and  in  the  fixed  and 
volatile  oils.  An  isomeric  (506)  liquid  terchloride,  the  vapour  of 
which  has  a density  of  4-082,  and  a composition  0CI3,  was 
obtained  by  Eegnault  by  passing  the  vapour  of  tetrachloride  of 
carbon  (0CI4)  through  a tube  heated  to  low  redness. 

Tetrachloride  (formerly  Bichloride)  of  Carbon  (0CI4)  ; 8p.  Gr. 
of  Liquid.,^  1-599  ; of  Vapour^  5-30  ; Aiol.  Vol.  | | j;  Boiling-pt. 
172°. — This  substance  w^as  obtained  by  Eegnault  from  wmod-spirit, 
from  choloroform,  and  from  other  derivatives  from  wood-spirit, 
by  exposing  them  in  the  sun  to  the  action  of  an  excess  of  chlorine. 
Kolbe  also  found  that  a mixture  of  the  vapour  of  bisulphide  of 
carbon  and  chlorine,  wdien  passed  through  a poreclain  tube  heated 
to  redness,  yielded  the  same  compound.  It  is  a colourless  liquid, 
which  is  insoluble  in  water,  but  soluble  in  alcohol  and  in  ether  ; 
an  alcoholic  solution  of  potash  decomposes  it  into  chloride  and  car- 

* The  names  of  these  various  chlorides,  it  will  be  observed,  do  not  correspond  to 
their  formulae,  but  they  are  for  the  present  partially  retained,  since,  though  not 
strictly  accurate,  they  are  in  general  use. 


OXYCHLORIDE  OF  CARBON BROIMINE. 


123 


bonate  of  potassimn  6 KHO  + OCl^  = 4 KOI  + + 3 II^O. 

Tetrachloride  of  carbon  becomes  a crystalline  solid  of  pearly  lustre 
at  — 9°  F.  If  passed  through  red-hot  tubes  it  is  decomposed 
into  free  chlorine  and  a mixture  of  ethylene-chloride  and  Fara- 
day’s sesqnichloride  of  carbon. 

(388)  Oxychloride  of  Carbon:  ChlorocarhoniG  Acid  j Phos- 
gene Gas  (OOCI2,  or  C^O^Cl^  = 99) ; Theoretic  Sp.  Gr.  3*42 ; 
Observed^  3*68  ; Mol.  Yol.  | | |. — When  equal  measures  of  carbonic 
oxide  and  chlorine  are  exposed  to  the  direct  rays  of  the  sun,  they 
combine  and  become  condensed  into  half  their  volume.  The  com- 
bination takes  place  slowly  in  the  difiiised  light  of  day ; but  no 
action  occurs  if  the  two  gases  are  mixed  together  and  kept  in  a 
dark  room.  There  are  other  modes  of  obtaining  this  compound 
indirectly  : thus  it  may  be  prepared  by  transmitting  carbonic  oxide 
gas  through  heated  perchloride  of  antimony ; the  action  of  light 
is  not  necessary  in  this  case.  This  reaction  may  sometimes  be 
usefully  employed  as  a test  for  carbonic  oxide  when  mixed  in 
small  quantity  with  other  gases,  the  pungent  odour  of  the  oxy- 
chloride which  is  formed  being  very  characteristic.  The  compo- 
sition of  the  gas  is  the  following  : — 


By  weight. 

By  volume. 

Sp.  gr. 

Carbonic  oxide  -GO 

= 28 

or  28‘28 

2 or 

1-0  = 

0-967 

Chlorine  CI2 

11 

'71-72 

2 

1-0  = 

2-453 

Phosgene  gas  GOCh 

= 99 

100-00 

2 

1-0  = 

3-420 

Oxychloride  of  carbon  is  a colourless,  suffocating  gas,  which  is 
immediately  decomposed  by  w^ater  into  carbonic  anhydride  and 
hydrochloric  acid : OOCl^  + + 2 HCl.  A similar  decom- 

position occurs  if  it  be  treated  with  many  of  the  metallic  oxides, 
such  as  an  oxide  of  zinc,  whilst  a chloride  of  the  metal  is  formed ; 
OOClj-f  ZnO='0O2  + ^i^Cl2.  If  heated  with  arsenicum  or  anti- 
mony, the  chlorine  is  removed  and  carbonic  oxide  is  liberated. 
Oxychloride  of  carbon  does  not  possess  the  characters  of  an  acid ; 
but  if  the  gas  be  mixed  with  ammonia  in  the  proportion  of  1 
volume  of  phosgene  to  4 volumes  of  ammonia,  both  gases  are  con- 
densed, and  form  a white  volatile  solid,  which  is  neutral  to  test- 
paper,  destitute  of  smell,  and  soluble  in  water  and  in  alcohol  slightly 
diluted,  but  insoluble  in  ether.  This  substance  consists  of  a mix- 
ture of  chloride  of  ammonium  and  carbamide  (urea  ; Hatanson) : — 

4 ii3]sr-feeci2=2  ii,]srci+ii:,isr2ee. 

§ II.  Bromine:  Br=80.* 

Atomic  Yol.  of  Ywpour  []] ; Theoretic  Sp.  Gr.  of  Yapour, 
5'528  ; Observed.,  5*54 ; of  Liquid  at  32°,  3-187 ; Melting- 
pt.  9°'5;  Boiling-pt.  145°'4. 

(389)  Bromine,  so  named  owing  to  its  irritating  odour  (from 
/SpwfAoc;  a stench),  was  discovered  by  Balard  in  tlie  year  1826, 
in  bittern.,  which  is  the  mother-liquor  of  sea  water  after  the  less 

* The  molecular  volume  of  free,  bromine  being  regarded  as  (Br  Br)— ! I T 


124 


PKEPAEATION  OF  BKOMIXE. 


soluble  salts  have  been  extracted  by  crystallization.  Bromine 
exists  in  sea  water  in  minute  quantity,  varying  from  one-third  of 
a grain  to  about  one  grain  in  each  gallon  ; the  waters  of  the  Dead 
Sea  also  contain  bromine  in  even  larger  quantity  than  this  : it 
appears  to  be  combined  with  magnesium,  as  bromide  of  mag- 
nesium. Many  saline  springs,  such  as  those  of  Kreuznach  and 
Kissingen,  likewise  contain  bromine  in  quantity  sufficient  to  render 
its  extraction  from  them  a source  of  profit.  Indeed,  few  deposits 
of  chloride  of  sodinm  exist  in  which  traces  of  bromine  have  not 
been  discovered.  It  has  also  been  found  in  a silver  ore  from 
Mexico,  and  it  is  abundant  in  the  mines  of  Chanarcillo,  in  South 
America  ; in  both  cases  the  bromide  of  silver  is  mixed  with  chlo- 
ride of  silver. 

Preparation. — In  order  to  obtain  bromine,  the  mother-liqnor 
from  the  brine,  after  all  the  salts  separable  by  crystallization  have 
been  removed,  is  subjected  to  a current  of  chlorine,  taking  care  to 
avoid  an  excess  of  this  gas,  which  would  occasion  inconvenience 
by  forming  a compound  with  the  liberated  bromine.  All  the 
bromides  are  decomposed  readily  by  chlorine,  the  attractions  of 
chlorine  being  more  powerful  than  those  of  bromine.  In  the 
foregoing  operation  chloride  of  magnesium  is  formed,  and  bromine 
is  set  free  : MgBr2-hCl2=MgCl2  + Br2 ; the  bromine  shows  itself 
by  giving  to  the  liquid  a beautiful  and  characteristic  yellow  colour. 
This  yellow  liquid  when  agitated  with  ether,  parts  with  its 
bromine,  which  is  dissolved  by  the  ether.  If  the  mixture  be 
allowed  to  stand  in  a glass  globe  closed  at  the  top  by  a stopper, 
and  fmmished  with  a glass  stopcock  at  the  bottom,  the  ether  rises 
to  the  surface,  where  it  forms  a beautiful  golden  yellow  layer. 
The  mother-liquor  is  di-awn  off  by  opening  the  stopcock,  and  the 
ethereal  solution  is  agitated  with  a solution  of  hydrate  of  potash  ; 
the  yellow  colour  immediately  disappears ; bromide  and  bromate 
of  potassium  are  formed  and  dissolved  in  the  water;  3 Br2-|- 
6 KHOi^KBi-Og  + S KBr-f  3 II2O  ; whilst  the  ether,  after  repose, 
rises  again  to  the  surface  despoiled  of  its  bromine,  and  may  again 
be  employed  in  a repetition  of  the  process  upon  a fresh  quantity 
of  bittern.  When  the  solution  of  potash  has,  by  repeated  charges 
of  bromine,  been  nearly  neutralized,  the  liquid  is  evaporated  to 
dryness  ; the  saline  mass  is  gently  ignited  to  decompose  the  bro- 
mate, after  which  it  is  mixed  with  peroxide  of  manganese  and 
distilled  in  a retort  with  sulphuric  acid : dense  red  vapours  of 
bromine  pass  over,  which  may  be  collected  in  a receiver  containing 
w^ater  and  kept  cool  by  ice.  The  decomposition  is  of  the  same 
nature  as  that  attending  the  liberation  of  chlorine  from  sea  salt 
by  means  of  oxide  of  manganese  and  sulphuric  acid  : — 

2 KBr-|-Mne2-|-2  H2Se,=K2Se,-f  MnSe,-f  2 H2e  + Br2. 

In  this  operation  a small  quantity  of  chlorine  passes  over  with 
the  bromine,  since  from  the  manner  in  which  the  bromide  of 
potassium  is  formed,  it  is  always  contaminated  with  a portion  of 
chloride  of  potassium.  The  chlorine  unites  with  part  of  the 
bromine,  forming  chloride  of  bromine,  which  is  partially  decom- 


HYDROBROMIO  ACID. 


125 


posed  and  dissolved  by  tlie  water  in  the  receiver,  while  the  bromine 
is  condensed  in  red  drops.  In  order  to  obtain  bromine  free  from 
chlorine  it  must  be  saturated  with  hydrate  of  baryta,  which  pro- 
duces a mixture  of  bromide  and  chloride  with  bromate  of  barium  ; 
this  mixture  must  be  heated  to  redness  in  order  to  convert  the 
bromate  into  bromide  of  barium,  and  the  residue  digested  in 
alcoliol,  which  dissolves  nothing  but  the  bromide.  The  bromide 
of  barium  is  obtained  by  evaporation  of  its  alcoholic  solution,  and 
when  heated  with  black  oxide  of  manganese  and  sulphuric  acid  it 
yields  pure  bromine. 

Properties. — Bromine  forms  a red  liquid,  so  deep  in  colour  as 
to  be  nearly  opaque.  It  has  a sp.  gr.  of  2*966  at  60°  : it  is  very 
volatile,  and  emits  dense  red  vapours  resembling  peroxide  of  ni- 
trogen in  colour  (vol.  i.  fig.  80).  In  smell  it  resembles  chlorine, 
and  is  extremely  irritating  to  the  nose  and  fauces  when  respired, 
even  if  largely  diluted  with  air.  When  swallowed  it  operates  as 
a powerfully  irritating  poison  ; it  acts  rapidly  on  all  the  organic  tis- 
sues, and  renders  the  skin  permanently  yellow.  Bromine  boils  at 
115° *4  F.  (Pierre),  and  when  exposed  to  a temperature  of  9° *5  it 
forms  a red  crystalline  solid.  The  properties  of  bromine  greatly 
resemble  those  of  chlorine,  though  they  are  less  strongly  developed. 
It  bleaches  many  vegetable  colours.  Its  vapour  will  not  support 
the  fiame  of  a burning  taper.  Bromine  is  slightly  soluble  in 
water,  and  gives  to  it  a yellow  colour ; it  also  forms  with  it  a 
hydrate  (Br,  5 H^O ; Lowig),  which  crystallizes  in  octohedra  at 
32°.  This  aqueous  solution  of  bromine  is  decomposed  by  sunlight 
into  hydrobromic  acid  and  oxygen.  Alcohol  dissolves  bromine 
freely,  and  ether  does  so  still  more  abundantly.  Olefiant  gas  is 
rapidly  absorbed  by  liquid  bromine,  and  a liquid  compound 
(OjH/Brd,  bibromide  of  ethylene,  is  formed.  Bromine  combines 
directly  with  phosphorus,  and  with  many  of  the  metals,  forming 
compounds  termed  bromides  (540),  the  act  of  combination  being 
often  attended  with  ignition,  as  in  case  of  antimony  and  of 
tin  ; even  gold  combines  with  it,  though  but  slowly  ; its  compound 
with  silver  furnishes  a material  of  considerable  value  in  photo- 
graphic operations. 

(390)  Hydrobromic  Acid  (IIBr— 81) ; Theoretic  Sp.  Gr. 
2*7986;  Observed.,  2*731;  Mol.  Yol.  | | |. — Bromine  resembles 
cldorine  in  its  power  of  combining  with  hydrogen,  and  forming 
with  it  a very  powerful  acid,  which  is  a gaseous  body  consisting 
of  equal  measures  of  hydrogen  and  bromine  vapour  united  with- 
out change  of  bulk.  The  mixture  of  bromine  vapour  and  hydrogen 
cannot  lie  detonated  by  tlie  approach  of  flame,  or  by  tlie  electric 
spark,  but  the  two  elements  may  be  made  to  unite  slowly,  by  sus- 
pending a red-hot  platinum  wire  in  the  mixture.  If  moisture  be 
present  the  occurrence  of  combination  instantly  shows  itself  by 
the  formation  of  white  fumes,  which  arise  from  the  union  of  the 
newly  produced  gaseous  acid  with  the  aqueous  vapour. 

Preparation. — 1.  Hydrobromic  acid  gas  may  be  procured 
abundantly  by  decomposing  bromide  of  potassium  with  a concen- 
trated solution  of  phosphoric  acid.  If  sulphuric  acid  be  used  for 


126 


HTDROBROMIC  ACID BEOMIDES. 


the  pni’pose,  the  product  is  impure,  since  this  acid  itself  undergoes 
partial  deoxidation. 

2. — It  may  also  be  obtained  by  decomposing  bromide  of  phos- 
phorus by  means  of  a small  quantity  of  water,  when  the  follow- 
ing reaction  occurs : — 

PBr3  + 3 H,e  = 3 HBr  + H3Pe3 ; 


Fig.  299. 


phosphorous  and  hydrobromic  acids  being  produced.  This  experi- 
ment may  be  easily  performed  with  the  aid  of  a tube  bent  as  in 
fig.  299.  In  the  bend  y?,  a few  fragments  of  phosphorus  and 
moistened  glass  are  placed,  bromine  is  poured  into  and  the  tube 
is  closed  by  a cork,  cy  on  apphnng  a gentle  heat  at  5,  the 

bromine  is  distilled  over  and  comes 
into  contact  with  the  phosphorus ; 
the  bromide  of  phosphorus  is  decom- 
posed by  the  water  at  the  moment  of 
its  formation,  and  hydrobromic  acid 
escapes  by  the  bent  tube,  t. 

Hydrobromic  acid  gas  is  colour- 
less, it  is  not  inflammable,  it  extin- 
guishes flame,  and  possesses  the  usual 
irritating  action  of  acid  gases  on  the  lungs.  Faraday  succeeded 
in  liquefying  the  gas  under  strong  pressure  ; and  in  a bath  of  solid 
carbonic  anhydride  and  ether,  he  even  obtained  it  in  the  form  of 
a solid,  which  melted  at  — 121°.  The  acid  has  the  following  com- 


By  weight. 

By  volume.  Sp.  gr. 

Bromine  . . . 

Br 

= 80 

or  98-76 

1 or 

0-5  = 2-764 

Hydrogen  . . . 

H 

= 1 

1-24 

1 

0-5  = 0-034 

Hydrobromic  ) 
acid  J 

HBr 

= 81 

100-00 

2 

1 CO 

05 

II 

o 

Hydrobromic  acid  gas  is  very  soluble  in  water,  forming,  when 
concentrated,  a fuming  solution  of  greater  density  than  hydro- 
chloric acid.  A solution  of  the  acid  of  sp.  gr.  1*186  (HBr,  5 
contains  about  17  per  cent,  of  the  anhydi’ous  acid ; it  boils  at 
259°,  and  may  be  distilled  without  change.  (See  p.  131.) 
Chlorine  decomposes  it  immediately  ; bromine  being  set  fi*ee  and 
hydrochloric  acid  produced. 

The  action  of  hydrobromic  acid  upon  the  metallic  oxides  is 
analogous  to  that  of  hydrochloric  acid  upon  them  ; bromide  of  the 
metal  and  water  being  produced ; thus  hydrobromic  acid  and 
hydrate  of  potash  form  bromide  of  potassium  and  water ; KHO 
-f  HBr  yielding  KBr-fH^O. 

(391)  Bromides. — The  bromides  are  all  solid  at  ordinary  tem- 
peratures : most  of  them  are  fused  by  a moderate  heat,  and  are 
partially  volatilized ; and  the  bromides  of  gold  and  platinum  are 
decomposed.  Most  of  the  bromides  are  readily  soluble  in  water. 
They  are  all  decomposed  by  chlorine,  and  when  in  solution  they 
may  be  recognised  by  the  yellow  colour  of  bromine  which  is  pro- 
duced by  the  addition  of  a few  drops  of  chlorine  water,  taking 
care  to  avoid  an  excess  of  chlorine.  On  agitating  this  yellow 


BROmC  ACID. 


127 


solution  with  ether,  the  bromine  is  dissolved  by  the  ether,  which 
on  standing  separates  as  a yellow  liquid,  at  the  top  of  the  colour- 
less aqueous  portion.  If  the  quantity  of  the  bromide  is  very 
minute,  a small  quantity  of  bisulphide  of  carbon  may  be  advan- 
tageously substituted  for  ether,  as  it  acquires  a yellow  tinge  with 
an  amount  of  bromine  too  small  to  act  upon  the  ether ; the  pres- 
ence of  sulphuric  or  of  sulphurous  acid  must  however  in  this  case 
be  avoided.  The  bromides,  when  heated  with  black  oxide  of 
manganese  and  oil  of  vitriol,  yield  red  vapours  of  bromine  ; strong 
nitric  acid  has  a similar  effect.  Nitrate  of  silver  and  nitrate  of 
lead  each  give  a white  precipitate  with  solutions  of  the  bromides, 
forming  bromide  of  silver  (AgBr),  or  bromide  of  lead  (PbBr^) ; 
the  bromide  of  silver  is  insoluble  in  cold  nitric  acid,  but  is  dis- 
solved by  a large  excess  of  ammonia ; but  the  bromide  of  lead  is 
dissolved  by  the  addition  of  diluted  nitric  acid.  Mercurous 
nitrate  also  gives  a white  precipitate  of  mercurous  bromide 
(HgBr)  when  added  to  solutions  of  the  bromides ; it  is  soluble  in 
chlorine  water  wdth  liberation  of  bromine. 

Bromine  often  combines  with  the  same  metal  in  more  than  one 
proportion,  and  the  compounds  of  bromine  correspond  almost 
always,  both  in  number  and  composition,  with  those  of  chlorine 
with  the  same  metal.  Oxybromides  may  be  formed  resembling 
the  oxychlorides  ; and  the  bromides  of  the  alkaline  metals 
form  double  bromides  with  the  bromides  of  the  metals  which 
yield  acids  with  oxygen. 

(392)  Bromic  Acid  (HBrOg,  or  H0,Br06=:129). — The  oxy- 
acids  of  bromine  are,  with  the  exception  of  bromic  acid,  nearly 
unknown,  and  this  compound  even  has  never  been  obtained  in  the 
form  of  anhydride.  The  bromic  corresponds  to  chloric  acid  in 
composition.  Bromate  of  potassium  is  procured  by  acting  on 
bromine  with  caustic  potash,  and  from  this  salt  the  acid  is 
obtained  by  a process  similar  to  that  employed  in  the  preparation 
of  chloric  acid  (382).  By  the  action  of  heat,  bromate  of 
potassium  is  decomposed,  bromide  of  potassium  being  formed, 
whilst  oxygen  is  liberated.  Any  solid  bromate,  when  mixed  witli 
concentrated  sulphuric  acid  and  heated,  gives  off*  red  fumes  of 
free  bromine,  while  oxygen  is  evolved.  Bromate  of  silver  and 
mercurous  bromate  are  anhydrous  and  sparingly  soluble  : bromate 
of  lead  retains  1 atom  of  water  (Bb  2 BrOg,  HjO) : it  likewise  is 
but  slightly  soluble.  When  heated  with  the  hydrochloric  acid 
these  precipitates  evolve  free  bromine.  All  the  salts  of  bromic 
acid  which  have  as  yet  been  prepared  are  monobasic. 

(393)  Chloride  of  Bromine  is  easily  obtained  by  transmitting 
chlorine  gas  through  liquid  bromine  ; it  is  a volatile,  reddish- 
yellow  liquid,  with  a very  pungent,  irritating  odour.  Water  dis- 
solves it,  forming  a deep  yellow  solution  possessed  of  considerable 
bleaching  power. 

Bromide  of  Nitrogen  may  be  obtained  by  digesting  bromide 
of  potassium  with  the  so-called  chloride  of  nitrogen  ; it  forms 
a detonating  oily-looking  liquid,  resembling  chloride  of  nitrogen 
in  appearance  and  properties. 


128 


IODINE. 


§ III.  Iodine:  I=12T.* 

Atomic  or  Corrib . Yol.  of  Yapour  Q,  Theoretic  Sp.  Gr.  of 

Yapour^  8-756 ; Observed^  8-716 : ISp.  Gr.  of  Sdid^  4-917 ; 

ALelting-pt.  225°  ; Boiling-pt.  347°. 

(394)  Iodine,  the  third  element  in  the  gronp  which  we  are 
now  examining,  is  still  denser  than  bromine,  as  it  assumes  the 
solid  form  at  the  ordinary"  temperature  of  the  air.  Its  discovery 
dates  hack  to  the  year  1811,  when  it  was  found  by  Comdois 
accidentally,  in  the  waste  liquors  produced  in  the  manufacture  of 
carbonate  of  sodium  from  the  ashes  of  sea-weed. 

Iodine  exists  in  the  ocean  in  quantities  still  smaller  than 
bromine.  It  is,  notwithstanding,  obtained  with  less  difficulty, 
since  the  fiici,  algse,  sponges,  and  other  marine  plants,  extract  it 
from  sea-water,  and  store  it  np  in  their  tissues.  These,  when 
burnt,  give  an  ash  which  is  technically  known  as  kelp  / it  contains 
iodine  in  the  form  of  iodide  of  sodium.  In  the  mineral  kingdom, 
iodine  has  been  found  in  one  or  two  rare  ores  ; thus  it  occiu’s 
combined  with  silver  in  Mexico,  and  ^vith  zinc  in  Silesia. 

Extraction. — Iodine  is  at  present  largely  manufactured  at 
Glasgow,  from  kelp  made  on  the  coasts  of  Scotland  and  Ireland  ; 
the  following  is  an  outline  of  the  process  adopted  in  procuring 
it : — The  sea-weed  having  been  ch'ied  in  the  sun,  is  burned  in 
shallow  excavations,  at  a low  heat ; owing  to  the  volatility  of  the 
iodide  of  sodium  at  a red  heat,  the  loss  of  this  salt  would  be  con- 
siderable if  the  temperature  were  allowed  to  rise  too  high.  The 
half-fused  ash,  or  kelp,  which  remains,  is  broken  into  fragments 
and  treated  with  boiling  water,  which  dissolves  about  one-half  of 
the  ash.  The  liquid  thus  obtained  is  then  evaporated  in  open 
pans,  and  all  that  can  be  separated  by  crystallization  is  removed ; 
a double  sulphate  of  potassium  and  sodium,  carbonate  of  sodium, 
and  chloride  of  potassium  are  thus  extracted.  The  iodine  remains 
in  the  mother-liquor,  which  still  retains  sulphide  of  sodium,  besides 
hyposulphite,  and  some  carbonate  of  sodium.  This  hquor,  or 
iodine  ley ^ is  now  mixed  with  one-eighth  of  its  bulk  of  oil  of  vitriol, 
and  allowed  to  stand  for  twenty-four  hours  ; carbonic  anhydi-ide, 
sulphurous  anhydride,  and  sulpliuretted  hydrogen  gases  escape,  and 
sulphate  of  sodium  crystallizes  out,  mixed  with  a considerable  quan- 
tity of  deposited  sulphur.  The  supernatant  liquid  is  next  trans- 
ferred to  a stoneware  or  leaden  retort,  which,  if  of  lead,  is  of 
cylindrical  form,  lig.  300,  supported  in  a sand-bath,  and  gently 
heated  from  beneath  by  a small  lire  ; the  head  of  the  retort,  J,  c, 
is  luted  on  with  clay,  and  the  contents  of  the  retort,  having  been 
heated  to  about  140°,  a quantity  of  powdered  black  oxide  of 
manganese  is  introduced  through  the  tubulure,  b.  The  process  must 
be  conducted  slowly,  at  a low  temperature  ; iodine  distils  over  and 
is  condensed  in  the  globular  receivers,  d.  It  is  purified  by  a second 
sublimation.  The  object  of  the  second  tubulure,  shown  at  c,  is  to 

* Taking  the  molecule  of  iodine  when  free  to  be  (I  I)  or  I2,  its  molecular  volume 
m the  state  of  vapour  will  be  n 


PROPERTIES  OF  IODINE. 


129 


facilitate  the  clearing  of  the  neck  of  the  retort  in  case  it  should 
become  obstructed  by  the  formation  of  crystals.  If  the  tempera- 
ture be  allowed  to  rise  as  high  as  212°,  the  chloride  of  sodium 

Fia.  300. 


retained  in  the  ley  is  decomposed,  chlorine  is  disengaged,  and 
combines  with  part  of  the  iodine,  forming  chloride  of  iodine,  which 
is  wasted. 

In  the  foregoing  process,  the  addition  of  the  sulphuric  acid 
occasions  the  decomposition  of  the  carbonate  and  hyposulphite  of 
sodium,  which  still  remain  in  solution,  as  well  as  of  any  sulphide 
of  sodium  that  may  be  present,  forming  sulphate  of  sodium  which 
is  removed  by  crystallization.  The  liquid  retains  an  excess  of 
sulphuric  acid,  and  all  the  iodide  of  sodium.  When  this  mixture 
is  heated  with  peroxide  of  manganese,  the  iodine  is  liberated, 
whilst  sulphates  of  sodium  and  manganese  remain  in  the  retort. 
The  process  resembles  that  for  bromine  : — 

2 NaI-hMne,-hII,Se,=IIa,Se,-f  WnSe,-f  2 H.O-f  I,. 

Properties. — The  crystalline  form  of  iodine  is  an  octohedron 
with  a rhombic  base  ; but  it  is  generally  obtained  in  bluish-black 
scales  resembling  plumbago  in  lustre.  It  is  a non-conductor  of 
electricity.  At  ordinary  temperatures,  and  especially  when  in  a 
moist  condition,  it  is  sensibly  volatile,  emitting  an  odour  like  that 
of  chlorine,  but  much  weaker  ; when  heated  it  undergoes  fusion  at 
225°  ; and  at  about  347°  it  boils  and  is  converted  into  a magniti- 
cent  purple  vapour,  whence  it  derives  its  name  (from  violet- 
coloured).  Iodine,  when  taken  internally,  acts  in  large  doses  as 
an  irritant  poison  ; but  in  small  quantities  it  is  a very  valuable 
medicine,  particularly  in  glandular  swellings,  and  in  certain  forms 
of  goitre.  It  stains  the  skin  and  most  organized  substances  of 
a brown  colour,  and  gradually  corrodes  them.  W ater  forms  with 
9 


130 


HYDKIODIC  ACID. 


it  a yellow  solution,  but  dissolves  it  only  in  very  small  quantity. 
Its  bleaching  properties  are  very  feeble.  Alcohol,  ether,  hydriodic 
acid,  and  solutions  of  the  iodides,  dissolve  it  freely,  forming  brown 
solutions.  LngoVs  Solution^  which  was  fonnerly  much  used  in 
medicine,  consists  of  20  grains  of  iodine  and  30  of  iodide  of 
potassium,  dissolved  in  an  ounce  of  water  ; it  is  of  a deep  brown 
colour.  Iodine  is  also  soluble  in  bisulphide  of  carbon,  to  which 
a minute  quantity  of  iodine  imparts  a characteristic  rich  violet 
colour.  Chloroform  and  benzol  likewise  dissolve  it,  forming  red 
solutions.  Iodine  attacks  many  of  the  metals  rapidly,  forming 
compounds  termed  iodides  / iron  or  zinc  is  readily  dissolved  by  it 
if  placed  with  it  in  water,  an  iodide  of  the  metal  being  formed. 
The  compounds  of  iodine  with  the  metals  and  with  hydrogen  are 
decomposed  by  chlorine,  and  even  by  bromine,  while  the  iodine 
is  set  free.  Advantao;e  is  taken  of  this  fact  in  ascertaining  the 
presence  of  iodine,  the  most  delicate  test  for  it,  when  uncom- 
bined, is  the  intense  blue  colour  which  it  strikes  with  starch  ; by 
its  means,  with  due  precaution,  1 part  of  iodine,  when  dissolved 
in  one  million  parts  of  water,  may  be  discovered. 

There  are  various  modes  of  applying  this  test : the  simplest 
consists  in  mixing  a little  cold  starch  paste  with  the  liquid  which 
is  suspected  to  contain  iodine ; if  it  be  present  in  an  uncombined 
form,  a beautiful  blue  colour  shows  itself.  If  the  iodine  be  in 
combination,  this  colour  does  not  appear  until  a drop  of  chlorine 
water  or  of  solution  of  bleaching  powder  be  added  to  set  the 
iodine  free.  An  excess  of  chlorine  must  be  avoided,  as  it  forms 
chloride  of  iodine,  and  prevents  the  action  of  the  test : David 
Price  recommends  the  use  of  a solution  of  nitrite  of  potassium  as 
a substitute  for  the  chlorine,  the  liquid  to  be  tested  being  slightly 
acidulated : no  inconvenience  arises  from  the  presence  of  the 
nitrite  in  slight  excess.  The  colour  fades  away  if  the  solution 
be  heated,  but  it  is  partially  restored  as  the  temperature  falls. 
Solutions  of  the  alkalies,  as  well  as  of  sulphurous  acid,  sulphuret- 
ted hydrogen,  and  reducing  agents  generally,  destroy  the  colour. 
As  starch  paste  cannot  be  long  kept  without  undergoing  decom- 
position, it  is  often  convenient  to  substitute  for  the  freshly  made 
paste,  paper  which  has  been  smeared  with  the  starch,  and  allowed 
to  become  dry.  If  kept  in  a dry  place,  such  paper  may  be  pre- 
served for  an  indefinite  length  of  time,  and  is  ready  for  use  at 
any  moment. 

(395)  Hydriodic  Acid  (HI  =:  128) ; Theoretic  Sjo.  Gr.  4T125 ; 
Observed^  4*413  ; Mol.  Yol.  \ \ |. — By  heating  iodine  in  hydro- 
gen, the  volume  of  the  gas  becomes  doubled,  and  a colourless  acid 
gas  is  produced ; but  it  is  never  prepared  for  use  in  this  manner. 
A better  mode  is  the  following : — Place  in  a small  retort  10  parts 
of  iodide  of  potassium  with  5 of  water,  and  20  of  iodine ; then 
di’op  in  cautiously  1 part  of  phosphorus  cut  into  small  fragments, 
and  apply  a gentle  heat.  Hydriodic  acid  gas  will  be  extricated 
abundantly,  and  may  be  collected,  by  displacement,  in  dry  bot- 
tles. The  result  of  the  reaction  is  explained  by  the  following 
equation : — 


HYDKIODIC  ACm IODIDES. 


131 


Iodide  of  Phos-  Phosphate  of  Hydriodic 

potassium.  Iodine.  phorus.  Water.  potassium.  acid. 

8 KI  + 10  I2  + P4  + 16  yield  4 + 28  HI. 

Hydriodic  acid  gas  is  not  combustible,  nor  does  it  support 
combustion.  It  fumes  in  the  air,  and  possesses  a powerfully  acid 
irritating  odour.  It  is  reduced  under  strong  pressure  to  a yellow- 
ish liquid,  which  freezes  at  60°.  Water  dissolves  the  gas  with 
great  avidity. 

A solution  of  hydriodic  acid  may  be  easily  prepared  by  sus- 
pending iodine  in  water,  and  transmitting  a current  of  sulphu- 
retted hydrogen  gas  through  the  mixture  until  the  brown  colour 
of  the  iodine  disappears ; sulphur  is  deposited  in  abundance,  and 
hydriodic  acid  is  formed.  The  liquid  gradually  becomes  clear  if 
left  at  rest ; it  may  then  be  decanted  from  the  precipitated  sul- 
phur : the  clecomposition  consists  simply  in  the  displacement  of 
the  sulphur  by  the  iodine ; 2 H2S  -h  2 I^  becoming  4 HI  -f 
This  liquid  may  be  concentrated  till  it  acquires  a density  of  1*7, 
when  it  consists  of  (2HI2IIH2O;  Bineau).*  It  then  distils 
unchanged  at  262°.  It  is  a powerful  acid,  and  dissolves  iodine 
freely,  forming  a brown  solution : by  exposure  to  the  air,  espe- 
cially if  placed  in  a strong  light,  it  absorbs  oxygen,  water  is 
formed,  and  the  liquid  becomes  brown  from  the  liberation  of 
iodine.  Chlorine  effects  its  instant  decomposition,  whether  it  be 
in  the  gaseous  form  or  in  solution.  Bromine  and  nitric  acid  act 
similarly  and  with  almost  equal  rapidity ; many  other  oxidizing 
agents  also  decompose  it.  Mercury  decomposes  it  gradually,  and 
combines  with  its  iodine.  A solution  of  hydriodic  acid  dissolves 
many  of  the  metals,  such  as  zinc  and  iron,  with  evolution  of 
hydrogen  and  formation  of  a metallic  iodide. 

The  composition  of  hydriodic  acid  may  be  ascertained  by 
heating  potassium  in  a measured  volume  of  the  gas.  Iodide  of 
potassium  is  formed,  and  hydrogen  remains  equal  in  bulk  to  half 
the  acid  gas  employed ; consequently  its  composition  may  be  thus 
represented : — 


By  weight.  By  vol.  Sp.  gr. 

Iodine I = 127  or  99*21  1 or  0*5  = 4*378 

Hydrogen H = 1 0*79  1 0*5  = 0*034 


Hydriodic  acid. .. . HI  128  100*00  2 1*0  = 4*412 

(396)  Iodides. — The  iodides  of  the  metals  are  all  solid  at 
ordinary  temperatures ; they  are  less  fusible  and  volatile  than  the 
corresponding  chlorides  and  bromides.  The  iodides  of  gold,  silver, 
platinum,  and  palladium  are  decomposed  by  heat  alone,  whilst 
the  metals  are  left  in  a state  of  purity ; but  most  of  the  iodides 
are  converted  into  oxides  when  heated  in  the  air, — the  oxygen 

* Roscoe  has  shown  that,  both  in  this  case  and  in  the  analogous  one  of  the  solu- 
tion of  hydrobromic  acid,  the  constancy  of  the  boiling  point,  as  well  as  the  apparent 
definite  character  of  the  hydrate,  is  accidental,  and  dependent  upon  causes  similar  to 
those  traced  in  hydrochloric  acid.  Hydrofluoric  acid  evidently  furnishes  a true 
hydrate,  but  it  was  found  to  be  partially  decomposed  by  varying  the  temperature  of 
evaporation. 


132 


OXIDES  OF  lODIXE IODIC  ACID. 


displacing  the  iodine.  All  the  iodides,  whether  solid  or  in  solu- 
tion, are  decomposed  by  chlorine  and  bromine,  as  well  as  by 
nitrous  acid  and  concentrated  nitric  acid,  with  liberation  of  iodine. 
Iodine  is  also  set  free  when  an  iodide  is  heated  with  oil  of  vitriol 
and  peroxide  of  manganese.  Water  dissolves  the  greater  number 
of  the  metallic  iodides  freely ; some  of  them  are  insoluble,  and 
exhibit  colours  of  great  brilliancy.  The  iodides  of  some  of  the 
metals  which  form  acids  with  oxygen,  such  as  those  of  tin,  arsenic, 
and  antimony,  are  decomposed  by  water.  The  soluble  iodides  of 
the  metals  may  be  obtained  by  the  direct  action  of  hydilodic  acid 
upon  the  metallic  oxide,  or  by  the  action  of  iodine  and  water 
upon  the  metal  itself.  These  iodides,  when  in  solution,  are  cha- 
racterized by  the  reaction  with  starch  already  mentioned.  With 
a solution  of  corrosive  sublimate  (HgCb)  they  give  a beautiful 
salmon-coloured  precipitate,  which  almost  immediately  changes  to 
a brilliant  scarlet : this  is  the  biniodide  of  mercury : it  is  soluble 
in  excess  both  of  iodide  of  potassium  and  of  corrosive  sublimate. 
Mercurous  nitrate  gives  a green  precipitate  in  solutions  of  the 
soluble  iodides.  With  nitrate  of  lead  they  yield  a bright  yellow 
precipitate  of  iodide  of  lead,  vdiich  is  slightly  soluble  in  boiling 
water,  especially  if  the  lead  salt  be  present  in  excess ; on  cooling, 
the  iodide  of  lead  is  deposited  in  very  beautiful  silky  scales. 
With  nitrate  of  silver  a buff-coloured  iodide  of  silver,  nearly 
insoluble  in  ammonia,  is  formed.  If  a mixture  of  green  sulphate 
of  iron  and  sulphate  of  copper  be  added  to  a solution  of  any 
iodide,  a white  sub-iodide  of  copper  (-GuI)  is  precipitated.  With 
chloride  of  gold  the  iodides  give  a lemon-yellow  precipitate ; and 
vdtli  salts  of  palladium  a brown  iodide  of  palladium  is  produced, 
which  is  sometimes  used  for  ascertaining  the  quantity  of  iodine 
present  in  a solution  in  which  it  occurs  mixed  with  chlorine,  since 
chloride  of  palladium  is  freely  soluble  in  water  (511). 

(397)  Oxides  of  Iodixe. — Iodine  has  a more  powerful  attrac- 
tion for  oxygen  than  either  chlorine  or  bromine,  and  forms  with 
it  two  compounds  which  by  their  action  upon  Avater  furnish  well- 
defined  acids,  viz.,  the  iodic  (IIIO3)  and  the  periodic  acid  (HIO^) 
besides  some  other  oxides  but  imperfectly  known. 

Iodic  AxHYDnroE  (I^O^  = 331  or  10^  = 167) ; Comjp.  in  100 
parts  ; iodine,  76‘04:;  oxygen,  23'96. — This  body  may  be  obtained 
by  the  cautious  application  of  heat  to  iodic  acid. 

Iodic  Acid  (IIIO3  or  110,103  = 176). — This  acid  corresponds 
in  composition  to  chloric  and  bromic  acids.  It  may  be  prepared  in 
several  Avays.  1. — It  may  be  procured  by  long  boiling  of  iodine 
in  concentrated  nitric  acid.  2. — Equal  parts  of  chlorate  of 
potassium  and  iodine  may  be  mixed  AAutli  5 parts  of  water  and  a 
little  nitric  acid ; chlorine  is  thus  evohmd  in  abundance,  whilst 
iodate  of  potassium  is  formed  and  dissolved  in  the  liquid : the 
chloric  acid  which  is  set  free  in  the  first  instance  by  the  nitric 
acid  imparts  its  oxygen  to  the  iodine,  chlorine  gas  escaping,  while 
the  iodic  acid  liberates  a fresh  portion  of  chloric  acid  from  the 
chlorate,  and  this  undergoes  a similar  decomposition  (Millon). 
3. — Liebig’s  plan  of  preparing  iodic  acid  consists  in  suspending 


IODIC  ACID lODATES. 


133 


iodine  in  water,  and  transmitting  tlirongli  it  a current  of  chlorine 
gas  till  the  iodine  is  dissolved  ; the  liquid  is  then  neutralized  by 
carbonate  of  sodium,  when  a copious  elfervescence  ensues,  attended 
by  a precipitate  of  iodine,  which  may  he  again  treated  similarly 
by  chlorine.  In  this  case  the  chlorine  combines  directly  with 
the  iodine  and  forms  terchloride  of  iodine,  which  is  dissolved  by 
water  unaltered.  It  is  decomposed  on  the  addition  of  the  alkaline 
carbonate  in  the  following  manner : — 

Terchloride  lodate  of  Carb. 

of  iodine.  Carb.  sodium.  Cblor.  sodium.  sodium.  Iodine,  anhydride. 


5 IOI3  + 9 = 15  NaCl  + 3 NalOs  + I2  + 9 

The  neutralized  liquid  contains  iodate  and  chloride  of  sodium. 
Chloride  of  barium  is  next  added;  an  abundant  precipitate  of 
iodate  of  barium,  which  is  but  sparingly  soluble,  is  formed ; this 
is  washed  from  adhering  salts,  and  is  decomposed  by  a quantity 
of  sulphuric  acid  just  sufficient  to  combine  with  the  barium  : 
iodic  acid  is  dissolved  by  the  water,  whilst  the  insoluble  sulphate 
of  barium  is  separated. 

Iodic  acid  may  be  obtained  by  spontaneous  evaporation  of  its 
aqueous  solution  in  crystals  composed  of  3 IllOg ; at  a tem- 
perature of  266°  it  loses  two-thirds  of  its  water,  and  becomes 
(III0-3,l205)  or  (HO,  3 10,) ; by  raising  the  heat  to  360°  it  is  con- 
verted into  the  anhydride,  and  at  about  100°  it  is  decomposed 
into  iodine  and  oxygen.  Its  solution  is  destitute  of  odour,  and 
has  a sour,  astringent  taste  : many  organic  bodies  decompose  it, 
and  owing  to  this  circumstance  litmus-paper  is  first  reddened  and 
afterwards  bleached  by  it. 

lodates. — Iodic  acid  offers  some  anomalies  in  its  combination 
with  bases.  Some  iodates  contain  1 atom,  some  2,  and  some  3 
atoms  of  anhydride  to  1 atom  of  base : for  example,  there  are 
three  iodates  of  potassium  ; they  may  be  represented  by  the  follow- 
ing formulae  : — the  normal  iodate,  KIO3 ; the  acid  iodate,  often 
called  the  biniodate,  KH  2 IO3 : and  the  teriodate  [2  (KH  2 IO3), 
I3O,?] . All  the  iodates  are  decomposed  by  heat,  and  give  off*  oxygen. 
If  the  metal  have  a stronger  attraction  for  iodine  than  for  oxygen, 
an  iodide  of  the  metal  is  formed  ; thus  iodate  of  potassium  2 KIO3 
becomes  2 KI  -f  3 : but  if  the  attraction  of  the  metal  be  greater 

for  oxygen  than  for  iodine,  the  oxide  is  left  behind  : iodate  of 
barium,  for  example,  is  converted  into  baryta,  oxygen  gas,  and 
free  iodine,  the  latter  escaping  witli  oxygen  in  violet  vapours ; 

2 (Ba  2 IO3)  yielding  2 BaO  -h  5 Oj  2 I^.  The  iodates  of  the  metals 
of  the  alkaline  earths,  if  not  heated  too  strongly,  leave  a l)asic 
periodate,  the  barium  salt  consisting  of  (Ba  2 IO„  4 BaO)  or 
5 BaO, 10,.  The  aqueous  solutions  of  tlie  iodates  are  decom- 
posed by  sulphurous  acid  ; for  example,  XIO3  -f-  3 lI^SOj  = Kl-f 

3 II3SO4 ; an  iodide  of  the  metal  is  formed,  and  then  the  iodine 
may  be  discovered  by  the  starch  test  in  the  usual  way.  With 
the  exception  of  the  iodates  of  the  alkali-metals  the  iodates  are 
but  sparingly  soluble.  The  calcium  salt  retains  6 II^O;  tliose  of 
strontium,  and  barium  (BaO  2 IO3,  II^O)  if  precipitated  from  hot 


134 


PERIODIC  ACID CHLORIDES  OF  IODINE. 


solutions,  retain  H20- ; whilst  tlie  iodates  of  lead  and  silver  are 
anhydrous  ; iodate  of  silver  is  insoluble  in  diluted  nitric  acid. 
Iodic  acid  forms  crystallizable  compounds  with  the  sulphuric  and 
many  other  acids. 

(398)  Periodic  Acid  (HIO^  or  110,10^=192). — This  acid  cor- 
responds in  composition  to  the  perchloric : the  anhydride  is  at 
present  unknown.  The  acid  is  obtained  by  transmitting  a cur- 
rent of  chlorine  gas  through  a solution  of  iodate  of  sodium,  to 
which  caustic  soda  has  been  added  in  the  proportion  of  3 atoms 
of  free  alkali  to  1 atom  of  iodate  of  sodium : a sparingly  soluble 
basic  periodate  of  sodium  is  formed.  The  reaction  which  occurs 
may  be  represented  by  the  following  symbols  : — 


Iodate  of 
sodium. 


Chlorine. 


2 NaI03  + 6 NaHO  + 2 CI2 


Basic  periodate  of 
sodium. 


]Sra20,  2 NaI04  + 


Chlor. 

sodium. 


4 NaCl 


-f- 


Water. 


3 020. 


The  basic  periodate  of  sodium,  which  when  crystallized  contains 
(JNa^O,  2 AalO^,  3 H^O)  is  dissolved  in  diluted  nitric  acid,  and 
precipitated  by  the  addition  of  nitrate  of  silver  ; the  periodate  of 
silver  is  then  dissolved  in  boiling  nitric  acid ; a normal  periodate 
of  silver  (AglOJ  crystallizes  as  the  liquid  cools,  and  this  salt, 
when  treated  with  water,  is  decomposed  into  basic  periodate  of 
silver,  which  is  insoluble,  and  periodic  acid,  which  is  dissolved. 
By  evaporation  of  the  solution  the  periodic  acid  may  be  obtained 
in  deliquescent  oblique  rhombic  prisms  (IIIO^,  2 H^O),  which  are 
somewhat  soluble  in  alcohol  and  in  ether.  The  periodates  are 
most  of  them  sparingly  soluble  in  water,  but  are  dissolved  freely 
by  diluted  nitric  acid.  The  normal  sodium  salt  (HalO^)  causes, 
with  solutions  of  normal  salts  of  barium,  a precipitate  of  a basic 
periodate  2 (Ba  2 lO^),  3 fiaO,  5 HjO.  Analogous  precipitates 
are  formed  with  salts  of  calcium,  of  lead,  or  of  silver,  whilst  the 
liquid  becomes  acid.  The  basic  silver  salt  is  pale  yellow  (2  AglO^, 
Ag20,  3 HaO)  if  precipitated  from  cold,  but  red  (2  AgIO„ 
Ag20,H20)  if  from  hot  solutions. 

(399)  Chlorides  of  Iodine. — Two  compounds  of  iodine  with 
chlorine,  a protochloride  (ICl)  and  a terchloride  (ICI3),  may  be 
obtained. 

T\\q  protochloride  is  a very  irritating,  volatile,  yellowish-brown 
liquid,  which  is  obtained  by  distilling  1 part  of  iodine  with  4 parts 
of  chlorate  of  potassium ; the  distilled  chloride  of  iodine  is  soluble, 
apparently  without  change,  in  alcohol  and  in  ether.  This  chloride 
when  hot  dissolves  iodine  readily,  and  deposits  it  in  beautiful 
crystals. 

Terchloride  of  iodine  is  procured  by  acting  upon  iodine  with 
excess  of  dry  chlorine  gas.  It  forms  magnificent  ruby-red  crystals, 
Y/hich  undergo  spontaneous  sublimation  in  closed  bottles : the 
vapor  is  extremely  irritating  to  the  eyes.  If  exposed  to  the  air 
it  attracts  moisture,  and  is  dissolved  by  water  without  expe- 
riencing decomposition,  xllkaline  solutions  decompose  it,  and 
iodine  is  precipitated  as  in  Liebig’s  method  of  preparing  iodic 
acid  (397). 


IODIDE  OF  NITROGEN ^NATURAL  RELATIONS  OF  THE  HALOGENS.  135 

Bromides  of  Iodine. — Iodine  also  combines  with  bromine,  and 
forms  compounds  with  it  which  are  possessed  of  properties  similar 
to  those  of  the  chlorides  of  iodine. 

(400)  Iodide  of  Nitrogen  ? (NHI^). — This  substance  may  be 
obtained  as  a black  powder  by  digesting  iodine  for  half  an  hour 
in  a cold  solution  of  ammonia.  The  brown  supernatant  liquid, 
which  contains  an  excess  of  iodine  held  in  solution  by  iodide  of 
ammonium,  is  decanted,  and  the  insoluble  powder  is  placed  upon 
filtering-paper  in  quantities  of  a grain  or  less,  and  allowed  to  dry 
spontaneously.  It  may  also  be  prepared  by  mixing  alcoholic 
solutions  of  iodine  and  ammonia,  and  diluting  with  water,  when 
it  falls  as  a black  powder,  which  may  be  washed  with  an  aqueous 
solution  of  ammonia.  When  dry,  it  explodes  upon  the  slightest 
touch,  and  indeed  it  often  detonates  without  any  assignable  cause : 
the  explosion  is  remarkably  sharp  and  sudden,  fumes  of  iodine  are 
produced,  and  a faint  light  is  emitted. 

The  experiments  of  Bineau,  the  results  of  which  have  been 
subsequently  confirmed  by  Gladstone,  have  shown  that  this  deto- 
nating compound  is  not  a mere  iodide  of  nitrogen,  but  that  it 
contains  hydrogen  also,  having  the  formula  NIII^.  The  mode  of 
its  preparation  admits  of  easy  explanation  by  the  following  equa- 
tion : 2 I^-fS  II3N  = 2 H^NI-I-NHI^,  the  reaction  of  4 atoms  of 
iodine  upon  3 of  ammonia  producing  2 of  iodide  of  ammonium, 
and  1 atom  of  the  detonating  substance.  Bunsen  assigns  to  the 
compound  obtained  by  precipitating  an  alcoholic  solution  of  iodine 
with  ammonia  the  formula  (NIl3,Nl3),  but  it  is  more  probable  that 
the  composition  attributed  to  it  by  Bineau  {Ann.  de  Chimie.^  III. 

► XV.  71)  is  correct. 

Iodide  of  nitrogen  becomes  slowly  decomposed  in  water ; am- 
monia retards,  but  potash  and  the  acids  accelerate  the  decomposi- 
tion ; chlorine,  bromine,  and  strong  nitric  acid  destroy  it  rapidly ; 
sulphuretted  hydrogen  also  effects  its  decomposition  quietly  but 
completely.  The  results  of  the  reaction  last  mentioned  afford  a 
means  of  ascertaining  the  relative  quantities  of  nitrogen  and  iodine 
contained  in  the  iodide  : 1 atom  of  the  black  powder,  when  treated 
with  2 atoms  of  sulphuretted  hydrogen,  furnishes  1 atom  of  iodide 
of  ammonium,  1 of  hydriodic  acid,  and  2 atoms  of  sulphur  : — 

mil,  4-  2 H3S  = IT,NI  4-  HI  -f  S3. 

(401)  Natural  relations  of  the  Halogens. — It  is  impossible  not 
to  be  struck  with  tlie  close  analogy  presented  by  the  three  ele- 
mentary bodies,  chlorine,  bromine,  and  iodine,  both  in  their 
uncombined  state  and  in  their  compounds  : they  indeed  form 
one  of  the  best  defined  natural  groups  of  simple  substances.  All 
these  elements  have  the  characteristic  peculiarity  of  combining 
with  hydrogen  in  the  proportion  of  1 volume  of  the  gas  or  vapour 
with  1 volume  of  hydrogen  ; the  union  occurring  without  change 
of  bulk,  and  the  compound  formed  lieing  powerfully  acid  and 
extremely  soluble  in  water.  Chlorine,  bromine,  and  iodine  are 
also  capable  of  displacing  hydrogen  from  many  of  its  organic 
compounds,  producing  substances  which  correspond  in  composition 


136 


NAXrKAL  RELATIONS  OF  THE  H^ALOGENS. 


\\Htli  the  original  body,  but  in  which  a certain  nnmber  of  atoms 
of  the  halogen  have  taken  the  place  of  a corresponding  number 
of  atoms  of  hydi’ogen. 

Tlie  specific  gravity,  fusing-point,  and  boiling-point  of  these 
elements  rise  as  the  atomic  weight  increases,  as  is  shown  in  the 
table  which  follows. 


Elements. 

Sp.  gravity. 

Melting- 
point  "F. 

Boiling- 
point  °F. 

Atomic 

weight. 

Diff. 
between 
at.  weights. 

Gaseous. 

Liquid  or 
solid. 

Fluorine • 

1-313? 

? 

9 

? 

19 

Chlorine 

2-47 

1-33 

? 

? 

35-5 

XD  D 

Bromine 

5 54 

3-187 

9-5 

145-4 

80-0 

0 

A'7*n 

Iodine 

8-716 

4-947 

225-0 

347-0 

127-0 

^ 1 u 

The  intensity  of  their  chemical  activity  decreases  as  the  com- 
bining number  increases.  At  ordinary  temperatures,  chlorine  is 
gaseous,  bromine  liquid,  iodine  solid  ; the  properties  of  bromine 
being  indeed  intermediate  between  those  of  chlorine  and  iodine. 
When  in  the  liquid  form,  the  three  elements  have  the  same  atomic 
volume ; and  y^hen  united  yfith  the  same  metal  the  salts  which 
they  furnish  are  isomorphous  ; the  chloride,  the  bromide,  and  the 
iodide  of  potassium,  for  examj^le,  all  crystallize  in  cubes.  Each 
of  these  elements  also  forms  a powerful  monobasic  acid  with  3 
atoms  of  oxygen.*  The  attraction  of  these  three  halogens  for 
oxygen  is,  however,  in  the  inverse  order  of  that  of  the  same 
halogens  for  hydrogen  and  the  metals.  Neither  iodic  anhydride, 
nor  the  acid  in  solution,  is  decomposed  by  free  chlorine  or  bro- 
mine : bromic  acid  and  the  bromates  are  also  unafiected  by  free 
chlorine ; but  iodic  acid  is  easily  obtained  by  the  decomposition 
of  chloric  or  bromic  acid  by  free  iodine,  though  bromine  is  only 
in  small  proportion  converted  into  bromic  acid  by  the  action  of 
bromine  on  chloric  acid.  The  table  on  the  following  page 
exliibits  some  of  the  con-esponding  compounds  with  hydrogen  and 
oxygen  which  are  formed  by  the  halogens. 

At  the  time  that  iodine  was  discovered,  chlorine  was  by  most 
chemists  regarded  as  a compound  of  muriatic  acid  and  oxygen, 
and  was  consequently  known  as  oxymuriatic  acid.  Indeed,  many 
of  the  reactions  which  it  presented  admitted  of  a simple  explana- 
tion on  this  hypothesis,  and  this  circumstance  prevented  chemists 
from  adopting  generally  the  views  which  had  a short  time  pre- 
viously been  put  forward  by  Davy,  maintaining  the  elementary 
nature  of  chlorine.  The  discovery  of  iodine,  however,  decided 
them,  and  assisted  materially  in  fixing  the  opinion  now  entertained 
respecting  the  compounds  of  fiuorine,  the  fourth  member  of  the 

* Nitrogen  is  remotely  connected  with  this  group  by  the  similarity  of  the  nitrates 
with  the  chlorates,  and  of  the  nitrites  with  the  chlorites : it  forms  an  intermediate 
link  in  the  natural  grouping  of  the  elements  between  the  halogens  and  the  elements 
belonging  to  the  phosphorus  family ; its  compound  with  hydrogen  (viz.,  ammonia) 
presenting  some  analogies  with  phosphuretted  hydrogen,  which  will  be  more  fully 
shown  hereafter. 


FLUORINE. 


137 


Hydrochloric  acid. 

Hydrobromic  acid. 

Hydrlodlc  acid. 

A 

HCl 

HBr 

HI 

Hypochlorous  acid. 

Hypobromous  acid. 

Hcie 

HBre 

Chlorous  acid. 

A 

HClOa 

Chloric  acid. 

A 

Bromic  acid. 

j. 

Iodic  acid. 

^ A ^ 

HClOa 

HBrOa 

HI03 

Perchloric  acid. 

Periodic  acid. 

HCIO4 

11104 

group,  and  of  wliicli  our  knowledge  is  in  a mucli  less  satisfactory  • 
condition. 


§ lY.  Fluorine  : F = 19. 

Theoretical  Density^  1*313  ; Comb.  Vol.  Q. 

(402)  Many  unsuccessful  attempts  have  been  made  at  various 
times  to  isolate  fluorine.  Its  chemical  activity  is  so  powerful,  and 
its  action  on  the  human  frame  is  so  irritating  and  deleterious,  that 
little  that  is  satisfactory  is  known  concerning  it  in  its  free  state. 
Ho  doubt,  however,  is  entertained  of  its  general  nature,  since  its 
compounds  are  closely  analogous  to  the  corresponding  ones  of  the 
three  elements  which  have  just  been  described.  According  to 
Kammerer  {Chemisclies  Centralblatt^  1862,  p.  523),  free 

fluorine  may  be  obtained  in  the  following  manner  as  a colourless 
gas  which  has  no  action  on  perfectly  dry  glass.  Into  a perfectly 
dry  glass  tube  iodine  is  introduced,  together  with  a thin  closed 
glass  cylinder  containing  well-dried  fluoride  of  silver  in  excess 
over  the  iodine.  The  air  must  be  completely  expelled  from  the 
tube  by  converting  a portion  of  the  iodine  into  vapour ; the  tube 
is  then  to  be  hermetically  sealed,  and  the  little  cylinder  of  fluoride 
of  silver  broken  ; after  which  the  tube  must  be  exposed  in  an  air- 
bath  for  24  hours  to  a temperature  of  from  160°  to  180°.  At  the 
end  of  this  time,  in  an  experiment  made  in  this  manner,  the 
iodine  had  entirely  disappeared,  and  a colourless  gas,  permanent 
over  mercury,  and  rapidly  absorbed  by  solution  of  potash,  was 
obtained. 

Fluor-spar,  or  fluoride  of  calcium  (OaF^),  is,  with  the  excep- 
tion of  cryolite  (3  HaF,  AIF3),  the  only  compound  of  fluorine 
which  exists  native  in  abundance ; and  from  it  all  the  prepara- 
tions of  fluorine  are  obtained.  Small  quantities  of  fluoride  of 
calcium  are  contained  in  a variety  of  minerals,  particularly  in  the 
phosphates  of  calcium  and  certain  kinds  of  mica.  It  exists  too 


138 


PEOPERTIES  OF  HTDEOFLTJORIC  ACID. 


in  minute  quantity  in  tlie  bones  of  animals,  and  especially  in  the 
teeth. 

(403)  Hydeofluoeic  Acid  : formerly  incorrectly  termed  Flu- 
oric Acid  (IIF=20). — Theoretic  Sp.  Gr.  of  Anhydrous  Vapour^ 
0*689 : Atomic  Yol.  \ \ |. — Fluorine  is  not  known  to  form  any 
oxide,  but  with  hydrogen  it  constitutes  a very  remarkable  acid. 

Preparation. — In  order  to  procure  hydrofluoric  acid  in  solu- 
tion in  a concentrated  form,  1 part  of  finely  powdered  fluor-spar, 
free  from  silica  and  the  metallic  sulphides,  is  mixed  with  2 or  3 
parts  oil  of  vitriol ; at  ordinary  temperatures  no  evolution  of 
vapour  occurs  if  the  fluor-spar  be  pure,  but  a transparent  gela- 
tinous mass  is  formed.  On  the  application  of  a gentle  heat  dense 
acid  fumes  of  an  extremely  deleterious  nature  arise,  and  a reaction 
takes  place  similar  to  that  wdiich  occurs  in  the  preparation  of 
hych’ochloric  acid : thus, 

eaF,  + H,SO,=2  HF-f  OaSe,. 

Owing  to  the  powerfully  corrosive  action  exerted  by  this  com- 
pound upon  glass,  which  it  deprives  of  its  silicon,  it  is  necessary 
always  to  prepare  it  in  metallic  vessels.  For  ordinary  purposes, 
the  distillation  may  be  conducted  in  a leaden  retort.  For  the 
convenience  of  removing  the  charge  after  the  operation  is  over, 
it  is  found  advantageous  to  make  the  retort  in  two  pieces,  a head 

and  a body ; the  head, 
<?,  fig.  301,  fits  accu- 
rately by  an  overlap- 
ping grooved  joint 
into  the  body,  h.  The 
heat  may  be  conve- 
niently applied  in  an 
equable  manner  by 
placing  the  body  of 
the  retort  in  a shal- 
low iron  tray,  (Z,  filled 
with  sand:  d is  the 
receiver  for  the  acid : 
it  consists  of  a leaden 
pipe  fitted  by  grind- 
ing to  the  neck  of  the  retort,  and  is  cooled  by  immersion  in  a 
mixture  of  ice  and  salt.  When  a perfectly  pure  acid  is  required, 
the  still  must  consist  of  platinum. 

The  concentrated  acid  obtained  by  the  foregoing  method  was 
long  believed  to  be  anhydrous;  but  the  researches  of  Louyet 
(yComptes  Rendus^  xxiv.  434)  have  proved  that  it  contains  water. 
He  distilled  it  wnth  an  excess  of  phosphoric  anhydi’ide ; the  water 
was  thereby  removed,  and  a colourless  gas  of  an  extremely  irritat- 
ing nature  was  set  free : it  produced  dense  fumes  on  escaping 
into  the  air,  had  but  little  action  on  perfectly  dry  glass,  and  was 
rapidly  condensed  by  water.  Fremy  {Ann.  de  Chimie.^  III.  xlvii.  5) 
prefers  to  subject  the  double  fluoride  of  potassium  and  hydrogen 
(KF,IIF)  to  distillation ; the  salt  is  first  rendered  anhydrous  by 


PEOPEETIES  OF  HYDEOFLUOEIC  ACID. 


139 


careful  desiccation,  and  by  afterwards  applying  a strong  beat,  tlie 
equivalent  of  hydrofluoric  acid  is  expelled : by  the  application  of 
a freezing  mixture  of  ice  and  salt,  the  anhydrous  acid  is  said  to  be 
obtained  in  the  form  of  a colourless,  mobile,  very  volatile  liquid. 
Premy  also  states  that  he  obtained  the  anhydrous  acid  by  decom- 
posing fluoride  of  lead  by  dry  hydrogen.  It  admits  of  doubt, 
however,  wdiether  the  liquid  obtained  by  either  of  these  processes 
was  really  anhydrous ; for  it  is  opposed  to  analogy  that  hydro- 
fluoric acid  should  be  condensed  more  readily  than  hydrochloric 
acid,  which  requires  a greater  pressure  to  liquefy  it  than  hydro- 
bromic  acid,  and  hydrobromic  acid  a greater  than  liydriodic  acid, 
the  facility  of  liquefaction  increasing  as  the  combining  number 
of  the  acid  becomes  more  elevated. 

Properties. — The  acid  obtained  by  distilling  fluor-spar  with 
oil  of  vitriol  is  a densely  fuming,  volatile,  colourless  liquid,  which 
boils  at  about  60°,  and  remains  unfrozen  at  — 1°.  The  prepara- 
tion of  this  acid  must  be  conducted  with  the  greatest  care,  and 
special  provision  must  be  made  for  carrying  ofl*  the  fumes  from  the 
operator.  The  liquid  acid  is  highly  dangerous,  from  its  caustic 
action  upon  the  skin  ; the  smallest  drop  occasioning  a deep  and 
painful  burn.  Indeed,  it  ought  never  to  be  preserved  in  the  con- 
centrated form.  When  poured  into  water  it  combines  with  it  with 
great  avidity,  and  with  the  evolution  of  so  high  a temperature  as 
to  produce  a hissing  noise,  resembling  that  caused  by  quenching  a 
red-hot  iron.  In  its  concentrated  form  it  has  a specific  gravity  of 
1*060,  but  by  the  addition  of  water  the  density  may  be  increased 
to  1*150,  beyond  wdiich  point  further  dilution  is  attended  with  a 
regular  decrease  in  density.  The  acid  of  sp.  gr.  1*150  (HF, 
2 Il20),  boils  at  248°,  and  may  be  distilled  unchanged.  (See  note, 
p.  131.)  Diluted  hydrofluoric  acid  gradually  dissolves  the  metals, 
excepting  platinum  and  some  of  the  metals  associated  with  it,  and 
gold,  silver,  lead,  and  mercury ; the  metal  whilst  undergoing  solu- 
tion displaces  hydrogen.  Potassium,  if  thrown  into  the  strong 
acid,  decomposes  it  with  explosion. 

Hydrofluoric  acid  is  easily  recognised  by  its  corrosive  action 
upon  glass.  In  order  to  detect  a fluoride  in  a compound  which  is 
suspected  to  contain  it,  the  material  is  reduced  to  a fine  powder 
and  mixed  in  a platinum  capsule  with  strong  sulphuric  acid ; a slip 
of  glass  is  warmed  and  rubbed  over  with  bees’-wax  so  as  to  coat  it 
uniformly ; a few  characters  are  next  traced  with  a point  tlirough 
the  w*ax,  so  as  to  expose  a portion  of  the  glass : this  etching  is 
then  inverted  over  the  platinum  capsule,  which  is  gently  warmed 
for  a few  minutes,  and  the  glass  is  cooled,  if  necessary,  with  a 
piece  of  moistened  filtering-paper,  in  order  to  prevent  the  wax 
from  becoming  melted.  If  fluorine  be  contained  in  the  mixture, 
the  glass,  on  cleaning  oft’  the  wax  with  a little  oil  of  turpentine, 
will  be  found  to  be  corroded  in  the  parts  exposed : if  the  traces 
be  very  faint,  they  may  be  rendered  visible  by  breathing  upon  the 
surface  of  the  plate. 

A weak  solution  of  hydrofluoric  acid  is  often  em])loyed  advan- 
tageously for  etching  on  glass  : in  this  way,  for  instance,  the 


140 


COMBINTN-G  PKOPOKTIOX  OF  FLUOPIXE. 


graduations  on  the  glass  stem  of  a thermometer  may  he  made 
with  great  precision  and  facility ; the  glass  tube  is  first  coated 
with  engravers’  etching  varnish,  the  divisions  are  traced  through 
the  varnish  with  a fine  point,  and  the  tube  is  plunged  into  a long 
leaden  tube  filled  with  the  diluted  acid  ; in  the  coiu’se  of  a few 
minutes  the  scale  is  permanently  engraved. 

Fluorides. — The  compounds  of  the  metals  vfith  fluorine  for 
the  most  part  fuse  easily  on  the  application  of  heat,  and  hence  the 
origin  of  the  terms  jiuor-^^2rc  and  fluorine  (from  fluo.,  to  fiow). 
When  ignited  in  a current  of  steam  many  of  them  are  converted 
into  the  corresponding  oxide,  whilst  hydrofluoric  acid  is  formed. 
A large  number  of  the  fluorides  are  insoluble,  or  only  sparingly 
soluble,  in  water.  They  are  all  decomposed  when  heated  with  oil 
of  vitriol,  and  evolve  hych’ofiuoric  acid ; but  they  are  not  so  readily 
attacked  by  nitric  acid.  If  heated  with  chlorine,  many  of  the 
fluorides  are  decomposed,  whilst  chlorides  of  the  metal  are  pro- 
duced. The  solutions  of  the  soluble  fluorides  corrode  the  glass 
vessels  in  which  they  are  contained ; they  give  no  precipitate  with 
nitrate  of  silver,  since  fluoride  of  silver  is  soluble  ; but  with  salts 
of  lead,  barium,  magnesium,  and  calcium,  insoluble  precipitates, 
consisting  of  the  fluorides  of  these  metals,  are  produced.  The 
fluoride  of  calcium  is  so  transparent  as  to  be  perceived  with  difii- 
culty  ; but  on  heating  the  liquid,  or  on  the  addition  of  ammonia, 
it  is  rendered  more  opaque. 

Many  metallic  fluorides  combine  with  an  additional  atom  of 
hydrofluoric  acid,  and  form  compounds  which  may  often  be 
obtained  in  crystals  that  are  soluble  in  water.  The  double  fluoride 
of  potassimn  and  hydrogen  (KF,HF)  has  been  already  mentioned 
as  a convenient  source  of  concentrated  hycbofluoric  acid.  Double 
fluorides  of  the  alkaline  metals,  with  the  fluorides  of  the  electro- 
negative metals  which  form  acids  ’with  oxygen  may  likewise  be 
obtained  with  facility.  Many  insoluble  metallic  anhydrides,  such 
as  the  tantalic,  titanic,  molybdic,  and  tungstic  anhydrides,  are 
thus  dissolved  by  hydrofluoric  acid,  fluorides  of  the  metals  being 
formed,  whilst  the  oxygen  of  these  compounds  produces  water 
with  the  hydrogen  of  the  hydi’ofluoric  acid  : the  metallic  fluorides 
so  formed  are  dissolved  by  the  excess  of  hydrofluoric  acid,  and 
give  rise  to  new  compound  acids.  Titanic  acid,  for  instance,  is  thus 
converted  into  fluotitanic  acid ; TiOj  -|-  6 IlF  becomins:  (2  HF, 
TiF,)-f  2 H^O.  Silica  yields  a similar  compound  (2  IIF,§iF,). 

Hydrofluoric  acid,  when  mixed  with  nitric  acid,  readily  dis- 
solves silicon  which  has  not  been  strongly  ignited. ; but  it  is 
remarkable  that  the  mixture  does  not  dissolve  either  gold  or 
jflatinum. 

Humorous  other  compounds  of  fluorine  have  been  prepared, 
but  they  are  not  of  sulflcient  practical  importance  to  require 
notice  here  : the  compounds  which  it  forms  with  silicon  and  Avith 
boron  will  be  described  hereafter  (478,  483). 

(404)  Determination  of  the  Combining  Proportion  of  Fluo- 
rine.— Although  the  chemist  has  hitherto  been  unable  to  isolate 
fluorine  in  a state  of  purity,  yet  its  combining  proportion  has 


NATTJEAL  RELATIONS  OF  THE  SULPHUR  GROUP. 


141 


been  determined  with  precision ; and  the  mode  of  proceeding 
offers  an  instructive  illustration  of  the  resources  of  chemical 
analysis  in  such  a case. 

The  method  of  operating  is  as  follows : — ^Pure  fluor-spar  is 
reduced  to  an  impalpable  powder,  and  dried ; 100  grains  of  this 
powder  are  accurately  weighed  into  a counterpoised  platinum 
crucible,  and  concentrated  sulphuric  acid,  also  perfectly  pure,  is 
added  in  quantity  sufficient  to  reduce  the  whole  to  the  consistence 
of  cream : after  standing  for  some  hours,  the  excess  of  acid  is 
expelled  by  the  heat  of  a lamp : the  temperature  is  raised  very 
cautiously,  and  the  crucible  and  its  contents  are  finally  heated  to 
bright  redness.  In  this  operation  the  whole  of  the  fluorine  is 
expelled  in  the  form  of  hydrofluoric  acid,  the  calcium  combining 
with  the  radicle  of  the  sulphuric  acid,  and  forming  sulphate  of 
calcium  which  remains  behind,  whilst  the  fluorine  unites  with  the 
hydrogen.  On  weighing  the  crucible  after  the  experiment  is 
completed,  the  sulphate  of  calcium  will  be  found  to  amount  to 
174‘36  grains. 

How  it  is  known  that  68  grains  of  sulphate  of  calcium  contain 
20  of  calcium  and  48  of  sulj^huric  acid  radicle,  20  being  the  com- 
bining number  or  equivalent  of  calcium,  though  its  atomic  weight 
is  40  (13) 

but  68  : 20  : : 174-36  : a?  (=:51-25) ; 

174*36  grains  of  sulphate  of  calcium  must  consequently  contain 
51-25  of  calcium ; 100  parts,  therefore,  of  fluor-spar,  if  it  consist 
only  of  fluorine  and  calcium,  must  be  composed  of  51*25  of  cal- 
cium and  48*75  of  fluorine.  The  combining  proportion  of  fluorine 
is  then  found  directly  by  the  following  calculation  : — 

Qty.  of  calcium  Comb.  No.  Qty.  of  fluorine  Comb,  No, 
in  loo  parts,  of  calcium.  in  100  paUs.  of  fluorine. 

51*25  : 20  ::  48*75  : 19. 

The  combining  proportion  of  fluorine  is  thus  ascertained  to  be  19. 


CHAPTEK  VII. 

SULPHUR SELENIUM TELLURIUM. 

(405)  Natural  Relations  of  the  Sulphur  Group. — Between 
sulphur,  selenium,  and  tellurium,  a marked  analogy  in  chemical 
character  is  observable.  They  are  all  characterized  by  a powerful 
attraction  for  oxygen.  The  properties  of  selenium  are  interme- 
diate between  those  of  sulphur  and  tellurium,  wliich  latter  presents 
so  much  of  the  external  characters  and  appearance  of  a metal, 
that  it  is  usually  described  with  the  metals.  The  specific  gravity 
and  fusing  point  of  these  elements  increase  as  tlie  atomic  weight 
increases,  as  will  be  seen  by  comparing  the  numbers  in  the  differ- 
ent cases : — 


142 


EELATIOXS  OF  THE  SrEPHEE  GKOEP. 


Difference 

Elements. 

Specific  gravity. 

Melting-pt. 

Boiling-pt. 

At.  wt. 

between  at.  wts. 

Sulphur 

2-05 

239° 

836° 

1 32 

4*l’b 

49-5 

1 Selenium 

4-788 

423° 

79-5 

! Tellurium 

6-65 

900° 

1 129- 

Amongst  the  compounds  of  each  of  these  bodies  with  oxygen  are 
two  anhydrides ; one  with  2 atoms  of  oxygen  corresponding  with 
snlphnrons  anhydride  SO2,  and  another  with  three  atoms  of  oxy- 
gen corresponding  with  sulphuric  anhydride  SO3.  One  Tolume 
of  the  vapour  of  each  of  these  three  elements  unites  with  2 volumes 
of  hydi’ogen  to  form  2 volumes  of  a sparingly  soluble  gaseous 
compound  possessed  of  a disgusting  odour  and  feebly  acid  charac- 
ter. Oxygen  also  presents  a certain  analogy  with  the  members 
of  this  group,  1 volume  of  oxygen  uniting  with  2 volumes  of  hy- 
drogen to  form  2 volumes  of  steam  ; and  the  oxides  and  sulphides, 
generally,  exhibit  many  points  of  resemblance. 

The  atomic  volume  of  solid  sulphur  is  101,  and  that  of  selenium 
103,  or  nearly  identical ; but  that  of  tellurium,  128,  is  one-fourth 
higher.  It  may  be  further  remarked  that  the  corresponding  com- 
pounds of  sulphur,  selenium,  and  tellurium  are  isomorphous. 

The  singular  numerical  relations  which  Dumas  and  others 
have  pointed  out  between  the  atomic  weights  of  the  members 
composing  these  groups  and  those  of  several  other  elements  equally 
closely  allied,  will  be  discussed  at  a future  point  (1031). 

It  will  be  sufficient  here  to  remark,  that  in  groups  of  electro- 
negative elements  of  similar  properties  it  is  usually  observable 
that  the  chemical  activity  of  each  element  of  the  group  is  usually 
greater,  the  smaller  is  its  combining  number  ; sulphur,  for  ex- 
ample, being  more  active  in  its  chemical  relations  than  selenium, 
and  selenium  than  tellurium  : so  again,  fluorine  is  more  energetic 
in  its  chemical  actions  than  chlorine,  chlorine  than  bromine,  and 
bromine  than  iodine.  In  the  metals,  or  basjdous  elements,  the 
order  of  their  activity  is  exactly  the  reverse,  potassium  being 
more  active  than  sodium,  and  sodium  than  lithium. 

The  following  table  exliibits  some  of  the  corresponding  com- 
pounds which  the  elements  of  this  group  form  with  oxygen  and 
hydrogen  : — 


Water. 

Sulphuretted 

hydrogen. 

Seleniuretted 

hydrogen. 

Telluretted 

hydrogen. 

HaO 

H2S 

HaSe 

Sulphurous 

acid. 

Selenious 

acid. 

Tellurons 

acid. 

HaSOa 

HaSeOa 

HjTeOs 

Sulphuric 

acid. 

Selenic 

acid. 

Telluric 

acid. 

H2se4 

' H2See4  ' 

H2Tee4  ' 

PROPERTIES  OF  SULPHUR. 


143 


§ I.  Sulphur  : S = 32,  or  S = 16.* 

Combining  Vohtme  below  1500°,  above  1900°  [H;  Specific 
Gravity  of  Yaponr^  6*617  at  900°  F.  / TheoreticSp.  Gr.  at 
1900°,  2*2168 ; Observed^  at  1900°,  2*23 ; Melting-pt.  239°  ; 
Boilinfpt.  836°. 

(406)  Most  of  the  sulphur  used  in  England  is  obtained  from 
Sicily,  where  it  occurs  in  the  native  or  uncombined  state  in  beds 
of  a blue  clay  formation,  stretching  from  the  southern  coast  of 
the  island  towards  the  base  of  Mount  Etna.  It  is  also  found 
abundantly  in  volcanic  districts  generally,  and  particularly  in 
those  which  border  the  Mediterranean.  Many  of  the  compounds 
of  sulphur  with  the  metals  occur  in  great  abundance  as  natural 
productions, — especially  the  sulphides  of  iron,  copper,  lead,  and 
zinc.  Bisulphide  of  iron  (iron  pyrites)  furnishes  a large  propor- 
tion of  the  sulphur  consumed  in  the  manufacture  of  oil  of  vitriol. 
Sulphur  is  still  more  extensively  distributed  in  the  oxidized  con- 
dition as  sulphuric  acid,  in  combination  with  various  earths  ; the 
sulphates  of  calcium,  magnesium,  barium,  and  strontium  being 
abundant  natural  productions.  Sulphur  is  likewise  an  essential 
constituent  of  many  bodies  of  organic  origin  ; it  enters  into  the 
composition  of  several  foetid  volatile  oils  ; it  is  a necessary  ingre- 
dient in  the  muscular  tissue  of  animals,  and  is,  indeed,  always 
contained  in  the  albuminoid  or  proteic  compounds. 

Properties. — Native  sulphur  is  found  either  in  amorphous 
masses,  or  in  transparent  yellow  crystals,  the  form  of  which  is 
derived  from  the  octohedron  with  a rhombic  base.  The  sulphur 
of  commerce  is  presented  either  in  the  form  of  a harsh,  yellow, 
gritty  powder,  known  as  fiowers  of  sulphur^  or  in  round  sticks, 
constituting  roll  sulphur  or  common  brimstone.  In  the  latter 
condition  it  is  a solid,  nearly  opaque,  brittle  substance,  of  a cha- 
racteristic yellow  colour,  with  a slight,  peculiar  odour.  It  is  inso- 
luble in  water,  and  is  consequently  tasteless  ; it  is  a bad  conductor 
of  heat,  and  when  grasped  with  a warm  hand  frequently  crackles 
and  falls  to  pieces  from  the  unequal  expansion  ; it  is  an  insulator 
of  electricity,  and  becomes  negatively  electric  by  friction. 

Sulplmr  is  highly  inflammable,  and  when  heated  in  the  air  it 
takes  Are  at  between  450°  and  500°,  burning  with  a blue  flame, 
and  emitting  pungent  suffocating  fumes  of  sulphurous  anhydride. 
At  239°  it  melts,  forming  a yellow  liquid  which  is  less  dense  than 
the  unmelted  sulphur.  In  closed  vessels  it  may,  by  a further  heat, 
be  distilled,  the  boiling-point  being  about  836°  (Regnault) ; at 
this  temperature  sulphur  yields  a deep  yellow  vapour  of  sp.  gr. 
6*617  : 1 volume  of  this  vapour  contains  3 atoms  of  sulphur. 
Biiieau  found  that  when  sulphur  is  heated  to  about  1800°  E.  the 
vapour  becomes  dilated  to  three  times  the  bulk  that  an  equal 
weight  of  the  vapour  occupies  at  900°,  and  that  at  tliis  higli  tem- 
perature the  volume  occupied  by  an  equivalent  of  sul[)hur  vapour 
corresponds  with  that  of  an  equivalent  of  oxygen  ; this  observa- 
tion has  recently  been  confirmed  by  Deville  and  l)ebray. 

* Molecular  volume  of  free  sulphur  (SS)  = | [~|. 


EXTEACTION  AXD  EEFIXIXG  OF  SELPHEE. 


U4: 


Sulphur  combines  readily  vdth  chlorine,  with  bromine,  and 
with  iodine,  especially  when  the  action  is  favom'ed  by  heat.  It 
also  enters  rapidly  into  combination  with  most  of  the  metals, 
many  of  which,  hke  copper,  iron,  and  silver,  if  in  a state  of  fine 
di^'ision,  burn  vividly  when  heated  in  its  vapour.  The  compounds 
of  sulphur  with  the  metals  are  termed  sulphides,  or  svlphurets. 
Generally  for  each  sulphide  a corresponding  oxide  exists,  each 
atom  of  oxygen  in  the  molecule  of  the  oxide  being  represented  in 
the  sulphide  by  an  atom  of  sulphur ; and  sulphur  often  displaces 
oxygen  by  double  decomposition  ; 1 atom  of  sulpliur  is  therefore 
equivalent  to  1 atom  of  oxygen  and  to  2 atoms  of  hydrogen  or  of 
chlorine. . 

Extraction. — ^TVTien  the  proportion  of  sulphur  in  the  matrix  is 
large,  the  earthy  impurities  are  removed  by  simply  melting  out 
the  sulphm  from  them ; but  when  the  proportion  of  sulphin  does 
not  exceed  S or  12  per  cent,  it  is  found  to  be  more  advantageous 
to  subject  the  mineral  to  a rough  distillation,  which  is  performed 
upon  the  spot  where  it  is  obtained.  For  this  purpose  a long  brick 
fimiace  is  constructed  so  as  to  contain  a double  row  of  upright 
earthenware  retorts,  each  of  a capacity  of  4 or  5 gallons : each 
retort  is  furnished  with  a large  apertme  at  the  top  for  charging 
it  with  the  sulphur,  and  with  a short  wide  tube,  which  proceeds 
from  the  side  at  the  upper  part,  and  slopes  downwards  through 
the  walls  of  the  furnace  into  an  earthen  receiver  of  a form  similar 
to  that  of  the  retort : from  the  bottom  of  the  receiver  a short  pipe 
carries  off  the  still  melted  sulphur  into  a vessel  containing  wate]’. 
It  is,  however,  still  very  impure,  and  requires  a second  more  care- 
ful distillation  before  it  is  fit  for  many  of  the  purposes  to  which 
it  is  applied  in  the  arts.  This  second  distillation  is  conducted  in 
retorts,  generally  of  iron,  furnished  with  a short,  wide,  lateral 
neck ; the  fumes  are  received  into  large  chambers  of  brickwork. 
If  the  walls  of  these  chambers  be  kept  cool,  and  the  process  be 
conducted  slowly,  the  sulphur  is  condensed  in  powder,  and  forms 
‘ flowers  of  sulphur ; ’ but  if  the  fire  be  urged,  and  the  masonry  be 
allowed  to  become  hot,  the  sulphur  melts,  runs  down,  and  is  then 
drawn  off  into  cylindrical  wooden  moulds,  which  give  it  the  usual 
form  of  roll  sulphur. 

AYhen  sulphur  is  prepared  from  p^n-ites  (FeS,),  the  mineral  is 
sometimes  distilled  in  closed  vessels,  and  by  this  means  about  one- 
third  of  the  sulphur  which  it  contains  is  volatilized  and  condensed, 
magnetic  pyrites,  FejS^,  remaining ; but  it  is  more  usual  to  con- 
duct the  operation  in  the  open  air,  as  a preliminary  step  in  the 
roasting  of  copper  pyrites  to  prepare  it  for  smelting.  Huge  heaps 
of  the  ore  are  arranged  in  the  form  of  a truncated  square  pyramid, 
the  base  of  which  is  about  30  feet  in  the  side.  A layer  of  powdered 
ore  is  placed  at  the  bottom,  and  over  this  one  of  brushwood ; in 
the  centre  is  constructed  a wooden  chimney,  which  communicates 
with  air- ways  left  between  the  fagots  ; fragments  of  ore  are  now 
piled  up  until  the  heap  is  about  S feet  high,  and  lastly  the  whole 
is  covered,  for  a depth  of  12  inches,  with  a layer  of  powdered 
ore.  Such  a heap  contains  upwards  of  2000  tons  of  pyrites,  and 


OCTOHEDEAL  AND  PRIS]MATIC  SULPHUR. 


145 


will  furnish  about  20  tons  of  sulphur.  When  the  construction  of 
the  heap  is  complete,  the  fire  is  kindled  in  the  centre  by  dropping 
lighted  fagots  down  the  chimney ; in  the  course  of  a few  days  the 
heat  becomes  diffused  throughout  the  mass,  and  sulphur  begins  to 
ooze  from  the  surface.  When  this  is  observed,  numerous  hemi- 
sperical  wells  or  excavations,  fitted  with  covers,  are  made  in  the 
superficial  layer  of  ore  for  the  reception  of  the  sulphur ; into  these 
cavities  it  drains,  and  is  daily  ladled  out  and  cast  into  moulds. 
The  process  of  roasting  such  a heap  occupies  five  or  six  months. 

Uses. — Sulphur  is  extensively  employed  in  the  arts ; from  its 
ready  infiammability  it  is  used  to  facilitate  the  combustion  of 
many  bodies,  as  in  the  preparation  of  matches ; and  large  quanti- 
ties are  consumed  in  the  manufacture  of  gunpowder.  It  is  em- 
ployed to  some  extent  as  a medicine,  especially  in  certain  forms 
of  cutaneous  disease ; when  converted  into  sulphurous  acid  it  is 
applied  to  the  bleaching  of  silks  and  flannels ; but  its  chief  con- 
sumption is  in  the  production  of  sulphuric  acid. 

(407)  Various  forms  of  SulpMir. — Sulphur  has  been  already 
pointed  out  (87)  as  affording  a striking  illustration  of  the  occur- 
rence of  allotropy : it  may  be  obtained  in  several  distinct  modifi- 
cations of  form,  or  in  difterent  allotropic  states. 

The  first  form  is  the  native  crystal  of  sulphur,  the  octohedron 
with  a rhombic  base.  It  may  be  obtained  artificially  by  allowini^ 
the  solution  of  sulphur,  in  chloride  of  sulphur,  or  in  bisulphide  of 
carbon,  to  evaporate  spontaneously.  It  is  semitransparent,  of  an 
amber  yellow  colour,  and  has  a density  of  2*05.  Its  crystals 
undergo  no  change  in  the  air : they  fuse  at  239°  F. 

The  second  variety  is  obtained  by  melting  a few  pounds  of 
sulphur,  and  allowing  it  to  solidify  on  the  surface ; if  the  crust  be 
pierced  with  a hot  wire,  the  still  fluid  portion  may  be  poured  off, 
and  the  solid  mass  beneath  will  be  found  to  be  lined  with  trans- 
parent brownish-yellow  needles,  belonging  to  the  oblique  pris- 
matic form ; these  have  a specific  gravity  considerably  less  than 
octohedral  sulphur,  viz.  1*98,  the  density  of  ordinary  roll  sulphur. 
According  to  Brodie,  it  melts  at  248°.  This  form  is  not  perma- 
nent in  the  air : in  a few  days,  or  (if  the  surface  of  the  crystals 
be  scratched)  in  a few  hours,  the  transparency  disappears,  and 
although  to  the  eye  the  crystals  retain  their  prismatic  outline, 
they  lose  their  coherence,  and  an  opaque  crumbling  mass  is  pro- 
duced, consisting  of  minute  rhombic  octohedra.  On  the  other 
hand,  if  an  octohedron  of  sulphur  be  placed  in  a liquid,  the  tem- 
perature of  which  is  slowly  raised  to  a point  between  220°  and 
230°,  it  loses  its  transparency,  owing  to  the  formation  of  pris- 
matic crystals. 

Mitscherlich  has  ascertained  that  in  the  passage  of  the 
prismatic  into  the  octohedral  form,  an  amount  of  heat  is  emitted 
which  would  raise  the  temperature  of  an  equal  weight  of  water 
4*09°  F.  This  conversion  of  the  prismatic  into  the  octoliedral 
variety  may  be  effected  suddenly,  by  immersing  the  prisms  in  a 
solution  of  bisulphide  of  carbon,  even  when  tliis  solvent  is  already 
saturated  with  sulphur  (^Ann.  de  Chimie.^  III.  xlvi.  124). 

10 


146 


ALLOTEOPIC  FORMS  OF  SrLPHTE. 


The  third  variety  is  even  more  remarkable  than  the  preceding 
forms : it  is  produced  by  the  action  of  a still  higher  temperature. 
The  influence  of  heat  upon  sulphur  is  indeed  very  peculiar.  It 
begins  to  melt  at  about  239°,  and  betvreen  250°  and  280°  it  forms 
a yellow,  transparent,  and  tolerably  limpid  liquid : as  the  tem- 
perature rises,  the  colour  deepens,  it  becomes  brown,  and  at  last 
nearly  black  and  opaque.  At  350°  these  changes  are  very  de- 
cided ; it  gradually  becomes  more  and  more  viscid  ; the  tempera- 
ture at  this  point  for  a while  becomes  stationary,  notwithstanding 
continued  accessions  of  heat  from  without,  so  that  heat  is  becom- 
ing latent,  as  in  the  analogous  case  of  the  melting  of  ice.  After 
a while,  if  the  application  of  heat  be  steadily  continued,  the  tem- 
peratiu’e  again  rises,  and  when  it  has  attained  to  nearly  500°  the 
sulphm*  once  more  liquefles,  though  it  never  becomes  as  fluid  as 
at  the  temperature  of  240°  when  tu'st  melted.  If  it  be  now  sud- 
denly cooled  by  pouring  it  in  a slender  stream  into  cold  water,  a 
soft,  tenacious  mass  is  produced,  which  may  be  drawn  out  into 
elastic  threads.  The  colour  of  tlie  cooled  threads  varies  from  a 
pale  amber  to  a deep  brown,  becoming  darker  in  proportion  to  the 
elevation  of  temperature  which  it  has  experienced.  Magnus  has 
shown  {Poggendorff^s  Annal.  xcii.  308)  that  this  deepening  in 
colour  of  the  melted  sulphur  is  due  to  the  formation  of  another 
modiflcation  of  sulphur,  which  is  black ; the  more  frequently  the 
sulphur  is  heated  up  to  about  600°,  and  then  suddenly  cooled,  the 
larger  is  the  quantity  of  this  black  sulphur  which  is  formed : the 
details  of  the  process  required  for  insulating  it  are  given  at  length 
in  the  memoir  above  referred  to.  A red  variety  of  sulphur  was 
also  obtained  by  Magnus,  which  Mitscherlich  proved  to  be  pro- 
duced only  when  a minute  quantity  of  some  fatty  body  was  present. 
Ductile  sulphirr  has  a sp.  gr.  of  only  1-957.  In  a few  hours  it 
becomes  yellow  and  opaque,  and  returns  to  the  brittle  form,  giving 
out  again  the  heat  which  it  had  absorbed ; it  also  increases  in 
density,  the  greater  part  of  it  assuming  the  octohedral  form.  If 
this  ductile  sulphur  be  heated  to  212°,  it  suddenly  returns  to  the 
brittle  condition,  the  temperature  rising  to  230°  during  the  change. 

(408)  According  to  Berthelot  {Ann.  de  Chimie^  ill.  xlix.  435) 
there  are  among  the  various  modifications  of  which  sulphur  is  sus- 
ceptible, two  principal  forms  which  are  more  stable  than  the  rest. 
These  are  the  octohedral.,  or,  as  he  terms  it,  the  electronegative 
variety,  the  most  permanent  condition  of  sulphur,  and  a pulveru- 
lent, or  electropositive  form,  which  is  insoluWe  in  bisulphide  of 
carbon. 

In  the  so-called  electronegative  or  octohedral  condition  it  is 
soluble  in  bisulphide  of  carbon.  This  variety  is  deposited  at  the 
positive  electrode  of  the  voltaic  battery  during  the  electrolysis  of 
an  aqueous  solution  of  sulphuretted  hydrogen.  To  this  variety 
the  prismatic  form,  and  the  white  precipitate  obtained  from  the 
alkaline  polysulphides  by  the  addition  of  an  acid,  also  belong.  It 
is  this  form  which  is  always  deposited  from  cold  solutions  of  sul- 
phur, whether  the  solvent  be  alcohol,  benzol,  bisulphide  of  carbon, 
or  chloride  of  sulphur. 


MODIFICATIONS  OF  SULPHUR. 


147 


Tlie  electropositive  condition  is  obtained  wlien  snlplinr  is  sepa- 
rated from  its  combinations  with  elements  which,  like  oxygen, 
bromine,  and  chlorine,  are  more  electronegative  than  snlplinr 
itself.  The  most  stable  variety  is  that  obtained  by  treating  flowers 
of  snlphnr  first  with  bisulphide  of  carbon,  then  with  alcohol,  and 
then  a second  time  with  the  bisnlphide  ; it  is  somewhat  less  stable 
when  procured  from  the  chloride  of  snlphnr  by  decomposing  it 
with  water ; if  the  precipitate  thus  occasioned  be  pnrified  by 
digestion  in  bisnlphide  of  carbon,  a yellow,  or  orange-yellow, 
amorphous  powder  is  procnred.  This  amorphons  snlphnr  is  mnch 
more  readily  oxidized  when  heated  with  nitric  acid  than  the  crys- 
talline modification.  If  maintained  at  230°  for  some  time,  it 
gradually  passes  into  the  octohedral  modification,  evolving  heat 
dnring  the  change.  If  amorphons  snlphnr  be  heated  to  572°,  then 
suffered  to  cool  very  slowly,  and  submitted  to  2 or  3 successive 
sublimations  at  a low  temperature,  it  becomes  converted  into  the 
electronegative  condition,  and  is  rendered  entirely  soluble  in  bi- 
snlphide of  carbon.  The  electropositive  variety  may  also  be  slowly 
converted  into  the  electronegative  form  by  contact  with  certain 
electropositive  substances,  as  by  digestion  for  some  days  in  a 
solution  of  liquid  ammonia,  in  one  of  sulphide  of  sodium,  or  in 
one  of  acid  sulphite  of  potassium,  in  which  case  a portion  of  the 
snlphnr  becomes  dissolved,  and  the  remainder  is  rendered  solnble 
in  bisnlphide  of  carbon.  Electropositive  snlphnr  is  deposited  at 
the  negative  electrode  of  the  battery  dnring  the  electrolysis  of 
snlphnrons  or  snlphnrie  acid.  Other  modifications  of  the  insolu- 
ble form  of  snlphnr,  which  pass  with  greater  facility  than  the 
foregoing  one  into  the  solnble  variety  (for  example,  by  exposnre 
to  212°  for  some  honrs),  may  be  obtained  by  decomposing  the 
oxidized  compounds  of  snlphnr,  such  as  the  hyposnlpliites,  by 
acids.  The  black  snlphnr  of  Magnus  is  also  insoluble  in  bisulphide 
of  carbon. 

Crystalline  snlphnr,  of  either  the  octohedral  or  the  prismatic 
form,  is  solnble  in  about  3 times  its  weight  of  bisnlphide  of  car- 
bon ; it  is  also  freely  dissolved  by  the  chloride  of  snlphnr  ; by 
spontaneons  evaporation  of  these  liqnids,  the  snlphnr  is  left  in 
octohedra.  Benzol  is  also  an  excellent  solvent  for  snlphnr,  espe- 
cially when  heated.  Boiling  oil  of  turpentine  likewise  dissolves 
snlphnr  freely,  and  retains  1*5  per  cent,  of  it  on  cooling : as  the 
liquid  cools,  the  snlphnr  crystallizes,  first  in  the  prismatic  form, 
afterwards,  as  the  temperature  continues  to  fall,  octohedra  are 
prodnced.  Yitreons  snlphnr  is  but  partially  solnble  in  bisnlpliide 
of  carbon  ; and  after  it  has  lost  its  vitreous  and  tenacious  cliar- 
acter  by  exposnre  to  the  air,  it  is  not  wholly  changed  into  the 
crystalline  form  of  snlphnr,  for  when  treated  with  bisulphide  of 
carbon  a pale  buff-coloured  powder  of  sp.  gr.  1'955  is  left ; it 
may,  by  fusion,  be  reconverted  into  ordinary  sulphur,  solnble  in 
bisulphide  of  carbon.  If  vitreous  snlphnr  be  left  in  contact  for 
24  honrs  with  an  aqueous  solution  of  sulphuretted  hydrogen,  it  is 
changed  into  the  amorphons  form. 

All  the  varieties  of  sulphur  are  solnble  to  a small  extent  in 


148 


StJLPHimOTJS  ACID. 


boiling  anhydrous  alcohol,  the  electropositive  varieties  becoming 
modified  as  they  are  dissolved : the  hot  solution  as  it  cools  de- 
posits minute  transparent  prismatic  crystals  of  the  electronegative 
variety.  Chloroform  and  ether  dissolve  sulphur  less  freely  than 
alcohol. 

When  sulphur  is  distilled  in  small  quantities,  and  received  into 
vessels  in  which  the  temperature  is  not  considerably  reduced,  the 
sulphur  is  condensed  in  red  drops,  which  remain  liquid  for  many 
hours.  Sulphur  is  also  frequently  liberated  in  the  ductile  form 
from  the  native  sulphides  of  the  metals  during  their  solution  in 
aqua  regia^  and  from  the  hyposulphites  when  decomposed  by  con- 
centrated hydrochloric  acid.  When  nitric  acid  is  used,  the  sul- 
phur is  separated  in  solid  flocculi. 

(409)  Compounds  of  Sulphur  with  Oxygen. — Two  oxides 
only  of  sulphur  are  known  in  the  anhydrous  state,  viz : — 


Mol.  wt.  Mol.  vol.  Sulphur.  Oxygen. 

Sulphurous  anhydride  . S02  = 64  | | ! 50*00  + 50*00  = 100 
Sulphuric  anhydride  . ..  &03=8O  r7~~]  40-00  + 60*00  = 100 


Sulphur,  however,  forms  numerous  oxidized  acid  compounds  : two 
of  them  (sulphurous  acid  and  sulphuric  acid)  have  been  long 
known  and  employed  on  a large  scale  in  the  arts  ; the  others  are 
less  important,  and  of  comparatively  recent  discovery.  Some  of 
these  acids  of  sulphur  are  interesting,  inasmuch  as  they  exhibit  a 
combining  ratio  different  from  any  which  we  have  as  yet  consi- 
dered, and  they  show  the  application  of  the  law  of  multiple  pro- 
portions to  the  case  of  the  sulphur,  as  well  as  to  that  of  the  oxy- 
gen which  they  contain. 

The  following  table  exhibits  the  composition  of  the  various 
oxy acids  of  sulphur,  the  existence  of  which  is  at  present  known. 
The  five  compounds  which  stand  last  on  the  list  are  often  spoken 
of  as  constituting  the  polythionic  series  (from  ‘jroXu,  many, 
sulphur),  in  allusion  to  the  multiple  proportion  in  which  the  sul- 
phur enters  their  composition. 


Sulphurous  acid 

Sulphuric  acid 

Hyposulphurous  acid 
Dithionic  “ 

Trithiouic  “ 

Tetrathiouic  “ 

Peutathiouic  “ 


HaSOs  = 82 
H2SO4  = 98 
028232^4  — 132 
H2S2O6  = 162 
H2S3O6  = 194 
= 226 
H2S5O6  = 258 


W e will  examine  first  the  sulphurous  acid,  then  the  sulphuric 
acid,  and  will  pass  slightly  over  the  other  acids,  the  compounds 
of  which,  with  the  exception  of  some  of  the  hyposulphites,  have 
as  yet  received  no  practical  applications. 

’ (410)  Sulphurous  Anhydride,  or  Sulphurous  Acid  : S02==64 ; 
Mol.  Vol.  1 I I,  (or  80^=32) ; Theoretic  Sp.  Gr.  of  Gas^  2*2112; 
Observed.,  2*247 ; of  Liquid.,  1*38,  at  60° ; Meltingpt. — 105°  ; 
Boiling-pt..,  13*9  (feegnault ; 14°  Faraday). — Sulphur  burns  in 
oxygen  with  a lilac-coloured  flame,  and  produces  a permanent  gas ; 
after  the  combustion  has  terminated,  and  the  gas  has  been  allowed 


SULPHUROUS  ANHTDRroE MODE  OF  PREPARATION. 


149 


to  regain  its  original  temperature,  the  bulk  of  the  gaseous  products 
is  found  to  be  the  same  as  before  the  experiment,  but  the  density 
of  the  gas  is  doubled.  This  experiment  furnishes  an  easy  proof 
of  the  composition  of  the  gas ; for  it  is  thus  shown  to  contain  equal 
weights  of  sulphur  and  oxygen.  Sulphurous  anhydride  is  the  sole 
product,  if  the  oxygen  be  dry. 

The  composition  of  sulphurous  anhydride  may  be  represented 


in  the  following 

way : 

By  weight. 

By  volume. 

Sp.  gr. 

Sulphur 

...  s 

= 32 

or  50 

1 

or  0'5 

= 1-1056 

Oxygen  .. 

...  02 

= 32 

50 

2 

1-0 

= 1-1056 

— 



— 

— 

— 

— 

Sulphurous 

anhydride 

|se, 

64 

100 

2 

1-0 

= 2-2112 

Properties. — This  gas  has  a pungent  suffocating  odour,  like 
that  of  burning  sulphur,  and  in  a concentrated  form  it  is  quite 
irrespirable ; but  if  breathed  in  a diluted  form  it  produces  the 
symptoms  of  ordinary  catarrh.  It  is  not  inflammable,  but  quickly 
extinguishes  the  flame  of  burning  bodies.  Sulphurous  anhydride 
combines  with  water  immediately,  and  becomes  converted  into 
sulphurous  acid,  H2SO3.  This  compound  has  never  been  isolated 
in  a pure  state,  and  a very  gentle  heat  is  sufficient  to  occasion 
the  decomposition  of  its  solution  into  the  anhydride  and  water. 
The  liquid  has  a taste  and  smell  similar  to  that  of  the  gas ; the 
solution  gradually  absorbs  oxygen  from  the  air,  and  becomes  con- 
verted into  sulphuric  acid.  A crystalline  hydrate  of  sulphurous 
acid  (SO2,  15  ; Schonfield) ; or  (S02,9  H^O,  Pierre)  may  also 

be  obtained  at  a low  temperature ; at  40°  this  hydrate  melts  and 
is  decomposed.  Water,  according  to  Bunsen,  takes  up,  at  32°, 
68*8  times  its  bulk  of  the  gas ; 43*5  times  its  bulk  at  59°  ; and  32 
at  75°.  Owing  to  the  solubility  of  sulphurous  anhydride  in 
water,  the  gas  must  always  be  collected  either  over  mercury,  or 
in  dry  bottles  by  displacement : from  the  high  density  of  the  gas 
(double  that  of  oxygen),  the  latter  method  is  easily  applied. 

Preparation. — 1.  When  required  in  a pure  state  sulphurous 
anhydride  is  always  prepared  by  depriving  oil  of  vitriol  of  part 
of  its  oxygen.  In  order  to  effect  this,  two  or  three  ounces  of 
sulphuric  acid  in  a concentrated  form  may  be  boiled  in  a glass 
retort  upon  half  an  ounce  of  copper  clippings  or  of  mercury. 
The  reaction  in  the  case  of  copper  may  be  seen  in  the  following 
equation : — 

Sulph.  Sulphurous 

Sulphuric  acid,  copper.  anhydride.  Water. 

Ou  + 2n^,  = -f-  2H^. 

The  gas  must  be  washed  by  allowing  it  to  bubble  up  through 
a bottle  containing  a small  quantity  of  water,  which  retains  sul- 
phuric acid  and  any  impurities  which  miglit  be  meclianically 
suspended  in  the  gas.* 

* According  to  Maumene,  a certain  quantity  of  the  subsulphide  of  copper, 
is  also  produced  during  this  operation,  after  which  a mixture  of  sulphide  and 
oxysulphide  of  copper  is  also  formed. 


150 


SULPHUROUS  Ai^HTDEIDE. 


2.  — Sulphuric  acid  may  be  more  economically  deoxidized  by 
means  of  charcoal  or  dry  sawdust,  but  the  gas  in  this  case  is 
accompanied  by  one-half  its  volume  of  carbonic  anhydride ; 
•0  + 2H2SO4  = 2 SO2 -h  OO2  + 2 H^O.  For  most  purposes,  how- 
ever, such  as  the  preparation  of  the  alkaline  sulphites,  the  pre- 
sence of  carbonic  anhydride  is  unimportant. 

3.  — Sulphurous  anhydride  may  also  be  procured  readily  by  a 
process  of  oxidation : for  example,  by  heating  in  a flask  an 
intimate  mixture  of  4 parts  of  flowers  of  sulphur  and  5 of  flnely 
powdered  peroxide  of  manganese,  sulphurous  anhydride  and 
sulphide  of  manganese  are  produced;  S2  -h  ^n02  = S02  + 3ifnS. 
A result  somewhat  similar  is  obtained  by  heating  a mixture  of  3 
parts  of  black  oxide  of  copper  vdth  1 part  of  sulphm’ ; 2 OuO-f-Sj 
becoming  -01128  -f  802- 

Sulphurous  anhydride  is  emitted  abundantly  from  the  craters 
of  volcanoes,  and  it  is  occasionally  met  with  in  solution  in  the 
springs  of  volcanic  districts. 

Sulphurous  anhydi’ide,  by  transmission  through  a tube  sur- 
rounded by  a mixture  of  ice  and  salt,  may  be  condensed  to  a 
colomdess,  transparent,  limpid  liquid,  which  dissolves  bitumen ; it 
freezes  at  —105°,  forming  a transparent,  colourless,  crystalline 
solid,  heawer  than  the  liquid ; in  closed  tubes,  at  60°  it  exerts  a 
pressm^e  of  2*54  atmospheres.  Fig.  302  shows  a method  of  lique- 


Fig.  302. 


fying  sulphurous  anhydride.  The  gas  is  generated  in  the  flask, 
A,  washed  and  dried  by  means  of  concentrated  sulphuric  acid 
placed  in  the  bottle,  b,  transmitted  through  the  pewter  worm,  c, 


INDUSTRIAL  APPLICATIONS SULPHITES. 


151 


which  is  surrounded  by  a freezing  mixture  of  ice  and  salt,  and 
collected  in  the  receiver,  d,  which  is  also  cooled  by  a freezing 
mixture;  the  liquefied  compound  is  stored  up  for  use  in  small 
tubes,  one  of  which  is  shown  at  e,  fig,  303 ; the  tube  having  been 
placed  in  the  freezing  mixture,  the  acid  is  poured  into  it  through 
a small  tube  funnel,  and  the  liquid  is  preserved  by  drawing  off 
and  sealing  the  tube  at  the  narrow  portion  in  the  fiame  of 
the  blowpipe,  whilst  the  receiver  still  remains  in  the  freezing 
mixture. 

Uses. — Sulphurous  acid  possesses  considerable  bleaching  pow- 
ers, and  is  extensively  employed  in  bleaching  straw  and  wool,  as 
well  as  silken  goods,  isinglass,  sponge,  and  other  articles  which 
would  be  injured  by  chlorine.  The  articles  to  be  bleached  are 
moistened,  and  suspended  in  closed  chambers  in  which  sulphur 
is  burned  in  an  open  dish  ; the  sulphurous  anhydride  is  absorbed 
by  the  damp  goods,  and  their  colour  is  discharged.  The  acid 
appears  to  act  by  forming  colourless  compounds  with  certain 
colouring  matters.  It  does  not,  like  chlorine,  decompose  the 
colouring  matter ; for  the  sulphm’ous  acid  may  either  be  expelled 
by  a stronger  acid,  or  it  may  be  neutralized  by  an  alkali,  and  the 
colour  will  be  restored : the  reproduction  of  the  yellow  colour 
in  new  flannel,  when  it  is  washed  with  an  alkaline  soap  for  the 
first  time,  affords  a practical  illustration  of  the  effect  of  an  alkali 
upon  goods  which  have  been  bleached  by  sulphurous  acid. 
Sulphurous  acid  is  also  highly  valuable  as  a disinfecting  agent. 
It  is  a powerful  antiseptic.  Meat  which  has  been  exposed  to  the 
action  of  the  gas,  and  then  sealed  up  in  metallic  canisters  filled 
with  nitrogen  to  which  a little  nitric  oxide  has  been  added  to  re- 
move the  last  traces  of  oxygen,  may  be  preserved  fresh  for  years 
(Hands). 

It  is,  however,  principally  as  a preliminary  step  in  the  manu- 
facture of  oil  of  vitriol  that  sulphurous  anhydride  is  made  upon 
the  large  scale,  and  in  this  case  it  is  always  obtained  by  burning 
sulphur,  or  a metallic  sulphide,  in  air. 

(411)  Sulphites. — Sulphurous  acid  is  a weak  dibasic  acid. 
With  the  alkalies  it  forms  two  kinds  of  salts,  one  of  which  is 
represented  by  the  ordinary  sulphite  of  sodium  (Ka^SOg,  7 H^O), 
while  the  other  class  is  represented  by  the  acid  sulphite  of  potas- 
sium (KIISO3),  often  called  the  bisulphite.  The  sulphites  of  the 
alkaline  metals  are  the  only  ones  which  are  freely  soluble  in 
water  ; but  those  of  barium,  strontium,  and  calcium,  are  dis- 
solved to  some  extent  by  an  aqueous  solution  of  sulphurous  acid. 

The  following  table  shows  the  composition  of  some  of  the 
sulphites  : — 

General  formulas. 


Acid II,S<>3 

Normal  salt M..HO3 

Acid  salt IIMSOj 

Double  salt MM tyOg 

Sulphite  of  potassium KiSOg 

Acid  sulphite  of  potassium KILSOg 

Sulphite  of  sodium NaaSOs,  7 HjO 


152 


STJLPHTJEOTJS  ACID SULPHITES. 


Acid  sulpMte  of  sodium NaHSOs,  4 H2O 

Sulphite  of  calcium -GaSOs 

Sulphite  of  barium fiaSOa 

Sulphite  of  magnesium MgSOs 

Sulphite  of  lead PhSOs 

Sulphite  of  silver AgaSOg 

Many  of  the  sulphites  are  decomposed  by  a strong  heat,  the 
acid  being  gradually  expelled.  They  are  also  decomposed  by 
sulphuric  or  by  hydrochloric  acid,  with  extrication  of  sulphurous 
acid,  which  is  known  by  its  peculiar  and  pungent  odour.  The 
best  test  for  detecting  small  traces  of  sulphites  consists  in  the 
addition  of  a fragment  of  zinc  and  a drop  or  two  of  hydrochloric 
acid  to  the  solution  ; the  sulphurous  acid  is  deoxidized,  the  sulphur 
combines  with  hydrogen,  and  sulphuretted  hydrogen  is  given  off; 
the  gas  last  named  may  be  detected  by  suspending  a piece  of 
paper  moistened  with  a solution  of  acetate  of  lead,  in  the  upper 
part  of  the  vessel,  which  should  be  closed  by  a glass  plate.  Salts 
of  silver  in  solution  give  a white  precipitate  with  solutions  of  the 
soluble  sulphites ; the  precipitate  is  soluble  in  excess  of  the  sul- 
phite, and  it  is  partially  reduced  to  metallic  silver  when  the 
liquid  is  boiled : a characteristic  reaction  is  the  formation  with 
chloride  of  barium  of  a white  precipitate  of  sulphite  of  barium, 
which  is  soluble  in  hydrochloric  acid,  but  the  solution  thus  ob- 
tained gives  a white  precipitate  of  sulphate  of  barium  on  the  ad- 
dition of  a solution  of  chlorine,  of  iodine,  or  of  bleaching  powder. 
The  sulphites,  when  moist,  absorb  oxygen  from  the  air;  and 
solutions  of  these  salts  are  often  used  as  deoxidizing  agents  : for 
example,  the  ferric  salts  are  reduced  by  them  to  ferrous  salts. 
Gold,  selenium,  and  tellurium,  are  precipitated  by  them,  from 
solutions  containing  excess  of  hydrochloric  acid,  in  the  reduced  or 
metallic  form  ; arsenic  acid  is  reduced  to  arsenious  acid,  and 
chromic  acid  to  a green  salt  of  chromium. 

Sulphurous  acid  dissolves  and  is  decomposed  by  the  metals 
which,  like  zinc,  iron,  tin,  and  cadmium,  evolve  hydi'ogen  with 
hydrochloric  acid.  Iron,  for  example,  is  rapidly  dissolved  by  sul- 
phurous acid  if  heated  with  its  solution,  sulphite  and  hyposul- 
phite of  iron  being  formed,  whilst  the  hjqiosulphite  is  speedily 
resolved  into  sulphide  and  tetrathionate  of  the  metal,  and  the 
tetrathionate  in  its  tmm  is  converted  into  sulphate  of  iron  and 
free  sulphur,  and  sulphm’ous  acid,  as  is  represented  in  the  annexed 
equations : — 

Sulphi^oufl  Hyposulphite  of  Sulphite  of 

acid.  iron.  iron. 

2 Fe  + 3 H2SO3  ==  FeSgll^O^  -f-  FeSOg  + 2 

Hyposulphite  of  Sulphide  Tetrathionate  Sulphite  of 

Iron.  of  iron.  of  iron.  iron. 

and  3 FeS,H  A = FeS  + FeS.O^  + 5^^  -f  3 H^O, 
whilst  further,  FeS^Og  = FeSO^  + SO,  -f  S,. 

The  sulphites  are  readily  formed  by  transmitting  a stream  of 


SULPHURIC  ACm THEORY  OF  ITS  FORMATION. 


153 


sulphurous  acid  through  water  in  which  the  oxide  or  the  carbo- 
nate of  the  metal  is  dissolved  or  suspended,  the  carbonates  being 
decomposed  with  effervescence. 

(412)  Sulphuric  Acid  (£[280^=98,  or  HO, 803=49). — This 
substance,  which  constitutes  one  of  the  most  important  products 
of  chemical  manufacture,  is  made  in  enormous  quantities.  In 
Great  Britain  alone  upwards  of  100,000  tons  are  annually  con- 
sumed. The  acid  is  occasionally  met  with  uncombined  with 
bases  in  thermal  springs,  particularly  in  those  of  volcanic  regions. 
Its  radicle,  when  united  with  calcium,  barium,  magnesium,  and 
some  other  metals,  forms  an  abundant  constituent  ot  the  crust  of 
the  earth. 

Preparation. — ^When  sulphur  is  boiled  in  aqua  regia^  or  in 
concentrated  nitric  acid,  it  is  gradually  oxidized  and  converted 
into  sulphuric  acid ; but  this  method  is  never  employed,  excepting 
for  experimental  purposes  in  the  laboratory.  On  the  large  scale 
it  is  made  by  a process  first  employed  by  Boebuck,  about  the 
year  1746,  since  which  period  the  mode  of  conducting  it  has 
undergone  several  modifications  and  improvements,  though  in 
principle  it  continues  to  be  the  same. 

The  changes  which  occur  in  the  process  are  remarkable  and 
instructive.  It  has  been  already  mentioned,  that  when  sulphur 
is  burned  in  air  or  in  oxygen,  the  product  is  sulphurous  anhy- 
dride ; this  gas,  if  made  to  combine  with  half  as  much  oxygen 
again  as  it  already  contains,  is  converted  into  sulphuric  anhydride. 
Direct  union,  however,  cannot  be  produced  between  the  two 
gases ; the  intervention  of  some  third  substance  becomes  neces- 
sary ; and  if  water  be  presented  to  them,  a very  gradual  com- 
bination occurs.  If  pure  and  di'y  oxygen,  mixed  with  twice  its 
bulk  of  sulphurous  anhydride,  be  transmitted  over  spongy  plati- 
num (65)  heated  in  a tube,  the  two  gases  combine,  and  sulphuric 
anhydi’ide  (SO3)  is  produced.  W ohier  has  also  observed,  that  the 
two  gases  unite  rapidly  when  transmitted  through  a tube  heated 
to  incipient  redness,  and  containing  a mixture  of  oxide  of  copper 
and  sesquioxide  of  chromium,  obtained  by  precipitation. 

The  following  table  represents  the  composition  of  sulphuric 
acid : — 

Anhydride.  Oil  of  Vitriol. 

Sulphur S = 32  or  40  S = 32  or  32‘65 

Oxygen O3  = 48  60  O4  = 64  65*31 

— Ha  = 2 2*04 


Sulphuric  ) 
anhydride  J 


..803  = 80  or  100 


HaSe4  = 98  100*00 


If  sulphurous  anhydride  mixed  with  oxygen  in  a moist  state 
be  presented  to  nitric  oxide,  or  to  any  other  of  the  higher  oxides 
of  nitrogen,  the  combination  maybe  effected  with  great  rapidity; 
and  further,  a small  proportion  of  the  oxide  of  nitrogen  will 
suffice  to  effect  the  combination  of  an  almost  indefinite  amount  of 
sulphurous  anhydride  and  oxygen,  if  water  be  also  present.  Upon 
these  facts  the  process  employed  in  the  manufacture  ot  sulphuric 
acid  is  founded.  The  reaction  is  easily  watched  upon  the  small 


154 


:MA^"TTACTTJEE  of  SULPBXlilC  ACID. 


scale  by  the  following  means  : — Into  a large  three-necked  receiver, 
A,  tig.  304,  tilled  with  atmospheric  air,  and  slightly  moistened  in 

Fig.  304. 


the  interior,  sulphurous  anhydinde  from  the  retort,  b,  and  nitric 
oxide  from  the  bottle,  c,  are  made  to  pass ; ruddy  fumes  of  perox- 
ide of  nitrogen  are  immediately  foiTued  by  the  combination  of  the 
nitric  oxide  with  atmospheric  oxygen,  and  in  a few  minutes  the 
inner  surface  of  the  receiver  becomes  coated  with  a white  crystal- 
line deposit,  into  the  composition  of  which  sulphurous  anhydride, 
peroxide  of  nitrogen,  and  water  enter.  As  soon  as  this  crystalline 
mass  is  treated  with  water,  it  is  decomposed  with  brisk  efrer- 
vescence;  yielding  IS'O+H^SO.  + a?-!  ; 

1 atom  of  nitric  oxide  escapes,  and  1 atom  of  sulphuric  acid 
remains  in  solution  ; the  nitric  oxide,  by  again  absorbing  oxygen 
from  the  air,  is  reconverted  into  peroxide  of  nitrogen ; this  com- 
bines again  with  a fresh  atom  of  sulphurous  anhydinde  in  the  pre- 
sence of  a small  quantity  of  water  ; fresh  crystals  are  formed,  and 
these  in  their  turn  are  decomposed  by  solution  as  before.  The 
nitric  oxide  is  thus  again  liberated,  and  may  go  through  the  same 
round  of  compositions  and  decompositions,  till  the  whole  of  the 
oxygen  in  the  air  has  been  consumed : the  oxide  of  nitrogen  thus 
acts  the  part  of  a carrier  of  oxygen  to  the  sulphurous  anhydi’ide. 
In  the  manufacture  of  sulphuric  acid  on  the  large  scale,  the  for- 
mation of  the  crystalline  body  and  its  destruction  are  simulta- 
neous, if  the  operation  be  properly  conducted,*  so  that  no  depo- 
sition of  crystals  actually  occurs. 

* The  true  composition  of  this  crystalline  body  has  been  the  object  of  much  dis- 
cussion and  numerous  experimental  inquiries.  IL  Rose  states  that  by  passing  pure 


MANUFACTURE  OF  SULPHUKIC  AGED. 


155 


(413)  In  the  manufacture  of  sulphuric  acid,  sulphurous  anhy- 
di’ide  is  procured  by  burning  either  sulphur,  or  iron  pyrites  (PeS^) ; 
provision  being  made  for  an  abundant  supply  of  atmospheric  air 
to  the  burning  material.  The  general  arrangements  adopted  in 
the  manufacture  are  shown  in  hg.  305.  a,  a,  represent  furnaces 

Fig.  305. 


in  which  the  sulphur  is  burned  : in  the  current  of  heated  gas  an 
iron  pot,  5,  is  suspended,  which  has  been  previously  charged  with 
a mixture  of  nitrate  of  sodium  and  oil  of  vitriol.  Yapours  of 
nitric  acid  are  thus  liberated ; they  pass  on  with  the  sulphurous 
anhydride,  by  suitable  flues,  into  immense  chambers,  f,  f,  con- 
structed of  sheet  .lead,  and  supported  by  a strong  timber  frame- 

nitric  oxide  into  a glass  vessel,  from  whicli  oxygen  is  carefully  excluded,  and  the 
interior  of  which  is  moistened  with  sulphuric  anhydride  (SO3),  a white,  hard,  amor- 
phous substance  is  formed ; and  this  compound  he  regards  as  the  essential  constituent 
in  the  crystals  above  described.  It  fuses  at  a high  temperature,  and  may  be  sublimed 
without  decomposition.  This  substance  Rose  considered  to  have  the  composition 
NO.SOs ; but  Briining  has  shown  that  during  the  formation  of  this  compound  sul- 
phurous anhydride  is  liberated,  in  the  proportion  of  1 atom  for  every  2 atoms  of 
nitric  oxide  absorbed ; and  he  found  the  crystalline  compound  to  have  a composition 
which  may  be  represented  by  the  formula  (ISTsOs,  2 8^3)-  Water  immediately  decom- 
poses it,  liberating  nitric  oxide,  whilst  the  sulphuric  acid  is  dissolved.  If  the  anhy- 
drous crystals  be  exposed  to  the  air,  they  absorb  moisture  and  emit  nitrous  fumes. 
Concentrated  sulphuric  acid  by  the  aid  of  heat,  dissolves  them  in  all  proportions  with- 
out change;  the  solution  crystallizes,  on  cooling,  in  rectangular  prisms,  which  appear 
to  contain  water  of  crystallization. 

Oil  of  vitriol  rapidly  absorbs  both  nitrous  anhydride  and  peroxide  of  nitrogen,  and 
forms  a crystalline  compound  similar  to  the  foregoing ; the  addition  of  water  imme- 
diately liberates  red  fumes  of  peroxide  of  nitrogen  from  it. 

There  are  many  other  methods  by  which  this  curious  substance  maybe  obtained, 
but  they  often  involve  very  complicated  considerations.  De  la  Provostaye  procures 
it  by  the  action  of  liquid  sulphurous  anhydride  on  liquid  peroxide  of  nitrogen ; he 
considers  it  when  anhydrous  to  consist  of  (SO3802,  2 NO2)  which  is  consistent  with 
the  analysis  of  Briining. 

Weltzien  found  that  sulphuric  acid  (II28O4)  combines  directly  with  nitrous  anhy- 
dride (N2O3)  in  proportions  forming  a white  crystalline  mass,  which  may  bo  repre- 
sented by  the  formula  (II2O,  2 8O3N2O3).  According  to  the  same  chemist,  sulphuric 
acid  also  forms  with  peroxide  of  nitrogen  a white  crystaUino  compound  fusible  at 
145°,  which,  even  when  the  peroxide  is  present  in  large  excess,  contains  the  two 
substances  in  a proportion  which  may  bo  represented  by  the  formula  (2  II2O,  3 8O3, 
2 NO2). 


156 


MODE  OF  CONDEIirSING  THE  NITEOES  FOIES. 


work.  These  chambers  are  often  12  or  15  feet  high,  15  or  20 
wide,  and  from  150  to  300  feet  in  length ; they  are  sometimes 
partially  intersected  by  incomplete  transverse  leaden  partitions, 
interposed  in  the  current  of  the  mixed  gases,  vdth  a view  of  effect- 
ing their  more  intimate  admixture.  W ater  to  the  depth  of  2 or 
3 inches  is  placed  upon  the  floor  of  the  chamber,  </,  to  condense 
the  acid ; and  the  mutual  reaction  of  the  atmospheric  oxygen, 
sulphurous  anhydride,  and  nitric  oxide  is  further  facilitated  by 
the  injection  of  steam  at  a pressure  of  about  10  lb.  upon  the  inch 
by  means  of  jets,  c,  c,  c,  supplied  from  the  boiler,  e.  The  nitric 
acid  extricated  fr’om  the  nitre  speedily  becomes  deoxidized  by  the 
sulphurous  anhydride  to  the  state  of  nitric  oxide,  and  then  the 
changes  already  pointed  out  rapidly  succeed  each  other,  and  sul- 
phuric acid  is  formed  in  large  quantity. 

In  a properly  managed  chamber,  the  gases  which  pass  off  by 
the  exit  flue,  c,  consist  only  of  nitrogen  and  nitric  oxide,  the  sul- 
phurous anhydride  and  oxygen  being  supplied  in  quantities  just 
sufflcient  to  effect  their  mutual  condensation,  fresh  atmospheric 
air  entering  at  the  other  end  along  with  the  sulphurous  anhydride. 

Gay-Lussac  has  taken  advantage  of  the  solubility  of  nitric 
oxide  in  oil  of  \utriol,  to  economize  the  consumption  of  nitre  in 
the  process,  which  upon  the  old  plan  amounts  to  from  one-eighth  to 
one-twelfth  of  the  weight  of  the  sulphur  consumed.  By  the  con- 
trivance to  be  mentioned  immediately,  the  quantity  of  nitre  for- 
merly requisite  has  been  reduced  by  one-half,  or  even  by  two- 
thirds.  The  improvement  consists  in  conducting  the  spent  gases 
into  a leaden  tower  fllled  with  fragments  of  coke,  through  which 
a stream  of  concentrated  sulphuric  acid  is  continually  trickling. 
The  acid  thus  becomes  charged  with  the  nitrous  vapours,  and  flows 
off  at  the  bottom  of  the  tower  to  a reservoir  from  which  it  is  again 
raised  by  a forcing-pump  to  the  top  of  a second  similar  tower  at 
the  entrance  of  the  chamber,  wdiere  it  is  deprived  of  the  nitrous 
compounds  by  the  sulphm*ous  anhydride  as  it  enters  from  the 
furnace. 

The  sulphuric  acid  which  collects  at  the  bottom  of  the  cham- 
bers is  in  too  dilute  a condition  for  sale  : it  is  not  found  advan- 
tageous to  allow  it  to  attain  a greater  degree  of  concentration  than 
1*60  in  the  chambers,  since  beyond  this  it  becomes  liable  to  absorb 
and  retain  the  nitrous  fumes.*  When  it  has  reached  a speciflc 
gravity  of  about  1‘60,  it  is  sufliciently  strong  for  the  manufacture 
of  salt-cake,  but  it  requires  concentration  for  other  purposes : with 
this  view  it  is  drawn  off  and  evaporated  in  shallow  leaden  pans 
till  it  has  acquired  a density  of  1’720  ; beyond  this  point  the  con- 
centration cannot  be  carried  in  these  vessels,  because  the  tempera- 
ture required  would  endanger  the  melting  of  the  leaden  pan  and 
its  corrosion  by  the  acid.  This  acid  of  sp,  gr.  1*720  forms  the  hr  own 
acid  of  commerce  ; it  is  extensively  employed  in  the  manufacture 
of  acid  phosphate  of  calcium  (superphosphate  of  lime)  for  manures, 
and  for  other  coarse  purposes.  When  required  in  a still  more 

* The  crude  acid  of  sp.  gr.  1*60  does  not  usually  contain  more  than  0*6  per  cent,  of 
nitrous  acid  (Mr.  Allhusen). 


CONCENTKATION  OF  SULPHUKIC  ACID. 


157 


concentrated  form,  the  brown  acid  is  transferred  into  glass  retorts, 
or,  as  is  practised  in  many  works,  into  platinum  stills  ; the  presence 
of  nitrous  compounds  must  be  avoided  when  platinum  is  employed, 
otherwise  the  metal  is  gradually  corroded ; in  these  it  is  again 
further  heated  until  white  fumes  of  oil  of  vitriol  pass  over. 
Beyond  this  point  it  is  useless  to  carry  the  operation,  as  the  con- 
centrated acid  distils  over.  Indeed  during  the  whole  operation 
some  acid  passes  over  with  the  water,  which  is  therefore  preserved, 
and  returned  to  the  leaden  chamber. 

The  acid  that  remains  in  the  retort  after  it  has  thus  been 
boiled  down,  is  the  concentrated  oil  of  vitriol  of  commerce  ; it  is 
a definite  compound,*  consisting  of  H^SO^. 

The  following  table  gives  the  proportion  of  sulphuric  acid  con- 
tained in  solutions  of  the  densities  therein  mentioned  :f — 

Strength  of  Sulphuric  Acid  of  Different  Densities  at  60°  F.  ( TIrei) 


Specific 

gravity. 

SOgin 
100  pts. 

Specific 

gravity. 

SO3  in 
100  pts. 

Rse,. 

Specific 

gravity. 

SOs  in 
100  pts. 

H2S04. 

1-8460 

81-54 

100 

1-5503 

53-82 

66 

1.2334 

26-09 

32 

1-8415 

79-90 

98 

1-5280 

52-18 

64 

1-2184 

24-46 

30 

1-8366 

78-28 

96 

1-5066 

50-55 

62 

1-2032 

22-83 

28 

1-8288 

76-65 

94 

1-4860 

48-92 

60 

1-1876 

21-20 

26 

1-8181 

75-02 

92 

1-4660 

47-29 

58 

1-1706 

19-57 

24 

1-8070 

73-39 

90 

1-4460 

45-66 

56 

1-1549 

17-94 

22 

1-7901 

71-75 

88 

1-4265 

44-03 

54 

1-1410 

16-31 

20 

1-7728 

70-12 

86 

1-4073 

42-40 

52 

1-1246 

14-68 

18 

1-7540 

68-49 

84 

1-3884 

40-77 

50 

1-1090 

13-05 

16 

1-7315 

66-86 

82 

1-3697 

39-14 

48 

1-0953 

11-41 

14 

1-7080 

65-23 

80 

1-3530 

37-51 

46 

1-0809 

9-78 

12 

1-6860 

63-60 

78 

1-3345 

35-88 

44 

1-0682 

8-15 

10 

1-6624 

61-97 

76 

1-3165 

34-25 

42 

1-0544 

6-52 

8 

1-6415 

60-34 

74 

1-2999 

32-61 

40 

1-0405 

4-89 

6 

1-6204 

58-71 

72 

1-2826 

30-98 

38 

1-0268 

3-26 

4 

1-5975 

57-08 

70 

1-2654 

29-35 

36 

1-0140 

1-63 

2 

1-5760 

55-45 

68 

1-2490 

27-22 

34 

1-0074 

0-815 

1 

(414)  or  HOjSOg,  often  called  Protohydrate  of  Sulphuric 

Add. — The  oil  of  vitriol  of  commerce  forms  a dense,  oily-looking, 

* De  Marignac  {Ann.  de  Chimie,  III.  xxxix.  189)  finds  that  it  always  contains  a 
slight  excess  of  water  beyond  the  atomic  proportion  calculated  from  the  formula 
HjOjSOa ; instead  of  18’36  per  cent,  of  water,  he  always  obtained  19‘62 ; and  a simi- 
lar observation  was  made  by  G-ay-Lussac.  Playfair  states  that  if  the  concentration 
of  the  acid  be  effected  by  a temperature  not  exceeding  500°,  the  true  compound 
II2SO4  of  sp.  gr.  1‘848  is  obtained;  but  if  heated  to  ebullition,  it  is  partially  decom- 
posed in  the  manner  stated  by  De  Marignac. 

f Bineau  has  more  recently  made  a careful  determination  of  the  strength  of  sul- 
phuric acid  of  different  densities  {Ann.  de  Ghimie^  III.  xxiv.  341),  but  his  results 
differ  but  slightly  from  those  of  Ure,  as  may  be  seen  from  the  annexed  table  (temp. 
59°  F.):— 


Specific 

gravity. 

H2SO4  in 
100  parts. 

Specific 

gravity. 

H2SO4  in 
100  parts. 

Specific 

gravity. 

112804  in 
100  parts. 

1-842 

100 

1-501 

60 

1-144 

20 

1-822 

90 

1-398 

50 

1-068 

10 

1-734 

80 

1-306 

40 

1-032 

5 

1-615 

70 

1-223 

30 

158 


HYDRATES  OF  STJLPHrEIC  ACID. 


colourless  liquid,  without  smell,  and  of  specific  gravity  1*842,  It 
is  intensely  caustic,  and  chars  almost  all  organic  substances,  from 
its  powerful  attraction  for  moisture.  With  water  it  mixes  com- 
pletely in  all  proportions,  and  the  mixture,  when  cold,  occupies 
less  bulk  than  the  two  liquids  did  when  separate.  Great  heat  is 
given  out  at  the  moment  the  mixture  is  made  ; the  dilution  should 
therefore  be  performed  gradually,  always  pouring  the  acid  into  the 
w*ater,  not  the  water  into  the  acid.  So  powerful  is  the  attraction 
of  the  acid  for  moisture,  that  if  it  be  exposed  in  a shallow  dish  to 
the  air  for  a few  days,  it  frequently  doubles  its  weight  by  absorb- 
ing aqueous  vapour  from  the  air.  In  the  laboratory,  advantage  is 
very  often  taken  of  this  property,  wdiich  enables  it  to  be  employed 
in  a variety  of  cases  as  a desiccating  agent  (66  and  185).  The  acid 
of  commerce  is  often  of  a dark  brown  colour,  occasioned  by  its 
charring  action  on  fragments  of  organic  matter,  such  as  straw  or 
wood,  which  have  accidentally  fallen  into  it.  Sulphuric  acid  does 
not  evaporate  at  the  ordinary  temperature  of  the  air.  If  a cbop 
of  the  diluted  acid  fall  upon  a cloth,  the  water  gradually  evapo- 
rates until  the  acid  which  is  left  behind  acquires  a certain  degree 
of  concentration.  On  approaching  a fire  or  other  source  of  heat, 
a further  portion  of  the  water  is  expelled,  and  the  acid  becomes 
more  concentrated,  until  it  chars  or  destroys  the  cohesion  of  the 
fibres ; this  is  one  cause  of  the  destructive  action  of  sulphuric  acid 
upon  linen,  even  when  very  much  diluted. 

De  Marignac  finds  that  the  true  sulphiu’ic  acid  when 

heated  emits  a small  quantity  of  the  vapour  of  the  anhydride,  and 
the  remaining  liquid  boils  at  640°  F.  Bineau  states  that  just 
above  the  boiling-point  of  the  acid  the  vapour  has  a sp.  gr.  of  2*15, 
which  would  represent  2 volumes  of  the  anhydride  and  2 volumes 
of  steam  (1  atom  of  each)  condensed  into  the  space  of  3 volumes, 
but  it  continues  to  expand  by  heat  until  at  880°  an  atom  of  the 
compound  occupies  the  space  of  4 volumes,  which  would  reduce  the 
density  of  the  vapour  to  1*692.  This  by  some  chemists  is  supposed 
to  be  produced  by  the  separation  of  the  compound  into  aqueous 
vapour  and  anhydride  by  the  process  of  dissociation  (see  note ; 
Part  I.  p.  88).  After  the  acid  has  been  frozen,  it  melts  at  51°, 
but  it  may  be  cooled  much  below  this  point  without  solidifying. 
On  dropping  into  the  cooled  acid  a crystal  of  the  acid  previously 
frozen,  congelation  immediately  occurs,  and  the  temperature  rises 
to  51°.  The  concentrated  acid  of  commerce  does  not  usually  freeze 
till  it  has  been  cooled  to  about  — 30°  ; but  when  frozen  it  does  not 
become  liquid  till  the  temperature  reaches  32°. 

(H2S0^,H20)  or  Second  Hydrate  of  Sulphuric  Acid. — If  water 
be  added  to  sulphuric  acid,  until  the  density  is  reduced  to  1*78,  a 
definite  hydrate  is  formed.  It  freezes  at  47°,  and  crystallizes  in 
splendid  rhombic  prisms,  the  sp.  gr.  of  which  is  1*951 ; from  this 
])roperty  it  is  often  termed  glacial  sulphuric  acid.  According  to 
Dalton,  it  boils  at  435°.  Graham  found  that  this  hydrate  may  be 
obtained  by  heating  a more  diluted  acid  to  400°  till  it  ceases  to 
give  off  water. 

Another  hydrate  (IIjSO^,  2 HjO)  may,  according  to  Graham,  be 


ANHYDROUS  SULPHURIC  ACID. 


159 


procured  by  evaporating  a dilute  acid  in  vaeuo  at  212°,  till  it 
ceases  to  lose  weight.  The  density  of  this  hydrate  is  1‘632,  and  its 
boiling-point  is  348°. 

(415)  Nordhausen  Sulphuric  Acid. — For  the  purpose  of  dissolv- 
ing indigo  in  the  process  of  dyeing  Saxony  blue,  an  acid  of  still 
higher  concentration  than  oil  of  vitriol  is  required.  Such  an  acid 
is  principally  prepared  at  the  town  of  Nordhausen,  in  Saxony,  and 
is  hence  known  as  Nordhausen  oil  of  vitriol.  The  old  name  for 
sulphate  of  iron  was  green  vitriol.,  and  this  circumstance,  taken  in 
conjunction  with  the  oily  consistence  of  the  concentrated  acid, 
gave  rise  to  the  name  of  oil  of  vitriol,  by  which  the  concentrated 
acid  of  commerce  is  still  frequently  known,  and  which  is  conveni- 
ent as  distinguishing  it  from  more  diluted  acids.  In  preparing 
the  N ordhausen  acid,  sulphate  of  iron  is  dried  at  a moderate  heat 
to  expel  its  water  of  crystallization,  and  is  then  distilled  in  earthen 
retorts  ; a dense,  brown,  fuming  liquid  passes  over,  of  sp.  gr.  about 
1-9. 

(416)  Sulphuric  Anhydride  (SOg). — If  this  fuming  Nor dliausen 
acid  be  placed  in  a glass  retort,  furnished  with  a receiver  which 
is  kept  cool  by  ice,  and  a gentle  heat  be  applied  to  the  retort, 
white  fumes  pass  over,  which  solidify  into  a white,  silky-looking 
fibrous  mass.  This  is  the  compound  frequently  called  anhydrous 
sulphuric  acid.  The  remainder  in  the  retort,  after  all  the  anhy- 
dride is  expelled,  consists  of  ordinary  oil  of  vitriol.  Sulphuric 
anhydride  may  also  be  obtained  from  the  acid  sulphate  of  sodium 
(NallSOj,  which  melts  at  a dull  red  heat,  and  is  deprived  of  its 
hydrogen  in  the  form  of  water;  after  which,  if  distilled  in  an 
earthen  retort,  it  yields  white  fumes  of  the  anhydride,  whilst  neu- 
tral sulphate  of  sodium  remains  in  the  retort. 

2 N allSO^  ==  N a^SO^  ,S0-3  -f  H^O,  and 

Na,se„se3  =:Na,se,  4-  se3. 

The  anhydride  forms  with  oil  of  vitriol  a compound  (Il2S0-4,SO3) 
that  crystallizes  in  plates  which  fuse  at  95°. 

Sulphuric  anhydride,  however,  possesses  no  acid  properties. 
It  is  tough,  ductile,  and  can  be  moulded  in  the  fingers,  like  wax, 
without  charring  the  skin.  It  fumes  in  the  air,  and  is  very  deli- 
quescent : when  thrown  into  water,  the  heat  emitted  is  so  intense 
that  it  hisses  as  a hot  iron  would  do.  The  solution  has  all  the 
properties  of  ordinary  sulphuric  acid.  The  anhydride  melts  at 
65°,  and  boils  at  about  110°,  forming  a colourless  vapour,  which, 
if  passed  through  ignited  porcelain  tubes  is  decomposed  into  2 vol- 
umes of  sulphurous  anhydride  and  1 of  oxygen ; 1 volume  of  sul- 
pliur  vapour  and  3 of  oxygen  being  condensed  in  the  anhydride 
into  the  space  of  2 volumes  of  vapour.  The  specific  gravity  of 
this  vapour  was  found  by  Mitscherlich  to  be  3 •01,  or  somewhat 
higher  than  its  calculated  amount,  which  is  2’764 : for — 

By  weight.  By  volume.  Sp.  gr. 

Sulphur S = 32  or  40  1 or  0*5  = 1-1056 

Oxygen O3  = 48  60  3 1-5  = 1 6584 


Sulphuric 

anliydride 


...SO: 


80  100 


2 1 


2-7640 


160 


COIVIMON  IMPTJEITIES  OF  SULPHIJEIC  ACID. 


According  to  De  Marignac,  sulphuric  anhydride  exists  under  two 
modifications ; one  of  which  melts  at  ahont  65°,  and  is  produced 
by  distillation,  or  by  fusion  at  a high  temperature ; hnt  when 
once  it  has  been  solidified,  it  passes  rapidly  into  the  other  form, 
which  melts  near  212°,  at  which  temperature  it  is  slowly  volatil- 
ized, and  becomes  reconverted  into  the  first  variety.  Sulphuric 
anhydride  in  some  cases  combines  with  the  anhydrous  bases ; if 
its  vapour  he  passed  over  baryta  heated  to  the  point  of  redness,  the 
two  combine  with  incandescence,  and  sulphate  of  barium  is 
formed.  Mercury,  when  heated  in  the  vapour,  is  converted  into 
mercuric  sulphate  with  liberation  of  sulphurous  anhydride.  Phos- 
phorus takes  fire  in  its  vapour,  setting  sulphur  free. 

Sulphuric  anhydride  combines  with  sulphur,  forming  solutions 
which  have  a brown,  green,  or  blue  colour,  according  to  the  pro- 
portion of  sulphur ; the  blue  compound  containing  the  smallest 
proportion.  It  likewise  dissolves  iodine,  and  with  one-tenth  of 
its  weight  of  iodine  forms  a green  crystalline  compound.  It  also 
combines  with  hydrochloric  acid,  and  forms  a liquid  tenued 
chlorhydrosidphuric  acid  (HChSOg),  which  boils  at  293°,  and  is 
decomposed  by  water.  Williamson  obtained  it  by  the  action  of 
pentachloride  of  phosphorus  upon  sulphuric  acid ; H2S04-l-PCl5= 
HChSOg  -h  HCl  -f-  POClg ; hydrochloric  acid  and  oxychloride  of 
phosphorus  being  formed  at  the  same  time. 

We  are  therefore  acquainted  with  the  following  definite  com- 
pounds of  sulphuric  anhydride  with  water ; starting  with  the  an- 
hydride : — 


Hydrate. 

Formula. 

Fusing 
point,  F. 

Boiling 
point,  “ F. 

Specific 

gravity. 

Sulphuric  anhydride  .... 

SO3 

65 

Dih^’^drate 

TJ  SLCX  g A 
Jl20v::/4jk5v73 

95 

Oil  of  vitriol 

H2S04 

51 

640 

1-848 

Glacial  acid 

H2S04,H20 

4’7 

435 

1-780 

Graham’s  hydrate 

H2SO4,  2 H2O 

348 

1-632 

Uses. — The  applications  of  sulphuric  acid  in  the  arts  are  very 
numerous.  Immense  quantities  of  it  are  consumed  in  the  man- 
ufacture of  sulphate  of  sodium  as  a preliminary  process  in  mak- 
ing carbonate  of  sodium;  and  it  is  in  constant  requisition  for 
the  preparation  of  nitric,  hydrochloric,  and  other  volatile  acids. 
Its  applications  in  the  laboratory  are  too  numerous  to  be  specified. 

(417)  Imjpurities  cominoii  in  the  Commercial  Acid. — The  oil 
of  vitriol  of  commerce  is  never  pure : it  always  contains  lead,  de- 
rived from  the  vessels  in  which  it  is  made.  The  greater  part  of 
the  sulphate  of  lead  is  precipitated  as  a white  powder  when  the 
acid  is  diluted.  It  is  also  frequently  contaminated  with  arsenic, 
derived  from  the  pyrites : the  diluted  acid  in  this  case  gives  a 
yellow  precipitate  when  exposed  to  a current  of  sulphuretted 
hydrogen  gas.  The  arsenic  is  still  more  easily  recognised  by 
what  is  termed  Marsh’s  test,  which  will  be  described  under  the 
head  of  arsenic  (846).  On  the  large  scale  this  impimty  is  effect- 


SULPHATES. 


161 


Lially  removed  by  adding  a small  quantity  of  sulphide  of  barium 
to  the  acid : sulphide  of  arsenic  and  sulphate  of  barium  are 
formed  ; they  are  both  insoluble  in  the  acid,  and  may  be  separat- 
ed by  subsidence  and  decantation.  The  greater  part  of  it  may 
also  be  got  rid  of  by  adding  hydrochloric  acid  and  boiling  the 
liquid,  when  the  arsenic  is  expelled  in  the  form  of  chloride  of 
arsenic  with  the  excess  of  hydrochloric  acid,  l^itric  acid  and 
some  of  the  lower  oxides  of  nitrogen  are  also  often  present : a 
strong  solution  of  green  vitriol  in  water,  when  added  to  the 
undiluted  acid,  shows  the  presence  of  these  impurities  by  strik- 
ing a characteristic  purplish-red  colour  at  the  point  of  contact  of 
the  two  liquids.  Sulphurous  acid  may  likewise  sometimes  be  de- 
tected in  the  acid,  as  may  also  hydrochloric  acid  and  sulphate  of 
potassium. 

When  required  in  a pure  form,  the  acid  must  be  re-distilled 
with  a little  sulphate  of  ammonium ; this  salt  decomposes  any 
nitrous  acid  which  may  be  present  (p.  95).  The  distillation  re- 
quires to  be  conducted  with  much  care,  as  the  boiling  takes  place 
with  violent  concussions  and  sudden  bursts  of  vapour : the  dan- 
ger may  be  avoided  by  distilling  it  from  freshly  broken  crystals  of 
quartz ; or  by  using  a gas-burner  in  the  form  of  a large  ring,  so 
as  to  apply  heat  to  the  sides,  and  not  to  the  bottom  of  the  retort, 
in  which  case  the  insoluble  matters  collect  at  the  bottom  of  the 
retort,  whilst  the  ebullition  takes  place  from  the  sides  tranquilly. 

(418)  Sulphuric  acid  in  its  concentrated  form  acts  but  feebly 
upon  metallic  bodies  in  the  cold,  but  when  boiled  upon  them  it 
in  some  cases  undergoes  decomposition : even  silver  is  dissolved 
by  it,  sulphurous  anhydride  being  formed,  whilst  the  sulphate 
of  the  metal  is  dissolved  in  the  excess  of  sulphuric  acid  ; thus 
2 Ag-f  2 H2SB^=Ag2S04-fS02  + 2 H2^.  Copper,  mercury,  ar- 
senic, antimony,  bismuth,  tin,  lead,  and  tellurium  are  acted  upon 
by  the  acid  in  a similar  manner.  Gold,  platinum,  rhodium,  and 
iridium  are  not  acted  upon  by  sulphuric  acid  even  when  boiled 
with  it.  The  more  oxidizable  metals  are  dissolved  by  this  acid 
when  diluted  with  water,  hydrogen  being  liberated,  whilst  the 
metal  unites  with  the  radicle  of  the  sulphuric  acid : zinc,  iron, 
cobalt,  nickel,  and  manganese  are  acted  upon  in  this  way.  The 
acid  is  also  decomposed  when  boiled  with  charcoal  or  with  sul 
phur,  sulphurous  anhydride  being  evolved. 

Sulphates. — The  salts  formed  by  sulphuric  acid  are  termed 
sulphates  / their  composition  is  such  as  to  allow  them  for  the  most 
jmrt  to  be  represented  (as  was  till  lately  the  uniform  practice)  as 
consisting  of  1 equivalent  of  acid  and  1 of  metallic  oxide,  like 
sulphate  of  potassium  (K0,S03,  or  KSO,).  There  are,  however, 
such  strong  grounds  for  believing  that  sulphuric  acid  is  what  is 
termed  a dibasic  acid,  that  most  chemists  have  now  agreed  so  to 
regard  it.  The  ordinary  formula  of  the  acid  would  in  this  case 
require  to  be  doubled,  and  would  be  written  2 II0,S20g : or, 
adopting  the  new  atomic  weights  for  oxygen  and  sulphur  it 
would  be  written  as  in  accordance  with  the  formula  given 

ill  the  preceding  pages.  With  the  alkalies  it  forms  acid  salts, 
11 


162 


SULPHATES. 


siicli  as  acid  sulphate  of  potassium  (KHSO^)  : in  a few  instances 
Ijasic  salts,  such  as  the  basic  sulphate  of  copper  (OuSO^,  2 OuH^O^), 
may  be  formed.  Many  of  the  sulphates  occur  native,  and  consti- 
tute important  and  well-known  minerals,  such,  for  instance,  as 
g}^sum  (-BaSO^,  2 H„0),  and  the  sulphates  of  barium,  strontium, 
and  lead.  Some  are  formed  by  the  spontaneous  or  artificial  oxida- 
tion of  the  sulphides,  as,  for  instance,  the  sulphides  of  iron  and  cop- 
per, which,  by  exposure  to  the  weather,  or  by  roasting,  can  furnish 
the  sulphates  of  the  metals.  The  soluble  sulphates  of  the  metals 
may  be  readily  prepared  by  dissolving  the  oxide  or  its  carbonate 
in  diluted  sulphuric  acid,  in  cases  in  which  the  metal  itself  is  not 
readily  attacked  by  the  acid.  The  insoluble  sulphates,  such  as 
those  of  barium  and  lead,  may  be  obtained  by  precipitating  a 
soluble  salt  of  the  base  by  means  of  some  soluble  sulphate,  such 
as  sulphate  of  sodium.  Many  of  the  sulphates  are  formed  as 
residues  during  the  preparation  of  the  volatile  acids  by  the  action 
of  sulphuric  acid  on  their  salts.  Sulphate  of  potassium  is  thus 
obtained  during  the  preparation  of  nitric  acid  from  saltpetre,  sul- 
phate of  sodium  as  a residue  from  common  salt  in  the  manufac- 
ture of  hydrochloric  acid,  and  so  on.  The  sulphates  of  potassium 
barium,  strontium,  lead,  silver,  and  of  both  the  oxides  of  mercury, 
are  anhydrous.  Sulphate  of  calcium  (gj^sum)  contains  BaSO^, 
2 HjO.  The  sulphates  of  zinc,  magnesium,  and  of  iron,  cobalt, 
and  nickel,  usually  crystallize  with  T H2O  ; biit  the  number  of 
atoms  of  water  in  these  salts  is  often  smaller  if  the  solution  is 
allowed  to  crystallize  at  a high  temperature,  the  proportion  of 
water  being  sometimes  5,  at  others  d,  and  under  some  circum- 
stances as  low  as  2 H^B.  The  sulphates  of  the  group  which 
are  isomorphous  with  sulphate  of  magnesium  contain  1 atom  of 
water  which  admits  of  displacement  by  an  atom  of  some  anhy- 
drous sulphate,  such  as  sulphate  of  potassium,  or  sulphate  of 
ammonium  : peculiar  double  salts  are  thus  formed,  which  retain 
6 atoms  of  water  of  crystallization,  but  these  double  salts  are 
still  isomorphous  with  sulphate  of  magnesium  (555).  Sulphate  of 
copper  crystallizes  with  5 HoB,  but  it  forms  double  salts  contain- 
ing 6 H2B : such  as  (BuSB^,  ^ H^B)  isomorphous  with 

those  just  mentioned.  Sulphate  of  sodium  crystallizes  usually  as 
(Xa2SB^,  10  II2B),  but  it  exhibits  some  singular  anomalies  (586). 

k^either  the  sulphate  of  lead  nor  the  sulphates  of  the  metals  of 
the  alkalies  and  alkaline  earths  are  decomposed  when  heated  to 
redness,  except  the  sulphate  of  magnesium,  which  loses  its  acid 
jDartially ; the  sulphates  of  zinc,  cadmium,  nickel,  cobalt,  copper, 
and  silver  require  an  intense  heat  to  decompose  them ; but  the 
other  sulphates  part  with  their  acid  without  difficulty  when 
strongly  ignited.  AVlien  heated  with  charcoal  the  sulphates  are 
all  decomposed ; those  of  the  metals  of  the  alkalies  and  alkaline 
earths  being  converted  into  sulphides : these  sulphides,  when 
moistened  with  hydrochloric  acid,  evolve  sulphuretted  hydrogen. 
The  sulphate  of  barium  may  be  easily  recognised,  even  in  small 
quantity,  if,  after  having  been  mixed  with  a little  charcoal  and 
folded  in  a piece  of  platinum  foil,  it  is  heated  in  the  flame  of  the 


HYPOSULPIIUROUS  ACID. 


163 


blowpipe;  BaSO-4+ 4 ■0=BaS  + 4 OQ;  tlie  carbonic  oxide  es- 
caping as  gas ; and  the  sulphide  of  barium,  when  moistened  wdth 
hydrochloric  acid,  is  converted  into  chloride,  and  evolves  hydro- 
sulphuric  acid;  BaS-1-2  HCl=BaCl2  + H2S.  The  sulphates  of 
the  metals  of  the  alkalies  and  alkaline  earths  may  also  be  con- 
verted into  sulphides  by  heating  them  to  redness  in  a glass  or 
porcelain  tube,  and  transmitting  a current  of  dry  hydrogen  gas 
over  them.  In  this  way  sulphate  of  potassium  is  reduced  without 
difficulty  to  sulphide  of  potassium,  water  being  formed  ; 

4 H2=K2S+4  H^e. 

The  composition  of  some  of  the  more  important  sulphates  is 
shown  in  the  following  list : — 


Neutral  salt 

M2SO4 

MO,  SO3 

Acid  salt 

MH&O4 

MO,  HO, 

2 SO3 

Double  salt  

M'MSe4 

M'O,  MO, 

2 SO3 

Sulphate  of  potassium 

K2SO4 

KO,  SO3 

Sulphate  of  sodium 

Na2S04 

. 10  H2O 

Na0,S03  , 

. 10  HO 

Acid  sulph.  of  potassium. . 

Kum, 

KO,HO,  S 

I SO3 

Sulphate  of  ammonium .... 

(H4N)2S04 

H4NO,  SO3 

Sulphate  of  calcium 

2 H2O 

Ca0,S03  . 

2 HO 

Sulphate  of  barium 

Ba&e4 

BaO,  SO3 

Sulphate  of  strontium 

. . SrS04 

SrO,  SO3 

Sulphate  of  lead 

PbS04 

PbO,  SO3 

Sulphate  of  silver 

AgO,  SO3 

Sulphate  of  magnesium .... 

MgS04  . 

, 1 H20 

MgO.SOa 

. 7 HO 

Sulphate  of  zinc 

EnS04  . 

7 H2O 

Zn0,S03  , 

, 7 HO 

Sulphate  of  iron  

FeS04  . 

7 H2O 

Fe0,S03  . 

7 HO 

Sulphate  of  cobalt 

■eoS04  . 

7 H2O 

CoO,S03  . 

7 HO 

Sulphate  of  copper 

-euse4 . 

5 H2O 

Cu0,S03  . 

. 5 HO 

Sulphate  of  alumina 

AI2  3 so 

4 . 18  H2O 

AI2O3,  3 

SO3  . 18 

Potash-alum 

. . KAl  2 so 

4 . 12  H2O 

KOSO3,  AI2O3  3 i 

3O3  . 24 

Sulphate  of  copper  and  } 
potassium  f ' ‘ 

. .■euso4,  K2SO4 . 6 H2O 

Cu0,S03,K0 

,S03  . 6 ] 

Basic  sulphate  of  copper . , . 

2 OUH2O2 

Cu0,S03, 

2 (CuO,  ] 

Sulphuric  acid  and  its  salts  are  easily  recognised  when  in 
solution  by  the  white  precipitate  of  sulphate  of  barium  which  is 
formed  on  the  addition  of  nitrate  of  barium ; this  precipitate  is 
very  insoluble  in  nitric  acid.  A white  precipitate  of  sulphate  of 
lead,  nearly  as  insoluble  as  the  sulphate  of  barium,  is  formed  on 
adding  a soluble  salt  of  lead  to  a solution  containing  sulphuric 
acid  or  a sulphate.  The  sulphates  of  strontium,  calcium,  and 
silver  are  but  sparingly  soluble  in  water ; the  others  are  readily 
soluble ; nearly  all  the  sulphates  are  insoluble  in  alcohol,  unless  a 
large  excess  of  acid  be  present.  The  sulphates  which  are  insoluble 
in  water  and  in  acids  may  be  entirely  decomposed  by  fusion  with 
an  excess  of  carbonate  of  sodium  or  potassium,  a sulphate  of  the 
alkaline  metals  being  formed,  which  may  be  dissolved  by  water, 
whilst  an  insoluble  carbonate  of  the  other  metal  is  left.  A 
solution  of  the  carbonate  either  of  potassium  or  sodium,  when 
boiled  with  the  insoluble  sulphates,  produces  a similar  but  less 
complete  decomposition. 

(419)  Hyposulphurous  Acid;  112821120,= 132. — Of  the  re- 
maining acids  of  sulphur,  the  only  one  of  any  practical  impor- 


m 


HYPOSULPHITES. 


tance  is  tlie  liyposHlpluirons  or  ditMonous  acid.  Its  sodium  salt 
lias  been  largely  employed  in  the  fixing  of  photographic  pictures. 
This  application  has  arisen  from  the  power  possessed  by  this  com- 
pound of  dissolving  those  salts  of  silver  which  are  insoluble  in 
water,  forming  with  them  soluble  double  salts ; the  surface  of  the 
photograph  is  freed  from  the  unaltered  argentine  compound  by 
immersion  in  a solution  of  the  hyposulphite,  whilst  the  portion 
which  has  been  blackened  by  light  is  left  unacted  upon ; if,  after 
tliis  operation,  the  picture  be  well  washed  with  water,  it  is  no 
longer  liable  to  alteration  by  exposure  to  light. 

Besides  its  application  in  photography,  the  hyposulphite  of 
sodium  is  employed  to  a considerable  extent  as  an  anticJilore^  for 
remo\dng  tlie  last  traces  of  chlorine  from  the  bleached  pulp 
employed  in  paper-making ; and  it  has  been  applied  by  Percy  as 
a solvent  in  the  separation  of  chloride  of  silver  for  metallurgical 
purposes. 

Pose  states  that  none  of  the  hj^osulphites  can  be  obtained  in 
the  anhydrous  form,  all  of  them  retaining  at  least  1 atom  of  water 
which  cannot  be  expelled  without  completely  decomposing  the 
salt,  so  that  their  true  formula  should  be  ; that. of  the 

barium  salt,  for  instance,  instead  of  being  fiaS203,H20,  should  be 

fiaS^II^e,. 

If  zinc  filings  be  digested  in  a solution  of  sulphurous  acid,  the 
metal  is  dissolved  without  any  extrication  of  gas ; it  is  oxidized 
at  the  expense  of  a portion  of  the  sulphurous  acid,  and  a mixture 
of  sulphite  and  hyposulphite  of  zinc  is  found  in  solution  : — 

Sulphurous  Hyposulphite  Sulphite 
acid.  of  zinc.  of  zinc. 

2 Zn  -f  3 TI2SO3  = 2118211204  -f-  2nS03  + 2 II2O. 

Hyposulphite  of  Sodium  (Pa2S2ll204,4  H2O  or  Na0,S202  5 HO,) 
is  manufactured  to  some  extent  by  transmitting  through  a solution 
of  impure  sulphide  of  sodium  (prepared  by  fusing  together  in  a 
covered  crucible  equal  weights  of  carbonate  of  sodium  and  pow- 
dered sulphur,  or  by  converting  sulphate  into  sulphide  of  sodium, 
by  calcining  the  sulphate  with  carbon),  a stream  of  sulphurous 
acid  until  it  ceases  to  be  absorbed ; the  liquid  is  then  filtered  and 
evaporated  ; hyposulphite  of  sodium  crystallizes  from  tlie  solution 
in  bold  striated  rhombic  prisms,  terminated  by  oblique  faces.  A 
still  better  plan  consists  in  digesting  a solution  of  sulphite  of 
sodium  on  powdered  sulphur : the  sulphur  is  gradually  dissolved 
and  forms  a colourless  solution,  which  on  evaporation  yields  crys- 
tals of  hyposulphite  of  sodium,  1 atom  of  sulphur  and  1 of  water 
combining  with  1 atom  of  sulphite  of  sodium;  ]Sra2S03-f  II2O  + S 
becoming  ]Sra2S2H204.  When  heated  in  closed  vessels  the  hjqio- 
sulphite  of  sodium  first  loses  water,  and  is  then  resolved  into  sul- 
phate and  pentasulphide  of  sodium;  4 Na2S2H204=:4ll20-|- 
3 Na2Se4-f-Ha283.  ^ 

The  hyposulphites  of  calcium  and  strontium  (0aS2H204,  5 H2O 
and  81*8211204,  4 H2O)  may  be  prepared  by  transmitting  sulphur- 
ous acid  through  the  sulphides  of  calcium  and  strontium  suspended 


HYPOSULPHITES. 


165 


in  water  ; their  solutions  are  decomposed  below  the  temperature 
of  212°  into  free  snlphiir  and  sulphites  of  the  earths. 

Hyposulphite  of  calcium  is  formed  spontaneously  in  large 
quantity  in  the  refuse  lime  from  the  gas-works,  and  in  the  refuse 
from  the  ball  soda  of  the  alkali  works,  consisting  chiefly  of  a mix- 
ture of  sulphide  of  calcium  with  lime  and  carbonate  of  calcium, 
and  is  now  employed  as  a valuable  source  of  hyposulphite  of 
sodium,  which  is  readily  obtained  from  it  by  double  decomposition 
with  carbonate  of  sodium. 

Hyposulphite  of  Barium  (BaS^H^O^)  may  be  obtained  in  small 
brilliant  crystals  by  mixing  dilute  solutions  of  chloride  of  barium 
and  hyposulphite  of  sodium.  It  is  impossible,  however,  to  obtain 
the  acid  in  the  form  of  a hydrate  either  from  this  or  from  any  of 
its  salts ; when,  for  example,  sulphuric  acid  is  added  to  the  hypo- 
sulphite of  barium,  sulphate  of  barium  is  precipitated  ; but  if  the 
solution  be  filtered,  the  clear  liquid  speedily  becomes  milky  from 
the  separation  of  sulphur,  and  the  odour  of  sulphurous  acid  is 
emitted  ; H2S2H20-4  becoming  decomposed  into  S-I-SO2+  2 H^O. 

The  soluble  hyposulphites  are  easily  recognized  by  the  facility 
with  \Yhich  they  dissolve  chloride  of  silver,  forming  double  hypo- 
sulphite of  sodium  and  silver,  which  yields  a solution  of  an 
intensely  sweet  taste;  AgCl-hhra2S2H204=NaCl  + HaAgS2H204. 
Solutions  of  the  hyposulphites  give  a white  precipitate  of  hyposul- 
phite of  lead  in  solutions  of  the  salts  of  lead ; tliis  precipitate, 
however,  becomes  decomposed  and  blackened  if  dried  at  212°, 
owing  to  its  partial  conversion  into  sulphide  of  lead  ; a solution 
of  mercurous  nitrate  is  immediately  decomposed  by  a solution  of 
tlie  hyposulphites  at  ordinary  temperatures  in  a similar  manner, 
the  black  sulphide  of  mercury  being  deposited.  These  salts  also 
give  a brown  precipitate,  consisting  of  sulphide  of  copper,  when 
heated  with  a solution  of  a salt  of  copper  acidulated  with  hydro- 
chloric acid.  An  alcoholic  solution  of  iodine  is  rendered  colourless 
by  admixture  with  an  excess  of  hyposulphite,  a tetrathionate  of 
the  metal  being  produced  (122). 

The  Hyposulphite  of  Gold  and  Sodium  (AuHag  2 82X12^^4)  is 
used  for  gilding  the  daguerreotype  plate,  and  for  colouring  the 
positive  proof  obtained  in  photographic  printing.  It  may  be 
prepared  in  a state  of  purity  by  mixing  concentrated  solutions  of 
1 part  of  chloride  of  gold  and  3 parts  of  hyposulphite  of  sodium  : 
chloride  of  sodium,  tetrathionate  of  sodium,  and  hyposulphite  of 
sodium  and  gold  being  formed  : on  the  addition  of  alcohol  the 
latter  salt  is  ])recipitated  ; the  precipitate  must  be  redissolved  in 
a small  quantity  of  water,  and  again  precipitated  by  alcohol.  It 
crystallizes  in  groiqis  of  colourless  needles,  which  are  very  soluble 
in  water,  luit  insoluble  in  alcohol.  It  may  be  mixed  with  diluted 
sulphuric  or  hydrochloric  acid  without  the  evolution  of  sulphurous 
acid.  The  formation  of  this  double  salt  is  explained  by  the  follow- 
ing equation  (Fordos  and  Gelis,  Ann.  de  Chimie.^  III.  xiii.  390) : — 

Tetrathion.  Hyposulphite  sodium  Ohior. 
llyposulpb.  sodium.  Chlor.  gold.  sodium  and  gold.  sodium. 

4 Na^Sall^  + AuCla  = Na^^e  + AuNaT^SsHaOl  + 3 NaCl  + 2 HaO. 


166 


DITHIOXIC  ACID TEITHIOXIC  ACID. 


(120)  Hyposulphuric  Acid  : Dithionic  — 

This  acid  is  more  stable  than  the  hTposnlphnroiis  acid,  and  may 
be  obtained  in  combination  with  water.  If  snlphnrons  anhydride 
be  transmitted  through  water  in  which  finely  divided  peroxide  of 
manganese  is  suspended,  the  gas  is  rapidly  absorbed,  and  if  the 
liquid  be  kept  cool,  Inqjosnlphate  of  manganese  is  formed ; 
MnOj  -r  2 SO2J  yielding  MnS.^Og.  If  the  temperature  be  allowed 
to  rise,  sulphate  of  manganese  is  formed  instead ; MnO^  + SOj, 
becoming  MnSO^.  It  is  difiicult  to  prevent  the  formation  of  a 
little  of  the  latter  salt,  but  the  two  salts  are  easily  separated ; 
by  adding  baryta-water  manganese  is  precipitated  as  hydrated 
protoxide  and  sulphate  and  hvposiilphate  of  barium  are  foiTned  ; 
MnSO,  -h  MnS^Og  -f  2 BaH^O^  = fiaSO,  + fiaS^Og  + 2 MnH^O^. 
The  hyposulphate  of  barium,  being  soluble,  may  be  separated 
from  the  insoluble  sulphate  of  barium  by  filtration,  and  it  may  be 
obtained  in  prismatic  efiiorescent  crystals  (fiaS^Og,  4 H.O)  by 
evaporation  below  12°  : at  higher  temperatures  it  yields  permanent 
crystals,  with  only  2 atoms  of  water,  which  belong  to  the  oblique 
system.  By  the  cautious  addition  of  diluted  sulphuric  acid  to  its 
solution,  until  a precipitate  ceases  to  be  formed  on  the  addition 
of  a drop  of  sulphuric  acid,  hyposulphuric  acid  is  liberated,  and 
may  be  filtered  from  the  sulphate  of  barium. 

Many  double  hyposulphates  may  be  obtained,  such  as  the 
h)q)Osulphate  of  sochum  and  barium  (BaXa„2S20g,  IH^O),  and 
the  corresponding  silver  salt  fAgXaS^Og,  2 H^O). 

The  h;\q)osulphates  are  all  soluble  in  water.  The  solid  salts 
when  heated  emit  sulphurous  acid,  whilst  a sulphate  of  the  metal 
remains  behind.  When  in  solution  they  may  be  oxidized  at  a 
boiling  heat  by  chlorine  or  by  nitric  acid,  and  two  atoms  of 
sulphuric  acid  are  formed ; HB^Og-f  H20-f-0=2  II„SO^.  In  the 
cold,  they  present  no  appearance  of  decomposition  when  treated 
'snth  sulphuric  acid,  but  if  heated  with  it,  sulphurous  anhydride 
is  evolved,  but  no  deposit  of  sulphur  occurs.  These  reactions 
distinguish  the  h;\q)Osulphates  from  both  the  sulphites  and  hypo- 
sulphites. 

(121)  Trithioxic  Acid  ('II.AgOg^lOl). — If  a saturated  solution 
of  the  acid  sulphite  of  potassium  be  digested  on  powdered  sulphur 
for  three  or  four  days,  till  the  yellow  colour  which  the  liquid 
acquires  at  first  has  disappeared,  sulphurous  anhydride  gradually 
escapes  and  trithionate  of  potassium  is  formed.  It  crystallizes  in 
anhydrous  four-sided  prisms,  temiinated  by  dihedral  summits.  A 
solution  of  the  salt  gives  a black  precipitate  with  mercurous  ni- 
trate, and  a white  with  the  mercuric  nitrate  ; with  nitrate  of  silver 
it  gives  a yellowish-white  precipitate,  which  soon  becomes  black. 
The  trithionate  of  potassium  may  be  decomposed  by  means  of 
tartaric  acid,  and  the  liberated  trithionic  acid  has  even  been  ob- 
tained in  prismatic  crystals,  but  its  solution  gradually  undergoes 
spontaneous  decomposition  into  sulphur  and  sulphurous  and 
sulphuric  acids;  H^O-f IIaS,Og=S-f IBSOg-hllaSO^.  ItYlien  the 
trithionates  are  heated  in  a closed  tube,  sulphur  is  sublimed,  sul- 
phurous anhydride  is  expelled,  and  sulphate  of  the  metal  is  left. 


PENTATIIIONIC  AND  CHLOKOSULPHUKIO  ACIDS.  167 

(122)  Tetrathionic  Acid  (H2S40e=226). — When  hyposul- 
phite of  barium  is  suspended  in  water,  and  iodine  is  added,  iodide 
of  barium  is  formed,  and  a new,  sparingly  soluble  salt,  the  tetra- 
thionate  of  barium,  is  separated  in  hydrated  crystals  which  con- 
tain 2 H.O:— 

2 BaS,HA  + I.=fiaI,  + BaSA,  2 H.O. 

The  tetrathionate  is  purified  by  recrystallization ; and  from  a solu- 
tion of  this  salt  a pure  solution  of  tetrathionic  acid  may  be  pre- 
pared by  the  addition  of  a quantity  of  sulphuric  acid  just  sufficient 
to  precipitate  the  whole  of  the  barium ; the  acid  may  be  concen- 
trated in  vacuo  over  sulphuric  acid.  By  boiling  the  solution,  sul- 
phur is  deposited,  sulphurous  anhydride  escapes,  and  sulphuric 
acid  remains  in  the  liquid. 

(123)  Pentathionic  Acid  : — A solution  of  sul- 

phurous acid  is  decomposed  by  transmitting  through  it  a current 
of  sulphuretted  hydrogen ; sulphur  is  deposited,  and  a new  acid 
remains  in  the  liquid;  10  + H2S=2 

18  H2O).  It  is  very  unstable : tetrathionic  and  trithionic  acids 
are  formed  by  the  decomposition  of  its  solution,  attended  with  a 
deposition  of  sulphur.  The  pentathionate  of  harium  (BaS^Og, 
H^O)  may  be  obtained  in  silky  scales  by  neutralizing  the  acid 
with  baryta-water,  and  precipitating  the  salt  from  its  aqueous 
solution  by  the  addition  of  alcohol : mercurous  nitrate  gives  a 
yellow  precipitate  in  its  solution ; and  nitrate  of  silver  a yellow 
precipitate,  which  quickly  becomes  decomposed  and  turns  black. 

The  action  of  sulphuric  acid  upon  the  salts  of  the  various 
oxy-acids  of  sulphur,  affords  a simple  means  of  distinguishing 
between  several  of  these  different  classes  of  salts.  When  con- 
centrated sulphuric  acid  is  poured  upon  the  sulphates,  it  evolves 
no  odour,  even  when  heated  with  them.  The  sulphites,  even  in 
the  cold,  yield,  with  diluted  sulphuric  acid,  an  odour  of  sulphur- 
ous acid.  The  hyposulphates  emit  no  odour  of  sulphurous  acid 
with  diluted  sulphuric  acid  in  the  cold,  but  evolve  sulphurous 
acid  by  the  aid  of  heat : whilst  diluted  sulphuric  acid  produces 
with  the  hyposidphites,  even  in  the  cold,  an  odour  of  sulphurous 
acid  attended  with  a deposit  of  sulphur. 

(424)  Chlorosulphuric  Acid^  or  Chloride  of  Sulp)huryl(f^fj\f^ 
Sp.  Gr.  of  Liquid^  1T)6;  of  Vapour^  theoretic^  4‘664;  observe f 
4‘703;  Mol.  Yol.  Ill;  Boiling-pt.  170°. — If  equal  measures  of 
sulphurous  anhydride  and  chlorine,  both  perfectly  dry,  be  mixed 
together,  no  change  occurs  in  diffused  daylight,  but  under  the  in- 
fluence of  bright  sunshine  they  unite  and  become  condensed  into  a 
colourless  liquid,  with  an  extremely  pungent  odour,  and  an  irritat- 
ing effect  upon  the  eyes.*  This  substance  can  scarcely  be  called 
an  acid,  for  it  does  not  form  any  peculiar  class  of  salts.  It  may  be 

* It  may  be  obtained  more  easily  by  distilling  an  intimate  mixture  of  penta- 
chloride  or  of  oxychloride  of  phosphorus  with  sulphate  of  load ; phosphate  of  lead 
and  chloride  of  sulphuryl  being  formed  (Carius) ; the  reaction  with  the  oxychloride 
being  as  follows:  — 

3 PbSe4  + 2 POCla  = 3 Pb,  2 pe4  + 3 se^cij. 


168 


COMPOUNDS  OF  SULPHUROUS  AND  NITROUS  ACIDS. 


distilled  iinchanged  from  caustic  lime  or  baryta ; but  by  admix- 
ture witli  water  it  is  immediately  decomposed  into  sulphuric  and 
hydrochloric  acids ; SO2CI2  + 2 H^O  = + 2 HCl.  An 

analogous  compound  may  be  formed  with  iodine.  These 

bodies  are  considered  by  H.  Rose  and  by  Berzelius,  as  compounds 
of  sulphuric  anhydride  with  chloride  or  iodide  of  sulphur ; 3 SO2CI2 
= 2 SOg,  SClg.  By  transmitting  the  vapours  of  sulphuric  anhy- 
dride into  chloride  of  sulphur  cooled  by  a freezing  mixture.  Rose 
obtained  a fuming,  oily-looking  compound  (SOg,  SO-2C12 ; sj).  gr. 
of  liquid^  1*818  ; of  vapour^  4*481),  which  boils  at  293°  F.  Rose 
and  Berzelius  regard  it  as  (5  803,8013) ; but  it  should  be  stated, 
in  opposition  to  this  view,  that  no  compound  of  chlorine,  8CI3  or 
SClg  is  known  to  exist,  and  the  density  of  the  vapour  of  chloride 
of  sulphuryl  is  in  favour  of  the  simpler  formula. 

(425)  NrrROSHLPHURio  Acid  (H2SO32NO  = 142)  ; not  known 
uncombined  with  metals. — Ritric  oxide  and  sulphurous  anhy- 
dride may  be  mixed  with  each  other  in  a dry  state  without  enter- 
ing into  combination,  but  if  a strong  solution  of  potash  be  throvm 
up  into  a jar  containing  a mixture  of  2 volumes  of  nitric  oxide 
and  1 volume  of  sulphurous  anhydride,  over  mercury,  the  gas  is 
gradually  and  completely  absorbed.  If  a concentrated  solution  of 
ammonia  be  saturated  with  sulphurous  acid,  then  mixed  with  four 
or  five  times  its  bulk  of  the  solution  of  ammonia,  and  a current 
of  nitric  oxide  be  slowly  transmitted,  whilst  the  liquid  is  artifi- 
cially kept  cool,  the  gas  is  in  a great  measure  absorbed,  and  beau- 
tiful snow-white  rhombic  crystals'  of  nitrosulphate  of  ammonium 
[(H^Is  )2S03  2 Is  O]  are  deposited ; they  may  be  collected  on  a fil- 
ter, washed  with  a little  ice-cold  solution  of  ammonia,  and  diled 
in  vacuo  over  sulphuric  acid. 

This  salt  is  a singularly  unstable  compound ; when  dissolved  in 
water  it  begins  to  undergo  decomposition  at  ordinary  tempera- 
tures : the  presence  of  a free  alkali  increases  its  stability.  If  an 
attempt  be  made  to  liberate  the  acid  by  the  addition  of  another 
acid  to  the  salt,  brisk  effervescence,  due  to  the  escape  of  nitrous 
oxide,  takes  place,  and  sulphuric  acid  remains  in  the  liquid, 
II2SO3  2 XO  giving  Il2S0,-fA20.  Mere  admixture  of  the  solu- 
tion of  the  nitrosulphate  of  ammonium  with  that  of  many  me- 
tallic salts,  such  for  instance  as  sulphate  of  copper,  produces  a 
similar  decomposition  : probably  a double  decomposition  occurs  ; 
OuSO,  -f-  (11,11)2803X0  becoming  (II,X)2804  + OuSOg  2 XO, 
whilst  the  nitrosulphate  of  copper  is  immediately  resolved  into  ni- 
trous oxide  and  sulphate  of  copper.  If  the  dry  nitrosulphate  of 
ammonium  be  heated  a little  above  230°,  it  is  decomposed  with 
explosive  evolution  of  the  nitrous  oxide. 

Tlie  nitrosulphates  of  potassium  and  sodium  are  rather  more 
stable.  Xo  insoluble  nitrosulphates  have  been  formed ; they  give 
no  precipitate  with  baryta  water.  The  nitrosulphates  of  the 
alkali-metals  are  neutral  to  test-paper,  and  have  a pungent  bit- 
terish taste. 

(426)  Compounds  of  Sulphurous  and  Nitrous  Acids  ; Sulph- 
azotized  Acids  of  Fremy. — A remarkable  series  of  salts  has  been 


COMPOUNDS  OF  SULPKUK  WITH  HTDTIOGEN. 


169 


described  by  Fremy  (Ann.  de  Chimie^  III.  xv.  408),  formed  by 
the  action  of  siilphiirons  anhydride  upon  a solution  of  nitrite  of 
potassium  containing  a large  excess  of  free  alkali.  Sulphurous 
anhydride  combines  with  the  elements  of  nitrite  of  potassium 
and  water  in  several  different  proportions,  and  forms  compounds 
which  crystallize  readily,  and  in  which  neither  sulphurous  nor 
nitrous  acid  can  be  detected  by  the  usual  tests.  The  solutions  of 
these  salts  produce,  in  solutions  of  salts  of  barium,  a precipitate 
which  contains  the  new  acid.  These  compounds  are  all  decom- 
posed by  boiling  their  solutions,  and  ammonia  and  sulphuric  acid 
are  amongst  the  products  : some  of  them  even  experience  a simi- 
lar decomposition  at  ordinary  temperatures. 

The  subjoined  formulae  will  sufficiently  indicate  the  derivation 
of  these  salts  from  potash,  water,  nitrous  and  sulphurous  anhy- 
drides : — 


Sulphazite  of  Potassium  3 K20,S3N2H60i2  or  3 K2O  + N2O3  + 3 SOq  + S H2O 
Sulphazato  “ 3 K20,S4]S[2H60i4  or  3 K2O  + N2O3  + 4 S02  + 3 H20' 

SulpliazotatG  **  3 K2^)S5N2E[0O'i6  or  3 K.2t)'  + N2'O'3  + 5S0'2  + 3 H2^ 

Sulphammonate  “ 4 K20,S8N2H6022  or  4 K2O  + N2O3  + 8 SO2  + 3 H2O 

It  is  remarkable  that  if  nitrite  of  sodium  be  substituted  for  nitrite 
of  potassium,  no  sulphazotised  salts  are  formed.  Indeed,  Fremy 
was  unable  to  procure  any  such  compound  which  contained 
sodium. 

The  sulphammonate  of  potassium  is  easily  formed  by  mixing 
a strong  solution  of  sulphite  of  potassium  with  one  of  nitrite  of 
potassium;  the  sulphammonate  is  deposited  in  beautiful  silky 
needles. 

Compounds  of  Sulphur  with  Hydrogen. 

(427)  Hydrosulphurio  Acid  : Sulphuretted  Hydrogen  / H^S 
'-=34;  Mol.  Yol.  | | | ; or  HS  = 17 ; Theoretic  Sp.  Gr.  1'174 ; 
Ohserved^  1T912. — Sulphur  forms  with  hydrogen  an  important 
compound  commonly  termed  sulphuretted  hydrogen,  but  which, 
as  it  possesses  feebly  acid  properties,  may  be  more  fitly  called  hy- 
drosulphuric  acid.  It  is  formed  in  small  cpiantities  when  sulphur 
is  heated  in  hydrogen  gas,  but  it  is  always  prepared  for  use  by 
decomposing  one  of  the  metallic  sulphides  with  an  acid. 

P reparation. — 1.  For  ordinary  purposes,  about  half  an  ounce 
of  sulphide  of  iron  (FeS),  in  small  fragments,  is  placed  in  a bottle, 
and  is  decomposed  in  the  cold  by  an  ounce  of  sulphuric  acid  di- 
luted with  6 or  8 times  its  bulk  of  water;  gas  is  immediately 
formed  in  abundance : the  iron  and  hydrogen  change  places,  the 
sulphate  of  iron  is  dissolved  in  the  act  of  formation,  and  sulphur- 
ettedjiydrogen  is  evolved;  FeS -f  II^SB-^ =1128+ FeSO^. 

The  gas  which  is  procured  in  this  manner  is  commonly  con- 
taminated with  free  hydrogen,  because  the  sulphide  of  iron  often 
contains  a portion  of  metallic  iron  disseminated  through  it.  Fig. 
306  shows  a convenient  method  of  mounting  an  apparatus  for 
disengaging  a continuous  current  of  the  gas  from  sulphide  of  iron. 
The  cork  through  which  the  tubes  pass  is  not  fitted  at  once  into 
the  bottle,  b or  c,  but  is  made  to  fit,  as  at  into  a piece  of  stout 


170  PKOPERTIES  OF  SELPHUEETTED  HYDKOGEN. 

glass  tube,  open  at  both  ends,  such  as  is  shown  in  fig.  307 ; this 
tube  is  ground  so  as  to  close  the  neck  of  the  bottle  air-tight, 
like  an  ordinary  stopper.  The  apparatus,  which  requires  to  be 


Fig.  306. 


frequently  dismounted  in  order  to  be  charged  afresh,  may  thus  be 
kept  in  a serviceable  condition  without  the  trouble  or  loss  of  time 
consequent  on  the  frequent  renewal  of  the  corks,  which  would  be 
needed  unless  this  expedient  were  adopted.  The  various  small 
tubes  are  connected  together  by  long  pieces  of  vulcanized  caout- 
chouc tubing. 

2. — When  the  gas  is  required  in  a state  of  purity,  1 part  of 
powdered  sulphide  of  antimony  is  substituted  for  the  sulphide  of 
iron  : in  this  case  it  is  necessary  to  employ  3 or  4 parts  of  hydro- 
chloric acid  of  sp.  gr.  IT,  and  to  apply  a gentle  heat  to  the  mix- 
ture ; the  apparatus  may  then  be  arranged  as  in  fig.  308.  In  either 

case  the  gas  requires  to 
J'lG-  308.  be  washed  before  col- 

lecting it,  in  order  to 
remove  any  particles  of 
the  acid  or  of  the  me- 
tallic salt  which  may 
have  been  carried  over 
with  it  in  mechanical 
suspension.  As  the 
compound  of  antimony 
with  sulphur  is  a sequi- 
sulphide  (Sb^Sg),  1 atom 
of  it  requires  6 atoms  of 
hydrochloric  acid  for 
its  decomposition,  and 
furnishes  2 atoms  of 
terchloride  of  antimony 
and  3 of  sulphuretted 
liydrogen  : ShA  + d HC1=2  SbCl3-f-3  HA 

ProjpeTties. — Hydrosulphuric  acid  is  a transparent  colourless 


COMPOSITION  OF  SULPHURETTED  HYDKOGEN.  ITl 

gas,  of  a disgusting  odor,  resembling  that  of  rotten  eggs.  It  is 
higlily  poisonous  when  respired  in  a concentrated  form,  and  even 
when  diluted  with  from  600  to  1200  times  its  bulk  of  air  is  rap- 
idly fatal  to  the  lower  animals.  It  is  inflammable,  and  burns  with 
a pale,  bluish  flame,  depositing  sulphur  if  the  supply  of  air  be 
insufflcient  for  complete  combustion.  If  transmitted  through 
tubes  heated  to  full  redness,  it  is  partially  decomposed  into  sulphur 
and  free  hydrogen.  Its  density  a little  exceeds  that  of  atmo- 
spheric air,  100  cubic  inches  weighing  rather  more  than  38  grains. 

Composition. — The  proportion  of  hydrogen  in  a given  volume 
of  the  gas  may  be  ascertained  by  heating  some  granulated  tin  in 
a small  retort  filled  with  sulphuretted  hydrogen  and  inverted  in  a 
vessel  of  mercury : the  sulphur  combines  with  the  tin,  whilst  the 
hydrogen  which  remains  occupies  when  cold  the  same  space  as 
the  gas  before  it  was  decomposed.^*  In  sulphuretted  hydrogen, 
1 volume  of  sulphur  vapour  and  2 volumes  of  hydrogen  are  there- 
fore condensed  into  the  space  of  2 volumes,  and  the  composition 
of  the  gas  may  be  thus  represented : — 

By  weight.  By  vol.  Sp.  gr 

Sulphur S =32  or  94-12  1 or  0-5=1-105 

Hydrogen. . Ha  = 2 5-88  2 1-0  = 0-069 

HaS  = 34  100-00  2 1-0  1-lU 

Sulphurous  anhydride  and  sulphuretted  hydrogen,  in  the  pre- 
sence of  moisture,  decompose  each  other,  half  the  oxygen  of  the 
sulphurous  anhydride  uniting  with  the  hydrogen  of  the  sulphu- 
retted hydrogen,  water  and  pentathionic  acid  (423)  being  formed, 
whilst  sulphur  is  deposited.  For  complete  decomposition,  equal 
volumes  of  sulphuretted  hydrogen  and  of  sulphurous  anhydride 
would  be  requisite  ; 10  SO^  + ld  Il2S=:5  83  + 8 H2O-I-2  li2S50-g. 
A large  proportion  of  the  sulphur  thus  deposited  is  in  the  electro- 
positive form  (408),  and  is  insoluble  in  bisulphide  of  carbon.  It 
is  probable  that  a large  proportion  of  native  sulphur  has  been 
deposited  from  the  gaseous  form  in  consequence  of  this  reaction. 

Hydrosulphuric  acid  is  also  immediately  decomposed  by  chlo- 
rine, bromine,  and  iodine ; sulphur  being  precipitated,  and  hydro- 
chloric, hydrobromic,  or  hydriodic  acid  being  formed  by  the 
hydrogen,  which  combines  with  one  or  other  of  the  elements 
above  mentioned. 

Under  a pressure  of  about  11  atmospheres,  sulphuretted  hydro- 
gen is  reducible  to  a colourless,  extremely  mobile  liquid,  which, 
according  to  Regnault,  boils  at  — 19*2°  ; it  freezes  to  a transparent 
mass  at  a temperature  of  — 122°. 

Abater  at  32°  dissolves  4*37  times  its  bulk  of  sulphuretted 
hydrogen  ; 3*23  times  its  bulk  at  59°,  and  2’66  at  75°  (Bunsen). 
The  solution  is  feebly  acid,  and  has  the  smell  and  taste  of  tlie  gas. 
AVhen  exposed  to  the  air,  this  solution  becomes  milky;  the  hydro- 
gen is  slowly  oxidized,  forming  water,  and  the  sulphur  is  sepa- 

* Potassium  cannot  be  employed  instead  of  tin  in  this  case,  because,  though  it 
decomposes  the  gas,  the  sulphide  of  potassium  which  is  formed  enters  into  combi 
nation  with  another  portion  of  the  gas  without  decomposing  it. 


172 


HYDKOSULPHATES,  OR  SELPHIDES. 


rated.  If  tlie  oxidation  of  snlpliiiretted  hydrogen  takes  place  in  a 
moist  atmosphere,  a little  snlphnric  acid  is  formed,  and  this  action 
is  favoured  by  the  presence  of  a base  to  combine  with  the  newly- 
formed  acid. 

Sulphuretted  hydrogen  is  formed  spontaneously  under  a variety 
of  circumstances.  Whenever  a soluble  sulphate  remains  in  con- 
tact with  decaying  animal  or  vegetable  matter,  the  sulphate  loses 
oxygen,  which  combines  with  the  elements  of  the  decaying  sub- 
stance, whilst  sulphide  of  the  metal  remains ; one  atom  of  sul- 
phate of  calcium,  for  example,  by  the  abstraction  of  4 atoms  of 
oxygen,  becomes  converted  into  sulphide  of  calcium ; thus  ^aSO^ 
— 2 O'2=‘0aS. 

In  this  way  soluble  sulphides  are  formed  in  many  springs, 
such  as  those  of  Harrogate,  giving  to  them  their  peculiar  sulphu- 
reous odour ; and,  in  a somewhat  similar  manner,  sulphuretted 
hydrogen  is  generated  in  large  quantities  in  stagnant  sewers  and 
cesspools. 

The  sulphides  thus  fonued  are  readily  decomposed  by  acids, — 
even  the  carbonic  acid  absorbed  from  the  atmosphere  being  suffi- 
cient to  cause  the  expulsion  of  sulphuretted  hydrogen,  and  in  this 
way  to  occasion  the  odour  observed  on  exposing  such  compounds 
to  a damp  air. 

(428)  HydrosvJphates^  or  Sulphides. — Hydi’osulphiiric  acid, 
though  a feeble  acid,  combines  readily  with  bases  : for  example,  if 
the  gas  be  transmitted  into  a solution  of  potash  or  solution  of 
ammonia,  it  is  rapidly  absorbed,  hydi’osulphate  of  potash,  K^O, 
HjS,  or  hydrosulphate  of  ammonia,  (H3X)2H2S,  being  formed. 
Such  solutions  are,  however,  generally  regarded  as  sulphides  of 
the  metals,  because  the  hydrogen  of  the  acid  is  exactly  equivalent 
to  the  oxygen  of  the  base,  and  is  capable,  as  in  the  analogous  case 
of  the  chlorides,  of  forming  water  and  a metallic  sulphide  : for 
example,  hydrosulphate  of  potash  (K20,H2S)  may  be  regarded  as 
sulphide  of  potassium  and  water,  or  as  K^S  -p  H^O.  Moreover,  the 
action  of  sulphuretted  hydrogen  in  cases  in  which  it  occasions  a 
precipitate  in  the  solution  of  a metallic  salt,  consists  in  the  forma- 
tion of  an  insoluble  metallic  sulphide ; when,  for  instance,  sulphate 
of  copper  in  solution  is  treated  with  sulphuretted  hydrogen,  an 
abundant  black  precipitate  of  sulphide  of  copper  is  produced,  water 
is  formed,  and  the  liquid  becomes  acid  from  the  liberation  of  sul- 
phuric acid ; HuSO,  -f  H^S + HI.O = H.SO,  -p  HuS,a?H20.  A large 
number  of  the  metallic  sulphides  when  thus  formed  combine,  it  is 
true,  with  water  at  the  moment  of  their  precipitation. 

Sulphuretted  hydrogen  is  in  continual  requisition  in  the  labo- 
ratory as  a test  for  the  discovery  of  metallic  iDodies : it  gives  cha- 
racteristic precipitates  with  many  metallic  salts  ; for  instance,  with 
the  compounds  of  lead  it  gives  a black,  with  those  of  arsenic,  a 
yellow,  and  with  those  of  antimony  an  orange-coloured  precipitate. 
Many  metallic  solutions,  such  as  those  of  zinc,  iron,  and  manga- 
nese, when  acidulated,  yield  no  precipitate  with  it : and  it  is  there- 
fore commonly  employed,  in  the  course  of  analysis,  to  separate 
these  metals  trom  others  which  are  thrown  down  by  it  in  the  form 


HYDROSULPHATES,  OR  SELPHIDES. 


173 


of  insoluble  siilpliides.  For  this  purpose  a current  of  the  gas  is 
transmitted  througli  the  solution  on  which  it  is  designed  to  act. 
In  these  cases  it  is  always  necessary  to  purify  it  from  particles 
held  in  mechanical  suspension,  and  carried  over  by  the  effer- 
vescence of  the  materials  employed ; it  is  therefore  first  allowed 
to  bubble  up  through  a layer  of  water  in  a W oulfe’s  bottle  inter- 
posed between  the  generator  and  the  liquid  to  be  submitted  to 
its  action,  as  shown  at  <?,  fig.  306. 

When  the  attraction  between  a metal  and  the  radicle  of  an 
acid  is  too  great  to  be  overcome  by  the  action  of  hydrosulphuric 
acid,  the  sulphide  may  notwithstanding  be  obtained,  provided 
that  an  alkali-metal  be  simultaneously  presented  to  the  acid 
radicle  of  the  metallic  salt ; this  may  easily  be  effected  by  mixing 
a soluble  sulphide  with  the  salt  to  be  decomposed : — if  sulphate 
of  iron  (FeSO^)  be  exposed  to  a current  of  sulphuretted  hydrogen 
it  will  experience  no  change  ; but  if  mixed  with  a solution  of  sul- 
phide of  potassium,  a black  precipitate  of  hydrated  sulphide  of 
iron  (FeS,^i?H20)  is  immediately  produced,  while  sulphate  of  potas- 
sium is  formed  in  the  solution : FeSO^  + -f- 

FeS,a?H20.  The  sulphides  thus  formed  are  very  commonly  hy- 
drated compounds : when  exposed  to  the  air  in  their  moist  con- 
dition, many  of  them  absorb  oxygen  rapidly ; solutions  of  the 
alkaline  sulphides  have  indeed  been  employed  for  absorbing 
oxygen  from  gaseous  mixtures.  The  results  of  oxidation  vary, 
some  being  converted,  like  sulphide  of  nickel,  into  sulphate ; 
?IiS,a?Il20-l-2  O2— ^liSO^-l-irH^O : whilst  others  are  simply  con- 
verted, like  sulphide  of  iron,  into  free  sulphur  and  the  metallic 
oxide  ; 4 FeS,a?H20  -f  3*02  becoming  2 Fe203,^rH20  + 2 S2. 

Hydrosulphuric  acid  is  usually  stated  to  have  a strong  dispo- 
sition to  combine  with  the  soluble  sulphides,  to  form  definite  com- 
pounds with  them.  These  compounds,  however,  are  most  easily 
represented  by  regarding  them  as  double  sulphides  of  the  metal 
and  hydrogen,  intermediate  between  the  hydrosulphuric  acid  and 
the  ordinary  sulphide— : — 

ITydrosul-  Ilydrosulph.  Sulphide  of 

pluiric  acid.  sulph.  poUvs.  potassium. 

HhF  ; KHs'  ; 

corresponding  with  the  compounds  in  the  oxygen  series  indicated 
by  the  formulae : — 

Hydrate  of  Anhydrous 

Water.  potash.  potash. 

mie  ; Km  ; xm 

To  this  class  of  double  sulphides  belongs  the  ordinary  test-liquid 
(H^NIIS),  which  is  used  in  the  laboratory  under  tlie  incorrect 
name  of  hydrosulphate  of  ammonia.  These  compounds  emit  a 
strong  odour  of  sulphuretted  hydrogen,  and  when  decomposed  by 
a metallic  salt,  the  hydrosulphuric  acid  is  set  at  liberty;  for 
example  ; 2 II.KIIS  -f  MnSe,=(H,N)2Se,  + MnS  + ll2S.  This 


174 


PERSULPHIDE  OF  IIYDEOGEX. 


evolntion  of  siilpliHretted  hydrogen  distinguishes  them  from  the 
simple  sulphides.  'No  snch  double  sulphides  are  formed  with 
hydrogen  and  the  biequivalent  metals,  such  as  those  of  the  earths 
proper  and  of  the  iron  groups. 

Many  of  the  hydrosulphates  and  sulphides  are  easily  detected 
by  the  odour  of  sulphuretted  hydrogen  which  they  evolve  when 
moistened  with  hydrochloric  acid.  A very  minute  trace  of  the 
gas  may  be  detected  by  enclosing  a piece  of  paper  moistened  with 
a solution  of  acetate  of  lead  in  the  upper  part  of  the  tube  or 
vessel  in  which  the  suspected  sulphide  has  been  mixed  with  acid ; 
if  sulphuretted  hydrogen  be  evolved,  a brown  or  black  tinge  oc- 
curs upon  the  paper  alter  the  lapse  of  a few  minutes,  owing  to  the 
formation  of  sulphide  of  lead.  The  proportion  of  free  sulphuretted 
hydrogen  or  of  a soluble  sulphide  in  any  solution,  may  be  accu- 
rately determined  by  mixing  the  liquid  to  be  tested  with  a small 
quantity  of  a cold  solution  of  starch  slightly  acidulated  with  acetic 
acid,  and  adding  a standard  solution  of  iodine  dissolved  in  iodide 
of  potassium  until  the  starch  assumes  a blue  tint  from  the  action 
of  excess  of  iodine;  in  this  reaction  the  sulphuretted  hydrogen 
converts  the  iodine  into  hydriodic  acid,  whilst  the  liquid  becomes 
milky  from  the  separation  of  sulphur;  2 H2S-f2  + 

Traces  of  soluble  sulphides  may  be  detected  in  neutral  or 
alkaline  solutions  by  the  magnificent  purple  colour  w^hich  they 
form  on  the  addition  of  a solution  of  the  nitroprusside  of  sodium. 
When  heated  before  the  blowpipe,  most  of  the  sulphides  emit  the 
odour  of  sulphurous  anhydride  (535,  536). 

(429)  Persulphide  of  Hydrogen  (H^S^  ? or  H^Sg  ?)  ; Sp.  Gr. 
of  Liquid^  l’T69. — In  order  to  procure  this  compound  it  is  usual 
to  begin  by  preparing  a persulphide  of  calcium  (OaS^),  which 
may  be  obtained  by  boiling  equal  weights  of  slaked  lime  and  pow- 
dered sulphur  in  water ; persulphide  of  calcium  mixed  with  a cor- 
responding amount  of  hyposulphite  of  calcium  is  formed,  and  enters 
into  solution  ; 3'0aOIl2O-|-6S2=‘0aS2H2O4-b2OaS5-h2H2O:  the 
undissolved  sulphur  is  separated  by  filtration.  On  allowing  the 
deep  yellow  liquid  to  fidl  into  hydrochloric  acid  diluted  with  twice 
its  bulk  of  water,  and  gently  warmed,  ]3ersulphide  of  hydrogen 
subsides  as  an  oily  liquid,  having  a smell  and  taste  resembling 
that  of  hydrosulphuric  acid : it  burns  with  a blue  flame.  In  many 
of  its  properties  it  presents  a striking  analogy  with  peroxide  of 
hydrogen  (485) ; it  possesses  bleaching  powers,  is  very  prone 
to  spontaneous  decomposition  into  sulphur  and  sulphuretted 
hydrogen ; it  is  rendered  more  stable  by  the  presence  of  acids, 
and  is  immediately  decomposed  by  alkalies.  The  latter  circum- 
stance renders  it  necessary  in  preparing  this  compound  to  add  the 
sulphide  of  calcium  to  the  acid,  not  the  acid  to  the  sulphide,  which 
would  be  attended  with  an  escape  of  hydrosulphuric  acid  and  a 
precipitation  of  finely  divided  sulphur.  The  sulphur  which  is 
precipitated  in  this  manner  from  an  alkaline  persulphide  was  for- 
merly employed  in  medicine  under  the  term  of  lac  sulphuris. 

Oxides  of  manganese  and  silver  decompose  persulphide  of 
liydrogen  by  mere  contact  with  the  liquid,  producing  a violent 


BISULPHIDE  OF  CAEBON. 


175 


effervescence,  owing  to  the  disengagement  of  snlphnretted  hydro- 
gen. Persulphide  of  hydrogen  dissolves  sulphur  freely,  and  hence 
its  composition  is  not  certainly  known,  since  a portion  of  sulphur 
derived  from  the  hyposulphite  of  calcium  formed  in  preparing  the 
sulphide  of  calcium  is  always  precipitated  along  with  the  persul- 
phide, and  becomes  dissolved  in  the  liquid  obtained,  which,  owing 
to  its  instability,  cannot  be  purified  by  distillation. 

(430)  Bisulphide  of  Cakbon  : Sulphocarhonic  Acid  (OB^=76) 
Sp.  Gr.  of  Liquid^  1-272  at  60°  ; of  Vapour^  Theoretic^  2-626  ; 
Observed^  2-6447 ; Mol.  Vol.  \ \ | ; Boiling-pt.  118-5°. — This 
compound  may  be  prepared  by  heating  fragments  of  charcoal  to 
bright  redness  in  an  earthen  retort,  furnished  with  a tubulure  into 
which  is  luted  a porcelain  tube,  passing  nearly  to  the  bottom  of 
the  retort : the  tube  is  provided  at  its  upper  extremity  with  a 
cork.  From  time  to  time  this  cork  is  withdrawn,  and  a fragment 
of  sulphur  is  dropped  into  the  retort ; the  cork  is  then  immediately 
replaced,  the  sulphur  melts,  and  is  converted  into  vapour ; at  this 
elevated  temperature  the  carbon  combines  with  it,  and  the  bisul- 
phide thus  obtained  may  be  condensed  in  vessels  properly  cooled. 
It  is  now  manufactured  on  a very  large  scale,  both  in  this  country 
and  in  France,  by  the  use  of  suitable  apparatus  constructed  on 
this  principle,  the  vapour  of  sulphur  being  di’iven  over  glowing 
coke.  It  is  yellow  when  first  formed,  and  contains  an  excess  of 
sulphur ; but  by  redistillation  it  may  be  obtained  in  a state  of 
purity.  It  is  a very  volatile,  colourless  liquid,  of  high  refracting 
power,  of  an  acrid,  pungent  taste,  and  a foetid,  peculiar,  sulphur- 
ous odour.  It  is  heavier  than  water,  in  which  it  is  insoluble,  but 
it  is  freely  soluble  in  ether  and  in  alcohol,  as  well  as  in  the  fixed 
and  volatile  oils  ; when  its  vapour  is  breathed,  it  produces  great 
depression  followed  by  coma.  Bisulphide  of  carbon  has  never 
hitherto  been  frozen ; hence  it  has  been  employed  sometimes  in 
the  construction  of  thermometers  destined  to  measure  very  intense 
degrees  of  cold. 

The  vapour  of  bisulphide  of  carbon  is  very  poisonous,  and 
hence  much  care  is  requisite  in  preventing  its  escape  into  the 
apartments  in  which  the  work-people  are  engaged.  Advantage 
has  been  taken  of  this  poisonous  property  to  free  grain  infested 
with  weevils  from  the  insect ; a small  quantity  of  the  bisulpliide 
enclosed  in  a tight  chamber  with^he  grain,  in  a few  hours  kills 
both  the  larvae  and  the  eggs  (Doyere),  and  does  not  injure  the 
grain  ; on  exposure  to  air  the  bisulphide  quickly  evaporates. 
Indeed  the  applications  of  the  bisulphide  in  the  arts  are  very 
numerous,  and  are  of  growing  importance. 

Bisulphide  of  carbon  is  highly  infiamrnable  ; when  its  vapour 
is  mixed  with  hydrogen  or  carbonic  oxide  it  takes  fire  below  420° 
(Frankland).  It  burns  with  a blue  flame,  producing  gaseous  sul- 
phurous and  carbonic  anhydrides.  It  dissolves  sulphur  freel}^ 
and,  by  spontaneous  evaporation,  leaves  it  in  rhombic  octohedra. 
Phosphorus  is  also  freely  dissolved  by  it,  and  may  be  obtained  in 
crystals  from  the  solution  by  slow  evaporation.  Iodine,  bromine, 
and  chlorine  are  likewise  readily  dissolved  by  the  bisulphide  of 


176 


BISULPHIDE  OF  CABBOX. 


carbon.  It  is  one  of  tlie  best  solvents  of  caontcbonc  ; it  may  be 
substituted  for  ether  as  a solvent  for  some  of  the  organic  bases, 
and  it  has  been  used  on  a very  large  scale  by  Deiss  as  a solvent 
for  extracting  oils  and  fats,  as,  for  example,  in  economizing  the 
last  portions  of  olive  oil  left  in  the  pulp  of  the  fruit  after  pressure. 

Bisulphide  of  carbon  offers  one  of  the  best  illustrations  of  the 
analogy  in  properties  between  oxygen  and  sulphur ; an  analogy 
which,  though  far  from  being  so  complete  as  that  of  the  different 
lialogens  with  each  other,  is  yet  in  some  respects  of  a striking 
character.  It  is  to  be  remarked  that  sulphur  is  the  only  non- 
metallic  element  excepting  oxygen  with  which  carbon  can  be 
easily  caused  to  unite  directly.  The  compound  of  carbon  and 
sulphur  so  obtained  affords  a good  instance  of  the  class  of  com- 
binations which  Berzelius  has  called  sulphur-acids^  these  sub- 
stances possessing  the  power  of  uniting  with  the  sulphides  of  the 
basic  metals,  and  forming  with  them  sidpho-salts^  corresponding 
in  composition  to  analogous  salts  which  contain  oxygen : — Bisul- 
phide of  carbon,  for  example,  may  be  regarded  as  the  analogue 
of  carbonic  anhydride  ; it  contains  2 atoms  of  sulphur  in  the  place 
of  2 atoms  of  oxygen,  the  composition  of  the  compound  being  the 
following : — 

By  weight.  By  vol.  Sp.  gr. 

Carbon e = 12  or  15*79  2?  or  1*0  = 0*4146 

Sulphur S.2  = 64  84*21  2 1*0  = 2*2117 

16  100-00  2 1-0  = 2-6263 

It  combines  with  the  sulphides  of  the  alkaline  metals,  forming  a 
species  of  salts  which  are  called  sulpho-carhmiates^  such  for  in- 
stance as  the  sulpho-carbonate  of  potassium  (Kj-GSg),  which  con- 
tains 3 atoms  of  sulphur  in  the  place  of  the  3 atoms  of  oxygen  in 
the  corresponding  carbonate,  K^-BOg.  The  soluble  sulpho-carbo- 
nates  are  easily  converted,  by  boiling  their  aqueous  solutions,  into 
carbonate  of  the  metal ; water  being  decomposed  whilst  an  evolu- 
tion of  sulphuretted  hydrogen  takes  place  ; for  example  : — 

K^eSg  -f  3 -f-  3 h^s  ; 

and  a similar  decomposition  takes  place  slowly  in  the  aqueous 
solution  at  ordinary  temperatures.  The  sulpho-carbonates  when 
decomposed  by  hydrochloric  acid  form  a yellow  oily  liquid,  con- 
taining the  elements  of  bisulphide  of  carbon  and  sulphuretted  hy- 
drogen ; for  instance  : — 

KgeSg-h2  iici==iig-eSg-f-2  Kci. 

Solutions  of  the  sulpho-carbonates  of  the  alkaline  metals  give  a 
brown  precipitate  with  solutions  of  the  salts  of  copper : they  yield, 
with  dilute  solutions  of  nitrate  of  silver  and  of  corrosive  sublimate, 
yellow  precipitates  ; and  with  salts  of  lead  they  give  a red  precipi- 
tate. All  these  precipitates  blacken  more  or  less  speedily  when 
kept,  owing  to  their  conversion  into  sulphides.  Aqueous  solutions 
of  the  hydrated  alkalies  gradually  discolour  the  bisulphide,  and 


CHLOKIDES  OF  SULPHUR.  177 

form  a brown  liquid  containing  carbonate  and  sulpbo-carbonate  of 
the  metal ; for  example  : — 

6 KH^+ 3 e^,=K,ee, + 2K,es3 + 3 H^e. 

(431)  CnLORroE  of  Sulphur  (82012=135;  Ifol.  Vol.  | | | ; 
or  S2C1=67'5)  : Sp.  Gr.  of  Liquid^  1-68  ; of  Vapour,  BoU- 

ing-pt.  280°. — Chlorine  and  sulphur  form  two  compounds  with 
each  other  ; they  combine  gradually  at  common  temperatures,  but 
if  heated  together  the  union  is  rapid.  In  preparing  the  chloride 
of  sulphur,  the  arrangement  shown  in  Fig.  309  may  be  adopted, 


Fig.  309. 


in  which  a steady  current  of  washed  and  dried  chlorine  is  directed 
towards  the  bottom  of  a retort  containing  melted  sulphur;  the 
resulting  chloride  must  be  collected  in  a perfectly  dry  receiver, 
kept  cool : it  may  be  purified  from  excess  of  chlorine  by  redistilla- 
tion from  powdered  sulphur ; a yellow  volatile  liquid,  of  penetrat- 
ing, peculiar,  and  disagreeal3le  odour,  is  thus  formed.  It  emits 
fumes  on  exposure  to  the  air,  owing  to  its  action  on  the  atmo- 
spheric moisture.  When  dropped  into  water,  it  falls  to  the  bottom, 
and  is  slowly  decomposed  into  hydrochloric  and  sulphurous  acids, 
mixed  with  some  of  the  polythionic  acids,  and  free  sulphur  in  the 
electro-positive  form.  It  acts  powerfully  on  mercury  when 
brought  into  contact  with  it,  and  dissolves  sulphur  freely ; with 
ammonia  it  combines  in  two  proportions,  forming  the  compounds 
2 Il3lI,SjjCl2,  and  4 Il3Fr,S2Cl2.  An  oxychloride  of  sulphur  (SjCl^ 
O3)*  is  obtained  in  crystals  by  transmitting  moist  chlorine  through 
the  chloride. 

* Two  other  oxychlorides  of  sulphur  are  also  known,  one  the  chloride  of  tliionyl 
(^^Clj)  corresponding  to  sulphurous  anhydride  in  which  one-half  of  the  oxygen  is 
displaced  by  chlorine.  It  is  a colourless  liquid,  which  boils  at  n9’6°,  and  is  obtained 
12 


1T8 


SULPHIDE  OF  NrrEOGEN — SELENHIM. 


Bichloride  of  Sulphur  (SCl^^lOS  ; Sp.  Gr.  of  Liquid^  1-625) 
may  be  formed  by  saturating  the  preceding  compound  witli  chlo- 
rine ; it  is  a deep-red  liquid,  which  fumes  strongly  in  the  air,  and 
is  decomposed  in  the  direct  rays  of  the  sun  into  chloride  of  sulphur 
and  free  chlorine.  It  is  partially  decomposed  by  boiling  it. 
Carius,  in  his  elaborate  examination  of  these  compounds  {Liebig’s 
Annal.  cvi.  291),  even  denies  its  existence  as  a separate  body,  re- 
garding the  red  liquid  as  a mixture  of  the  chloride  with  a higher 
chloride  of  sulphur  (SCl^)  not  yet  isolated. 

The  bromides  of  sulphur  are  liquids  analogous  to  the  chlorides. 
The  iodide  (SJs)  is  a crystalline,  brittle,  steel-grey  solid,  but  the 
compound  is  unstable  and  gradually  loses  iodine  by  exposure  to 
the  air. 

(432)  Sulphide  of  bTiTEOOEN  (SX ; Fordos  and  Gelis,  Ann. 
de  Chimie^  III.  xxxii.  389). — This  compound  is  obtained,  though 
in  small  quantity  only,  when  chloride  of  sulphur  is  dissolved  in 
10  or  12  times  its  bulk  of  bisulphide  of  carbon,  and  decomposed 
by  a current  of  dry  ammoniacal  gas.  The  gas  is  transmitted  till 
the  brown  colour  of  the  precipitate  which  is  formed  disappears  ; 
the  yellow  liquid  is  filtered  from  the  muriate  of  ammonia,  and 
left  to  spontaneous  evaporation  ; beautiful  golden  yellow  rhom- 
bic crystals  of  sulphide  of  nitrogen,  mixed  with  crystals  of  sulphur, 
are  speedily  formed ; the  sulphur  may  be  removed  by  digestion  in 
cold  bisulphide  of  carbon.  The  reaction  which  attends  its  forma- 
tion is  very  complicated,  and  has  not  been  completely  ascertained. 
Sulphide  of  nitrogen  detonates  powerfully  by  percussion,  and  ex- 
plodes when  heated  to  314°.  It  has  a faint  odour,  adheres  strong- 
ly to  paper  if  rubbed  on  it,  and  irritates  the  mucous  membrane 
of  the  eyes  and  nose  most  painfully.  Bisulphide  of  carbon  takes 
up  about  g-J-Q  of  its  weight  when  boiled  upon  it ; alcohol,  ether, 
and  oil  of  turpentine  dissolve  it  very  sparingly  ; water  does  not 
dissolve  it,  but  slowly  decomposes  the  compound.  Sulphide  of 
nitrogen  combines  with  the  chlorides  of  sulphur  in  several  pro- 
portions. 

§ II.  Selexittm.'^  Se  = 79*5,  or  Se  = 39’75. 

Theoretic  Sp.  Gr.  of  Vapour.^  5*526;  Observed  at  2590°,  5*68; 

Atomic  Yol.  ; Sp.  Gr.  Cryst.  4*788. 

(433)  Selenium  is  a mythological  name  from  (TeX^vr),  the 
moon,  given  by  Berzelius  to  a rare  elementary  body,  discovered 

by  decomposing  pentachloride  of  phosphorus  by  means  of  dry  sulphurous  anhydride. 
The  other  compound  has  already  been  described  under  the  name  of  chlorosulphuric 
acid  (SO2CI2),  or  chloride  of  sulphuryl  (424),  corresponding  to  sulphuric  anhydride  in 
which  an  atom  of  oxygen  has  been  displaced  by  its  equivalent  (2  atoms)  of  chlorine. 

These  oxychlorides  of  sulphur  and  Williamson’s  clilorhydro-sulphuric  acid  (41 G) 
form  a series,  some  relations  of  which  will  be  rendered  evident  by  writing  their  for- 


mulae  as  follows:— 

Chloride  of  thionyl S2O2CI4 

Crystalline  oxychloride S2O3CI4 

Chloride  of  sulphuryl S2O4CI4 

Chlorhydro-sulphuric  acid S2O6H2CI2 


* Molecular  volume  of  free  selenium  vapour  (SeSe)  = | ~|  1. 


SELENIUM EXTRACTION PROPERTIES. 


179 


by  him  during  the  year  1817,  in  the  refuse  of  a sulpliiiric  acid 
manufactory  near  Fahlun.  It  derives  its  chief  interest  from  the 
remarkable  analogy  to  sulphur  which  it  presents.  Selenium 
always  occurs  in  combination  ; the  compounds  which  it  forms  are 
termed  selenides.  The  native  selenides  are  very  rare  minerals, 
the  most  abundant  of  them  being  the  selenides  of  iron,  copper, 
and  silver. 

Extraction. — In  order  to  obtain  selenium  in  an  isolated  form, 
the  Fahlun  selenium  residue  is  mixed  with  nitrate  and  carbonate 
of  potassium,  and  deflagrated ; that  is  to  say,  the  mixture  is 
thrown  in  small  quantities  at  a time  into  a red-hot  crucible,  in 
which  it  burns  vividly.  The  selenium  and  other  bodies  with 
which  it  is  associated  are  oxidized  at  the  expense  of  the  oxygen 
of  the  nitre,  whilst  seleniate  of  potassium  is  produced  by  acting  on 
the  disengaged  potash  of  the  nitre.  The  mass  is  digested  in  water, 
acidulated  with  hydrochloric  acid  and  evaporated  down'to  a small 
bulk.  The  selenic  acid  is  thus  reduced  to  selenious  acid ; and  the 
selenious  acid,  when  treated  with  sulphurous  acid,  yields  a preci- 
pitate of  reduced  selenium  as  a red,  flocculent,  amorphous  powder  ; 
2 H,See3  -h  4 + 4 H.SO,  -f  2 H.O. 

Properties. — Selenium  may  be  obtained  in  the  amorphous,  in 
the  vitreous,  and  in  the  crystalline  condition.  When  collected 
and  dried,  the  pulverulent  selenium  begins  to  soften  at  a tempera- 
ture below  that  of  boiling  water,  and  at  a few  degrees  above  212° 
it  melts ; on  cooling,  it  forms  a brittle  solid,  with  glassy  fracture, 
metallic  lustre,  and  deep  brown  colour,  varying  in  specific  gravity 
from  4'3  to  4*8.  It  has  neither  taste  nor  smell ; it  is  insoluble 
in  water,  and  is  a non-conductor  of  heat  and  of  electricity.  It  is 
soluble  in  oil  of  vitriol,  forming  a green  solution  which,  when 
diluted,  deposits  unaltered  selenium.  When  melted  it  is  ductile, 
and  may  be  drawn  out  into  fine  threads.  The  statements  regard- 
ing its  point  of  fusion  are  discordant,  owing  to  its  power  of  exist- 
ing, like  sulphur,  in  several  distinct  modifications.  If  it  be  main- 
tained for  some  hours  at  200°  F. — i.e.  below  its  melting-point — 
the  temperature  suddenly  rises  till  it  reaches  320°,  after  which 
the  selenium  is  found  to  have  become  granular  and  crystalline. 
The  fusing-point  of  this  variety  is  423°  (Hittorf).  It  may  also  be 
obtained  with  some  difliculty,  crystallized  in  minute  rhomboidal 
prisms  of  sp.  gr.  4*5,  from  its  solution  in  bisulphide  of  carbon, 
which,  at  its  boiling  point,  dissolves  about  1 per  cent,  of  vitreous 
selenium.  If  these  crystals  be  heated  to  about  334°  they  become 
almost  black,  and  increase  in  sp.  gr.  to  4*7,  experiencing  a mole- 
cular change,  in  consequence  of  which  they  are  no  longer  soluble 
in  bisulphide  of  carbon ; when  this  black  mass  is  melted  and 
quickly  cooled,  it  resumes  its  solubility  in  this  menstrumn  owing 
to  its  reconversion  into  the  vitreous  condition.  When  heated  in 
the  air,  selenium  does  not  readily  take  fire;  it  burns  with  a blue 
flame,  but  a portion  of  it  is  volatilized  in  red  fumes,  emitting  an 
odour  resembling  that  of  bisulphide  of  carbon : this  is  probably 
due  to  the  formation  of  a protoxide  of  selenium,  which,  however, , 
is  not  acid.  If  heated  in  closed  vessels,  selenium  boils  at  a tern- 


180 


SELEXIOTJS  AJS^HYDEIDE — SELEXITES. 


peratiire  below  a red  beat,  and  gives  off  a deep  yellow  vapour, 
wbicb,  according  to  Deville  and  Troost,  is  of  sp.  gr.  8*2  at  1580°, 
but  which  when  heated  to  1900°  F.  exjDands,  as  in  the  case  of 
sulphur,  till  it  occupies  a bulk  nearly  equal  to  that  of  an  equiva- 
lent of  oxygen,  when  it  has  a sp.  gr.  of  6*37 ; at  2590°  it  is  5*68. 
The  specific  gravity  of  selenium  vapour  calculated  on  the  sup- 
position that  it  exactly  corresponds  with  the  volume  of  an  equiva- 
lent of  oxygen  is  5*526.  The  vapoui*  condenses  in  red  flowers  or 
in  opaque  metallic-looking  drops.  Selenium  forms  with  oxygen, 
two  compounds,  which  when  acted  on  by  water,  furnish  acids  ; 
the  flrst  corresponding  with  sulj)hurous,  and  the  second  with 
sulphuric  acid. 

(131)  Selexious  Axhydride,  (Se02=lll‘5  ; Theoretic  Sp.  Gr. 
of  Vapour.,  3*8119  ; Observed  1*03  ; Mol.  Yol.  | | |,)  may  be  ob- 
tained by  burning  selenium  in  a current  of  oxygen,  but  it  is  usually 
prepared  by  boiling  selenium  with  nitric  acid  or  with  aqua  regia. 
The  selenium  is  gradually  oxidized  and  dissolved ; the  excess  of 
nitric  acid  may  be  expelled  by  heat,  leaving  the  selenious  anliy- 
dride  as  a white  mass,  which  does  not  melt  on  further  urging  the 
heat,  but  sublimes  below  redness,  forming  a yellow  vapour,  and 
condensing  again  in  beautiful  snow-white  prismatic  needles. 
The  crystals  are  deliquescent ; their  aqueous  solution  is  strongly 
acid,  and  has  a sour  burning  taste.  Selenious  acid  (Il2Se03)  in 
solution  is  speedily  deoxidized  by  iron  or  by  zinc,  either  of  which, 
when  digested  in  the  liquid,  occasions  the  deposition  of  selenium 
in  the  form  of  a reddish-brown  powder.  A solution  of  sulphurous 
acid  also  readily  reduces  selenium  from  the  acid. 

Selenites. — Most  of  the  selenites,  except  those  of  the  metals 
of  the  alkalies,  are  insoluble  in  water,  but  soluble  in  nitric  acid. 
With  the  alkaline  metals  three  classes  of  salts  may  be  formed : 
normal  selenites,  with  the  general  formula  M^SeOg,  like  selenite 
of  sodium,  iSrajSeOg;  acid  selenites,  with  the  general -formula 
MH,Se03,  like  acid  selenite  of  sodium  (AaHSeO,,  IFO) ; and 
h}q)eracid  selenites,  with  the  sreneral  formula  MH3  2 SeOj,  like 
quadriselenite  of  sodium  2 (XaHg  2 SeOg)  H^O.  The  selenites  are 
easily  recognised  when  heated  on  charcoal  before  the  blowpipe  in 
the  reducing  flame,  by  the  peculiar  odour  of  selenium  which  they 
emit;  the  selenites  in  solution,  when  treated  with  sulphurous 
acid,  give  a reddish-brown  precipitate  of  reduced  selenium. 

(435)  Selexic  Acid  : 112800^= 145  *5. — The  anhydride  of  this 
acid  is  not  known.  The  acid  itself  is  best  obtained  in  solution 
by  deflagrating  selenium  or  any  selenite  with  nitre ; the  residue 
is  dissolved  in  water,  and  mixed  with  a solution  of  nitrate  of  lead ; 
an  insoluble  seleniate  of  lead  is  precipitated,  and  this,  if  suspended 
in  water,  may  be  decomposed  by  a current  of  sulphuretted  hydro- 
gen. Sulphide  of  lead  is  thus  formed,  and  selenic  acid  is  set 
at  liberty;  PbSeO,-fH2S=H2SeO^-|-PbS.  The  acid  may  be 
separated  by  flltration,  and  concentrated  by  evaporation  till  it 
has  a speciflc  gravity  of  2*6;  if  heated  beyond  550°  it  is  decom- 
posed into  selenious  anhydride,  water  and  oxygen.  Selenic  acid 
dissolves  iron  and  zinc  with  evolution  of  hydrogen ; it  also  attacks 


TELLURIUM. 


181 


copper  and  even  gold,  if  boiled  upon  these  metals,  which  are 
oxidized  at  the  expense  of  the  acid,  selenious  acid  being  disen- 
gaged ; platinum  is  not  attacked  by  it.  Sulphurous  acid  is  with- 
out effect  upon  selenic  acid,  but  hydrochloric  acid  decomposes 
it  when  heated  with  it,  chlorine  and  selenious  acid  being  liber- 
ated ; H^SeO^  + 2 HCl = H^SeOg  -f  -f  CI2.  Selenic  acid  closely 

resembles  sulphuric  acid  in  its  properties,  and  its  salts  are  iso- 
morphous  with  the  sulphates  of  the  same  metals. 

Seleniates. — Solutions  of  the  seleniates  give  white  precipitates 
with  salts  of  barium,  strontium,  and  lead,  owing  to  the  formation 
of  insoluble  seleniates  of  these  metals.  These  precipitates  are  in- 
soluble in  diluted  nitric  acid.  When  the  soluble  seleniates  are 
boiled  with  hydrochloric  acid,  selenic  acid  is  liberated,  and  is 
reduced  to  the  form  of  selenious  acid : sulphurous  acid  will  then 
precipitate  reduced  selenium  from  the  solution.  Seleniate  of 
barium  may  be  similarly  decomposed,  and  may  thus  be  distin- 
guished from  the  sulphate  of  barium.  When  heated  on  charcoal 
before  the  blowpipe  in  the  reducing-flame,-the  seleniates  emit  the 
characteristic  odour  of  selenium. 

(436)  Seleniuretted  Hydrogen  ; Hydroselenic  Acid  (H^Se 
= 81*5);  Sp.  Gr.  2*795;  Mol.  Yol.  | | . — This  substance  is  a 
colourless  inflammable  gas,  which  resembles  hydrosulphuric  acid, 
but  its  odour  is  much  more  offensive.  Berzelius  found  that  by 
the  application  of  the  nose  to  a bubble  of  the  gas  no  larger  than 
a pea,  he  was  deprived  of  the  sense  of  smell  for  several  hours. 
Seleniuretted  hydrogen  is  obtained  by  acting  on  selenide  of 
potassium  or  of  iron,  with  diluted  hydrochloric  or  sulphuric  acid. 
This  gas  is  soluble  in  water,  and  precipitates  many  metals  from 
their  salts  in  the  form  of  selenides.  Its  solution  has  a feebly 
acid  reaction  ; if  exposed  to  the  air  it  absorbs  oxygen  and  deposits 
selenium.  The  selenides  of  the  alkali-metals  are  soluble  in 
water : those  of  cerium,  zinc,  and  manganese,  are  flesh-coloured  ; 
most  of  the  others  are  black. 

(437)  Chlorides  of  Selenium. — Selenium  unites  directly 
with  chlorine,  forming  two  compounds,  one  a brownish  volatile 
liquid  (Se2Cl2)  heavier  than  water,  and  slowly  decomposed  by  it ; 
the  other  a volatile  white  crystalline  mass,  SeCl^,  which  is  imme- 
diately decomposed  by  water  into  selenious  and  hydrochloric 
acids. 

§ III.  Tellurium  : Te  = 129,  or  Te  = 64*5. 

Sp.  Gr.  of  Solid  6*65.  Observed  Sp.  Gr.  of  Vapour  at  2530°, 
9*00.  Theoretic  Sp.  (xr.  8*913  ; Atomic  Yol.  [ |.^ 

(438)  Tellurium  is  a rare  substance  discovered  by  Muller  in 
1782,  but  first  investigated  by  Klaproth  in  1798,  and  named  by 
him  from  tellus^  the  earth.  It  is  found  chiefly  in  the  mines  of 
Hungary  and  Transylvania,  occasionally  native  and  nearly  ])ure, 
but  generally  combined  with  various  metals,  such  as  gold,  silver, 
bismuth,  copper,  or  lead  ; it  is  usually  also  accompanied  by  small 

* If  free  tellurium  be  (TeTe),  the  vapour  volume  of  its  molecule  will  be  f 1 !• 


182 


TELLUEOUS  AND  TELLUKIC  ACIDS. 


quantities  of  arsenic  and  selenium.  Its  most  common  ore  is  the 
black,  foliated  tellurium  ore  of  hsagyag,  which  contains  about  13 
per  cent,  of  tellurium  in  the  form  of  tellur  ides  of  gold,  lead,  and 
silver,  mixed  with  sulphides  of  antimony  and  lead.  It  may  be 
extracted  from  this  mineral  by  digestion  of  the  finely-powdered 
ore  in  hydrochloric  acid,  which  removes  the  sulphides  of  lead  and 
antimony  ; the  residue  is  washed  and  heated  with  nitric  acid, 
the  solution  of  nitrate  of  tellurium  is  decanted,  evaporated  to 
dryness,  and  treated  with  hydrochloric  acid,  after  which  the 
tellurium  is  thrown  down  as  a brown  powder  by  the  addition  of 
sulphite  of  sodium  to  the  acid  liquid.  For  additional  particulars 
regarding  the  extraction  of  tellurium,  the  reader  is  referred  to  the 
Lehrhuck  of  Berzelius  (German  edition,  1844,  vol.  ii.  p.  229). 

Properties. — Most  English  writers  on  chemistry  class  tellurium 
amongst  the  metals.  It  presents,  however,  a close  analogy  with 
sulphur  and  selenium,  though  it  possesses  a high  metallic  lustre, 
and  resembles  bismuth  in  colour.  It  fuses  between  800°  and 
900°,  and  at  a high  temperature  it  is  converted  into  a yellow 
vapour  which,  according  to  Deville  and  Troost,  has  a density  of 
9 ’00  at  a temperature  of  2530°.  The  distillation  of  tellurium  is 
best  conducted  by  heating  it  very  strongly  in  a porcelain  tube, 
and  transmitting  a current  of  dry  hydrogen  gas  over  it ; the 
vapour  of  tellurium  is  thus  mechanically  carried  forward,  and  it 
is  condensed  in  drops  and  fiexible  crystalline  needles  in  the  cooler 
parts  of  the  apparatus.  According  to  Mitscherlich,  tellurium, 
when  solidified  after  fusion,  exhibits  a rhombohedral  cleavage,  a 
circumstance  which  appears  to  indicate  its  isomorphism  with  arse- 
nicum  and  antimony.  Tellurium  is  a bad  conductor  of  heat  and 
of  electricity.  When  heated  strongly  in  the  air  it  takes  fire,  burns 
with  a blue  fiame  edged  with  green,  and  emits  a peculiar  character- 
istic odour,  whilst  thick  white  fumes  of  tellurous  anhydride  are 
produced.  Like  sulphur  and  selenium,  tellurium  is  soluble  in 
cold  concentrated  sulphuric  acid,  to  which  it  gives  a fine  purple- 
red  colour  ; on  dilution  it  is  precipitated  unchanged.  Minute 
quantities  of  tellurium,  when  taken  internally,  impart  a persistent 
and  intolerable  odour  of  garlic  to  the  breath. 

Tellurium  forms  two  oxides  (TeO^ ; TeOg),  which  correspond 
in  composition  to  sulphurous  and  sulpliuric  anhydrides. 

(439)  Tellurous  Acid  (Il^TeOg  = 179). — Tellurium  is  readily 
dissolved  by  nitric  acid  of  sp.  gr.  1*25.  If  the  solution  be  poured 
into  water  immediately,  a white,  bulky  hydrate  of  tellurous  acid 
subsides.  It  is  slightly  soluble  in  water,  reddens  litmus,  and 
combines  with  the  alkaline  bases ; these  compounds  are  soluble. 
Tellurous  acid  has  a bitter  metallic  taste  : its  anhydride  may  be 
obtained  by  gently  heating  the  hydrate,  or  by  boiling  the  nitric 
acid  solution,  when  it  is  de})osited  in  crystalline  needles,  which 
are  very  slightly  soluble  in  water.  The  anhydride  (TeO^  = 161) 
fuses  easily,  forming  a transparent  glass,  which  is  yellow  while 
hot,  but  becomes  white  and  crystalline  on  cooling.  Tellurous  anhy- 
dride possesses  considerable  volatility:  if  fused  with  hydrate  of 
potash,  tellurite  of  potassium  is  formed.  Tellurites  may  be  formed 


TELLUKETTED  HYDEOGEN. 


183 


of  three  classes — normal  salts,  M^TeOg ; acid  salts,  MIlTeOg, 
and  hyperacid  salts,  or  quadritellurites,  MHTeO-gjH^^eOg.)  The 
tellnrites  of  the  alkali-metals  are  soluble,  those  of  the  alkaline 
earths  very  sparingly  so.  This  anhydride  also,  like  many  of  the 
metallic  anhydrides,  combines  with  the  stronger  acids  : the  com- 
pounds which  it  thus  furnishes  have  a metallic  taste,  and  are  said 
to  act  powerfully  as  emetics.  Its  salts  with  oxalic  and  tartaric 
acid  are  soluble.  All  the  soluble  salts  in  which  tellurium  acts  as 
a base  are  decomposed  if  mixed  with  hydrochloric  acid  and  heated 
with  sulphurous  acid : reduced  tellurium  is  precipitated  under 
these  circumstances.  With  sulphuretted  hydrogen  a black  sul- 
phide of  tellurium  is  produced. 

(440)  Telluric  Acid  (H^TeO^  = 195)  is  obtained  by  gently 
heating  tellurium  or  tellurous  acid  with  nitre.  A tellurate  of 
potassium  is  formed,  from  which  the  acid  is  transferred  to  barium, 
and  the  barium  is  separated  by  sulphuric  acid.  It  crystallizes  in 
striated  hexagonal  prisms,  which  have  a nauseous  metallic  taste  ; 
they  exert  but  a feeble  action  on  litmus.  These  crystals  are  com- 
posed of  (HgTeO^,  2 HgO).  If  heated  nearly  to  redness  they  fur- 
nish telluric  anhydride,  and  then  assume  an  orange-yellow  colour. 
This  anhydride  (TeOg  = 177)  is  completely  insoluble  in  water,  and 
in  nitric  and  hydrochloric  acids,  as  well  as  in  alkaline  solutions. 
Telluric  acid  has  but  a feeble  chemical  attraction  for  bases,  but, 
like  selenic  acid,  it  forms  three  classes  of  salts  which  may  be 
represented  by  the  general  formula3,  M^TeO^ ; MTITeO^ ; and 
MIITeO^HgTeO^.  ^heir  solutions,  when  acidulated,  yield  a 
black  precipitate  with  sulphuretted  hydrogen.  When  telluric  acid, 
or  one  of  its  salts,  is  heated  to  redness,  oxygen  is  disengaged  and 
the  telluric  is  converted  into  tellurous  anhydride,  or  the  tellurate 
into  a tellurite  of  the  basyl. 

Two  chlorides^  TeClg  and  TeCl^,  have  been  obtained  by  the 
direct  action  of  chlorine  upon  tellurium  : both  of  them  are  volatile ; 
the  vapour  of  the  bichloride  is  of  a violet  colour ; they  are  de- 
composed by  a large  quantity  of  water. 

(441)  Tellueetted  TIydeogen;  HgTe^lSl;  Sjp.  Gr.  4*489; 
Atomic  Vol.  I I I;  or  ITTe=:65*5. — The  most  interesting  com- 
pound of  tellurium  is  that  which  it  forms  with  hydrogen.  It  is  a 
gaseous  body  analogous  to  sulphuretted  hydrogen,  and  is  possessed 
of  feebly  acid  properties.  It  may  be  obtained  by  decomposing 
the  alloy  of  tellurium  with  zinc  or  tin,  by  means  of  hydrochloric 
acid.  The  gas  which  escapes  burns  with  a blue  flame  ; it  reddens 
litmus,  and  has  an  odour  which  cannot  be  distinguished  from  tliat 
of  sulphuretted  hydrogen  : witli  water  it  forms  a colourless  solu- 
tion, wliich  becomes  brown  by  exposure  to  the  air,  owing  to  tlie 
oxidation  of  the  hydrogen  and  se])aration  of  tellurium.  Telluret- 
ted  hydrogen  precipitates  most  of  the  metals  from  their  solutions, 
in  the  form  of  tellurides  which  have  a close  analogy  with  the 
corresponding  sulphides.  The  tellurides  of  the  alkaline  metals 
are  soluble  in  water. 

Tellurium,  whether  in  the  form  of  a soluble  tellurite  or  in 
that  of  a tellurate,  is  thrown  down  from  its  solutions  in  the  reduced 


184 


NATURAL  RELATIONS  OF  THE  PHOSPHORUS  GROUP. 


form  hj  zinc  or  iron ; neutral  solutions  of  the  salts  of  both  its 
acids  are  also  reduced  by  ferrous  sulphate  and  by  stannous 
chloride ; in  these  cases  the  tellurium  falls  in  bi’own  flocculi.  The 
tellurates  of  the  alkaline  metals,  when  heated  to  redness  in  a tube 
with  charcoal,  are  reduced  to  tellurides,  which  are  soluble  in  water, 
and  form  a red  liquid. 


CHAPTEK  YIII. 

§ I.  Phosphorus:  P=31.* 

Atomic  Yol.  [],  or  ^ ; Theoretical  Sjp.  Gr.  of  Yajpour^  4-284 ; 

Olserved  Sj).  Gr.  of  Yajpour.^  4-50. 

(442)  Natural  Relations  of  the  Phosphorus  Group. — Phos- 
phorus is  described  here  for  the  sake  of  convenience,  and  not 
because  it  exhibits  any  relation  to  the  sulphur  group ; it  has,  how- 
ever, a close  connexion  with  arsenic  and  antimony,  two  bodies 
which  will  be  described  with  the  metals. 

Phosphorus,  arsenic,  and  antimony  afford  good  instances  of 
the  terequivalent  or  triad  group  of  elements,  as  in  most  cases 
when  in  combination  they  represent  3 atoms  of  hydrogen,  though 
sometimes  they  are  quinquequivalent,  or  represent  5 atoms. 
These  three  elements  are  indeed  related  much  in  the  same  way  as 
sulphur,  selenium,  and  tellurium ; each  of  them  unites  with  hy- 
drogen, and  forms  a gaseous  compound,  in  which  6 volumes  of 
hydrogen  combine  with  1 volume  of  the  tapour  of  the  other  ele- 
ment— the  compound  which  is  formed  occupying  the  space  of  4 
volumes — these  gaseous  compounds  exhibiting  a tendency  to 
alkalinity.  Each  of  these  elements  unites  with  oxygen  in  the 
proportion  of  2 atoms  with  3,  and  2 with  5 atoms  of  oxygen,  form- 
ing compounds  in  which  the  acid  character  is  less  and  less  marked 
as  the  atomic  weight  of  the  combustible  element  increases.  The 
isomorphous  relations  of  arsenious  anhydride  and  oxide  of  anti- 
mony have  long  been  known,  and  the  corresponding  tribasic 
phosphates  and  arseniates  offer  some  of  the  most  striking  exem- 
plifications of  isomorphism.  Chlorine  unites  with  the  members 
of  this  group  in  the  proportion  of  3 atoms  to  1 atom  of  phosphorus, 
arsenic,  or  antimony.  Bismuth  is  also  related  to  this  group  by 
the  composition  and  character  of  its  oxides  and  chloride,  although 
no  bismuthated  hydrogen  is  at  present  known.  Kitrogen,  as 
already  pointed  out,  is  connected  with  the  phosphorus  group  by 
its  combination  with  hydrogen  (HgA),  and  by  its  formation  of 
anhydrides  with  3 and  with  5 atoms  of  .oxygen.  An  interesting 
isomorphous  relation  exists  between  the  members  of  the  sulphur 
and  those  of  the  phosphorus  group ; sulphur  being  isomorphous 

* The  vapour  volume  of  phosphorus  appears  to  be  tetratomic ; for  if  the  molecule 
of  free  phosphorus  be  taken  as  P4  it  -will  furnish  two  volumes  of  vapour.  Arsenic 
resembles  phosphorus  in  this  respect. 


PHOSPHORUS — SOURCES  OF. 


185 


witli  arsenic,  as  is  shown  in  the  correspondence  in  form  between 
crystals  of  iron  pyrites  (FeSj)  and  those  of  mispickel  (FeSAs). 
(See  note^  Part  I.  p.  115.) 

The  following  table  exhibits  some  of  the  corresponding  com- 
pounds of  the  5 triads  just  mentioned : — 


Ammonia. 

Phosphuretted 

hydrogen. 

Arseniuretted 

hydrogen. 

Antimoni  uretted 
hydrogen. 

HsN- 

H3P 

H3AS 

Chloride 

nitrogen. 

Terchlor. 

phosphorus. 

Terchlor. 

arsenic. 

Terchlor. 

antimony. 

Terchlor. 

bismuth. 

CI3N? 

^ cCp 

CI3AS 

Cl3Sb 

Pentachlor. 

phosphorus. 

Pentachlor. 

antimony. 

^ ^ 

CI5P 

Nitrous 

anhydride. 

Phosphorous 

anhydride. 

Arsenions 

anhydride. 

Sesquiox. 

antimony. 

Sesquiox. 

bismuth. 

NaOa  ^ 

P2O3 

f \ 

AS2O3 

Sb2e3 

PbOs 

Nitric 

anhydride. 

A 

Phosphoric 

anhydride. 

Arsenic 

anhydride. 

A 

Antimonic 

anhydride. 

A 

Bismuthic 

anhydride. 

N2O5 

P2O5 

AS2O5 

SbaOa 

A gradation  of  properties  is  observed  in  these  elements,  and 
particularly  in  the  three  intermediate  ones  : phosphorus  is  the 
least  dense,  the  most  fusible  and  volatile ; next  follows  arsenic, 
and  then  antimony,  in  the  order  of  their  atomic  weights.  The 
acid  properties  of  the  oxidized  compounds  are  most  marked  in 
nitrogen,  then  in  phosphorus  ; they  are  weaker  in  arsenic,  still 
weaker  in  antimony,  and  are  scarcely  apparent  in  bismuth.  The 
compounds  with  hydrogen  follow  the  same  order  : ammonia  is  a 
])owerful  base  and  requires  a high  temperature  for  its  decomposi- 
tion, phosphuretted  hydrogen  a very  feeble  base  ; in  arseniuretted 
hydrogen  the  basic  character  is  not  perceived,  although  manifest 
in  some  of  its  derivatives,  and  the  same  thing  is  true  of  antimony ; 
each  of  tlie  three  hydrides  last  mentioned  being  in  succession 
more  easily  decomposed  by  simple  exposure  to  heat,  whilst  the 
attraction  of  bismuth  for  hydrogen  is  so  feeble  that  its  hydride  is 
unknown. 

(443)  Pliosphorus  was  discovered  by  Brandt  in  1669.  It  is 
never  met  with  in  nature  in  the  uncombined  state,  but  it  occurs 
in  small  proportion  as  phosphate  of  calcium,  as  a coTistituent  of 
the  primitive  and  volcanic  rocks,  by  the  gradual  decay  of  wliich 
it  passes  into  the  soil : from  tlie  soil  it  is  extracted  by  plants, 
which  accumulate  it,  particularly  in  their  seeds,  in  quantity  suth- 
cient  for  the  support  of  the  various  tribes  of  animals  which  they 
supply  with  food.  In  the  animal  system  it  is  collected  in  large 
amount,  and  when  combined  with  oxygen  and  calcium,  as  phos- 


186 


PHOSPHOEIJS EXTRACTION. 


pliate  of  calcium,  it  forms  the  principal  earthy  constituent  of  the 
bones  of  the  vertebrata.  Phosphorus  also  appears  to  be  essential 
to  the  exercise  of  the  higher  functions  of  the  animal,  since  it  exists 
as  a never-failing  ingredient  in  the  substance  of  which  the  brain 
and  nerves  are  composed.  It  is  likewise  contained  in  albumen 
and  in  hbrin  in  small  proportions,  and  is  present  in  the  form  of 
phosphates  of  the  metals  of  the  alkalies  and  of  the  earths  in  the 
urine  and  solid  excrements  of  animals. 

Extraction. — Prosphorus  was  originally  extracted  from  the 
salts  contained  in  urine,  but  it  is  now  obtained  almost  exclusively 
from  the  bones  of  animals.  In  order  to  prepare  it,  bones  were 
formerly  always  burned  to  whiteness  by  calcining  them  in  an 
open  fire  for  some  hours,  then  reduced  to  powder ; but  now  the 
gelatin  of  the  bones  is  first  economized  by  heating  them,  under 
pressure,  with  water  ; or  the  bones  are  distilled  in  closed  vessels, 
the  ammonia  and  volatile  products  are  collected,  whilst  the  bone 
black  is  employed  in  sugar-refining,  and  after  it  has  become  use- 
less for  this  purpose,  it  is  burned  in  the  open  fire.  Three  parts 
of  bone-ash  obtained  by  any  of  these  methods  are  mixed  with  2 of 
concentrated  sulphuric  acid,  and  18  or  20  parts  of  water.  The 
mixture  is  allowed  to  stand  for  two  or  three  days,  after  which  it 
is  placed  upon  a strong  linen  filter,  and  the  acid  liquid  is  sepa- 
rated from  the  sulphate  of  calcium  by  pressure ; the  residue  is 
further  washed  with  water,  and  the  washings  are  added  to  the 
filtered  solution.  In  tliis  process  the  sulphuric  acid  is  added  in 
such  quantity  as  partially  to  decompose  the  phosphate  of  calcium  ; 
two-thirds  of  the  calcium  are  removed  by  it  in  the  insoluble  form, 
as  sulphate  of  calcium,  the  remaining  third  being  left  as  an  acid 
salt,  in  combination  with  the  whole  of  the  phosphoric  acid,  with 
which  it  forms  a compound  readily  soluble  in  water,  frequently 
described  as  superphosphate  of  lime  (H^Oa  2 PO^).  The  reaction 
may  be  thus  expressed  in  symbols  : — 

Bone  ash,  Sulph.  acid.  Acid  phosph.  calcium.  Sulph.  calcium. 

Oa3  2 PO,  -f-  2 H,Se,  = H^Oa  2 PO,  -f  2 OaSO,. 

This  acid  solution  is  evaporated  to  the  consistence  of  a syrup, 
then  mixed  with  one-fourth  of  its  weight  of  charcoal,  and  heated 
to  incipient  redness  in  an  iron  pot,  stirring  constantly.  The  mass, 
when  dry,  is  transferred  to  an  earthen  retort  ((X,  fig.  310),  which 
is  covered  externally  with  a thin  paste,  consisting  of  a mixture 
of  equal  parts  of  borax  and  fire-clay,  with  a view  of  rendering  the 
retort  less  porous.  It  is  then  exposed  to  a heat  which  is  slowly 
raised  to  a full  red.  Phosphorus  gradually  rises  in  vapour,  and  is 
conveyed  by  means  of  a wide  copper  tube,  bent  as  at  J,  so  as  to 
dip  into  water  contained  in  a vessel  provided  with  a smaller  tube, 
open  at  both  ends,  for  conveying  the  uncondensed  gases  into  a 
chimney.  The  phosphorus  is  condensed  in  yellow  drops.  In  this 
operation  it  is  found  necessary  to  convert  the  phosphate  into 
acid  phosphate  of  calcium ; since  the  bone-ash,  when  heated 
with  charcoal,  does  not  part  with  its  phosphorus.  The  acid 


PHOSPHOKUS PKOPEKTIES. 


187 


phosphate  in  contact  with 
charcoal  is  decomposed ; 
the  calcium  retains  suffi- 
cient phosphoric  acid  rad- 
icle to  reconstitute  bone- 
earth,  which  remains  un- 
changed in  the  retort,  while 
the  excess  of  acid  and  the 
water  which  the  mass  al- 
ways retains  are  decom- 
posed by  the  charcoal ; 
hydrogen,  carbonic  oxide, 
and  phosphorus  are  the 
results.  Gaseous  matters 
escape,  therefore,  during 
the  whole  operation,  which 
may  be  regarded  as  con- 
sisting of  two  stages,  the 

first  fcing  the  decomposition  of  the  acid  phosphate  of  calcium 
into  bone-ash  and  phosphoric  acid  : — 

3 (H.Oa  2 Pej^Oa^  2 PO.  + d H3PO,; 

whilst  the  second  stage  consists  of  the  deoxidation  of  the  liberated 
acid : — - 

4 H3Pe,+i6  e=p,+6  H3+16 

With  a view  to  render  the  phosphorus  perfectly  pure,  it  is 
fused  under  warm  water,  squeezed  through  wash-leather,  and  again 
melted,  first  under  ammonia,  and  then  under  a solution  of  acid- 
chromate  of  potassium  in  diluted  sulphuric  acid.  The  easy  fusi- 
bility of  phosphorus  enables  it  to  be  moulded  into  sticks  with 
facility ; it  is  melted  under  water  and  forced  into  tubes,  in  which 
it  is  allowed  to  solidify. 

Properties. — Phosphorus  is  a soft,  semi-transparent,  colourless, 
waxy-looking  solid,  which,  however,  becomes  hard  and  brittle  at 
low  temperatures : it  fumes  in  the  air,  emitting  white  vapours  of 
an  alliaceous  odour.  It  has  a specific  gravity  of  1*83  at  50° 
(Schrotter).  It  fuses  at  111°*5,  and  if  melted  under  an  alkaline 
liquid  and  allowed  to  cool  undisturbed,  it  will  long  continue  fluid 
at  ordinary  temperatures,  but  when  touched  with  a wire  or  a glass 
rod  it  solidifies  suddenly.  Pliosphorus  is  a non-conductor  of  elec- 
tricity, both  in  the  solid  and  the  liquid  state.  It  is  extremely 
inflammable,  taking  fire  in  the  open  air  at  a temperature  very 
little  above  its  fusing-point.  If  it  contain  impurities,  such  as 
oxide  of  phosphorus,  it  takes  fire  still  more  easily.  Great  caution 
is  therefore  required  in  handling  it ; it  is  better  always  to  cut  it 


Fig.  310. 


* Phosphorus  may  also  be  obtained  by  heating  an  intimate  mixture  of  charcoal 
and  phosphate  of  calcium  to  bright  redness  in  a current  of  hydrochloric  acid  gas, 
carbonic  oxide  and  hydrogen  being  liberated  along  with  vapour  of  phosphorus  while 
chloride  of  calcium  is  formed ; — 

2 (eaa  2 POO +16  0+12  H01=P4  + 16  00  + 6 II2  + 6 OaClj. 


188 


DIFFERENT  FORMS  OF  PHOSPHORUS. 


under  water.  The  burns  occasioned  by  melted  phosphorus  are 
deep  and  often  extremely  severe,  from  the  difficulty  of  extinguish- 
ing the  flame. 

Phosphorus  burns  with  a brilliant  white  flame,  and  emits  dense 
wdiite  fumes  of  phosphoric  anhydride.  In  closed  vessels  it  boils 
at  about  550°,  giving  off  a colourless  vapour,  of  which  100  cubic 
inches  weigh  about  135  grains.  An  atom  of  phosphorus,  there- 
fore, gives  off  a volume  of  vapour  ecpial  to  only  half  that  of  an 
atom  of  oxygen ; and,  according  to  Deville,  no  alteration  in  the 
relative  volumes  of  the  two  is  effected  by  a temperature  of  1900°. 
Phosphorus  is  insoluble  in  water ; it  is  slightly  soluble  in  ether, 
but  more  so  in  benzol,  in  oil  of  turpentine,  and  in  the  fixed  and 
essential  oils.  It  is  also  freely  dissolved  by  chloride  of  sulphur, 
by  terchloride  of  phosphorus,  and  by  the  bisulphide  of  carbon  ; by 
allowing  its  solution  in  bisulphide  of  carbon  to  fall  upon  filtering- 
paper  in  the  open  air,  the  finely  divided  phosphorus  absorbs  oxy- 
gen so  rapidly  that  it  takes  fire  as  soon  as  the  solvent  has  evapo- 
rated. If  the  solution  be  allowed  to  evaporate  slowly  in  a current 
of  hydrogen  or  carbonic  anhydride,  the  phosphorus  may  be 
obtained  crystallized  in  rhombic  dodecahedra. 

Phosphorus  is  always  preserved  under  water,  for  when  exposed 
to  the  air,  at  all  temperature  above  32°  it  gradually  combines  with 
oxygen,  and  undergoes  a slow  combustion ; under  these  circum- 
stances, in  a darkened  room  it  emits  a pale  greenish  light  (hence 
its  name,  from  0^^,  light,  (popk,  bearing)  attended  with  the  pro- 
duction of  the  white  fumes  and  the  garlic  odour  already  men- 
tioned. The  luminosity  of  phosphorus  is  prevented  by  the  admix- 
ture of  certain  inflammable  vapours  and  gases  in  minute  quantity 
with  the  atmosphere;  if  air  be  mixed  with  either  of  its 
bulk  of  olefiant  gas,  y-gVo  naphtha,  or  of  oil  of  turpentine, 
a stick  of  phosphorus  no  longer  appears  luminous  when  exposed 
to  its  action  (Graham). 

It  is  remarkable  that  in  pure  oxygen  the  luminosity  is  not 
observed  until  the  temperature  rises  to  60°,  unless  the  gas  be 
rarefied,  or  be  diluted  with  some  other  gas. 

(444)  Different  forms  of  Phosphorus. — Phosphorus  assumes 
several  different  forms  under  the  influence  of  causes  apparently 
trifling.  The  transparent  variety  has  been  already  mentioned ; 
this,  when  kept  exposed  to  light  under  water,  assumes  a second 
form,  consisting  of  small  plates ; it  then  appears  white  and  opaque, 
and  is  somewhat  less  fusible.  It  has  a sp.  gr.  of  1’515:  white 
phosphorus  becomes  reconverted  into  the  vitreous  variety  by  a 
temperature  not  exceeding  122°.  A third  form  is  obtained  by 
suddenly  cooling  melted  phosphorus ; it  is  perfectly  hlach  and 
opaque,  but  by  sinqile  fusion  and  slow  cooling  it  again  becomes 
transparent  and  colourless ; whilst  a fourth  or  viscous  modification, 
analogous  to  viscous  sulphur,  may  be  obtained  by  heating  very 
pure  phosphorus  to  near  its  boiling-point  and  suddenly  cooling  it. 
A fifth  form  occurs  in  the  shape  of  red  scales,  which  are  obtained 
by  the  spontaneous  sublimation  of  phosphorus  in  the  Torricellian 
vacuum  when  exposed  to  the  rays  of  the  sun. 


RED  PHOSPHORUS. 


189 


Red  or  amorphous  Phosphorus. — The  red  form  of  phosphorus 
has  been  carefully  studied  by  Schrbtter  {Ann.  de  Chimie^  III. 
xxiv.  406).  It  may  be  obtained  by  placing  a quantity  of  dried 
common  phosphorus  in  the  bulb  of  a flask,  a,  flg.  311,  to  the  neck 


Fig.  311. 


of  which  a long  narrow  tube,  5,  bent  downward,  is  attached ; the 
open  end  of  this  tube  dips  into  a little  mercury ; the  air  in  the 
flask  is  displaced  by  means  of  a current  of  carbonic  anhydride, 
which  is  supplied  from  the  bottle  e,  and  dried  by  passing  through 
the  tube,  f,  filled  -with  chloride  of  calcium;  the  tube  is  then 
sealed  at  the  narrow  portion,  and  the  apparatus  which  supplied 
tlie  carbonic  anhydride  is  removed.  Heat  is  next  applied  to  the 
flask  by  means  of  an  oil-bath,  c : the  phosphorus  melts  readily,  but 
by  regulating  the  heat  steadily  between  450°  and  460°,  by  means 
of  the  thermometer,  and  maintaining  it  for  30  or  40  hours, 
almost  all  the  phosphorus  will  become  converted  into  the  solid 
amorphous  variety.  When  the  change  appears  to  be  complete, 
the  apparatus  is  allowed  to  cool : bisulphide  of  carbon  is  then 
poured  upon  the  mass  in  the  flask,  and  digested  on  it  for  some 
hours : this  is  poured  off,  and  fresh  bisulphide  added,  the  digestion 
being  repeated  so  long  as  any  phosphorus  is  dissolved ; this  may 
be  known  by  allowing  a few  drops  of  the  decanted  liquid  to  eva- 
porate spontaneously  in  a watch-glass ; any  dissolved  phosphorus 
will  be  left  behind. 

The  red  powder  of  which  the  undissolved  portion  consists,  if 
not  quite  free  from  unaltered  phosphorus,  takes  fire  spontaneously 
when  exposed  to  the  air ; if  quite  pure,  it  does  not  take  fire ; but 
it  absorbs  oxygen  very  slowly,  the  oxidation  being  more  ra])id  if 
the  powder  be  moist ; phosphorous  acid  is  gradually  formed,  and 


190 


RED  PHOSPHORUS. 


from  its  deliquescent  character  the  powder  becomes  damp.  This 
oxidation  occurs  so  slowly  that  it  was  at  first  imagined  that 
amorphons  phosphorus  underwent  no  change  by  exposure  to  the 
air.  The  higher  the  temperature  at  which  the  transformation  is 
effected,  the  deeper  is  the  colour  of  the  product,  which  in  the  finest 
specimens  rivals  that  of  vermilion.  By  heating  the  phosphorus 
more  strongly  during  its  preparation,  the  change  may  be  produced 
much  more  rapidly,  but  the  phosphorus  then  assumes  the  form  of 
reddish-brown  friable  masses,  with  a conchoidal  fracture.  This 
form  of  phosphorus  has  been  manufactured  at  Birmingham  on  a 
considerable  scale.  The  process,  however,  is  not  unattended  with 
danger ; for  if  the  red  powder  be  heated  up  to  the  point  at  which 
its  re-conversion  into  the  transparent  variety  takes  place,  the  whole 
mass  suddenly  passes  back  into  the  ordinary  form,  with  a copious 
evolution  of  heat,  followed  by  the  sudden  formation  of  a large 
volume  of  the  vapour  of  phosphorus.  The  purification  from 
ordinary  phosphorus  may  be  effected  by  digesting  the  mass  with 
a solution  of  caustic  soda  so  long  as  phosphuretted  hydrogen  is 
formed.  The  residual  red  phosphorus  is  then  thoroughly  washed 
from  the  hypophosphite  of  sodium,  and  afterwards  dried.  The 
changes  produced  in  phosphorus  by  heat  may  be  readily  watched 
by  placing  a few  fragments  of  well-dried  phosphorus  in  a tube, 
upon  which  two  or  three  bulbs  have  been  blown,  then  expelling 
the  air  by  a current  of  carbonic  anhydride,  and  sealing  one  end 
of  the  tube, — the  open  end  being  made  to  dip  into  mercury. 
On  applying  heat  to  the  phosphorus,  it  becomes  red,  but  on 
continuing  to  raise  the  temperature  it  distils  over  in  perfectly 
colourless  transparent  drops,  which  frequently  remain  liquid  for 
some  hours,  though  they  ultimately  solidify  to  a transparent  co- 
lourless mass. 

Bed  or  amorphous  phosphorus  differs  remarkably  in  many  of 
its  properties  from  the  w^axy-looking  stick  phosphorus.  It  may  be 
exposed  to  the  air  without  emitting  any  odour.  It  is  not  soluble 
in  either  bisulphide  of  carbon,  terchloride  of  phosphorus,  or  ben- 
zol. The  density  of  amorphous  phosphorus  exceeds  that  of  the 
vitreous  form ; the  red  powder,  according  to  Brodie,  having  a 
specific  gravity  of  2T4.  It  may  be  heated  in  the  open  air  with- 
out change  till  the  temperature  reaches  500° ; at  this  point  it 
melts  and  bursts  into  flame,  and  burns  with  the  dazzling  bril- 
liancy of  common  phosphorus,  emitting  dense  fumes  of  phosphoric 
anhydride.  Chlorine  acts  directly  upon  red  phosphorus  without 
the  application  of  heat : the  temperature  rises,  but  the  phosphorus 
does  not  take  fire.  When  rubbed  with  chlorate  of  potassium  it 
detonates,  very  slight  friction  being  sufficient  to  produce  the 
action : peroxide  of  manganese  and  peroxide  of  lead  act  with  it 
in  a similar  way,  but  less  readily. 

The  principal  consumption  of  phosphorus  is  in  the  manufac- 
ture of  lucifer  matches.  In  the  usual  mode  of  preparing  these 
matches,  the  ends  of  the  pieces  of  wood  are  first  gummed  and 
dusted  over  with  sulphur,  and  then  tipped  with  a mixture,  in 
which  the  chief  ingredients  are  an  emulsion  of  phosphorus  in 


OXIDES  OF  PHOSPHORUS PHOSPHORIC  AHHYDRIDE.  191 


glue,  and  chlorate  of  potassium,  or  black  oxide  of  manganese. 
The  manufacture  is  one  attended  with  danger,  from  the  highly 
inflammable  and  explosive  nature  of  the  ingredients  used ; but, 
in  addition  to  this  risk,  those  employed  in  the  business  are  liable 
to  a distressing  form  of  caries  of  the  lower  jaw,  arising  from  the 
action  of  the  fumes  of  phosphorus  upon  those  w^ho  inhale  them. 
Of  these  evils,  the  flrst  is  greatly  lessened,  and  the  second  alto- 
gether avoided,  by  the  use  of  amorphous  phosphorus.  An  in- 
genious plan  for  diminishing  the  risk  of  fires  from  the  use  of 
lucifer  matches  consists  in  mixing  the  amorphous  phosphorus  with 
the  grit  which  is  used  as  a rubbing  surface  for  kindling  the 
matches ; the  composition  with  which  they  are  tipped  takes  fire 
when  rubbed  upon  the  phosphorized  surface,  but  not  by  ordinary 
friction  upon  any  other  substance,  as  the  match  itself  contains  no 
phosphorus. 

Although  vitreous  phosphorus  acts  as  a powerful  irritant 
poison  upon  animals  when  taken  internally,  the  amorphous  va- 
riety may  be  swallowed  with  impunity ; the  vitreous  phosphorus 
forms  the  active  ingredient  in  the  phosphorus  paste  frequently 
used  to  destroy  cockroaches  and  other  kinds  of  vermin. 

Owing  to  its  strong  attraction  for  oxygen,  phosphorus  reduces 
some  of  the  oxidized  compounds  of  the  metals  to  the  metallic 
state ; a stick  of  phosphorus  placed  in  a solution  of  chloride  of 
gold  or  of  nitrate  of  silver,  becomes  speedily  incased  in  reduced 
gold  or  silver.  Salts  of  palladium,  platinum,  and  copper,  are 
also  reduced  gradually  when  a stick  of  phosphorus  is  immersed 
in  their  solutions. 

(4d5)  Oxides  of  Phosphorus. — ^Phosphorus  is  usually  stated 
to  furnish  four  compounds  with  oxygen,  but  only  two  of  them 
are  known  in  the  anhydrous  condition,  viz. : — 

In  100  parts. 


Phosphorus, 

Phosphorous  anhydride P2O3  = 110  56-;i6 

Phosphoric  anhydride P2O5  = 142  43'66 


Oxygen. 

43*64 

56*34 


Phosphorus  forms  three  oxidized  acids,  which  are  respectively 
monobasic,  dibasic,  and  tribasic,  in  proportion  as  the  quantity  of 
oxygen  increases : these  acids  are  the  following : — 


Ilypophosphorous  acid  (monobasic)  HPIPO^ 

Phosphorous  acid  (dibasic) H^PHOg 

Phosphoric  acid  (tribasic) IlgPO^ 

(44f))  Phosphoric  Anhydride:  Y ^0^=142. — Tlie  most  im- 
portant of  the  oxides  of  phosphorus  is  that  which  when  acted  on 
by  water  forms  phosphoric  acid ; it  occurs  native  in  considerable 
quantity  in  the  form  of  phosphate  of  calcium.  The  anliydride  of 
this  acid  is  the  sole  product  of  the  rapid  combustion  of  phospho- 
rus in  dry  oxygen  or  in  atmospheric  air.  By  means  of  the  appa- 
ratus shown  in  fig.  312,  a large  quantity  of  phosphoric  anliydride 
may  be  readily  obtained  in  a few  hours  : e is  a three-necked 
globe,  in  the  centre  of  which  is  suspended  a porcelain  dish,  c ; 
this  dish  is  attached  by  means  of  platinum  wire  to  the  wide  tube 


192 


HYDEATES  OF  PHOSPHOEIC  ACID, 


<2,  1)^  which  is  closed  at  a with  a cork ; the  bottle,  /*,  is  connected 
by  the  tube  with  an  aspirator,  or  other  convenient  means  of 
maintaining  a continuous  current  of  air  through  the  apparatus  : 


Fig.  312. 


the  air  as  it  enters  is  thoroughly  dried  by  passing  over  pumice 
moistened  with  sulphuric  acid,  in  the  tube,  d.  A fragment  of 
well-dried  phosphorus  is  placed  in  the  dish,  <?,  and  kindled  by 
touching  it  with  a hot  wire.  As  the  phosphorus  burns  away 
fresh  pieces  are  added  through  the  aperture  which  is  again  im- 
mediately closed  with  the  cork.  The  anhydride  thus  obtained 
generally  contains  traces  of  one  of  the  lower  oxides  of  phospho- 
rus. It  forms  a snow-white,  flocculent,  non-crystalline,  anhy- 
drous, but  extremely  deliquescent,  powder,  which  fuses  at  an 
elevated  temperature,  and  by  a still  stronger  heat,  approaching 
to  whiteness,  may  be  sublimed.  When  dropped  into  water  it 
combines  with  it,  emitting  a hissing  noise  ; the  greater  part  is 
instantly  dissolved,  leaving  a few  gelatinous  flocculi,  which  slowly 
disappear.  After  it  has  once  been  dissolved,  it  cannot  again  be 
converted  into  the  anhydride  by  mere  elevation  of  temperature, 
as  the  whole  compound  is  gradually  dissipated  in  vapour.  It 
does  not  emit  vapour  at  ordinary  temperatures,  and  owing  to  its 
powerful  attraction  for  water,  this  anhydride  is  often  used  as  a 
desiccating  and  dehydrating  agent ; and  for  this  purpose  it  sur- 
passes in  efficacy  almost  every  known  substance. 

(417)  Hydrates  of  Phosphoric  Acid. — The  pure  acid  is 
generally  procured  in  a hydrated  state,  by  boiling  1 part  of  phos- 
phorus in  13  parts  of  nitric  acid  of  sp.  gr.  1-20.  The  phosphorus 
becomes  oxidized  by  the  nitric  acid,  which  is  decomposed  with 
escape  of  nitric  oxide,  and  the  phosphoric  acid  is  dissolved  as  it  is 
formed.  When  the  phosphorus  has  all  disappeared,  the  excess  of 
nitric  acid  is  expelled  by  evaporating  the  liquid  in  a platinum 
vessel  until  dense  white  iuines  begin  to  arise ; on  cooling,  the  acid 


HYDSATES  OF  PHOSPHOKIC  ACID. 


193 


solidifies  to  a transparent  glassy  mass,  frequeotly  termed  glacial 
2?liosphoriG  acid.  This  glacial  acid  is  extremely  deliquescent,  pro- 
ducing a solution  which,  when  saturated,  has  a sp.  gr.  of  2'0.  It 
is  intensely  acid,  hut  not  caustic. 

The  oxidation  of  phosphorus  by  nitric  acid  furnishes  an  easy 
means  of  ascertaining  the  composition  of  phosphoric  anhydride. 
For  this  purpose,  31  grains  of  phosphorus  are  boiled  in  a glass 
retort  with  pure  diluted  nitric  acid.  The  greater  part  of  the 
excess  of  water  and  nitric  acid  having  been  distilled  off,  the  acid 
solution  is  added  to  350  grains  of  oxide  of  lead,  in  a weighed  pla- 
tinum dish  : the  liquid  is  slowly  evaporated  and  the  residue  ignit- 
ed ; by  a red  heat  tlie  whole  of  the  nitric  acid  is  expelled,  and  the 
phosphoric  anhydride  alone  remains  in  combination  with  the  oxide 
of  lead.  The  oxide  and  anhydride  together  will  be  found  to  weigh 
421  grains,  showing  an  increase  in  weight  upon  the  phosphorus 
and  oxide  of  lead  of  40  grains  : 31  parts  of  phosphorus  therefore 
require  40  parts  of  oxygen  for  conversion  into  phosphoric  anhy- 
dride. 

A less  pure  acid  is  procured  by  adding  to  a solution  of  super- 
phosphate of  lime  (prepared  from  bones  by  the  process  already 
described  as  a preliminary  step  towards  procuring  phosphorus) 
carbonate  of  ammonium  till  effervescence  ceases ; tribasic  phos- 
phate of  calcium  is  precipitated,  leaving  phosphate  of  ammonium 
in  solution.  The  precipitated  phosphate  of  calcium  is  separated  by 
filtration,  the  liquid  evaporated  to  dryness,  and  the  residue  ignited. 
Ammonia  is  expelled,  and  phosphoric  acid  (contaminated  with  all 
the  soluble  salts  which  the  bones  contained)  remains  beliind. 

There  are  three  different  hydrates  of  phosphoric  acid,  each  of 
which  possesses  the  properties  of  a distinct  acid  : viz. — 

Metaphosphoric  acid or  H0,P05 

Orthophosphoric  or  ordinary  phosphoric  acid.H^PO^  or  3 II0,P05 
Pyrophosphoric  acid H.P^O^  or  2 II0,P05 

These  different  hydrates  of  the  acid  retain  their  peculiar  cha- 
racteristics when  dissolved  in  water,  and  combine  with  1,  with  3, 
or  with  4 equivalents  of  basyls  to  form  salts,  according  as  the 
metaphosphoric,  the  orthophosphoric,  or  the  pyrophosphoric  acid 
is  employed.  Owing  to  the  important  inffuence  which  the  study 
of  these  combinations  has  exercised  upon  the  theory  of  saline  com- 
binations in  general,  it  will  be  necessary  to  examine  them  some- 
what in  detail. 

(448)  Orthophosphoric  or  Tribasic  Phosphoric  Acid  (IlgPO^ 
or  3H0,P()5).  If  the  liquid  formed  by  dissolving  the  glacial  acid 
in  water  be  boiled  for  some  time,  and  carbonate  of  sodium  be  then 
added  until  tlie  solution  becomes  sliglitly  alkaline,  a tribasic  plios- 
phate  of  sodium  and  hydrogen  is  obtained,  wliich  on  evaporation 
crystallizes  in  large  transparent  rhombic  prisms  (ISTa^IIPO,, 
12  lIjO).  If  this  solution  be  mixed  with  a neutral  solution  of 
nitrate  of  silver,  a canary-yellow  precipitate  of  tril)asic  phosphate 
of  silver  ( AggPO,)  is  formed.  Although  this  solution  was  neutral 
or  slightly  alkaline  before  admixture  with  nitrate  of  silver,  it  will 
13 


194: 


ORTHOPIIOSPHORIC  OR  TRIBASIC  PHOSPHORIC  ACID. 


be  found  afterwards  to  have  a decidedly  acid  reaction  upon  litmus, 
nitric  acid  having  been  liberated : — 


]NXHPe,  + 3 AgNB,  =Ag3Pe,  + 2 + 


Acetate  of  lead  may  be  used  as  a precipitant  instead  of  nitrate 
of  silver,  and  in  this  case  a white  tribasic  phosphate  of  lead 
(Pbg  2 PO^)  subsides.  If  this  phosphate  of  lead  be  well  washed, 
suspended  in  water,  and  exposed  to  the  action  of  a current  of 
sulphuretted  hydrogen,  pure  orthophosphoric  acid  is  liberated  and 
becomes  dissolved  in  the  liquid,  whilst  the  black  insoluble  sul- 
phide of  lead  is  formed  ; Pbg  2 PO^-f  3 ==  2 H3P04H-3  PbS. 

The  sulphide  of  lead  may  be  removed  by  filtration,  and  the  acid 
obtained  in  deliquescent,  hard,  brittle,  prismatic,  transparent 
crystals,  by  evaporation  in  vactio  over  sulphuric  acid.  It  requires 
three  atoms  of  uniequivalent  basyl  for  saturation.  The  salts  of 
this  hydrate  form  the  orthophosphates  or  common ' trihasio 
phosphates. 

There  are  three  varieties  of  these  salts,  which  may  be  indicated 
by  general  formulge  as  follows  : — 


1 Basic  phosphates . . 
1 Neutral  phosphates 
3 Acid  phosphates . . . 


It  is  not  necessary  that  the  3 equivalents  of  basyl  should 
consist  of  the  same  metal  in  these  salts  ; two  or  even  three  difier- 
ent  basyls  may  coexist  in  the  salt ; as,  for  example,  in  micro- 
cosmic  salt,  or  phosphate  of  sodium,  ammonium  and  hydrogen 


(NaH,NIlPe„  4 HgO). 


In  the  first  class,  the  three  atoms  of  hydrogen  in  the  acid  have 
been  displaced  by  3 equivalents  of  a metal,  as,  for  example,  in  the 
tribasic  phosphate  of  sodium  (NagPO^,  12  H^O)  ; these  salts  when 
soluble  have  a strongly  alkaline  reaction  : in  the  second  class  2 
atoms  of  the  basic  hydrogen  have  been  displaced  by  2 equivalents 
of  a metal ; they  are  like  the  ordinary  rhombic  phosphate  of 
sodium  (NagllPO,,  12  H^O)  ; the  soluble  salts  of  this  class  are 
neutral,  or  have  a feebly  alkaline  reaction  : whilst  the  third  class 
contains  only  1 equivalent  of  metal  with  2 atoms  of  basic  hydro- 
gen ; they  are  of  the  form  of  the  salt  (Nall^PO-^,  HgO)  frequently 
called  the  biphosphate  of  soda  ; these  salts  have  a strongly  acid 
reaction,  and  are  often  spoken  of  as  the  superphosphates. 

The  soluble  orthophosphates  are  characterized  by  the  yellow 
phosphate  of  silver  which  their  neutral  solutions  form  with  nitrate 
of  silver ; this  precipitate  is  freely  soluble  both  in  nitric  acid  and 
in  ammonia.  They  also  yield  a crystalline  precipitate  when  a 
clear  solution  of  sulphate  of  magnesium,  rendered  alkaline  by 
ammonia,  is  briskly  stirred  with  them  ; this  precipitate  is  inso- 
luble in  water  which  contains  free  ammonia ; it  consists  of 
(Mg"H,NP04,  ^ HgO) : when  ignited,  the  water  and  ammonia 
are  expelled,  and  it  becomes  converted  into  pyrophosphate  of  mag- 
nesium (MggPgO,),  a compound  frequently  employed  as  a means 
of  estimating  the  amount  of  phosphates  in  solutions  which  contain 


PYROPIIOSPnOKIC  ACID. 


195 


tliem ; 100  parts  of  fhe  ignited  residue  containing  Od'O  of 
Neutral  solutions  of  the  orthophosphates  give  precipitates  with 
salts  of  barium  and  calcium  ; the  pliosphates  of  barium  and  cal- 
cium are  readily  soluble  in  acetic  acid  ; but  free  phosphoric  acid 
gives  no  precipitate  in  solutions  of  the  nitrates  of  calcium,  barium, 
silver,  or  sescpiichloride  of  iron  ; when  molybdate  of  ammonium  is 
added  to  a solution  of  a phosphate  acidulated  with  nitric  acid, 
a characteristic  yellow  precipitate  of  molybdophosphate  of  ammo- 
nium is  formed.  The  quantity  of  phosphoric  acid  in  a solution 
may  also  be  ascertained,  if  neither  sulphuric  nor  hydrochloric 
acid  be  present,  by  means  of  acetate  of  lead  ; the  solution,  before 
this  salt  is  added  to  it,  should  be  neutralized  by  ammonia,  and 
then  acidulated  freely  with  acetic  acid  » the  precipitate  (PbHPO^) 
should  be  well  washed  and  ignited,  by  which  means  it  is  rendered 
anhydrous  ; 100  parts  of  the  ignited  residue  represent  23*65  of 
(PjOJ.  Chancel  has  lately  shown  that  the  acid  solution  of 
nitrate  of  bismuth  furnishes  an  admirable  method  of  separating 
phosphoric  acid  from  many  metals,  such  as  iron,  calcium,  and 
aluminum,  which  form  phosphates  soluble  only  in  acidulated 
liquids.  Care  is  requisite  to  remove  any  chlorine,  or  sulphuric 
acid  from  the  liquid,  before  adding  the  solution  of  bismuth,  which 
is  prepared  by  dissolving  1 part  of  the  crystallized  nitrate  in  4 
parts  of  nitric  acid  of  sp.  gr.  1*36,  adding  30  parts  of  water,  then 
boiling,  and  filtering  if  necessary.  In  separating  the  ortho- 
phosphate of  bismuth  by  this  reagent,  the  liquid  must  be  boiled, 
and  the  precipitate  well  washed  with  boiling  water  and  carefully 
dried  : 100  parts  of  the  phosphate  of  bismuth  (BiPOJ  correspond 
to  23*28  of  phosphoric  anhydride  (P2O5).  With  ferric  salts 
phosphoric  acid  forms  an  insoluble  buff-coloured  precipitate 
(PePO^,  2 H^O),  which  is  also  sometimes  employed  to  estimate  the 
quantity  of  phosphoric  acid  in  a solution. 

(449)  PyrojpliosjplioriG  Acid  (H.P^O,  or  2 HO,P05). — When 
rhombic  phosphate  of  sodium  (Na^ITPO^,  12  H2O)  is  exposed  to 
heat,  it  melts  in  its  water  of  crystallization ; and  by  continuing 
to  apply  to  it  a temperature  not  exceeding  300°,  it  may  be 
reduced  to  a hard,  white,  saline  mass,  which  may  be  redissolved 
in  water  with  all  its  former  properties.  The  dry  mass  consists  of 
Na2lIP04.  If,  however,  it  be  heated  to  redness  before  redissolv- 
ing, two  atoms  of  the  salt  coalesce  and  a new  salt  is  formed;  1 
atom  of  water  is  expelled;  2 Na2lIPO,  becoming  Na4P20,-(-Il20 ; 
on  redissolving  the  residue  in  water  and  evaporating  the  solution, 
the  liquid  no  longer  yields  rhombic  crystals,  but  furnishes  acicular 
crystals,  composed  of*  Na4P20„  10  H2O ; and  the  solution,  instead 
of  yielding  a yellow  precipitate  with  nitrate  of  silver,  now  gives 
a white  one,  consisting  of  Ag4P20,.  In  this  case,  the  solution,  if 
neutral  to  litmus  before  intermixture  with  the  silver  salt,  remains 
neutral  afterwards,  because  no  free  acid  is  liberated : — 

4 AgN03  + Na,P2e,  = 4 NaNe3  -b  Ag,P2e,. 

* The  arseniates  {^ve  precipitates  both  with  ammoniacal  salts  of  magnesium  and 
molybdic  acid,  similar  to  those  furnished  by  the  phosphates. 


196 


PHOSPHATES. 


a solution  of  acetate  of  lead  the  pyrophosphate  of  sodium 
also  occasions  a white  precipitate,  the  composition  of  which  is 
represented  by  the  formula  Fb.PoO, : and  if  the  lead  salt  be  sus- 
pended in  water,  and  decomposed  with  sulphuretted  hydrogen,  it 
yields  a solution  of  pp’ophosphoric  acid  (H\P20,).  The  excess 
of  sulphuretted  hydi’ogen  must  be  got  rid  of  by  exposure  to  the 
air  (not  by  heat,  otherwise  the  tribasic  acid  is  formed  by  the 
assimilation  of  water ; IpO  + H^P20,  = 2 HgPO^),  and  the  acid 
may  be  obtained  in  crystals  by  evaporation  in  vacuo  over  sul- 
phuric acid.  This  phosphate  of  sodium,  from  the  mode  in  which 
it  is  obtained,  is  often  termed  (from  c-Jp,  fire)  lyyrojphosjpJiate  of 
sodium,  and  the  corresponding  salts  of  the  acid,  pyrajyhosjphates. 
Xo  solid  pyrophosphate  of  potassium  or  of  ammonium  can  be 
obtained  ; these  salts  are  stable  while  in  solution,  but  on  evapora- 
tion they  become  converted  into  tribasic  phosphates  by  the  assimi- 
lation of  water  (Graham).  Two  classes  of  pyrophosphates  may 
be  procured ; one  with  4 atoms  of  a fixed  basyl,  with  the  foiumda 
M^PgO.  like  the  ordinary  pyrophosphate  of  sodium  (ISTa^P^O,,  10 
H^O) ; the  other  containing  two  atoms  of  hydi’ogen  and  two  of 
uniequivalent  metal  (M2H2P2O,),  corresponding  in  composition 
to  the  acid  pyrophosphate  of  sodium  (Xa.H^PoO,). 

Xeutral  solutions  of  the  pyi'ophosphates  also  give  in  solutions 
of  salts  of  calcium  and  barium  white  precipitates,  which  are  the 
pyrophosphates  of  these  metals ; salts  of  nickel  and  copper  give 
with  pyrophosphate  of  sodium  double  salts,  containing  2 atoms 
of  sodium  to  3 of  the  other  metal ; 2 Xa^PjO.  -|-  3 Gu''  2 XO3  = 
Gu'^Xa^  2 P^e,  + 6 XaX03. 

The  following  table  furnishes  a synoptic  view  of  some  of  the 
principal  phosphates,  metaphosphates,  and  pyrophosphates : — 


I.  Orthophosphates. 


iIsP04  ; ; MH.PO^ 


Subphosphate  of  sodium 

Rhombic  phospht.  of  sodium.  . . 
Acid  phosphate  of  sodium  . . . . 

Microcosmic  salt 

Basic  phosphate  of  calcium  - . . . 
Superphosphate  of  calcium  . . . 
Phosphate  of  magnesium  and  ^ 
ammonium  ) 

Ferric  phosphate 

Phosphate  of  lead 

Phosphate  of  bismuth  

Phosphate  of  silver  (yellow) . . . 


Xa.P04 . 12  H2O 

. . .XaoHP04 . 12  Hoe 

NaHoPOi  . HoO 

.XaH4XHPe4 . 4 HoO 

ea"3  2 pe4 

ea  'H4  2 pe4 

Mg''H4X.Pe4  . 6 HoO 

Fe'''Pe4  . 2 H-oO 

Pb"3  2 pe4 

Bi'"pe4 

Ag3Pe4 


IT.  Hetaphosphates.  HPO3. 


I 


Metaphosphate  of  sodium  NaPOs  ! 

Metaphosphate  of  lead Pb  ' 2 POa  j 

Metaphosphate  of  silver AgPOa 

III.  Pyrophosphates.  M4P2e7;  MM’sPoeT 

Pyrophosphate  of  sodium N’a4P2e7  . 10  HaO  j 

Pyrophosphate  of  lead Pb''2P2e7 

Pyrophosphate  of  copper  and  sodium.  .eu''3Na22  P2e7 
Pyrophosphate  of  silver Ag4P2eT  I 


3 NaOPOs  . 24  HO 

2 Xa0,H0,P05 . 24  HO 
XaO,  2 HO.PO5  . 2 HO 
XaO.H4HO,HO,P05 . 8 HO 

3 Cab.POs 
CaO,  2 HOpOs 

2 Mg0,H4X0,P05 . 12  HO 

FeoOsPOs  . 4 HO 

3 PbOpOs 
BiOsjPOs 

3 AgOpOs 


HaOpOs 

PbO.POa 

AgOpOa 


2 NaOpOs  . 10  HO 

2 PbOpOs 

3 CuOPaO,  2 POs 
2 AgOpOs 


METAPIIOSPIIORIC  ACID. 


197 


(450)  Metajjhosphoric  Acid  (HPOg). — If,  in  preparing  the 
rhombic  phosphate  of  sodium  (448),  two  eqnal  portions  of  phos- 
phoric acid  be  taken,  and  after  neutralizing  one  portion  with 
carbonate  of  sodium,  as  above  directed,  the  second  quantity  of 
acid  be  added  to  the  neutralized  solution,  a tribasic  phosphate  of 
sodium,  consisting  of  HaH^PO^,  will  be  obtained  on  evaporating 
the  liquid  to  dryness ; but  on  igniting  the  residue,  the  2 atoms 
of  hydrogen  will  be  expelled  in  the  form  of  water,  and  a fusible 
monobasic  phosphate,  or  metaphosphate ^ of  sodium  (HaPOg)  will 
remain  in  the  form  of  a transparent  glass.  This,  if  dissolved  in 
water,  gives  with  nitrate  of  silver  a gelatinous  white  precipitate 
(AgPOg)  dilferent  in  appearance  and  composition  from  either  of 
the  former  phosphates  of  silver ; it  is  soluble  in  excess  of  the 
sodium  salt.  With  acetate  of  lead  a white  precipitate  also  is 
formed  (Pb  2 POg) : it  is  fusible  in  boiling  water,  and  when 
decomposed  with  sulphuretted  hydrogen  it  yields  the  correspond- 
ing acid  (HPOg),  which  is  distinguished  from  the  other  hydrates 
by  its  power  of  coagulating  the  albumen  of  white  of  egg.  It 
also  gives  white  precipitates  with  chloride  of  barium  and  ni- 
trate of  silver.  Acetic  acid  does  not  coagulate  albumen,  neither 
does  a solution  of  metaphosphate  of  sodium ; but  if  the  two  solu- 
tions be  mixed,  the  acetic  acid  liberates  metaphosphoric  acid,  and 
the  albumen  becomes  coagulated.  Tribasic  phosphoric  acid  by 
prolonged  heating  to  redness  loses  water,  the  glassy  residue  being 
converted  almost  entirely  into  metaphosphoric  acid.  Metaphos- 
phate of  sodium  is  capable  of  combining  with  water  of  crystal- 
lization, and  retains  1 atom  if  dried  at  212° : this  water  is  not 
basic,  for  on  again  dissolving  the  salt,  it  gives  the  usual  reactions 
of  the  metaphosphates.  If,  however,  the  salt  be  heated  to  300°, 
it  does  not  lose  weight,  but  becomes  converted  into  the  acid  pyro- 
phosphate of  sodium,  the  water  by  the  application  of  heat  having 
changed  its  function  in  the  salt,  its  hydrogen  having  now  become 
basic  (Graham) : — 

Hydrated  metaphosphate  Pyropliosphate  of  sodium  and 

ofso.ium.  hydrogen. 

. ^ ^ . ^ s 

2 HaP03,H20  becomes  HaJIgP^O,. 

This  change  of  properties  in  the  salt,  without  any  change  in  the 
proportions  of  its  components,  here  admits  of  a satisfactory  ex- 
])lanation ; and  it  is  a striking  and  instructive  illustration  of  the 
facility  with  which  chemical  compounds,  by  a change  in  molecular 
constitution,  may  sometimes  give  rise  to  substances  the  properties 
of  which  may  be  very  different,  though  the  results  of  their  analysis 
in  100  parts  may  numerically  coincide. 

Metaphosphate  of  sodium  forms  with  salts  of  barium  a white 
insoluble  metaphosphate  of  barium  (Ha  2 POg) ; but  this  precipi- 
tate when  boiled  becomes  gradually  dissolved,  assimilating  2 atoms 
of  water,  and  becoming  converted  into  the  acid  tribasic  phosphate 
of  barium  (HaII,2  PO^).  The  compounds  of  this  modification  of 
phosphoric  acid  are  monobasic.  Their  solutions  redden  litmus 


198 


MODIFICATIONS  OF  METAPIIOSPDOKIC  ACID. 


The  aqueous  solution  -of  metapliosphoric  acid,  when  boiled, 
becomes  converted  into  the  ordinary  tribasic  acid,  consequently  it 
cannot  be  concentrated  by  the  action  of  heat,  HPOg  + H^O  be- 
coming : but  the  solution  may  be  preserved  at  common 

temperatures  without  change. 

Fleitmann  and  Henneberg  {LieMg’s  Ann.  Ixv.  321)  have  de- 
scribed two  classes  of  salts  which  are  probably  anhydro-phosphates. 
By  melting  pyi'ophosphate  and  metaphosphate  of  sodium  together, 
in  the  proportion  of  1 atom  of  pyrophosphate  and  2 of  metaphos- 
phate, they  obtained  a salt,  «,  consisting  of  2 Xa3P04,P205;  and 
by  fusing  8 atoms  of  the  metaphosphate  of  sodium  with  1 atom 
of  the  pyrophosphate,  a definite  sodium  salt,  h,  was  obtained, 
which  consisted  of  1 XagPO^,  3 PoO. ; both  these  salts  are  very 
unstable,  and  in  solution  pass  quickly  into  a mixture  of  pyrophos- 
phate and  metaphosphate.  Definite  salts  of  silver  and  of  magne- 
sium corresponding  to  these  compounds  were  obtained. 

Odling  proposes  to  represent  these  various  classes  of  salts  as 
follows,  comparing  quantities  of  each  which  contain  equal  amounts 
of  metallic  basyl,  the  quantity  of  phosphoric  anhydride  suc- 
cessively increasing  in  each  series : — 

Orthophosphates 6 M^O,  2 P2O5  or  1 MgPO^ 

Pyi'ophosphates 6 M.O,  3 PaO^  3 M^P^O, 

Fleitmann  and  Henneberg,  a 6 1 PjO^  2 MgP^Oij 

Do.  do.  I 6 M'A  5 PA  M,3P,oe3. 

Metaphosphates 6 M^O,  6 PsO-^  12  MPO3 

and  he  represents  the  pyrophosphates,  as  well  as  the  salts  dis- 
covered by  Fleitmann  and  Henneberg,  as  compounds  of  the 
orthophosphates,  with  different  proportions  of  a metaphosphate. 
A p^Tophosphate,  for  example,  may  be  represented  thus : — • 
Ha3P0^,AaP03=:AaA^7  j Fleitmann  and  Henneberg’s  salt  a 
being  XagPO,,  3 AaP03=XagP  As?  the  salt  h being  Xa3P04, 
9 XaPO^^Xa^^PjA^. 

Modifications  ofi  Metapliosphoric  Acid. — If  the  ordinary  or 
glassy  metaphosphate  of  sodium  be  fused  and  allowed  to  cool  very 
slowly  it  furnishes  a beautiful  crystalline  mass,  which,  when  dis- 
solved in  a small  quantity  of  hot  water,  forms  a liquid  which 
divides  into  two  strata ; the  smaller  of  these  contains  unchanged 
metaphosphate  of  sodiiun  ; but  the  bulk  of  the  liquid  is  a solution 
of  the  crystalline  salt,  which  may  be  obtained  on  evaporation  in 
oblique  rhombic  prisms  (6  XaP03,12  H^O) : the  solution  of  this 
salt  is  neutral.,  and  has  a cooling  saline  taste,  whilst  that  of  the 
ordinary  or  vitreous  metaphospTiate  is  insipid.  The  crystalline 
salt,  by  boiling,  is  rapidly  converted  into  the  acid  orthophosphate 
(XaH^POJ;  a beautifully  crystallized  silver  salt,  consisting  of 
6 AgP03,  2 HjO,  may  be  obtained  from  the  crystalline  sodium 
salt  "by  precipitation,  and  a similar  lead  salt  (3  Pb  2 P03,3  H^O) 
may  also  be  procured. 

Maddrell  {Proceed.  Chein.  Soc.,  1847,  p.  273)  has  described  a 
series  of  monobasic  metaphosphates  which  are  anhydrous,  crystal- 
line, and  insoluble  in  water,  but  soluble  in  oil  of  vitriol.  They 


PHOSPHOKOUS  ACID PHOSPHITES. 


199 


were  formed  by  beating  a solution  of  the  sulphate  or  nitrate  of 
the  metal  with  an  excess  of  phosphoric  acid,  until  the  sulphuric 
or  other  acid  of  the  salt  was  expelled.  Salts  of  potassium,  sodium, 
aluminum,  copper,  nickel,  and  others  were  thus  procured.  The 
sodium  salt,  if  prepared  with  phosphoric  acid  which  contains 
magnesium  or  any  metal  isomorphous  with  magnesium,  forms  an 
insoluble  double  metaphosphate : the  magnesium  double  salt  is 
crystalline,  and  consists  of  3 Mg  2 PO3,  2 iN^aPOg.  These  dif- 
ferent varieties  of  metaphosphates  are  supposed  to  be  due  to  the 
existence  of  several  polymeric  varieties  of  metaphosphoric  acid. 

(451)  Phosphorous  Anhydride  (P2O3)  may  be  procured  by 
burning  phosphorus  in  a limited  current  of  drj  air.  A white, 
volatile,  deliquescent,  inflammable  powder,  destitute  of  crystalline 
structure,  is  thus  obtained,  often  mixed  with  small  quantities  of 
oxide  of  phosphorus  and  phosphoric  anhydride. 

Phosphorous  acid  (H2PHO3)  may  be  obtained  in  solution  by 
transmitting  a stream  of  chlorine  very  slowly  through  a deep 
layer  of  phosphorus  melted  under  water,  so  that  each  bubble  of 
gas  shall  be  completely  absorbed  by  the  phosphorus ; terchloride 
of  phosphorus  (PCI3)  is  formed,  and  is  immediately  decomposed 
by  the  water  into  hydrochloric  and  phosphorous  acids  ; PClg  + B 
H20=H2PH03-f  3 HCl.  If  the  acid  liquid  be  concentrated  by 
a heat  not  exceeding  400°,  hydrochloric  acid  is  expelled,  and  the 
acid  is  obtained  in  deliquescent  rectangular  prisms.  When  ex- 
posed to  the  air  it  gradually  absorbs  oxygen  ; and  by  a high  tem- 
perature it  is  decomposed  into  phosphoric  acid  and  phosphuretted 
hydrogen  (4H2PH03  = 3 H3PO4  + H3P).  It  is  also  furnished  in 
a less  pure  form,  by  the  slow  combustion  Avhich  occurs  when 
phosphorus  is  left  exposed  to  the  action  of  the  atmosphere ; this 
may  be  safely  effected  by  placing  sticks  of  phosphorus  separately 
in  tubes  open  at  both  ends,  the  lower  aperture  of  the  tube  being  a 
little  contracted  so  as  to  prevent  the  phosphorus  from  falling  out ; 
a number  of  these  tubes  are  then  placed  in  a funnel,  and  the  dense 
acid  liquid  which  is  gradually  formed  drains  into  a vessel  placed 
for  its  reception.  In  this  process  phosphorous  acid  is  first  pro- 
duced ; the  acid  being  deliquescent  attracts  moisture  from  the 
air,  and  then,  by  gradually  absorbing  oxygen,  it  forms  phosphoric 
acid.  The  oxidation  never  proceeds  so  far  as  to  convert  the  whole 
into  phosphoric  acid  ; the  liquid  therefore  contains  a mixture  of 
phosphorous  and  phosphoric  acids,  which  was  at  one  time  supposed 
to  be  a peculiar  oxide  of  phosphorus,  and  was  "iQYwiQd  phosphatic 
acid. 

Phosphites. — Phosphorous  acid  is  dibasic,  and  forms  two  class- 
es of  salts,  the  general  formula  of  its  normal  salts  being  M^PIlO-j, 
and  that  of  the  acid  phosphites  is  MIIPlIOj.  Keiitral  phosphite 
of  sodium,  for  instance,  consists  of  IIa2PII03,  5 II^O ; when 
heated  to  572°,  the  5 atoms  of  water  are  expelled.  The  acid 
phosphite  of  barium,  dried  at  212°,  consists  of  (Balia  2 PIIO3). 
The  acid  phosphites  when  heated  emit  hydrogen  gas,  whilst  a 
metaphosphate  remains  behind;  thus  (Ball,  2 PIIO3)  becomes 
Ba  2 PO,  -f-  2 II3.  The  normal  phosphites  when  heated  also  emit 


200 


HYPOPnOSPIIITES. 


phosplinretted  hydrogen  ; for  instance,  in  the  case  of  phosphite  of 
lead,  5 PhPHOg  yield  Pbg  2 PO,  + Ph2P20,  + H3P  + H2.  Free 
phosphorons  acid  does  not  immediately  reduce  permanganate  of 
potassium,  unless  heated  with  it ; a reaction  which  distinguishes 
it  from  hypophosphorous  acid,  which,  even  in  the  cold,  rapidly  dis- 
charges the  colour  of  the  permanganate  in  acid  solutions.  The 
normal  phosphites  of  the  alkali-metals  are  freely  soluble,  most 
others  but  sparingly  so : amongst  them  the  phosphite  of  lead  is 
the  least  soluble  ; it  is  also  insoluble  in  acetic  acid.  With  a solu- 
tion of  corrosive  sublimate  (p[gCl2),  acidulated  with  acetic  acid, 
the  phosphites  give  a white  precipitate  of  calomel,  the  formation 
of  which  is  hastened  by  heating  the  liquid.  Another  characteris- 
tic reaction  is  the  reduction  of  sulphurous  acid  by  a solution  of 
the  phosphites,  with  evolution  of  sulphuretted  hydrogen,  attended 
by  simultaneous  precipitation  of  sulphur,  owing  to  the  action  of 
the  sulphurous  acid  on  the  sulphuretted  hydrogen  : — 

3 H2PH03-bH2Se3=3  H3Pe,-f  H^S. 

(452)  Hypophosphorous  Aero  (HPH^O^). — This  compound 
was  formerly  considered  to  be  an  acid  of  phosphorus  with  a still 
smaller  quantity  of  oxygen  than  the  preceding,  but  its  anhydride 
has  never  been  obtained.  It  is  produced  whenever  phosphorus 
is  boiled  with  a solution  of  caustic  potash  or  soda,  or  with  a 
hydrate  of  one  of  the  alkaline  earths.  It  may  be  procured  in 
combination,  by  Pose’s  method  of  boiling  phosphorus  with  hydrate 
of  baryta  in  water;  phosplinretted  hydrogen  escapes,  and  on 
evaporation  a barium  salt  is  obtained,  composed  of  Ba  2 PII202, 
owing  to  the  following  decomposition:  3 (Ba0,H20)-f-2  P^-f-B 
1120= 3 (Ba  2 PIl202)  + 2 H3P ; and  on  adding  sulphuric  acid 
cautiously,  pure  hypophosphorous  acid  is  obtained  in  solution, 
whilst  the  barium  is  separated  as  sulphate.  The  hypophosphite 
of  barium  may  also  be  prepared  by  heating  phosphorus  with  a 
solution  of  sulphide  of  barium,  when  free  hydrogen  with  phos- 
phuretted  and  sulphuretted  hydrogen  escape  ; the  last  traces  of 
sulphide  of  barium  are  removed  by  the  addition  of  a little  sul- 
phate of  lead.  Hypophosphorous  acid  forms  an  uncry stalliz able 
syrup,  which  has  a sour,  bitterish  taste  ; its  acid  pro^ierties  are 
but  feebly  marked,  and  its  solution  gradually  absorbs  oxygen 
from  the  air.  When  heated,  it  first  loses  water  ; and  by  a stronger 
heat  is  decomposed,  emitting  phosplinretted  hydrogen,  whilst 
phosphoric  acid  is  set  free ; 2 HPH2O2  becoming  H3PO4  -f  H3P. 
Owing  to  the  partial  decomposition  of  the  phosplinretted  hydro- 
gen, a little  phosphorus  is  generally  deposited  at  the  same  time, 
and  a corresponding  quantity  of  hydrogen  is  liberated. 

Hypophosphites. — The  researches  of  Dulong,  of  Bose,  and  of 
Wurtz  have  shown  that  the  hypophosphites  are  monobasic,  con- 
sequently the  acid  forms  but  a single  class  of  salts,  of  which  the 
normal  formula  is  MPH202-  Hypophosphite  of  sodium,  for  ex- 
ample, consists  of  HaPH202 ; that  of  lead  may  be  represented  as 
Pb  2 PH2O2.  They  correspond,  therefore,  to  the  monobasic  phos- 
phates ; but  2 atoms  of  hydrogen  have  taken  the  place  of  1 atom 


niOSPHUKETTED  HYDROGEN  GAS. 


201 


of  oxygen  in  the  phosphoric  acid.  The  hypophosphites  are  all 
soluble  in  water ; many  of  them  crystallize  easily,  by  spontaneous 
evaporation  ; the  crystallized  salts  may  be  preserved  unchanged, 
but  their  solutions,  when  evaporated  at  a high  temperature,  are 
gradually  converted  into  phosphites  by  absorption  of  oxygen. 
Like  phosphorous  acid  they  reduce  gold  and  silver  from  their 
salts.  The  hypophosphites  of  the  alkaline  metals  contain  no 
water  of  crystallization  ; they  are  deliquescent,  and  also  soluble  in 
alcohol.^  The  hypophosphite  of  calcium  (Oa  2 requires 

about  6 parts  of  cold  water  for  solution,  and  is  scarcely  more 
soluble  in  boiling  water.  Each  atom  of  the  barium  salt  retains 
an  atom  of  water  when  crystallized  at  ordinary  temperatures, 
but  if  crystallized  from  a boiling  solution  is  deposited  in  an- 
liydrous  tables  (Ba  2 PH2O2).  The  hypophosphite  of  magnesium 
(Mg  2 PLl202,6  H^O)  crystallizes  in  brilliant,  regular,  octohedra, 
which  are  efflorescent.  The  hypophosphites  of  nickel,  cobalt,  and 
iron,  also  retain  6 ; those  of  zinc  and  manganese  retain  but 

1 atom  of  water  of  crystallization,  which  they  lose  at  300°. 

Hypophosphorous  acid  is  distinguished  from  phosphorous  acid 
by  a remarkable  reaction  with  the  salts  of  copper ; if  to  an  excess 
of  free  hypophosphorous  acid  a solution  of  sulphate  of  copper  be 
added,  and  the  liquid  be  warmed  to  about  130°,  a solid  insoluble 
hydride  of  copper  (OuH)  is  precipitated.  On  raising  the  liquid 
which  contains  the  precipitate,  to  the  boiling-point,  this  hydidde 
is  decomposed  into  hydrogen  gas  and  metallic  copper. 

(453)  OxroE  OF  Phosphorus  (P4O). — A still  lower  degree  of 
oxidation  of  phosphorus  exists,  which  possesses  neither  acid  nor 
alkaline  properties.  It  is  always  formed  in  small  quantity  when 
phosphorus  is  burned  in  air,  and  is  one  of  the  constituents  of  the 
yellow  or  red  residue  after  the  combustion  has  terminated.  It  is 
not,  however,  a compound  of  any  importance.  Oxide  of  phos- 
phorus has  neither  smell  nor  taste,  and  is  quite  insoluble  in 
water. 

(454)  Phosphides  of  Hydrogen. — Hone  of  the  compounds  of 
phosphorus  with  hydrogen  is  possessed  of  acid  characters : these 
compounds  are  three  in  number  : viz.  HgP,  H^P,  and  HP^.  The 
first  is  gaseous,  the  second  liquid,  and  the  third  solid,  at  ordinary 
temperatures. 

Phosphnretted  Hydrogen  Gas : (HgP  = 34) ; Theoretic  Sp.  Gr. 
1T75  ; Observed^  1T85  ; Atomic  and  Mol.  Vol.  | | |. — Phosphu- 
retted  hydrogen  is  a highly  inflammable  colourless  gas,  with  a 
fVjetid  alliaceous  odour,  liquefiable  under  pressure  ; it  is  slightly 
soluble  in  water ; when  transmitted  through  solutions  of  certain 
metallic  salts  such  as  those  of  lead,  copper,  or  mercury,  it  is 
absorbed  and  decomposed ; phosphides  of  the  metals  are  produced 
and  are  precipitated.  Those  of  lead  and  copper  are  black,  that  of 
mercury  is  yellow.  Solutions  of  the  salts  of  gold  and  silver  are 
reduced  to  the  metallic  state,  and  phosphoric  acid  is  found  in 

* Hypophosphite  of  sodiura,  wliich  is  now  prepared  largely  for  medicinal  pur- 
poses, sometimes  explodes  spontaneously  during  the  evaporatiou  of  its  aqueous 
solution. 


202 


PHOSPHUKETTED  HYDEOGEN’ PEEPAEATIOX. 


solution.  When  the  gas  is  piu'e  it  is  wholly  absorbed  by  a solution 
of  chloride  of  lime.  It  is  decomposed  by  sulphurous  acid  as  well 
as  by  chlorine,  bromine,  and  iodine.  A mixture  of  the  gas  with 
air  or  with  oxygen  explodes  at  a temperature  of  300°,  or  some- 
times even  at  common  temperatures,  if  the  pressure  be  suddenly 
diminished.  In  tliis  gas  1 volume  of  the  vapour  of  phosphorus 
and  6 volumes  of  hydrogen  are  condensed  into  the  space  of  4 vo- 
lumes. Its  composition  may  therefore  be  thus  represented  : — 

Bv  weight  By  voL  Sp.  gr. 

Phosphorus P = 31  or  91*18  0 5 or  0*25  = 1*071 

Hydrogen 03=  3 8*82  3 0 1*5  = 0*104 

34  10000  2-0  1-0  = 1-I'i5 

The  combining  volume  of  phosphuretted  hydi’ogen  is  the  same 
as  that  of  ammonia,  to  which  it  is  analogous  in  composition  ; but 

it  is  without  action  upon  either  red  or  blue  litmus.  Some  indi- 

cation of  a basic  character  is,  however,  shown  by  it,  for  it  com- 
bines with  certain  of  the  acids  in  definite  proportions.  For 
example,  its  compound  with  hydriodic  acid  (HjP,!!!)  is  formed 
by  the  union  of  equal  volumes  of  the  two  ^ases,  which  in  act  of 
combination  do  not  undergo  condensation,  lor  its  vapour,  accord- 
ing to  Bineau,  has  a density  of  2*77 ; it  crystallizes  in  cubes, 
which  fuse  at  a moderate  heat,  and  if  air  be  excluded  it  may  be 
sublimed  without  alteration.  These  crystals  are  deliquescent,  and 
are  decomposed  by  water  into  hydriodic  acid  and  phosphuretted 
hydi*ogen  gas.  This  compound  is  easily  prepared  by  introducing 
into  a small  retort  127  parts  of  dry  iodine  ground  up  with  pow- 
dered glass,  and  31  parts  of  phosphorus  in  small  fragments,  then 
adding  20  parts  of  water ; the  vapours  which  come  off  consist  of 
the  compound  mixed  with  an  excess  of  hydriodic  acid ; the  hydri- 
odate  of  phosphuretted  hydrogen  is  condensed  in  crystals  in  the 
neck  of  the  retort  if  it  be  kept  cool.  A similar  compound  may 
be  obtained  with  hydrobromic  acid.  Hofmann  and  Cahours  have 
shown  that  by  displacing  the  hydi’ogen  in  gaseous  phosphide 
of  hydrogen,  by  ethyl  and  other  analogous  hydrocarbons,  com- 
pounds may  be  obtained  which  neutralize  acids,  and  are  power- 
fully basic. 

Phosphuretted  hydrogen  combines  with  the  perchloridee  of 
many  of  the  metals,  such  as  those  of  tin,  titanium,  antimony,  and 
iron.  These  compounds  are  decomposed  by  water  with  escape  of 
phosphuretted  hydrogen  gas. 

Preparation. — Phosphuretted  hydrogen  gas  may  be  obtained 
in  a state  of  purity  by  the  decomposition  of  phosphorous  acid 
by  heat ; 4 H^PHO,  yielding  3 H3PO,  + H^P ; hvpophospho- 
rous  acid  gives  an  analogous  result,  2 HPH3O,  becoming  HjPO^ 
+ H3P. 

Phosphuretted  hydrogen,  however,  is  generally  prepared  by 
heating  fragments  of  phosphorus  with  a strong  solution  of  hydrate 
of  potash,  or  with  cream  of  lime  ; hypophosphite  of  the  base  is 
formed,  with  extrication  of  phosphuretted  hydrogen  ; P4-I-3  H,0 


PHOSPHIDES  OF  hydpogeh. 


203 


+ 3 KHO  becoming  3 KPH^Oa  + Hj-  When  potash  is  used,  free 
liydrogen  is  also  evolved,  owing  to  the  gradual  decomposition  of 
the  hypophosphite  when  boiled  with  excess  of  free  alkali,  and  the 
formation  of  phosphate.  The  gas  so  obtained  has  the  remarkable 
property  of  taking  fire  spontaneously  in  atmospheric  air  or  in 
oxygen  gas:  if  allowed  to  escape  into  the  air  in  bubbles,  each 
bubble  as  it  breaks  produces  a beautiful  white  wreath  of  phosphoric 
anhydride,  composed  of  a number  of  ringlets  revolving  in  vertical 
planes  around  the  axis  of  the  wreath  itself,  as  it  ascends  ; thus 
tracing  before  the  eye,  with  admirable  distinctness,  the  rapid 
gyratory  movements  communicated  to  the  air  contained  in  a 
bubble,  when  it  is  allowed  to  burst  upon  the  surface  of  a still 
sheet  of  water.  If  the  bubbles  be  allowed  to  arise  into  a jar  of 
oxygen,  a brilliant  flash  of  light,  attended  with  a slight  concussion, 
accompanies  the  bursting  of  each  bubble.  Owing  to  the  spon- 
taneous inflammation  of  the  gas  it  should  be  made  in  small  vessels 
containing  but  little  atmospheric  air.  Graham  has  shown  that 
the  addition  of  small  quantities  of  the  vapour  of  some  inflammable 
bodies,  such  as  ether,  naphtha,  and  oil  of  tur^^entine,  destroys  this 
self-lighting  power ; and  that  porous  bodies,  such  as  charcoal,  also 
remove  it.  On  the  other  hand,  the  gas  obtained  from  phospho- 
rous acid  is  not  self-lighting,  but  the  addition  of  so  small  a quantity 
as  xo,oT7  bulk  of  the  vapour  of  nitrous  anhydride  confers 

this  property  upon  it. 

(155)  Liquid  Phosphide  of  Hydrogen  : H2P,  or  ? — The 

singular  property  which  phosphuretted  hydrogen  possesses,  in 
certain  cases,  01  igniting  spontaneously  when  mixed  with  free 
oxygen  long  remained  without  explanation ; as  a careful  analysis 
indicated  little  or  no  difference  in  composition  between  the  self- 
lighting  gas  and  the  other  variety,  which  does  not  possess  this 
property.  The  true  cause  of  the  phenomenon  was,  however, 
traced  a few  years  ago  by  P.  Thenard,  to  the  presence  of  a minute 
quantity  of  the  vapour  of  another  phosphide  of  hydrogen 
which  takes  fire  the  instant  that  uncombined  oxygen  is  presented 
to  it  {Ann.  de  Chimie^  III.  xiv.  5).  This  compound  exists  at  or- 
dinary temperatures  as  a volatile  liquid,  which  by  exposure  to 
liglit  is  decomposed  into  a yellow,  solid,  and  but  slightly  inflamma- 
ble phos])liide  (IIP2),  and  into  the  non-self-lighting  gas  (II3P) ; for 
II,oP5=IIP2-f-3  II3P.  It  had  long  been  remarked,  although  an- 
alysis showed  no  difference  between  the  self-lighting  and  the  com- 
mon gas,  that  when  the  former  was  exposed  to  sunlight  for  a few 
hours,  a solid  yellow  compound  was  deposited  in  small  quantity 
upon  the  sides  of  the  vessel,  whilst  the  gas  lost  its  self-lighting 
power  ; and  that  this  power  was  also  destroyed  by  exposing  the 
gas  to  a great  degree  of  cold.  This  effect  is  evidently  due,  in  the 
case  of  the  exposure  to  sunlight,  to  decomposition  of  the  inflamma- 
ble compound,  and  in  the  case  of  the  application  of  cold,  to  its 
condensation  into  the  liquid  form. 

Liquid  pliosphide  of  hydrogen  may  be  prepared  by  conduct- 
ing the  gas  which  is  disengaged  by  the  action  of  water  upon 
phosphide  of  calcium  (OaP),  through  a bent  tube  immersed  in 


CHLOEIDES  OF  PHOSPHOEFS. 


20-i 

a freezing-mixture  of  ice  and  salt ; a colourless  liquid  of  higli  re- 
fracting power  is  thus  condensed.  It  takes  fire  the  instant  that 
it  comes  into  contact  with  air,  and  burns  with  the  intense  white 
light  of  phosphorus.  Solar  liglit  quickly  decomposes  it  into  the 
solid  phosphide  (IIP2)  and  into  the  gaseous  phosphuretted  hydro- 
gen. If  a little  of  the  vapour  of  this  liquid  be  allowed  to  diffuse 
itself  through  hydrogen,  carbonic  oxide,  or  any  other  combustible 
gas,  it  confers  upon  it  the  property  of  taking  fire  spontaneously 
when  mixed  with  atmospheric  air  or  with  oxygen. 

(156)  Solid  Phosphide  of  Hydrogen  (IIP2). — The  liquid  phos- 
phide is  immediately  decomposed  by  hydrochloric  acid,  and  the 
solid  yellow  phosphide  of  hydrogen  is  ibrmed.  This  substance  is 
readily  prepared  by  treating  phosphide  of  calcium  (649)  with  hot 
hydi’ochloric  acid.  It  is  insoluble  in  water  and  in  alcohol.  AVIien 
heated  with  a solution  of  hydi’ate  of  potash  the  compound  is  dis- 
solved, and  phosphuretted  hydrogen  gas  is  liberated.  There  ap- 
pear to  be  two  varieties  of  the  solid  phosphide,  one  of  a yellow, 
the  other  of  a green  colour ; they  do  not  differ  fr-om  each  other  in 
composition.  The  solid  yellow  hydride  of  phosphorus  takes  fire 
at  about  300°. 

(457)  Chlorides  of  Phosphorus. — With  chlorine  phosphorus 
forms  two  compounds,  a terchloride,  PCI3,  corresponding  to  phos- 
phorous anhydride,  and  a pentachloride,  PCL,  which  corresponds 
to  phosphoric  anhydride.  So  strong  is  the  chemical  attraction 
between  these  elements,  that  in  an  atmosphere  of  chlorine,  phos- 
phorus immediately  takes  fire.  The  following  table  shows  the 
composition  of  these  chlorides,  and  of  two  of  their  derivatives  : — 

In  100  parts. 


Terchloride  of  phosphorus PCI3  = 

Pentachloride  of  ditto PCI5  = 

Oxychloride PCI3O  = 

Sulphochloride PCI3S  = 


137*5 

208*5 

Phospb.  1 Chlorine. 
22.54  1 77*46 
14-86  85*14  , 

Oxygen. 

1 

Sulphur. 

153-5 

20*19 

69-38 

10*43 

1 

169*5  ! 

18*28  I 

62*84  1 

18*88 

(458)  TeiHloydde  of  Phospho7'iis(FQ\^=lZi’o)  : Sp.  Gr.  of  Va- 
pour^ Theoretic^  4*750  ; Ohserred^  4*875  ; of  Liquid,  1*616  at  32°  ; 
Boiling-pt.  173°*4 ; Mol.  Yol.  | | |. — This  liquid  is  sometimes 
prepared  by  causing  the  vapour  of  phosphorus  to  pass  over  corro- 
sive sublimate  placed  in  a long  tube,  and  gently  heated ; but  it 
may  be  obtained  more  easily  and  abundantly  by  transmitting  a 
gentle  stream  of  perfectly  dry  chlorine  gas  through  dry  and  melt- 
ed phosphorus  contained  in  a retort ; the  operation  may  be  con- 
ducted in  the  same  manner  as  in  the  preparation  of  the  chloride 
of  sulphur  (fig.  309) ; the  chloride  distils  as  a very  volatile,  trans- 
parent, colourless,  fuming  liquid.  It  dissolves  phosphorus  freely, 
and  is  itself  soluble  in  benzol  and  in  bisulphide  of  carbon ; alco- 
hol and  ether  decompose  it  with  evolution  of  great  heat,  giving 
rise  to  various  new  compounds.  It  is  also  immediately  decompos- 
ed by  a large  excess  of  water,  and  forms  phosphorous  and  hydro- 
chloric acids;  PCl3-f3Il30,  yielding  H^PHOg-f  3 HCl.  Ter- 
chloride of  phosphorus  absorbs  chlorine  greedily,  and  is  converted 


SULPHOCHLOEIDE  OF  PHOSPHOKrS. 


205 


into  the  pentachloride ; at  a boiling  temperature  it  also  absorbs 
oxygen  and  furnishes  the  oxychloride. 

^59)  Pentachloride  or  Perchloinde  of  Phosphorus  (PCl^^: 
208'5) ; Theoretic  Sp.  Gr.  of  Vapour^  3’601 ; Observed^  at  572°, 

3 ‘654 ; Mol.  Yol.  j — j — |. — This  compound*  is  obtained  by  placing 


dry  phosphorus  in  a flask  provided  with  a stopcock,  exhausting 
the  air,  and  allowing  chlorine  to  enter  so  long  as  it  is  absorbed ; 
or  it  may  be  formed  by  treating  terchloride  of  phosphorus  in 
a tall  glass  with  an  excess  of  chlorine.  Pentachloride  of  phos- 
phorus is  also  now  prepared  on  a considerable  scale  by  dis- 
solving phosphorus  in  bisulphide  of  carbon,  and  transmitting 
dried  chlorine  in  excess  through  the  solution  which  is  cooled  arti- 
ficially during  the  operation ; the  pentachloride  is  deposited  in 
crystals  from  the  solution  on  evaporation.  It  forms  a white  crys- 
talline solid,  which  volatilizes  below  212°  whilst  still  solid,  but  it 
may  be  fused  under  pressure.  In  the  flame  of  a lamp  it  burns, 
producing  chlorine  and  phosphoric  acid : with  ammonia  it  com- 
bines readily.  It  is  very  deliquescent,  and  by  a large  excess  of 
water  is  immediately  decomposed  into  phosphoric  and  hydro- 
chloric acids  ; PCl^-fd  H^O  forming  Il^PO^-hS  HCl. 

(460)  Oxychloride  of  Phosphorus  (PCl30= 153*5) ; Bp.  Gr.  of 
Liquid.,  1*7  ; qf  Vapour.,  5*29  ; Boiling-pt.  230°  ; Mol.  Yol.  | j |. 
— This  compound  is  formed  when  the  vapour  of  water  is  allowed 
to  mingle  slowly  with  that  of  the  pentachloride,  hydrochloric 
acid  and  oxychloride  of  phosphorus  being  the  result.  The  reac- 
tion is  as  follows : PCl^  -f-  Il20=:PCl30  + 2 IICl.  The  oxychloride 
is  a limpid,  volatile,  fuming  liquid,  which  is  decomposed  by  the 
further  addition  of  water  into  phosphoric  and  hydrochloric  acids. 

Oxychloride  of  phosphorus  may  be  obtained  with  facility  by 
Gerhardt’s  plan  of  distilling  1 part  of  crystallized  boracic  acid 
with  4|-  parts  of  pentachloride  of  pliosphorus,  when  the  follow- 
ing reaction  occurs  : 3 PCl^  + 2 (IIB0-3,Il30)  = 3 PCI3O  + 6 IICl  + 
B2O3.  The  oxychloride  is  readily  condensed,  whilst  hydrocliloric 
acid  passes  off  in  the  form  of  gas,  leaving  boracic  anhydride  in 
the  retort.  Crystallized  oxalic  acid  may  be  substituted  for  boracic 
acid  in  this  operation,  but  it  does  not  answer  quite  so  well. 
Tlie  oxychloride  may  also  be  prepared  by  heating  the  pentachlo- 
ride with  phosphoric  anliydride  ; 3 PCl5  4-P30^=5  PCI3O. 

Both  the  chlorides  and  the  oxychloride  of  phosphorus  liave 
been  extensively  used  in  the  preparation  of  various  organic  sub- 
stitution-products, particularly  the  oxychlorides  and  anhydrides 
of  the  organic  acids. 

(461)  Bulphochloride  of  Phosphorus  (PCljS^  169*5 ; Bp.  Gr. 
of  Liquid.,  1*631;  of  Vapour.,  5*878;  Mol.  Yol.  | | | ; Boiling- 

* The  vapour  volume  of  this  compound  is  anomalous.  Perchlorido  of  phosphorus 
may  be  supposed  to  be  formed  by  the  union  of  equal  volumes  of  chlorine,  and  the 
vapour  of  the  terchloride  (Cahours).  In  a large  number  of  cases  where  two  bodies 
combine  in  the  proportion  of  equal  volumes  of  their  components,  no  condensation 
occurs,  as  was  long  since  indicated  by  Gay-Lussac. 


206 


BROMIDES  Am)  IODIDES  OF  PIIOSPHOEES. 


pt.  25Y°)  is  a compound  corresponding  to  tlie  oxycliloride,  but 
containing  snlpbiir  instead  of  oxygen.  It  is  obtained  by  decom- 
posing pentacbloride  of  pbospborns  with  siilplniretted  hydrogen : 

yielding  PClgS-f  2 HCl.  It  may  be  procured  still 
more  easily  by  the  gradual  addition  of  powdered  sulphide  of  anti- 
mony to  the  pentachloride  of  phosphorus ; 3 PCl^  -|-  — 

3 PCI3S  + 2 SbClg.  Sulphochloride  of  phosphorus  is  a fuming, 
colourless  liquid,  wdiich,  if  heated  with  a solution  of  caustic  soda 
in  excess,  exchanges  its  chlorine  for  oxygen ; chloride  of  sodium 
is  formed,  and  a sidjphoxy -phosphate  of  sodium  may  be  obtained 
in  six-sided  tabular  crystals  which  contain  12  H^O.  The  compo- 
sition of  this  salt  is  analogous  to  that  of  the  tribasic  phosphate 
of  sodium,  but  the  two  are  not  isomorphous.  The  following 
equation  explains  the  changes  which  accompany  its  production 
(Wurtz) : — 

PCI3S  + 6 XaHO  = -f  3 iS^aCl  + 3 H,e. 

One  half  of  the  soda  is  decomposed,  imparting  its  oxygen  to  the 
sulphochloride,  from  which  it  receives  a corresponding  amount  of 
chlorine.  Corresponding  compounds  wnth  barium,  calcium,  and 
strontium  may  be  formed  by  double  decomposition  with  the 
sodium  salt ; they  are  white  and  insoluble. 

(462)  Bromides  of  Phosphorus. — A Terbromide  {Sp.  Gr.  at 
32°,  2 '925  ; Boiling-pt.  347° *5).  Pentabromide  and  Oxybromide 
of  phosphorus,  analogous  to  the  corresponding  compounds  with 
chlorine,  may  be  formed  by  similar  methods. 

(463)  Iodides  of  Phosphorus. — Two  iodides  of  j)hosphorus 
may  be  formed,  viz.,  a biniodide  and  a teriodide  (Corenwinder, 
Ann.  de  Chimie^  III.  xxx.  242).  The  Biniodide  (Pl2=:285)  may 
be  obtained  by  dissolving  1 part  (or  1 atom)  of  phosphorus  in  bi- 
sulphide of  carbon  and  adding  parts  (or  2 atoms)  of  iodine  : by 
cooling  the  mixture  artificially,  thin  fiexible  prismatic  crystals  of 
the  iodide  are  deposited,  of  a bright  orange  colour.  This  iodide 
melts  at  230°,  and  is  decomposed  by  water,  hydriodic  acid  being 
one  of  the  products. 

Teriodide  of  Phosphorus  (Pl3=412). — This  compound  may 
be  obtained  in  a manner  similar  to  the  last,  by  dissolving  1 part 
of  phosphorus  and  124  parts  of  iodine  in  bisulphide  of  carbon ; 
the  liquid  is  concentrated  by  evaporation,  and  on  cooling  it  by  a 
freezing  mixture,  dark  red  six-sided  plates  are  formed ; it  melts 
between  120°  and  130°,  and  on  cooling  crystallizes  in  fine  prisms. 
It  deliquesces  rapidly  when  exposed  to  the  air. 

Brodie  ((>.  J.  Chem.  Soc.  v.  289)  finds  that  iodine,  when 
heated  with  phosphorus  in  the  proportion  of  1 atom  of  iodine  to 
100  atoms  of  phosphorus,  converts  nearly  the  whole  of  the  phos- 
phorus into  the  red  variety  described  by  Schrotter.  lYhen  phos- 
phorus was  placed  in  a long  tube,  and  heated  till  it  just  melted, 
and  iodine  was  projected  gradually  into  the  phosphorus,  the  iodine 
was  dissolved,  colouring  the  phosphorus  slightly  red ; when  heated 
by  an  oil-bath  to  212°,  the  colour  became  deep  red;  and  between 
250°  and  266°,  a scarlet  powder  was  deposited  on  the  sides  of  the 


SULPHTOES  OF  PHOSPHORUS. 


207 


tube ; at  284°  tlie  mass  was  quite  solid,  and  on  raising  the  heat  to 
392°  F.,  a sharp  explosion  took  place : a sudden  evolution  of  heat 
occurred,  and  the  cork  which  closed  the  tube  was  blown  out  by 
the  vapour  of  phosphorus.  The  red  mass  may  be  distilled  in 
closed  tubes,  and  when  it  is  condensed  in  the  cooler  portions  of 
the  tubes  it  is  still  in  the  red  modification.  The  changes  which 
occur  in  the  process  are  supposed  to  be  the  following : first  the 
formation  of  biniodide  of  phosphorus ; next,  the  transformation  of 
this  iodide  by  heat  into  an  allotropic  iodide ; and  thirdly,  the  de- 
composition of  this  new  iodide  into  red  phosphorus  and  a volatile 
iodide,  which  acts  upon  a further  portion  of  the  phosphorus ; and 
thus  the  action  is  indefinitely  continued. 

(464)  Phospham  (HN^P  ?). — If  terchloride  of  phosphorus  be 

cooled  by  a freezing  mixture,  and  saturated  with  ammoniacal  gas, 
a white  saline  mass  (5  H3N,PCl3)  is  obtained ; it  is  to  be  introduced 
into  a tube  of  Bohemian  glass,  and  heated  to  redness  in  a current 
of  dry  carbonic  anhydride  as  long  as  any  sal  ammoniac  is  sub- 
limed : a yellowish- white  bulky  amorphous  powder  remains 
behind:  this  substance  is  phosphide  of  nitrogen  but  there 

can  be  no  doubt  that  it  contains  hydrogen,  it  is  the  phospham  of 
Gerhardt ; probably  its  composition  should  be  represented  by  tlie 
formula  given  above.  In  closed  vessels  it  sustains  a red  heat 
without  fusion  or  volatilization,  but  when  heated  in  air  it  is  slowly 
oxidized,  with  formation  of  phosphoric  anhydride;  if  projected 
into  fused  hydrate  of  potash,  it  is  decomposed  with  incandescence, 
phosphate  of  potassium  being  formed,  whilst  ammonia  and  nitro- 
gen are  disengaged : but  it  is  remarkable  that  dry  chlorine  and 
hydrochloric  acid  gases,  and  the  vapour  of  sulphur,  are  without 
action  upon  it,  even  at  a red  heat;  and  it  is  but  very  slowly 
attacked  by  concentrated  nitric  acid.  Solutions  of  the  alkalies 
exert  scarcely  any  action  upon  it.  When  heated  in  hydrogen, 
ammonia  is  formed.  It  combines  with  sulphuretted  hydrogen, 
and  if  heated  in  a current  of  this  gas,  the  new  compound  as  it  is 
formed  is  slowly  sublimed  in  the  form  of  a white  powder. 

(465)  Sulphides  of  Phosphorus. — Sulphur  and  phosphorus 
may  be  melted  together  in  all  proportions  : several  definite  com- 
pounds exist  between  them,  corresponding  in  composition  with 
the  oxides  of  phosphorus  ; and  in  addition  to  these,  a combination, 
PSg,  may  be  formed  (Berzelius).  All  the  sulphides  of  phosphorus 
are  more  fusible  than  either  element  separately,  and  are  exceed- 
ingly inflammable  ; most  of  them  may  be  obtained  in  crystals. 
They  combine  with  the  sulphides  of  the  alkaline  metals,  and  form 
a series  of  definite  salts.  The  combination  of  sulphur  with  phos- 
phorus should  be  gradually  effected  under  warm  water;  great 
neat  is  extricated  by  their  union,  and  the  experiment  requires  to 
be  conducted  very  carefully,  in  order  to  avoid  explosion. 


208 


SILICON,  OE  SILICrCM. 


CHAPTER  IX. 


SILICON  AND  BOEON. 


§ I.  Silicon,  oe  Silicium  : Si  = 28 ; or  Si  ==  14. 


(466)  Analogies  of  the  Silicon  Group. — Silicon  presents  a 
certain  analogy  with  boron  in  its  tendency  to  unite  with  fluorine 
and  with  nitrogen  : but  its  relationship  to  niobium  and  tantalum 
is  still  more  strongly  marked,  not  only  in  these  particulars,  but  in 
its  tendency  to  form  an  acid  with  two  atoms  of  oxygen,  and  in  its 
production  of  a volatile  liquid  perchloride.  Silicon  likewise 
exhibits  a similar  resemblance  to  titanium  and  tin.  Zirconium 
forms  a solid  perchloride,  but  in  its  habits  it  is  also  closely  allied 
to  silicon.  These  elements  might  be  arranged  thus  in  parallel 
series : — 


Silicon 

Titanium 

Tin 


Zirconium 

Xiobium 

Tantalum. 


These  elements  all  belong  to  the  class  of  tetrads,  being  equivalent 
in  their  most  usual  combinations  to  4 atoms  of  hydrogen. 

(467)  SiLicox"  when  in  combination  with  oxygen  is  the  most 
abundant  solid  component  of  the  earth’s  crust.  It  is  the  essential 
constituent  of  Silex  or  flint,  and  hence  the  origin  of  the  term 
silicon.  In  order  to  obtain  the  element  in  its  uncombined  form, 
a mixture  of  fluor-spar  with  flne  quartzose  sand  or  ground  flints  is 
heated  with  concentrated  sulphuric  acid ; a gaseous  fluoride  of 
silicon  is  formed,  which  is  partially  soluble  in  water,  producing  an 
acid  solution.  This  acid  liquid,  when  neutralized  with  a solution 
of  caustic  potash,  yields  a sparingly  soluble  salt  (2  IvF,SiF4). 
Tliis  silicofluoride  of  potassium  is  to  be  thoroughly  dried,  and 
mixed  in  a glass  or  iron  tube  with  eight  or  nine-tenths  of  its  weight 
of  potassium,  and  heated.  Fluoride  of  potassium  is  formed,  whilst 
silicon  is  reduced  and  partially  combined  with  the  excess  of  po- 
tassium ; (2  KF,SiF4)-f  2 K^^Si-f  6 KF.  The  mass,  when  cold, 
is  treated  with  cold  water,  which  produces  a copious  extrication 
of  hydrogen  gas,  owing  to  the  decomposition  of  the  water  by  the 
excess  of  potassium.  The  washing  with  cold  water  is  continued 
so  long  as  any  alkaline  reaction  upon  test-paper  is  observed ; when 
this  ceases,  it  may  Anally  be  well  washed  with  boiling  water,  so 
long  as  anything  is  dissolved.  Sodium  may  be  advantageously 
substituted  for  potassium  in  this  experiment,  in  the  proportion  of 
1 part  of  sodium  to  2 of  the  silicofluoride.  Silicon  may  also  be 
obtained  by  heating  in  a current  of  the  vapour  of  chloride  of 
silicon  potassium  or  sodium  placed  in  porcelain  trays,  in  a glass 
tube,  which  it  is  best  to  protect  by  lining  it  with  thin  plates  of 
mica. 

Silicon  may  be  obtained  in  three  distinct  modifications:  viz., 
the  amorphous.^  the  graphitoid^  and  the  crystalline  modiflcation. 


GEAPHITOID  AND  CfiYSTALLINE  SILICON. 


209 


1.  Amorphous  Silicon. — ^Wheii  procured  by  tlie  processes 
above  described,  silicon  presents  the  appearance  of  a dull  brown 
powder,  insoluble  in  water,  in  which  it  sinks.  It  is  a non-con- 
ductor of  electricity  ; it  soils  the  fingers  when  touched  ; it  is  not 
acted  upon  by  nitric  or  sulphuric  acid,  but  is  readily  soluble  in 
hydrofluoric  acid,  and  in  a warm  solution  of  caustic  potasli.  When 
heated  in  air  or  in  oxygen  it  burns  brilliantly,  and  is  converted 
into  silica,  which  fuses  from  the  intense  heat  emitted,  and  forms 
a superficial  coating  over  the  unburnt  silicon. 

2.  Graphitoid  Silicon. — The  brown  powder  just  described,  if 
heated  intensely  in  a closed  platinum  crucible,  parts  with  a trace 
of  hydrogen,  shrinks  greatly,  becomes  much  denser,  and  darker  in 
colour,  and  undergoes  a remarkable  change  in  properties.  After 
such  ignition,  the  silicon  may  be  heated  strongly  in  air  or  in 
oxygen,  even  when  urged  in  the  blowpipe  flame,  without  taking 
fire  : it  has  become  sufficiently  heavy  to  sink  in  oil  of  vitriol,  and 
it  resists  the  action  of  pure  hydrofluoric  acid,  although  if  treated 
with  a mixture  of  nitric  and  hydrofluoric  acids  it  is  rapidly  dis- 
solved. It  may  even  be  fused  with  nitre  or  with  chlorate  of  potas- 
sium without  undergoing  oxidation  ; but  if  the  heat  be  urged  to 
whiteness,  the  silicon  burns  brilliantly  in  the  nitre  ; the  oxidation, 
however,  is  much  hastened  by  the  addition  of  a little  carbonate  of 
potassium  ; the  mixture  then  deflagrates  briskly,  even  though  it 
may  be  at  a much  lower  temperature : by  fusion  with  carbonate 
of  potassium  alone,  silicon  is  easily  and  completely  oxidized ; in 
both  cases  silica  is  formed,  and  is  immediately  dissolved  by  the 
melted  alkali.  The  properties  of  this  compact  form  of  silicon 
much  resemble  the  graphitoid  modification  described  by  Deville 
and  by  W older,  who  obtained  the  silicon  in  hexagonal  plates,  by 
treating  an  alloy  of  silicon  and  aluminum  in  succession  with  boil- 
ing hydrochloric  and  hydrofluoric  acids,*  when  the  silicon  remains 
behind  in  the  form  of  hexagonal  plates,  which  have  a sp.  gr.  of 
2*4:9, t and  a metallic  lustre.  It  may  also  be  obtained  by  fusing 
1 part  of  aluminum  with  5 of  glass  free  from  lead,  and  10  of  pow- 
dered cryolite,  treating  the  black  mass  with  hydrochloric  acid, 
and  then  with  hydrofluoric.  In  this  form  silicon  is  a conductor  of 
electricity  ; it  may  be  heated  to  whiteness  in  a current  of  oxygen 
without  undergoing  change,  but  it  is  gradually  dissolved  by  a mix- 
ture of  hydrofluoric  and  nitric  acids,  though  it  is  oxidized  but 
very  slowly  when  fused  with  hydrate  of  potash.  When  heated  in  a 
current  of  hydrocidoric  acid,  a volatile  liquid,  the  hydrochlorato 
of  chloride  of  silicon  (Sigll^Cljo?)  is  formed  (4:77),  whilst  hydrogen 
gas  is  liberated. 

3.  Crystalline  Silicon. — According  to  Deville  {^Ann.  de  Ghimie.^ 
III.  xlix.  65),  silicon  requires  for  its  fusion  a temperature  between 


* Silicon  appears  to  have  the  same  sort  of  tendency  to  combine  witli  ainmmum 
that  carbon  has  to  unite  with  iron.  The  alloy  is  easily  formed  by  heating  aluminum 
iu  a Hessian  crucible  with  from  20  to  40  times  its  weight  of  dry  silicofluoride  of 
potassium,  fusing  the  two  together  for  a quarter  of  an  hour,  and  then  allowing  the 
crucible  to  cool  slowly. 

f I found  a sample  of  graphitoid  silicon  to  possess  a sp.  gr.  of  2'33'I. 

14 


210 


CEYSTALLIXE  SILICOX. 


the  melting  point  of  cast  iron  and  that  of  steel.  In  order  to  fuse 
it,  he  introduces  the  silicon  into  a platinum  crucible  lined  with 
lime  and  protected  by  an  outer  clay  crucible  : the  whole  is  then 
intensely  heated  in  a wind  furnace.  If  the  lining  of  lime  cracks, 
and  the  silicon  reaches  the  platinum,  the  crucible  is  spoiled,  owing 
to  the  formation  of  a silicide  of  platinum.  Fused  silicon  may  also 
be  prociu’ed  when  the  mixtm’e  of  chloride  of  sodium  with  reduced 
silicon  (obtained  by  igniting  sodium  in  the  vapour  of  chloride  of 
silicon),  detached  as  far  as  possible  from  adliering  fragments  of 
porcelain,  is  placed  in  a crucible  lined  with  charcoal,  and  exposed 
to  intense  heat  in  a forge ; the  chloride  of  sodium  becomes  vola- 
tilized, and  the  silicon  is  fused  into  globules  in  the  midst  of  the 
melted  glass.  These  globules  frequently  show  well-marked  indica- 
tions of  crystallization  in  forms  probably  belonging  to  the  prismatic 
system ; they  have  a dark  steel-grey  colour,  and  a lustre  like  that 
of  specular  iron  ore : now  and  then  the  silicon  is  found  crystallized 
in  regular  double  six-sided  pyi'amids.  It  may  also  be  obtained 
in  regular  six-sided  prisms,  terminated  by  three-sided  pyi’amids, 
derived  from  the  octohedron,  by  exposing  pm’e  aluminum  in  porce- 
lain trays,  heated  intensely  in  a porcelain  tube,  to  a cnn'ent  of  the 
vapour  of  chloride  of  silicon  ; the  aluminum  is  volatilized  as  chlo- 
ride of  aluminmn,  leaving  the  silicon  in  crystals  which  have  a red- 
dish lustre ; they  are  hard  enough  even  to  cut  glass  like  the  diamond. 
Crystals  of  silicon  may  likewise  be  procured,  and  with  less  diffi- 
culty, by  heating  an  earthen  crucible  to  redness,  and  introducing 
a mixture  of  3 parts  of  silicofluoride  of  potassium  with  1 part  of 
sodium,  cut  into  small  pieces,  and  4 of  pure  granulated  zinc.  The 
mixture  must  be  maintained  at  a red  heat,  but  below  the  tempe- 
rature necessary  to  volatilize  the  zinc,  until  the  slag  is  completely 
melted ; it  must  then  be  allowed  to  cool  slowly.  The  mass  of 
zinc  thus  obtained  contains  long  needles  of  silicon  formed  of 
rhombic  (?)  octohedra,  inserted  one  into  the  other  : much  of  the 
zinc  may  be  extracted  by  partial  fusion  at  a low  temperature,  and 
the  zinc  which  runs  from  the  pasty  mass  in  which  the  silicon  is 
retained  may  be  employed  again  in  a similar  operation  : the  zinc 
which  still  adheres  to  the  silicon  may  be  removed  by  digestion,  first 
in  hydrochloric,  and  afterwards  in  boiling  nitric  acid.  If  a very 
high  temperature  be  employed  in  this  operation  the  whole  of  the 
zinc  may  be  expelled,  and  the  silicon  obtained  in  the  fused  condi- 
tion. Deville  and  Caron  have  in  this  way  {^Ann.  de  CMmie^  III. 
Ixvii.  440)  fused  several  hundred  grammes  of  silicon  under  a layer 
of  silicofluonde  of  potassium  at  a temperature  near  that  at  which 
cast  iron  melts,  and  they  have  cast  it  into  large  cylindrical  bars 
without  sensible  loss  by  oxidation.  These  bars  exhibited  a brilliant 
surface,  which  was  not  altered  by  exposure  to  air. 

Silicon  fonns  with  oxygen  but  a single  oxide,  the  weU-knoAvn 
compound,  silica,  or  silicic  anhydride. 

Wohler  has,  however,  discovered  a remarkable  series  of  com- 
pounds into  the  composition  of  which  both  oxygen  and  hydrogen 
enter  : one  of  these  he  calls  silicon  (SigH^O,?)  reserving  the  term 
silicium  for  the  element ; another  he  has  named  leukon^  SijHgOj ; 


SILICA,  OK  SILICIC  ANHYDRIDE. 


211 


these  bodies  are  evidently  analogous  to  those  obtained  by  Brodlc 
from  graphite  {note^  p.  60). 

(468)  Silicic  Anhydride  or  Silica  (SiO2=60  ; or  SiO2=30), 
Sp.  Gr.  cryst.  2'642 ; Amorphous  2*2 — 2-3  : Comp,  in  100  parts., 
Si,  46*66  ; O,  53*34. — Berzelius  represented  this  compound  as  a 
teroxide,  giving  the  equivalent  of  silicon  as  22,  if  that  of  oxygen 
be  8.  There  are,  however,  reasons  which  render  it  more  probable 
that  it  contains  only  2 atoms  of  oxygen,  and  that  it  corresponds  in 
composition  to  carbonic  anhydride  : for  example,  1 atom  of  chlo- 
ride of  silicon,  when  converted  into  vapour,  instead  of  forming  an 
exception  to  the  general  rule,  as  it  does  upon  the  theory  of  Berze- 
lius, would  then  produce  2 volumes  of  vapour  as  usual : and  in 
decomposing  fused  carbonate  of  potassium  by  the  addition  of  finely 
divided  silica,  it  is  found  that  the  whole  of  the  carbonic  anhydride 
is  expelled  when  the  proportion  of  silica  is  to  the  carbonate  as  60 
to  138.*  This  view  has  the  advantage  of  greater  simplicity,  and 
it  will  be  employed  in  this  work.  According  to  the  experiments 
of  Dumas,  100  parts  of  silica  contain  46*7  of  silicon,  and  53*3  of 
oxygen. 

Silica  occurs  in  two  modifications,  the  crystalline  and  the 
amorphous.  In  the  crystalline  state  it  has  the  higher  specific 
gravity. 

Pure  crystalline  silica  occurs  in  rode  crystal  and  in  some  forms 
of  quart2.^  crystallized  in  six-sided  prisms,  transversely  striated,  and 
terminated  by  six-sided  pyramids.  Amethyst  is  a purple  variety 
coloured  with  oxide  of  iron  (ferric  acid  ?).  Silica  is  found  nearly 
pure  in  agate  and  calcedony.^  which  consist  of  a mixture  of  the 
crystallized  and  amorphous  varieties.  Calcedony  in  alternate 
layers  of  difierent  colours  constitutes  onyx.  Carnelian  is  a red  or 
brown  variety  containing  oxide  of  iron.  Flint  is  a variety  of 
calcedony,  chiefly  found  in  the  upper  chalk  ; and  opal  consists  of 
the  amorphous  variety  with  a varying  quantity  of  water.  Silica 
constitutes  the  principal  ingredient  of  all  sandstones ; and  it  entere 
largely  into  the  composition  of  felspar,  and  of  a vast  variety  of 
minerals.  Pure  crystallized  silica  is  perfectly  transparent  and 
colourless  ; in  hardness  it  approaches  the  precious  gems.  A heat 
as  intense  as  that  of  the  oxy hydrogen  blowpipe  is  required  for  its 
fusion  ; it  then  melts  to  a transparent  glass,  which  may  be  drawn 
out  into  fine,  flexible,  elastic  threads  which  belong  to  the  amor- 
phous variety.  Native  silica  is  insoluble  in  water,  and  in  all  acids 
except  the  hydrofluoric.  It  is  not  volatile  when  heated  alone,  but 
it  is  said  when  heated  in  a current  of  steam  to  undergo  partial 
sublimation,  and  to  have  been  found  in  the  throats  of  furnaces, 
forming  concretionary  nodules,  somewhat  resembling  calcedony  in 
appearance. 

Preparation. — Finely  divided  silica  has  the  aspect  of  a white 

* The  experiments  of  Colonel  Yorke  {Phil.  Trans.  1857)  have,  however,  shown 
that  the  proportion  of  carbonic  anhydride  expelled  by  equal  weights  of  silica  from  an 
excess  of  the  different  carbonates,  varies  with  the  nature  of  the  base;  carbonate  of 
sodium  losing  a larger  proportion  than  carbonate  of  potassium,  and  carbonate  of  lithi- 
um more  than  carbonate  of  sodium,  where  equal  quantities  of  silica  were  employed. 


212 


HYDRATES  OF  SILICA. 


earth,  but  though  insoluble  it  possesses  the  power  of  uniting  with 
bases,  as  is  shown  by  the  usual  process  of  obtaining  it  in  a state  of 
])urity  : — A mixture  of  carbonates  of  potassium  and  sodium  is 
fused  by  a red  heat,  and  one-third  of  its  weight  of  ground  flint,  or 
some  other  siliceous  mineral  in  flne  powder,  is  added  in  small 
quantities  to  the  melted  mass ; on  each  addition  a brisk  efierves- 
cence,  due  to  the  escape  of  carbonic  anhydiide,  takes  place ; the 
mixture  is  then  heated  strongly  for  some  minutes.  It  is  after- 
wards allowed  to  cool,  and  if  digested  in  water  the  mass  is  slowly 
dissolved,  with  the  exception  of  a portion  of  the  impurities,  such 
as  oxide  of  iron  and  titanic  anliydride,  which  the  siliceous  material 
may  have  contained.  A larger  quantity  of  silica  than  that  above 
indicated  would  still  yield  a mixture  which  might  be  fused  by  a 
strong  heat ; but  it  becomes  less  soluble  in  proportion  to  the  ex- 
cess of  silica,  till  at  length  a point  is  reached  at  which  it  is  no 
longer  soluble  in  water  or  in  the  common  acids ; indeed,  it  forms 
the  basis  of  glass.  When  it  is  proposed  to  obtain  pure  silica,  how- 
ever, an  excess  of  alkali  is  always  used ; the  resulting  compound 
is  then  easily  attacked  by  acids,  in  which  it  is  wholly  dissolved,  if 
the  acid  be  dilute  and  in  suificient  quantity.  If  the  solution  in 
hydrochloric  acid  be  evaporated,  the  silica  is  separated  as  a gela- 
tinous hydrate,  which  by  continuing  the  heat,  is  converted  into  a 
white  earthy-looking  powder  no  longer  soluble  in  acids : after 
being  digested  with  oil  of  vitriol  to  remove  traces  of  titanic  anhy- 
dride, and  decanting  the  strong  acid,  it  must  be  well  washed  as 
long  as  anything  is  dissolved  ; if  then  dried  and  ignited,  it  is  per- 
fectly pure.  As  thus  procured,  silica,  like  charcoal  and  other  por- 
ous bodies,  rapidly  absorbs  aqueous  vapour  from  the  air,  without 
becoming  sensibly  moist. 

Perfectly  pure  silica  may  also  be  procured  by  transmitting  the 
gaseous  fluoride  of  silicon  into  water ; a partial  decomj^osition  of 
the  gas  occurs,  and  one-third  of  its  silicon  is  oxidized  and  deposited 
in  white  hydrated  flocculi,  which,  if  washed  and  ignited,  furnish 
silica  of  snowy  whiteness ; 3 SiF^  -f  2 H^O,  yielding  SiO,  -f  2 
(2  IIF,SiF^).  Silica  may  likewise  be  obtained  nearly  pure  by 
heating  colourless  quartz  to  redness,  and  quenching  it  in  water ; 
the  mineral  is  rendered  friable  by  this  treatment,  and  is  then 
easily  reduced  to  a flne  powder:  common  flints  treated  in  a 
similar  manner  give  a very  white  powder,  which  is  nearly  pure 
silica.  All  the  artiflcial  forms  of  silica  are  amorphous,  and  are 
much  more  easily  attacked  by  solvents  than  the  crystalline 
variety. 

(169)  Hydrates  of  Silica. — Insoluble,  however,  as  silica  gene- 
rally is  in  water,  and  thougli  silica,  when  once  deposited  even  in 
tlie  gelatinous  form,  is  almost  insoluble  either  in  water  or  in  acids, 
a modiflcation  of  it  exists  which  may  be  dissolved  completely  at 
the  moment  of  its  liberation  from  some  of  its  compounds  which 
are  already  in  solution.  For  instance,  if  a dilute  solution  of  an 
alkaline  silicate  be  poured  into  a considerable  excess  of  hydi’o- 
chloric  acid,  the  whole  of  the  silica  is  retained  in  solution : but  it 
may  be  precipitated  from  this  acid  solution  by  the  gradual  addi- 


HYDRATES  OF  SILICA. 


213 


tion  of  a solution  of  potash,  so  as  to  neutralize  the  acid  : and  if 
to  a solution  of  an  alkaline  silicate  in  water  hydrochloric  acid  be 
added  gradually,  the  silica  is  precipitated  in  a gelatinous  form  in 
proportion  as  the  alkali  is  neutralized. 

From  the  solution  of  alkaline  silicate  in  excess  of  hydro- 
chloric acid,  Graham  obtains  a pure  solution  of  hydrate  of  silica, 
by  subjecting  the  liquid  to  dialysis  in  a hoop  dialyser  of  parch- 
ment-paper (62).  If  a stratum  of  liquid  4-tenths  of  an  inch  in 
depth  be  subjected  for  4 or  5 days  to  dialysis,  changing  the  water 
in  the  outer  vessel  at  intervals  of  24  hours,  the  hyclrochloric  acid 
and  the  soluble  chlorides  will  be  found  to  have  difiused  so  com- 
pletely that  the  liquid  in  the  dialyser  will  give  no  precipitate 
with  nitrate  of  silver. 

A solution  may  thus  be  obtained  containing  5 per  cent,  of 
silica,  and  it  may  be  concentrated  till  the  quantity  of  silica 
reaches  14  per  cent,  if  the  liquid  be  boiled  down  in  a flask.  In 
open  vessels  it  is  apt  to  gelatinize  on  the  edge,  and  the  \vhole 
then  solidifies.  The  solution  is  tasteless,  limpid  and  colourless, 
with  a feebly  acid  reaction,  rather  greater  than  that  of  carbonic 
acid  ; 100  parts  of  silica  require  1*85  of  potash  (Ka^)  to  neutralize 
this  effect  on  litmus.  The  solution  is  not  easily  preserved  many 
days,  becoming  converted  into  a solid  transparent  jelly  which, 
even  in  closed  vessels,  shrinks,  whilst  water  is  separated  from  it. 
The  coagulation  is  retarded  by  hydrochloric  acid,  and  by  small 
quantities  of  caustic  potash  or  soda.  Sulphuric,  nitric,  and  acetic 
acids  are  without  action  on  the  solution,  but  it  is  slowly  coagu- 
lated by  a few  bubbles  of  carbonic  acid.  Its  coagulation  is  also 
effected  in  a few  minutes  by  the  addition  of  y^,^-o-o  of  any 

alkaline  or  earthy  carbonate  in  solution,  but  not  by  caustic  am- 
monia nor  by  neutral  nor  acid  salts.  Alcohol  and  sugar,  gum 
and  caramel,  are  without  action,  but  solutions  of  gelatin,  soluble 
alumina,  and  soluble  peroxide  of  iron,  immediately  cause  a gela- 
tinous precipitate : when  solution  of  silica  is  gradually  added  to 
one  of  gelatin  in  excess,  the  precipitate  obtained  consists  of  100  of 
silica  and  92  of  gelatin  {Phil.  Trans.  1861,  p.  204). 

By  evaporation  in  vacno  at  60°,  the  silica  is  left  behind  in  the 
form  of  a transparent  glassy  mass  of  great  lustre,  containing, 
after  exposure  for  two  days  over  sulphuric  acid,  21 ‘99  of  water, 
which  corresponds  nearly  to  the  formula  II2G,  SiOa. 

There  is,  however,  considerable  ditflculty  in  obtaining  a defi- 
nite hydrate  of  silica,  for  it  easily  loses  a portion  of  its  water  at 
low  temperatures,  and  is  moreover  a very  liygroscopic  substance.'^ 
Ebelmen,  by  the  action  of  moist  air  upon  silicic  ether,  obtained  a 
transparent,  glassy  liydrate,  which  had  a composition  represented 
by  the  formula  3 lijO,  2 SiO^ ; and  a compound  which  gave 
similar  results  on  analysis  was  procured  by  Doveri,  on  drying  the 
ordinary  gelatinous  hydrate  of  silica  in  vacuo  over  sulphuric  acid 
without  the  aid  of  heat.  Fuchs  obtained  two  hydrates  of  silica, 

* From  the  occurrence  of  a mixed  ether  coneisting  of  3 OoHo,  SiOj)  it  ap- 

pears that  the  silicic  is  really  a tetrabasic  acid,  though  from  the  facility  with  which 
its  basic  hydrogen  escapes  as  water,  the  composition  of  the  hydrate  is  doubtful. 


214:  AETmCIAL  STONE SOLUBLE  AND  INSOLUBLE  SILICA. 

one  containing  from  9*1  to  9*6  per  cent,  of  water,  corresponding 
to  the  formula  H20-,  3 SiO^j  which  requires  9'1  per  cent.,  the 
other  between  6*6  and  7 per  cent.,  agreeing  nearly  with  the  for- 
mula H^O,  4 SiOj,  which  would  contain  6*9  per  cent,  of  water. 

A very  white  and  light  hydrate  of  silica  occurs  naturally  in 
abundance  in  beds  situated  at  the  base  of  the  chalk  formation, 
between  the  upper  greensand  and  the  gault : the  proportion  of 
hydrated  silica  in  these  deposits  varies  very  greatly,  ranging  from 
5 to  as  much  as  72  per  cent.,  being  most  abundant  in  the  upper 
portion  of  the  deposit  (Way).  A mixture  of  this  material  with 
slaked  lime,  when  made  into  a paste  with  water,  is  in  a few 
weeks  converted  into  a silicate  of  calcium,  and  the  change  is 
accelerated  by  the  presence  of  2 or  3 per  cent,  of  soda. 

Insoluble  silica  may  be  gradually  converted  into  the  soluble 
variety  by  long  digestion  with  solutions  of  the  alkalies.  Even 
hints  in  their  unground  condition  may  be  dissolved  in  strong 
solutions  of  caustic  alkali  (sp.  gr.  1*16),  if  the  solution  be  digested 
upon  them  under  pressure  at  a temperature  of  between  300°  and 
400°.  The  very  concentrated  solution  of  silicate  of  potassium  or 
of  sodium  of  glairy  consistence  which  may  thus  be  formed,  has 
been  used  by  Mr.  F.  Kansome,  of  Ipswich,  as  a cement  for  con- 
solidating siliceous  sand  into  an  artihcial  stone  : — Finely  divided 
siliceous  sand,  mixed  with  suitable  colouring  material,  is  moistened 
with  this  cement,  and  pressed  into  moulds  ; after  gradual  drying 
the  mass  is  bred  : at  a high  temperature  the  silicate  becomes  semi- 
vitrihed,  and  agglutinates  the  grains  of  sand  ; a very  hard,  durable, 
artihcial  sandstone,  which  previous  to  being  hred  can  be  moulded 
into  any  desired  form,  is  thus  obtained. 

Finely  divided  hydrate  of  silica  is  also  dissolved  by  the  alka- 
line carbonates  : the  carbonates  are  only  partially  decomposed  by 
the  silica  which  is  dissolved.  It  appears  to  be  owing  to  the  solu- 
bility of  silica  in  solutions  of  the  carbonates  that  almost  all  spring 
and  river  waters  contain  silica  in  solution  in  minute  quantity ; on 
evaporation  the  silica  is  obtained  in  the  insoluble  form.  When 
the  action  of  the  alkaline  liquid  is  aided  by  that  of  a high  tempe- 
rature, as  is  the  case  with  the  Geysers  or  boiling  springs  of  Iceland, 
very  large  quantities  of  silica  are  dissolved,  which,  as  the  liquid 
cools,  are  deposited  as  ‘ petrifactions  ’ on  surrounding  objects 
exposed  in  the  basin  or  in  the  stream. 

Silica  also  exists  in  the  soluble  form  in  a class  of  minerals 
termed  zeolites,  which  are  hydrated  siliceous  compounds  (670) 
found  in  the  ca^hties  of  the  amygdaloid  rocks.  The  zeolites,  if 
hnely  powdered,  and  treated  with  hydrochloric  acid,  swell  up  to 
a transparent  jelly  ; this  gelatinous  mass  consists  of  hydrate  of 
silica. 

These  observations  on  the  various  conditions  under  which 
silica  may  be  rendered  soluble  derive  their  interest  from  the 
extensive  formation  of  crystallized  silica,  so  abundantly  diffused 
over  the  surface  of  the  earth,  and  the  difficulty  of  crystallizing  it 
by  artihcial  means.  The  zeolites  may  have  been  obtained  by 
deposition  from  solution ; calcedony  possibly  by  spurious  subli- 


SILICATES. 


215 


mation;  quartz  and  agate  by  crystallization  from  an  aqueous 
solution. 

(470)  Silicates. — The  silicates  are  most  abundant  natural  pro- 
ductions. All  the  forms  of  clay,  felspar,  mica,  hornblende,  and  a 
large  number  of  other  common  minerals,  are  compounds  of  this 
description. 

Silica  combines  with  bases  in  several  different  proportions  ; 
most  of  its  compounds  are  found  in  the  form  of  crystallized  mine- 
rals, many  of  which  are  double  silicates  of  very  complex  composi- 
tion. It  is  highly  probable  that  silicic,  like  phosphoric  acid, 
admits  of  modifications  which  differ  in  basic  power.  Odling 
{Phil.  Mag.  Kov.  1859)  proposes  to  call  the  silicates  of  the  type 
M^SiO^,  orthosilicates  / those  of  the  type  M^SiOj,  metasilicates., 
with  an  intermediate  class  formed  by  the  combination  of  one 
atom  of  each  of  the  two.  The  combinations  with  bases  which 
are  of  most  usual  occurrence  belong  to  one  or  other  of  the  follow- 
ing classes,  the  orthosilicates  being  regarded  as  the  normal 
salts : — 


Orthosilicates 
M4Si04  or 
N"2Si04 
Metasilicates 
M2Si03  or 
N''Si03 
^ Silicates 

M4Sie4,  2 SiOa 
Acid  silicates 
M^SiOs,  Si02  or 
N"  Si03,  Si02 


fDioptase ■Gu"H2Si04 

Olivine (MgFe)"2Si04 

Forge  cinder Fe"2Si04 

( VVoUastonite 0a"Si03 

•<  Picrosraine 2 (Mg"Si03)  H20 

( Augite (0aMgy'Si03 

j Meerschaum Mg''2Si04,  2 (Si02,H20) 

I Silicate  of  lime 0a"2Si04,  2 Si02 


JThe  composition  of  many  of  the  ordinary  varieties  of  glass 
may  be  approximately  represented  by  mixtures  of  different 
silicates  which  have  this  formula. 


In  the  above  formula  M stands  for  1 atom  of  any  metallic 
monad,  such  as  potassium,  and  IS"  for  1 atom  of  any  metallic 
dyad,  such  as  calcium. 

In  most  cases,  however,  in  the  formulae  of  the  silicates  I shall 
adhere  to  the  custom  of  representing  them  as  compounds  of  the 
bases  with  the  anhydride  silica.  Their  diversified  forms  have  not 
liitherto  been  satisfactorily  classified. 

Most  of  the  silicates  are  fusible  ; their  fusibility  is  increased 
by  mixture  with  each  other  ; those  which  contain  readily  fusible 
oxides  melt  at  the  lowest  temperature,  and  in  general  the  basic 
silicates  fuse  more  readily  than  those  which  are  normal  in  compo- 
sition, or  which  contain  excess  of  silica.  All  the  silicates  are  in- 
soluble in  water,  with  the  exception  of  those  of  the  alkalies  whicli 
contain  a large  proportion  of  base.  The  hydrated  silicates,  and 
those  which  contain  the  largest  proportion  of  base,  are  those  most 
easily  decomposed  by  acids  ; but  the  anhydrous  normal  and  acid 
silicates  of  the  earths  are  not  decomposed  by  any  acid  except  the 
hydrofluoric.  The  silicates  may  be  detected  by  fusing  them  with 
carbonate  of  sodium  or  of  potassium,  and  then  heating  the  residue 
with  acid,  and  evaporating  to  dryness  ; on  treating  what  is  left 
with  hot  water,  the  silica  remains  undissolved  in  the  form  of  a 
white  powder,  which,  when  fused  with  carbonate  of  sodium  upon 
platinum  foil  before  the  blowpipe,  yields  a colourless  bead  of  glass. 


216 


SILICATES — SILICONE. 


The  fi*eedom  of  silica  from  bases  may  be  ascertained  by  its  being 
volatilized  without  residue  when  evaporated  in  platinum  with 
pure  hydrofluoric  acid  in  excess.  Pure  silica  is  not  attacked  by 
fusion  with  microcosmic  salt,  but  is  left  as  a spongy  mass  in  the 
clear  bead  ; if  any  earth  or  base  be  present,  the  bead  is  generally 
more  or  less  opalescent.  Borax  dissolves  silica  slowly,  when  fused 
with  it,  forming  a clear  colourless  bead. 

The  acid  character  is  so  feebly  marked  in  silica,  that  the  ordi- 
nary vegetable  acids,  such  as  the  acetic,  the  oxalic,  and  the  tar- 
taric, precipitate  silicic  acid  from  its  combinations  with  the 
alkalies ; and  a current  of  carbonic  acid,  or  even  the  gradual  ab- 
sorption of  carbonic  acid  from  the  atmosphere,  produces  a similar 
result.  At  a high  temperature,  however,  the  action  is  reversed  ; 
for  as  silica  is  not  volatilized  to  any  perceptible  extent  by  the 
heat  of  a furnace,  it  decomposes  the  carbonates  and  the  salts  of 
all  the  volatile  acids  wlien  ignited  with  them ; hence  even  the 
sulphates  yield  up  their  bases  to  the  silica,  whilst  the  sulphuric 
anliydride  is  expelled. 

(dTl)  If  coarsely-powdered  sihcide  of  calcium  (649a)  be  di- 
gested in  fuming  nitric  acid,  in  a vessel  kept  cool  by  immersion 
in  water,  an  extrication  of  hydi’ogen  takes  place,  and  a new  com- 
pound, to  which  "Wohler  has  given  the  name  of  silicone  (objec- 
tionable, because  already  appropriated  to  the  element  itself),  is 
gradually  formed.  The  mixture  is  to  be  agitated  frequently  and 
kept  for  some  time  in  a dark  place  until  no  further  extrication  of 
gas  occurs.  The  mixture  is  then  to  be  diluted  with  T or  8 parts 
of  water,  and  the  insoluble  material  collected,  washed,  pressed 
between  blotting-paper,  and  dried  in  the  dark  in  vacuo^  over  sul- 
phuric acid. 

Silicone  (SigHgOJ),  or  chryseon^  as  it  might  be  fitly  termed  in 
allusion  to  its  colour,  is  a bright  orange-yellow  mass,  insoluble  in 
water,  alcohol,  bisulphide  of  carbon,  terchloride  of  phosphorus,  or 
chloride  of  silicon.  When  heated  it  deepens  in  colour,  and  after- 
wards takes  fire  with  slight  explosion  and  the  emission  of  sparks, 
leaving  silica,  which  is  brown,  owing  to  the  presence  of  silicon. 
If  heated  without  access  of  air,  it  evolves  hydrogen,  leaving  a 
residue  of  silica  and  amorphous  silicon  in  shining  brown  flakes. 
The  decomposition  begins  even  at  212°.  If  heated  with  water  in 
a sealed  tube  to  384°  it  is  speedily  converted  into  white  flakes  of 
silica,  whilst  pure  hydi'ogen  is  evolved,  and  is  retained  under  great 
pressure  in  the  tube. 

In  the  dark  it  may  be  preserved  without  alteration,  either  in 
a moist  or  dry  state ; but  if  exposed  to  diffused  daylight  it  slowly 
becomes  paler,  with  evolution  of  hydrogen.  If  exposed  to  the 
sun’s  rays  under  water,  it  immediately  begins  to  evolve  hydrogen, 
and  a white  residue  is  left,  which  W older  has  termed  leukon. 

Silicone  is  not  attacked  by  chlorine  nor  by  fuming  nitric  or- 
sulphuric  acid,  even  when  boiling  : hydrofluoric  acid  dissolves  it 
completely.  But  its  characteristic  reaction  is  the  rapid  manner 
in  which  it  is  dissolved  by  solutions  of  the  caustic  alkalies,  with 
rise  of  temperature  and  violent  extrication  of  hydrogen.  Am- 


LEUKON. 


217 


monia,  even  in  very  dilute  solutions,  has  a similar  effect.  The 
carbonates  of  the  alkali-metals  dissolve  it  more  slowly.  Silicone 
acts  as  a powerful  reducing  agent,  especially  in  the  presence  of 
alkalies.  Salts  of  copper,  gold,  silver,  palladium,  and  osmium 
yield  with  it  dark  silicates  of  a suboxide. 

(471<^)  Leukon  (SigH^O^?),  Wohler  {Li^.  Ann.  cxxvii.  257). — 
This  compound  was  first  described  as  a hydrated  oxide  of  silicon, 
but  it  has  subsequently  been  further  examined  by  Wohler,  who 
has  changed  its  name  to  leukon  in  allusion  to  its  aspect,  from 
\swhg  white.  When  crystallized  silicon  is  heated  to  barely  visible 
redness  in  a current  of  gaseous  hydrochloric  acid,  hydrogen  is 
liberated,  and  a volatile  liquid,  hydrochlorate  of  chloride  of  silicon 
(SigH^Cljo)  is  formed ; this  compound  when  mixed  with  water  is 
immediately  decomposed  into  hydrochloric  acid  and  a voluminous 
white  powder,  which  is  leukon  ; SigH^Cl.o  + 5 HgO  becoming 
SigHA  + 10  HCl. 

Leukon  at  temperatures  above  32°,  when  in  contact  with 
water,  undergoes  oxidation,  and  evolves  hydrogen.  Wohler  and 
Buff  [Ann.  cle  Cliimie.,  lii.  276)  describe  this  body  when  dry  as  a 
snow-white  powder,  sufficiently  light  to  float  upon  water,  though 
it  sinks  in  ether.  The  caustic  alkalies  and  their  carbonates  dis- 
solve it  rapidly  with  brisk  effervescence,  owing  to  the  formation 
of  a silicate  of  the  base,  whilst  hydrogen  escapes.  Ammonia  also 
decomposes  it  with  slow  evolution  of  hydrogen.  The  acids,  wdth 
the  exception  of  the  hydrofluoric,  do  not  act  upon  it.  It  may  be 
heated  in  air  to  570°  without  alteration;  but  at  a somewhat 
higher  temperature  it  takes  fire,  burning  with  scintillation,  and 
emitting  a phosphorescent  light,  at  the  same  time  giving  off  hy- 
drogen gas,  which  burns  explosively.  If  heated  in  a closed  cruci- 
ble it  is  decomposed  into  a mixture  of  silicon  and  silica ; hydride 
of  silicon  (472)  being  liberated,  but  undergoing  immediate  decom- 
position. Leukon  is  slightly  soluble  in  water,  but  the  liquid 
quickly  undergoes  decomposition,  evolving  hydrogen  gas.  The 
solution  exerts  a strong  reducing  power,  precipitating  gold  and 
})alladium  from  neutral  solutions  of  their  salts,  in  a metallic  form. 
It  also  instantly  bleaches  a solution  of  permanganate  of  potas- 
sium ; and  throws  down  reduced  selenium  and  tellurium,  from 
solutions  of  selenious  and  tellurous  acids  in  hydrochloric  acid. 
Wohler  and  Buff,  however,  think  it  probable  that  this  solution 
contains  a still  lower  oxide  of  silicon  than  the  one  above  de- 
scribed. 

Leukon  is  best  prepared  by  placing  crystallized  silicon  in  a 
wide  glass  tube  connected  with  a U-tube  cooled  by  a mixture  of 
ice  and  salt,  whilst  the  apparatus  terminates  in  a bent  tube  dip- 
ping into  ice-cold  water;  the  silicon  is  to  be  raised  to  a barely 
visible  red  heat,  and  a current  of  dry  hydrochloric  acid  gas  trans- 
mitted ; liydrochlorate  of  chloride  of  silicon  is  formed,  and  in  part 
condensed  in  the  U-tube,  and  the  portion  which  passes  on  is  de- 
composed by  the  water.  The  voluminous  white  precipitate  thus 
formed  consists  of  leukon,  and  is  to  be  quickly  pressed  between 
folds  of  blotting-paper  and  dried  in  vacuo  over  sulphuric  acid. 


218  HYDKIDE,  NITRIDE,  SULPHIDE,  AND  CHLORIDE  OF  SILICON. 

(472)  Hydride  of  Silicon  (H^Si  ?). — Along  with  the  foregoing 
componnd,  Wohler  and  Bnlf  have  also  described  a remarkable 
gaseous  combination  of  hydrogen  and  silicon.  It  has  not  been 
procured  in  a pure  state,  but  may  be  obtained  mixed  with  a large 
quantity  of  free  hydrogen  as  a spontaneously  inflammable  gas, 
when  a wire  or  plate  of  aluminum  combined  with  silicon  is  placed 
in  a solution  of  chloride  of  sodium  and  made  the  positive  pole  of 
a feeble  voltaic  battery.  A large  surface  of  aluminum  and  the 
avoidance  of  any  considerable  elevation  of  temperature  are  neces- 
sary to  insure  the  maximum  production  of  the  hydride. 

The  electrolytic  gas  is  colourless ; when  allowed  to  burn  in 
the  air,  it  emits  white  fumes,  consisting  of  amorphous  silica.  If 
a cold  plate  of  porcelain  or  of  glass  be  introduced  into  a jet  of  the 
burning  gas,  a brown  fllm  of  reduced  silicon  is  deposited  upon  its 
surface.  It  is  also  decomposed  by  transmission  through  a glass 
tube  heated  to  redness,  when  a coating  of  reduced  silicon  is  depo- 
sited, and  the  gas  is  found  to  have  lost  its  self-lighting  power. 
Its  exact  composition  is  not  known.  This  gas  precipitates  many 
metallic  solutions,  such  as  sulphate  of  copper,  nitrate  of  silver, 
and  chloride  of  palladium ; but  it  is  without  action  upon  the  solu- 
tions of  lead  and  of  platinum ; the  precipitates  in  most  cases  con- 
tain silicon. 

Hydride  of  silicon  may  also  be  obtained  by  decomposing  with 
cold  diluted  hydrochloric  acid  an  impure  silicide  of  magnesium 
obtained  by  mixing  intimately  40  parts  of  fused  chloride  of  mag- 
nesium, 35  of  dried  silicofluoride  of  sodium,  and  10  of  fused 
chloride  of  sodium ; these  are  mixed  in  a warm  dry  tube,  with  20 
parts  of  sodium  in  small  fragments,  and  thrown  into  a Hessian 
crucible,  heated  to  redness,  which  is  immediately  covered ; the 
heating  is  to  be  continued  till  the  vapours  of  sodium  cease  to  burn. 

(473)  Hitride  of  Silicon  may  be  obtained  by  the  direct 
action  of  nitrogen  upon  silicon  at  a very  high  temperature ; crys- 
tallized silicon,  when  heated  in  nitrogen  gas,  becoming  coated  with 
a light-bluish  fibrous  compound  of  the  two  elements.  This  nitride 
may  be  heated  to  redness  in  chlorine  without  undergoing  decom- 
position. When  heated  to  full  redness  in  a current  of  steam, 
ammonia  is  disengaged  abundantly  and  silica  is  formed. 

(474)  Sulphide  of  Silicon  : SiS^  ==  92. — ^A  sulphide  corre- 

sponding in  composition  to  silica  is  formed  by  transmitting  the 
vapour  of  bisulphide  of  carbon  over  a mixture  of  finely  divided 
silica  and  carbon  : and  when  either  compact  or  pulverulent  silicon 
is  strongly  heated  in  an  atmosphere  of  sulphur,  combustion  occurs 
with  a red  glow ; a white  earthy-looking  sulphide,  which  rapidly 
absorbs  moisture  from  the  air,  is  the  result : this  compound  is  com- 
pletely soluble  in  water,  but  it  is  decomposed  whilst  undergoing 
solution  ; SiS,  + 2 H^O  becoming  SiO^  -j-  2 H^S ; sulphuretted 
hydrogen  and  soluble  silica  being  formed : the  silica  may  be  ob- 
tained as  a jelly  by  evaporation.  

(475)  CHLORmE  OF  Silicon  (SiCl,  = 170) ; JIol.  Vol.  \ \ j ; 
TheoretiG  Sp.  Gr.  of  Vapour,  5*873 ; Observed,  5*939 ; of 
liquid  at  32°,  1*5237 : Boiling-point  138°. — This  compound 


CHLOKIDE  OF  SILICON. 


219 


may  be  formed  by  beating  silicon  in  cblorine,  or  more  economi- 
cally by  the  following  indirect  method : — Finely  powdered  silica 
is  made  up  into  a paste  with  oil  and  charcoal,  and  heated  in  a 
covered  crucible ; the  charred  mass  in  fragments  is  transferred  to 
a porcelain  tube,  in  which  it  is  ignited,  and  subjected  to  a current 
of  dry  chlorine : neither  chlorine  nor  carbon  separately  can  decom- 
pose silica,  but  together  they  effect  its  decomposition  easily,  car- 
bonic oxide  escaping,  wdiilst  chloride  of  silicon  is  formed ; Si02  -p 
2 CI2 + -02 = 2 00  4-  BiCl^.  The  product  is  received  into  vessels  cool- 
ed with  a freezing-mixture.  Fig.  313  shows  a form  of  apparatus  by 


which  the  chloride  may  be  readily  prepared : n is  a porcelain  tube, 
which  contains  the  mixture  of  charcoal  and  silica ; chlorine  is 
liberated  from  the  flask  a,  washed  with  water  in  b,  dried  by 
transmitting  it  over  pumice  and  sulphuric  acid  contained  in  the 
tube  c,  and  allowed  to  pass  through  the  tube  d,  which  with  its 
contents  is  exposed  to  a red  heat  in  the  furnace ; the  chloride  of 
silicon  distils  over  into  the  bent  tube,  e,  where  it  is  condensed  by 
immersion  in  a freezing-mixture  of  ice  and  salt ; a tube  fused  into 
the  bend  of  the  tube  e,  conveys  the  chloride  into  a bottle,  o, 
which  may  also  be  kept  cool  by  ice. 

Chloride  of  silicon  is  a transparent,  colourless  liquid,  with  a 
pungent,  acid,  irritating  odour ; it  is  very  volatile,  and  fumes 
strongly  in  the  air.  Its  composition  is  the  following  : — 

By  weight.  By  volume.  8p.  gr. 

Chlorine  CU  = 142  or  83-58  4 =20  = 4 906 

Silicon  Si  = 28  16-4t  2?  = 1?  = 0967 

|siCl4  = 170  100-00  2 = 1-0  = 5 873 


220 


HYDKOCHLOKATE  OF  CHLORIDE  OF  SILICON. 


Water  immediately  decomposes  chloride  of  silicon,  depositing 
hydi'ated  silica,  and  forming  hydrochloric  acid.  A moist  atmo- 
sphere also  decomposes  the  chloride,  cansing  the  deposition  of 
silica  in  opaque  lamellar  plates,  which  like  the  mineral  hydro_phane 
become  transparent  when  immersed  in  water,  but  resume  their 
opacity  on  drying ; the  siliceous  deposit  obtained  from  the  joints 
of  the  bamboo,  known  as  tabasheer^  exhibits  the  same  peculiarity. 
The  liquid  chloride  does  not  act  on  potassium,  but  if  the  metal  be 
heated  in  its  vapour,  chloride  of  potassium  is  produced,  and  silicon 
is  set  free ; this  is  one  of  the  best  methods  of  obtaining  sili- 
con. 

Two  compounds  between  the  sulphide  and  the  chloride  of  sil- 
icon have  been  obtained  (Pierre) ; they  may  be  represented  by  the 
formulae  (SiS2  2SiCl4;  Sp.  Gr.  of  vapour^  5*24)*  and  (2  SiS^, 

SiCl,). 

Bromide  of  Silicon  (SiBr^;  Sp.  Gr.  of  Liquid  at  32°, 
2*813  ; Boiling-pt.  308°)  is  analogous  in  properties  to  the  chloride  : 
it  may  be  formed  in  a similar  manner. 

(477)  Hydrochlorate  of  Chloride  of  Silicon  (SigH^Cljo  or 
4 HC1,3  SiCl2=443);  Sp.  Gr.  of  Liquid,  1*65  ; Boiling-pt.  108°; 
(Wohler  and  Buff,  Annal.  de  Cliimie,^  III.  Hi.  269). — This  com- 
pound is  a colourless,  highly  mobile  liquid,  which  fumes  power- 
fully on  exposure  to  the  air,  depositing  a wdiite  film  upon  sur- 
rounding bodies,  and  emitting  a vapour  of  suffocating  odour.  It 
is  highly  inflammable,  and  burns  with  a greenish,  feebly  luminous 
flame,  depositing  silica  and  emitting  hydrochloric  acid.  If  its 
vapour  be  mixed  with  oxygen,  it  explodes  violently  on  the  trans- 
mission of  the  electric  spark,  silica  being  deposited,  w^hilst  hydi'o- 
chloric  acid  and  chloride  of  silicon  are  formed.  The  liquid  may 
be  boiled  upon  sodium  without  undergoing  decomposition.  If 
passed  through  a tube  heated  to  redness,  it  is  decomposed  into  a 
mixture  of  chloride  of  silicon  and  hydrochloric  acid,  whilst  half 
its  silicon  is  deposited  in  the  form  of  a brown  amorphous  crust 
exhibiting  a metallic  lustre.  AVater  decomposes  it  immediately 
with  great  elevation  of  temperature,  leukon  and  hydrochloric  acid 
being  formed  : SigH^Cljo-fh  yielding  SigH.O^-flO  HCl. 

The  mode  of  preparing  this  compound  by  transmitting  dry 
hydrochloric  acid  over  crystallized  silicon  heated  to  dull  redness, 
has  already  been  described  w*hen  speaking  of  the  preparation  of 
leukon  (471(2.) 

A similar  liquid  compound  (SigH^Br^o  ? ; Sp.  Gr.  2*5)  may  be 
obtained  in  like  manner  by  means  of  hvdrobromic  acid.  "The 
corresponding  compound  of  iodine  (SigHJ^g?)  forms  a fusible 
crystalline  solid. 


* The  calculated  density  of  this  substance,  supposing  it  to  give  3 volumes  of  va- 
pour, or  1 volume  of  the  vapour  of  sulphide  of  silicon  and  2 of  chloride  of  silicon 
united  without  condensation,  is  5*018;  for 

By  volume.  Sp.  pr. 

SiSa  = 1 or  0-33  = 3*959 

2 SiCl4  = 2 0 67  = 1059 


1*00 


5*018 


FLUORIDE  OF  SILICON SILICOFLUOEIC  ACID. 


221 


(478)  Fluoride  of  Silicon  (SiF^=104) : Theoretic  Sp.  Gr.^ 
3'687 ; Observed,  3 '60  ; Mol.  Yol.  | " | |. — The  fluoride  is  one  of 
the  most  remarkable  compounds  of  silicon : so  powerful  is  the 
attraction  between  fluorine  and  silicon  that  hydrofluoric  acid  sep  - 
arates  silicon  from  its  most  intimate  combinations,  such  as  silica 
and  glass.  In  order  to  prepare  the  fluoride  of  silicon,  equal  parts 
of  finel j-powdered  fluor-spar  and  siliceous  sand,  or  powdered  glass, 
are  mixed  in  a capacious  flask  or  retort,  with  twelve  times  their 
weight  of  oil  of  vitriol.  On  the  application  of  heat,  a colourless 
gas,  with  a peculiar,  pungent,  acid  odour,  is  given  off : hydro- 
Suoric  acid  is  liberated,  and  this  immediately  attacks  the  silica,  as 
is  shown  in  the  following  representation  of  the  reaction  : — 

OaF,4-H,Se,  2 HF  -f  OaSO, ; 
and  4 HF  -h  SiO,  2 11,0  + SiF,. 

The  composition  of  the  gas  may  be  thus  represented : — 


Silicon Si 

By  weight. 

==  28  or  26'9 

By  vol. 

2 ? or  1 ? 

Sp.  gr, 
= 0 967 

Flourine F4 

= 76  or  73-1 

4 

2 

= 2-626 

Fluoride  of  silicon  SiF4 

= 104  100-0 

2 

1 

= 3-593 

Fluoride  of  silicon  fumes  strongly  in  air ; it  is  not  inflam- 
mable, but  extinguishes  a lighted  taper  ; under  strong  pressure  it 
was  liquefied  by  Faraday ; and  according  to  Natterer  it  becomes 
solid  at  — 220°.  The  gas  is  dissolved  and  partially  decomposed 
by  water ; it  must  therefore  be  collected  over  mercury,  and  in 
jars  which  have  been  perfectly  dried  at  a high  temperature ; the 
slightest  trace  of  moisture  on  the  surface  of  the  jar  causes  a de- 
position of  silica,  which  adheres  very  firmly  to  the  glass  and  ren- 
ders it  opalescent.  Fluoride  of  silicon  combines  with  twice  its 
volume  of  ammoniacal  gas,  and  forms  with  it  a crystalline  vola- 
tile compound. 

(479)  SiLicoFLuoRic  Acid  : Ilydrofluosilicic  Acid  (2  IIF,SiF4 
= 144). — When  a stream  of  gaseous  fluoride  of  silicon  is  trans- 
mitted through  water,  it  is  partially  decomposed  and  partially 
dissolved.  Two  atoms  of  water  react  on  3 of  fluoride,  and  pro- 
duce the  silicofluoric  acid,  which  is  dissolved,  whilst  one-third  of 
its  silicon  is  deposited  as  silica  in  the  form  of  hydrate : — • 

3 SiF,  + 2 H,e=Sie,  -f  2 (2  IIF,SiF0. 

In  the  preparation  of  this  acid,  the  tube  from  wdiich  the  fluo- 
ride is  escaping  must  not  plunge  at  once  into  water,  otherwise  it 
will  speedily  become  obstructed  by  the  deposited  silica.  This  in- 
convenience may  be  prevented  by  placing  a little  mercury  at  the 
bottom  of  the  vessel,  in  order  that  the  tube  may  dip  beneath  the 
mercury,  as  shown  in  fig.  314.  Each  bubble  as  it  rises  becomes 
surrounded  by  a siliceous  envelope,  and  finally  the  liquid  sets  in- 
to a gelatinous  mass  w the  acid  liquid  is  separated  by  pressure  in 
linen  from  the  deposit,  which  when  freed  from  adhering  acid, 
constitutes  a pure  hydrate  of  silica.  A more  easy  method  of  ob- 
taining the  acid,  when  it  is  required  in  quantity,  consists  in 
dissolving  silica  in  diluted  hydrofluoric  acid. 


222 


BORON. 


A saturated  solution  of  silicofluoric  acid  forms  a very  sour, 

faming  liquid.  In  solu- 
tion it  does  not  attack  glass, 
but  it  does  so  if  allowed  to 
evaporate  upon  it ; the 
fluoride  of  silicon  becomes 
volatilized,  leaving  free  hy- 
drofluoric acid,  which,  re- 
acting on  the  silica,  pro- 
duces water  and  fluoride  of 
silicon,  as  in  the  ordinary 
process  for  making:  that  g:as  ; 

4HF-j-_Si©,=2‘H,e  + Si 

F^.  Silicofluoric  acid  com- 
bines with  bases  to  form 
salts,  if  the  base  be  not 
added  in  excess ; if  an  ex- 
cess of  base  be  employed, 
silica  is  precipitated,  and 
the  whole  of  the  fluorine 
is  separated  as  a metallic 
fluoride.  In  the  flrst  case  the  action  may  be  thus  represented : 
2 IvIIO-+2  IIF,SiF^=2  H„0-|-2  IvF,SiF^.  In  the  second  case  : 6 
KllO-f  2 IIF,SiF^  = I IlJO-fGKF-f-SiO^.  Dilute  solution  of 
silicofluoric  acid  produces  transparent  jelly-like  precipitates  in 
the  alkaline  salts ; it  is  frequently  employed  as  a precipitant  of 
potassium,  AYith  salts  of  barium  the  acid  gives  a white  crystal- 
line precipitate. 

§ II.  Boron:  B=10*9. 

(480)  Boron  is  the  characteristic  combustible  element  of  the 
acid  contained  in  borax,  whence  it  derives  its  name.  In  nature  it 
is  always  met  with  in  combination  with  oxygen.  It  is  a body 
which  occiu’s  in  comparatively  sparing  quantities,  and  only  in  a 
few  localities.  Though  one  of  the  triad  elements,  it  presents 
considerable  analogy  with  silicon  in  its  properties,  and  its  mode 
of  combination,  and,  like  it,  may  be  obtained  in  three  distinct 
modifications,  the  crystalline,  the  graphitoid,  and  the  amorphous. 

Amorphous  Boron. — Berzelius  obtained  boron  by  a process 
analogous  to  that  employed  in  the  case  of  silicon.  The  borofluo- 
ride  of  potassium,  a sparingly  soluble  salt,  is  made  by  saturating 
hydrofluoric  with  boracic  acid,  neutralizing  the  liquid  with  car- 
bonate of  potassium,  and  wasliing  the  compound  with  cold  water ; 
it  is  then  dried  at  a heat  a little  below  redness.  AYhen  cold  it  is 
mixed  with  an  equal  weight  of  potassium,  and  heated  in  a cov- 
ered iron  crucible.  The  fluoride  of  potassium  is  removed  by  hot 
water  : 2 (KF,BF3)  -f  3 = 8 KF  + 2 B. 

Boron  as  thus  obtained  is  an  amorphous,  dull  olive-green 
powder,  which,  before  it  has  been  strongly  ignited,  soils  the 
fingers,  and  is  dissolved  by  pure  water  in  small  quantity,  forming 
a greenish  yellow  solution  ; from  which,  however,  it  is  precipitat- 


Fig.  314. 


CRYSTALLIZED  BORON. 


223 


ted  nnclianged  on  adding  a little  solution  of  sal  ammoniac.  Boron 
is  not  oxidized  by  exposure  to  air,  to  water,  or  to  solutions  of  the 
alkalies,  whether  cold  or  boiling.  It  is,  however,  easily  oxidized 
when  treated  with  nitric  acid  or  with  aqua  regia.  After  exposure 
to  intense  heat  in  vessels  from  which  air  is  excluded,  it  becomes 
denser,  and  darker  in  colour.  It  may  be  fused  by  the  application 
of  a heat  still  more  intense  than  that  required  to  melt  silicon. 
As  first  obtained,  boron  exhibits  a strong  attraction  for  oxygen, 
and,  if  heated  in  air  or  in  oxygen,  takes  fire  below  redness,  burn- 
ing with  a reddish  light  and  emitting  vivid  scintillations ; it  is 
thus  converted  superficially  into  boracic  anhydride,  which  melts 
and  protects  a portion  of  the  boron.  If  mixed  with  nitre  and 
heated  to  redness,  it  deflagrates  powerfully.  It  is  also  oxidized 
when  ignited  with  hydrate  of  potash ; and  when  heated  with 
carbonate  of  potassium  in  fusion  it  sets  carbon  free,  and  forms 
borate  of  potassium.  Pulverulent  boron,  like  silicon,  is  a non- 
conductor of  electricity. 

Boron  may  be  obtained  in  the  amorphous  form  in  large  quan- 
tity by  the  following  method  (W ohler  and  Deville ; Liebig^ s 
Annal.  cv.  67) : — 1500  grains  of  fused  boracic  anhydride  is 
coarsely  powdered  and  mixed  rapidly  with  900  grains  of  sodium 
cut  into  small  pieces.  The  mixture  is  then  introduced  into  a 
cast-iron  crucible  previously  heated  to  bright  redness  ; 700  or  800 
grains  of  solid  but  previously  fused  chloride  of  sodium  are  placed 
upon  the  top  of  the  mixture,  and  the  crucible  is  covered.  As 
soon  as  the  reaction  is  over,  the  still  liquid  mass  is  thoroughly 
stirred  with  an  iron  rod,  and  poured,  whilst  red  hot,  in  a slender 
stream,  into  a large  and  deep  vessel  containing  water  acidulated 
with  hydrochloric  acid.  The  pulverulent  boron  is  then  collected 
on  a filter  and  washed  with  acidulated  water  till  the  boracic  acid 
is  got  rid  of ; after  which  the  washing  may  be  continued  with 
pure  water,  until  the  boron  begins  to  run  through  the  filter.  It 
must  finally  be  dried  upon  a porous  slab  without  the  application 
of  heat. 

Crystallized  Boron. — In  order  to  convert  the  amorphous  into 
the  crystallized  form,  the  following  method  may  be  adopted : — A 
small  Hessian  crucible  is  lined  with  the  pulverulent  boron  made 
into  a paste  with  water,  and  the  boron  is  pressed  in  strongly,  as 
in  the  ordinary  mode  of  lining  a crucible  with  charcoal.  In  the 
central  cavity  a piece  of  aluminum  weighing  from  60  to  90  grains 
is  placed ; the  cover  is  luted  on  and  the  crucible  enclosed  in  a 
second,  the  interval  between  the  two  being  filled  with  recently 
ignited  powdered  charcoal.  The  outer  crucible  is  next  closed 
with  a luted  cover,  and  the  whole  exposed  for  a couple  of  hours 
to  a heat  sufficient  to  fuse  nickel.  The  temperature  is  then 
allowed  to  fall ; and  when  cold  the  contents  of  the  inner  crucible 
are  digested  in  diluted  hydrochloric  acid,  which  dissolves  out  the 
aluminum ; beautiful  crystals  of  boron  are  left,  generally  trans- 
parent, but  of  a dark  brown  colour.  A quantity  of  graphitoid 
scales  of  boron  are  formed  at  the  same  time,  in  pale,  copper- 
coloured,  opaque  six-sided  plates. 


224 


BORA.CIC  ANHYDRIDE  AND  ACID. 


Crystallized  boron  lias  a sp.  gr.  of  2'68 ; it  assumes  the  form 
of  transparent  octohedra  belonging  to  the  pyramidal  system. 
These  crystals  when  pure  are  nearly  colourless,  but  they  usually 
contain  traces  of  foreign  matters,  which  give  them  a pale  yellow 
or  red  colour : they  refract  light  powerfully,  and  are  hard  enough 
to  scratch  the  ruby,  and  even  sensibly  to  wear  away  the  diamond. 
Crystallized  boron  burns  imperfectly  in  oxygen  when  heated  to 
full  whiteness,  and  becomes  coated  with  a layer  of  fused  boracic 
anhydride.  It  however  burns  easily  when  heated  to  redness  in 
dry  gaseous  chlorine,  becoming  converted  into  the  gaseous  terchlo- 
ride  of  boron.  Ho  acid  or  mixture  of  acids  has  any  action  upon 
either  crystalline  or  graphitoid  boron. 

Boron,  like  titanium,  enters  into  direct  combination  with 
nitrogen  at  a high  temperature ; a quantity  of  this  nitride  is 
formed  as  a gray  coherent  mass  during  the  preparation  of  crystal- 
lized boron.  Pulverulent  boron,  when  heated  in  a current  of  dry 
ammoniacal  gas,  becomes  incandescent,  and  is  converted  into 
nitride,  whilst  hydrogen  is  liberated.  Boron  in  all  its  forms  burns 
freely  in  chlorine : when  ignited  in  contact  with  steam,  with  sul- 
phuretted hydrogen,  and  with  hydrochloric  acid,  it  decomposes 
them,  but  the  latter  is  attacked  with  some  difficulty ; boracic  acid, 
sulphide  of  boron,  and  chloride  of  boron  being  formed  respec- 
tively, whilst  hydrogen  is  liberated. 

(481)  Boracic  Anhydride  (B203=69'8  ; or  B03-l-34‘9) : Crys- 
tallized Acid  (TIB02,H20). — This  is  the  only  known  compound 
of  oxygen  and  boron.  It  is  found  combined  with  sodium  as  an 
acid  borate  in  the  tincal  obtained  from  Thibet,  and  in  a crystal- 
lized borate  of  calcium  and  magnesium  from  the  western  coast 
of  South  America ; quite  recently  borax  and  boracic  acid  have 
been  found  in  California ; but  its  most  abundant  source  is  the 
maremma  of  Tuscany,  where  it  is  met  with  in  the  uncombined 
state,  and  accompanied  by  sulphuretted  hydrogen : it  issues  in 
small  quantity  along  with  the  jets  of  steam  {fumerolles  oy  sqffioni)^ 
maintained  by  the  action  of  subterranean  tire.  These,  at  Monte 
Cerboli  and  Monte  Botondo,  in  Tuscany,  are  directed  into  small 
lagoons  or  artificial  basins,  such  as  those  shown  in  fig.  315,  the 
waters  of  which  on  evaporation  yield  a crude  boracic  acid,  from 
which  a large  proportion  of  the  borax  of  commerce  is  now  manu- 
factured. According  to  the  ingenious  suggestion  of  Lardarello, 
the  heat  supplied  by  the  fumerolles  themselves  is  employed  in  this 
evaporation.  Water  from  tlie  adjacent  springs  is  directed  into 
the  uppermost  basin,  a ; here  it  stays  for  twenty-four  hours,  and 
is  run  off  after  successive  intervals  of  twenty-four  hours  into  each 
of  the  four  lower  basins,  J,  c,  d^  e.  From  the  last  of  these  it  flows 
into  settling  vats, /*,/’,  where  in  the  course  of  twenty-four  hours 
more  the  suspended  matters  subside.  The  supernatant  liquid, 
which  contains  from  to  2 per  cent,  of  boracic  acid,  is  then 
decanted  into  shallow  leaden  evaporating  pans,  y,  heated  by 
the  vapours  of  several  fumerolles,  which  circulate  underneath  in 
flues.  A,  arranged  for  the  purpose.  In  twenty-four  hours  the 
liquor  is  reduced  to  about  half  its  bulk ; it  is  then  transferred  to 


PEEPAEATION  OF  BORACIC  ACID. 


225 


a smaller  pan,  on  a lower  level,  where  it  is  allowed  to  evaporate 
for  twenty-four  hours  longer  : it  is  again  transterred  to  a smaller 
pan,  when  after  the  lapse  of  twenty-four  hours  more  it  has 


Fig.  315. 


acquired  a density  of  1*07  or  1*08,  and  is  sufficiently  concentrated 
to  crystallize  on  cooling.  Sulphate  of  calcium  in  abundance  is 
deposited  in  the  pans  during  these  evaporations,  and  it  requires 
removal  from  time  to  time.  About  two  thousand  tons  of  the 
crude  acid  are  annually  thus  procured  in  Tuscany.  The  crude 
acid,  however,  seldom  contains  more  than  three-fourths  of  its 
weight  of  tlie  pure  crystallized  acid,  the  remainder  consisting 
principally  of  sulphates  of  ammonium  and  magnesium,  with  small 
quantities  of  sulphate  of  aluminum  and  of  other  alkaline  and  earthy 
sulphates,  a peculiar  organic  matter,  and  a small  proportion  of 
silica.  By  boring  into  the  volcanic  strata  artificial  soffioni  have 
been  formed  which,  as  at  Travale,  yield  a large  quantity  of  horacic 
acid,  by  treatment  similar  to  that  above  described. 

The  commercial  acid  is  purified  by  adding  to  it  carbonate  of 
sodium  as  long  as  efiervescence  occurs,  and  thus  forming  borax, 
which  is  obtained  nearly  pure  by  crystallization  (592). 

In  order  to  procure  the  acid,  purified  borax  is  dissolved  in  4 
parts  of  boiling  water,  and  to  the  hot  solution,  oil  of  vitriol  equal 
in  weight  to  that  of  one-fourth  of  the  borax  employed  is  added 
after  dilution  with  a little  water.  In  this  process  sulphate  of 
sodium  is  formed,  and  boracic  acid  is  liberated.  Tlie  s])aringly 
soluble  boracic  acid  crystallizes  out  on  cooling,  in  pearly-looking 
scales  which  feel  greasy  to  the  touch.  It  is  not,  however,  quite 
pure,  as  it  always  retains  a little  sulphuric  acid.  To  remove  this, 
the  crystals  are  washed  with  ice-cold  water,  dried  and  fused  in  a 
])latinum  crucible,  and  on  redissolving  the  mass  in  4 times  its 
weight  of  boiling  water,  the  acid  crystallizes  on  cooling,  in  a state 
of  pirrity. 

15 


226 


PROPEETIES  OF  BOEACIC  ACID BOEATES. 


The 


composition  of  this  acid  is  the  following  : 

Anhydride,  • ttt 


Crystallized:  HBOa,  H2O. 


Boron B.2 

Oxygen  . . . O; 
Water 


= 21-8  or  31-23 
= 48  68-77 


B 
O3 
3 HO 


= 10-9  or  ) 

= 24-0 

= 27-0  43-61 


Boracic  acid  B2O3  = 69-8  100-00  (BO3,  3 HO)  61-9 


100-00 


Properties. — The  crystals  of  boracic  acid  effloresce  and  lose 
two-thirds  of  their  water  at  a gentle  heat,  and  at  a slight  increase 
of  temperature  become  converted  into  the  anhydride  ; at  a red 
heat,  or  a little  below,  the  anhydride  fuses  to  a transparent,  viscid, 
ductile  glass,  which  remains  clear  as  it  cools.  It  2:radually  absorbs 
moisture  from  the  air  and  crumbles  to  pieces.  Boracic  acid  com- 
municates to  its  compounds  the  property  of  ready  fusibility  ; 
indeed  it  is  chiefly  on  this  account  that  it  is  valued.  Many  of  the 
borates  are  admirably  adapted  for  fluxes,  which  are  used  in  the 
glazing  of  porcelain,  and  in  the  melting  of  gold  and  silver. 

Boracic  acid  is  sparingly  soluble  in  cold  water,  but  it  is  dissolved 
by  3 times  its  weight  of  boiling  water  : the  solution  has  a bitter- 
ish and  scarcely  sour  taste  ; if  allowed  to  evaporate  upon  tnnneric 
paper,  it  turns  the  paper  brown,  as  an  alkali  would  do  ; it  gives  to 
litmus  a purplish  red  tint,  instead  of  the  usual  bright  red  of  the 
stronger  acids.  It  gradually  decomposes  solutions  of  the  carbonates 
even  in  the  cold ; but,  on  the  other  hand,  a brisk  current  of  carbonic 
acid  or  of  sulphuretted  hydrogen  will  cause  a separation  of  boracic 
acid  in  crystals  from  a strong  solution  of  borax.  Boracic  acid  is 
soluble  in  alcohol,  and  the  solution  burns  with  a characteristic 
green  flame,  which  when  shewed  through  the  spectroscope  is  seen 
to  exhibit  5 well-marked  green  bands  (rart  I.  fig.  80,  Ho.  6).  It  is 
not  possible  to  evaporate  a solution  of  boracic  acid  either  in  alcohol 
or  in  water  without  losing  a portion  of  the  acid,  for  the  vapour 
always  carries  with  it  an  appreciable  amount  of  the  acid ; and  if 
steam  at  a high  temperature  be  transmitted  over  boracic  acid  or 
borate  of  calcium,  the  acid  is  volatilized  in  considerable  quantities 

Borates. — Boracic  anhydride  is  but  very  slowly  volatilized  by 
ignition,  and  hence,  though  its  chemical  activity  is  very  feeble,  it 
at  high  temperatures  expels  all  anhydrides  more  volatile  than  itself, 
when  fused  with  their  salts.  It  enters  into  combination  with  the 
alkaline  bases  in  a great  variety  of  proportions,  resembling  silica 
in  this  respect  as  in  some  others.  Although  many  of  these  salts 
contain  more  than  1 atom  of  acid,  they  all  restore  the  colour  of 
reddened  litmus  paper.  A sexborate  of  potassium  (2  KBO^, 
10  IIBO2,  5 H^O)  may  be  obtained  in  crystals,  and  a terborate 
(KBOj,  2 IIBO2,  3 H^O)  has  also  been  crystallized.  The  borates 
of  the  alkaline  metals  are  freely  soluble,  those  of  the  other  metals 
are  only  imperfectly  soluble  ; none  of  the  borates,  however,  are 
so  insoluble  as  to  ftirnish  an  accurate  mode  of  ascertaining  the 
quantity  of  boracic  acid  present  in  solution  by  the  formation  of  a 
precipitate.  All  the  sparingly  soluble  borates  are  dissolved  by 
diluted  nitric  acid.  In  analyzing  a borate  it  is  usual  to  deter- 
mine the  amount  of  all  the  other  acids  and  metals,  and  other  con- 


FLUORIDE  OF  BORON BOROFLUORIC  ACID, 


227 


stitiients,  and  to  estimate  the  deficiency  as  boracic  acid.  It  is 
not  unlikely  that  boracic  acid  may  have  been  overlooked  in  many 
minerals,  as  its  detection  in  small  quantities  is  rather  difficult 
except  by  the  aid  of  the  spectroscope.  (Part  I.  p.  155). 

(482)  A sulphide^  a chloride^  and  a bromide  of  boron  may  be 
prepared  by  methods  similar  to  those  employed  to  obtain  the 
corresponding  compounds  of  silicon.  The  chloride  of  boron 
(BCl3=117'4  ; Sp.  Gr.  3*942  ; Mol.  Vol.  | fH)  is  gaseous  at  ordi- 
nary temperatures;  it  fumes  strongly  in  air,  and  is  instantly 
decomposed  by  water  into  hydrochloric  and  boracic  acids.  It 
has  the  following  composition  : — 


By  weight. 

By  volume. 

Sp.  gr. 

Boron 

..  B 

= 10-9 

or  9*29 

2?  or 

0*5 

= 0*376 

Chlorine. . 

..  CI3 

= 106-5 

90-71 

3 

1*5 

= 3-679 

Chloride  of  ) 
boron  ) 

BCI3 

= 117*4 

100*00 

2 

1 

= 4-055 

Two  volumes  of  this  chloride  unite  with  3 volumes  of  ammonia, 
and  become  condensed  into  a volatile  crystalline  saline  body. 

(483)  Fluoride  of  Boron  (BFg  = 67*9) ; Sp.  Gr.  2*312 ; 
Mol.  Vol.  I I |. — Boron  forms  with  fiuorine  a com])ound  analo- 
gous to  the  fluoride  of  silicon.  It  is  best  prepared  as  follows  : 

2 parts  of  fluor-spar  and  1 of  vitrified  boracic  anhydride,  both 
in  fine  powder,  are  intimately  mixed,  and  intensely  ignited  in  a 
wrought-iron  tube  closed  at  one  end  : decomposition  occurs  thus  : 

3 OaF,  -f-  4 = 3 (Oa  2 BO^)  -f-  2 BFg.  Borate  of  calcium 

remains  in  the  tube,  and  the  fluoride  of  boron  passes  over  as  a 
colourless  gas,  which  may  be  collected  over  mercury.  The  com- 
position of  the  fluoride  of  boron  is  the  following  : — 

By  weight.  By  volume.  Sp.  gr. 

Boron B = 10-9  or  16-07  2 ? or  1 ? = 0-376 

Fluorine P3  = 57-0  83  93  3 1*5  = 1*969 


Fluoride  of 
boron 


BFg 


= 67-9  100-00  2 1*0  = 2-345 


Fluoride  of  boron  does  not  support  combustion  ; it  has  an  irritat- 
ing odour,  and  fumes  densely  in  the  air.  It  is  instantly  absorbed 
by  water,  which  dissolves  700  times  its  volume  of  the  gas,  with 
rapid  rise  of  temperature,  whilst  it  increases  in  density  to  1*77, 
and  forms  an  oily-looking,  fuming,  and  corrosive  acid  liquid, 
which  chars  organic  matter  as  powerfully  as  oil  of  vitriol.  This 
solution  has  been  called  borofluorie  acid.  The  reaction  wdiich 
occurs  when  the  gas  comes  into  contact  with  water  is  sufficiently 
simple,  2 BFg  -f  3 HgO,  yielding  (B203,6  IIF).  When  heated,  a 
part  of  the  gas  escapes,  and  the  specific  gravity  of  the  liquid 
becomes  reduced  to  1*584 ; when  of  this  density  it  distils  un- 
changed, and  contains  two  atoms  of  water,  the  formula  of  tlie 
aqueous  solution  becoming  (B^Og,  6 IIF,  2 H^O).  Borofluorie 
acid  is  also  easily  prepared  by  saturating  hydrofluoric  acid  with 
boracic  acid,  keeping  the  mixture  cool,  and  then  concentrating  it 
in  platinum  vessels  till  dense  fumes  arise. 

When  largely  diluted  with  water,  one-fourth  of  the  boron  is 
separated  in  the  form  of  boracic  acid,  and  another  compound  is 


228 


PEROXIDE  OF  HTDROGEX. 


found  in  solution,  termed  JiyclrqfluoboriG  acid.  In  composition 
this  body  somewhat  resembles  the  silicotluoric  acid,  though  it  is 
not  strictly  analogous  to  it.  Its  formation  is  readily  explained  by 
the  following  equation,  from  which  it  will  be  seen  that  hydrofluo- 
boric  acid  contains  the  elements  of  1 atom  of  hydrofluoric  acid  and 
1 atom  of  fluoride  of  boron  : — 

8 BF3  + 4 H,e  = 2 HBO,  + 6 (HF,BF3). 

So  strong  is  the  tendency  to  the  formation  of  this  compound  in 
dilute  solutions,  that  if  boracic  acid  be  added  to  a solution  of 
fluoride  of  potassium  or  of  ammonium,  for  each  equivalent  of 
boracic  acid  present,  3 equivalents  of  potash  or  of  ammonia  are 
liberated,  and  fluoboride  of  the  basvl  is  formed,  for  example,  8 KF 
+ 2 HBO3  + 2 II3O  2 (KF,BF3)  + 6 KHO. 

(484)  Xn'RiDE  OF  Boron  (BX). — As  already  mentioned,  boron 
combines  with  nitrogen  at  a red  heat  with  great  avidity.  Xitride 
of  boron  may  also  be  obtained  by  transmitting  a current  of  dry 
nitrogen  gas  over  a mixture  of  1 part  of  pure  flnely-powdered 
charcoal  with  4 parts  of  fused  boracic  anhydride,  exposed  to  a full 
white  heat  in  a porelain  tube.  It  may  likewise  be  procured 
readily  by  mixing  1 part  of  anhydrous  borax  with  2 parts  of  sal 
ammoniac,  and  heating  it  to  full  redness  in  a covered  platinum 
crucible ; a white,  infusible,  porous  mass  is  left,  which,  when 
boiled  with  diluted  hydrochloric  acid  and  well  washed,  yields  the 
nitride  of  boron  as  a white,  light,  amorphous,  insoluble  powder, 
which  feels  like  talc  when  rubbed  upon  the  skin.  It  may  be 
heated  in  hydi’ogen  or  in  chlorine  without  change ; it  is  but  very 
slowly  acted  upon  by  concentrated  acid  or  alkaline  solutions ; but 
' when  fused  with  hydrate  of  potash  it  is  converted  into  ammonia 
and  borate  of  potassium,  3 IvIIO  + BX  = KBO^  + K^O  + 
II3X.  In  a current  of  steam  it  is  completely  converted  into  borate 
of  ammonium;  BX  + 2 II^O  yielding  H^XBO,.  It  is  also  de- 
composed when  heated  with  easily  reducible  metallic  oxides,  such 
as  those  of  lead  or  copper,  nitric  oxide  being  evolved. 


CHAPTEK  X. 

OTHER  COMPOUNDS  OF  THE  NON-METALLIC  ELEMENTS. 

§ I.  Compounds  of  Hydrogen  and  Oxygen. 

(485)  Peroxide  or  Del^oxide  of  Hydrogen  ; Oxygenated 
Water ! (HjO^  = 34,  or  HO,  = IT) : Sp.  Gr.  of  Liquid.,  1*453. — 
Water  is  not  the  only  compound  of  oxygen  with  hydrogen. 
Thenard,  in  the  year  1818,  discovered  a remarkable  substance, 
which,  as  it  contains  2 atoms  of  oxygen  in  combination  with  2 
atoms  of  hy  di’ogen,  is  termed  peroddde  of  hydrogen.  It  is  a colour- 


PREPAHATTON  OF  PEKOXIDE  OF  HYDKOGEN. 


229 


less  liquid,  of  syrupy  consistence,  with  an  odour  somewhat 
resembling  that  of  chlorine  very  much  diluted ; it  remains  liquid 
at  a temperature  of  — 22°.  This  peroxide  is  a very  unstable  com- 
pound ; a temperature  of  about  70°  F.  is  sufficient  to  cause  the 
oxygen  to  begin  to  escape  in  small  bubbles,  and  when  heated  to 
the  boiling-point  of  water,  the  gas  is  evolved  with  a rapidity 
almost  amounting  to  an  explosion.  The  liquid  is  soluble  in  water 
in  all  proportions ; when  diluted  it  is  less  easily  destroyed  by  ele- 
vation of  temperature,  though  ebullition  for  a few  minutes  is  suf- 
hcient  to  expel  the  whole  of  the  additional  atom  of  oxygen,  water 
alone  remaining.  This  circumstance  furnishes  an  easy  method 
of  analysing  the  peroxide  of  hydrogen.  A given  weight  of  the 
liquid  is  placed  in  a small  retort,  and  diluted  with  10  or  12  times 
its  bulk  of  water ; the  temperature  is  raised  to  ebullition,  oxygen 
is  given  off  freely,  and  the  gas  is  collected  over  mercury,  and 
measured  when  cool : the  weight  of  the  oxygen  can  be  calculated 
from  its  bulk,  and  deducting  the  weight  thus  obtained  from  that 
of  the  peroxide  operated  upon,  it  will  be  found  that  for  each  16 
grains  of  oxygen  expelled,  18  of  water  remain ; consequently,  as 
Avater  contains  2 grains  of  hydrogen  combined  with  16  of  oxygen, 
the  peroxide  of  hydrogen  will  contain  2 grains  of  hydrogen  united 
Avith  32  of  oxygen. 

Peroxide  of  hydrogen  bleaches  a solution  of  litmus,  and  many 
vegetable  colours ; a drop  of  it,  if  placed  upon  the  tongue,  blanches 
it,  and  destroys  sensation  for  a time ; the  taste  of  the  liquid  is 
astringent,  and  someAvhat  metallic.  By  means  of  peroxide  of 
hydrogen  the  black  sulphide  of  lead  (PbS)  is  converted  into  the 
Avhite  sulphate  of  the  metal  (PbSO^),  and  many  metallic  protoxides 
become  oxidized  to  the  maximum. 

The  peroxide  of  hydrogen,  however,  is  not  only  decomposed 
by  substances  which  possess  an  attraction  for  oxygen,  but  the  mere 
contact  of  many  finely  divided  metals  and  metallic  oxides  which 
do  not  undergo  any  permanent  change,  occasions  its  decomposi- 
tion ; gold,  silver,  and  platinum  produce  an  instantaneous  evolu- 
tion of  oxygen  gas,  which  is  the  more  rapid  the  finer  the  subdi- 
vision of  the  body  by  which  the  decomposition  is  occasioned.  A 
similar  effect  is  produced  by  contact  Avith  the  oxides  of  these 
metals,  or  Avith  the  peroxide  of  manganese  or  of  lead.  It  is  espe- 
cially to  be  remarked  that  the  oxides  of  silver,  of  gold,  and  of 
platinum,  not  only  decompose  the  peroxide  of  hydrogen,  but  they 
are  themselves  reduced  to  the  metallic  state.  These  decomposi- 
tions are  all  rendered  less  rapid  by  tlie  addition  of  a fcAV  drops  of 
sulphuric  or  hydrochloric  acid,  but  are  hastened  by  tlie  addition 
of  a little  free  alkali.  If  tlie  peroxide  of  hydrogen  in  its  concen- 
trated form  be  allowed  to  fall  drop  by  drop  upon  oxide  of  silver, 
peroxide  of  manganese,  or  upon  metallic  silver,  ydatinum,  or 
osmium  in  a finely  divided  state,  it  is  decomposed  Avith  explosion 
and  great  elevation  of  temperature. 

Preparation. — OAving  to  the  unstable  character  of  the  peroxide 
of  hydrogen,  its  preparation  is  attended  Avitli  groat  difficulty, 
although  in  principle  the  process  is  simple.  An  indirect  method 


230 


PEROXroE  OF  HYDROGEN. 


is  resorted  to  for  procuring  it : canstic  baryta  (BaO),  when 
heated  to  dull  redness  in  a current  of  oxygen  gas,  combines  wdth 
an  additional  equivalent  of  oxygen,  and  becomes  peroxide  of 
barium  (BaO^) : when  this  substance  is  moistened  with  water  it 
forms  a hydrate  (BaO-25  d The  peroxide  of  hydrogen  is 

obtained  from  this  hydrated  compound  by  decomposing  it  by  means 
of  hydrochloric  acid.  The  hydrated  peroxide  of  barium  is  reduced 
to  a paste  by  grinding  it  in  a mortar  with  water,  and  is  added  in 
small  quantities  at  a time  to  hydrochloric  acid  diluted  Avith  water, 
and  kept  cool  by  immersing  the  vessel  in  ice  and  water ; the 
peroxide  is  gradually  dissolved  Avitliout  etfervescence,  chloride  of 
barium  and  peroxide  of  hydrogen  being  formed;  Ba02,6 
2 HCl  yielding  H2O2  + 6 II2O+  BaCl.,.  When  the  hydrochloric 
acid  is  nearly  saturated  with  the  peroxide,  the  chloride  of  barium 
is  decomposed  by  the  cautious  addition  of  diluted  sulphuric  acid  ; 
an  insoluble  sulphate  of  barium  is  precipitated,  whilst  hydrochloric 
acid  is  set  free,  and  is  able  to  decompose  a fresh  quantity  of  per- 
oxide of  barium,  Avhich  must  be  added  with  the  same  ^precautions 
as  at  first.  The  addition  of  sulphuric  acid  produces  no  change 
on  the  peroxide  of  hydrogen  which  is  present  in  the  solution  : it 
is  merely  an  expedient  for  getting  rid  of  the  barium  and  liberat- 
ing the  hydrochloric  acid.* 

The  sulphate  of  barium  is  next  removed  by  filtration,  and  the 
liquid  thus  left  is  simply  a very  dilute  solution  of  peroxide  of 
hydrogen  Avith  an  excess  of  hydrochloric  acid.  This  acid  is  again 
able  to  decompose  a fresh  portion  of  the  peroxide  of  barium. 
The  same  series  of  operations  is  repeated  upon  the  liquid  three 
or  four  times  in  succession,  alternately  adding  peroxide  of  barium, 
and  removing  the  barium  in  the  form  of  sulphate  of  barium ; 
until  a liquid  is  obtained  Avhich  consists  of  dilute  peroxide  of  hy- 
drogen containing  30  or  40  times  its  bulk  of  oxygen,  and  a large 
quantity  of  hydrochloric  acid.  The  hydrochloric  acid  has  noAv  to 
be  removed,  and  this  is  efiected  by  adding  sulphate  of  silver,  until 
a trace  only  of  hydrochloric  acid  is  left  in  the  liquid. t Sulphuric 
acid  is  thus  substituted  for  the  hydrochloric  acid,  Avhich  is  precipi- 
tated in  the  form  of  the  insoluble  chloride  of  silver,  Avhile  the 
peroxide  of  hydrogen  remains  unchanged  in  the  liquid. 

The  sulphuric  acid  is  now  got  rid  of  by  the  careful  addition 
of  baryta  Avater,  Avhich  is  at  last  added  drop  by  drop,  so  as  to  re- 
move the  Avhole  of  the  sulphuric  acid  without  introducing  any 
excess  of  baryta : the  liquid  is  once  more  filtered,  and  is  noAV  a 
pure  solution  of  the  peroxide  of  hydrogen  in  Avater ; finally,  it  may 
be  transferred  to  a basin  and  placed  over  sulphuric  acid  in  the 
exhausted  receiver  of  the  air-pump.  The  water  evaporates  much 


* Pelouze  substitutes  silicofluoric  for  hydrochloric  acid  in  decomposing  the  per- 
oxide of  barium  ; it  shortens  the  operation  by  removing  the  barium  at  once  in  the 
form  of  an  insoluble  silieofluoride  of  barium.  Peroxide  of  barium  may  also  be  de- 
composed by  suspending  it  in  water,  and  transmitting  a current  of  carbonic  anhydride, 
but  the  solution  so  obtained  is  dilute. 

f Oxide  of  silver  cannot  be  substituted  for  the  sulphate,  as  it  would  immediately 
occasion  the  evolution  of  the  additional  atom  of  oxygen  in  the  compound. 


OLEFIANT  GAS PKEPAKATION. 


231 


more  rapidly  than  the  peroxide  of  hydrogen,  which  is  thus  at 
length  obtained  in  a concentrated  form. 

Schonbein  has  shown  (Ann.  de  Chimie.,  III.  Iviii.  4Y9)  that  in 
various  processes  where  ozone  is  formed,  small  quantities  of  per- 
oxide of  hydrogen  are  also  produced ; and  in  the  electrolysis  of 
acidulated  and  saline  solutions  when  ozone  is  formed,  traces  of 
peroxide  of  hydrogen  are  likewise  produced  if  the  operation  is 
conducted  at  a low  temperature,  the  proportion  of  gaseous  oxygen 
collected  in  the  voltameter  being  then  always  a little  below  the 
theoretical  quantity. 

§ II.  Compounds  of  Carbon  and  Hydrogen. 

(486)  The  compounds  of  carbon  with  hydrogen  are  numerous. 
They  are  all  derived  from  the  decomposition  of  bodies  of  organic 
origin.  Many  of  these  bodies  exhibit  absolute  identity  in  the 
proportion  of  the  two  elements  which  compose  them,  although 
they  are  endowed  with  properties  perfectly  distinct ; and,  from 
the  different  densities  of  these  bodies  in  the  gaseous  or  vaporous 
condition,  it  is  obvious  that  the  condensation  of  their  particles  is 
different.  For  example,  the  following  are  a few  of  the  many 
compounds  which  contain  in  100  parts  85 ’71  of  carbon  and  14’29 
of  hydi^ogen  : — 


Mol.  vol. 


OleSant  gas 

....  

2 

Oil  gas 

....  ■e4H8 

“ “ 1-852 

2 

Naphthene 

“ “ 3-900 

2 

Cetylene 

“ “ 8-007 

2 

Such  bodies  are  said  to  be  polymeric.  At  present  it  will  not  be 
necessary  to  describe  more  than  three  compounds  of  carbon  and 
hydrogen — viz.,  oleffant  gas,  marsh  gas,  and  oil  gas. 

(487)  Olefiant  Gas  ; Elayl^  or  Ethylene  (OJT^  or  C4H4=28); 
Theoretic  Sp.  Gr.  0-967 ; Observed^  0-9784 : ALol.  Vol.  \ f |. 

Preparation. — 1. — If  2 measures  of  concentrated  sulphuric 
acid  be  mixed  with  1 measure  of  alcohol,  in  a retort  capable  of 
containing  at  least  four  times  the  bulk  of  the  liquid  introduced, 
on  distillation  a transparent  colourless  gas  is  obtained,  consisting 
of  carbon  and  hydrogen.  It  is  accompanied  by  the  vapour  of 
ether,  and  towards  the  close  of  the  process  by  sulphurous  acid  in 
large  quantity.  The  oleffant  gas,  as  this  compound  of  carbon  and 
hydrogen  is  termed,  at  first  comes  off*  freely,  but  by  degrees  the 
mixture  blackens  and  becomes  thick,  and  froths  up  considerably, 
so  that  the  operation  requires  careful  watching  in  its  latter  stages : 
this  tendency  to  frothing  may  be  much  diminished  by  adding  to 
the  mixture,  before  applying  heat,  a quantity  of  sand  equal  in 
weight  to  half  that  of  the  acid  employed.  The  gas  may  be  puri- 
fied by  causing  it  first  to  pass  through  an  empty  bottle,  kept  cool 
by  immersion  in  water,  in  order  to  condense  the  vapours  of  alco- 
hol and  ether ; then  washing  it  in  a solution  of  potash,  to  absorb 
sulphurous  acid,  removing  the  last  traces  of  ether  by  allowing  it 
to  bubble  up  through  concentrated  sulphuric  acid,  and  finally 


232 


PEOPEETIES  OF  OLEFLiXT  GAS. 


drying  it,  when  necessary,  by  causing  it  to  traverse  a tube  filled 
with  fragments  of  pumice  moistened  with  oil  of  vitriol. 

This  remarkable  decomposition  may  be  thus  explained : alco- 
hol enters  into  combination  with  sulphuric  acid,  and  foimis  a 
peculiar  compound  acid,  the  sulphovinic  or  ethylsulphuric  acid, 
which  is  decomposed  by  a high  temperature  : the  sulphuric  acid 
is  liberated  in  an  unchanged  condition,  whilst  the  alcohol  breaks 
up  into  water  and  olefiant  gas ; at  the  same  time  a portion  of  the 
water  with  which  the  acid  was  at  first  diluted  distils  ofl:’,  and 
accompanies  the  olefiant  gas  : — 

Alcohol.  Sulph.  acid.  Ethylsulphuric  acid.  Water. 

becomes  -f  ; 

and  by  heat 

Ethylsulphuric  acid.  Sulphuric  acid. 

becomes  -f 

2. — Olefiant  gas  is  also  obtained,  mixed  with  various  other 
gaseous  compounds,  during  the  destructive  distillation  of  a large 
number  of  bodies  of  organic  origin — ^particularly  the  resins,  the 
fats  and  oils,  and  the  dinerent  varieties  of  pit-coal.  It  forms  an 
important  component  of  coal-gas. 

Properties. — Olefiant  gas  is  transparent  and  colourless  ; it  has 
a faint,  sweetish,  alliaceous  odour,  and  is  soluble  in  about  12 
times  its  bulk  of  cold  water.  It  was  liquefied  by  Faraday  imder 
great  pressure,  but  remained  unfi'ozen  at  — 166°.  Olefiant  gas 
does  not  support  hfe  or  combustion,  but  is  itself  very  infiammable, 
and  burns  with  a white  luminous  fiame,  depositing  carbon  abun- 
dantly upon  cold  bodies  which  are  introduced  into  its  fiame.  If 
it  be  transmitted  through  porcelain  tubes  heated  to  bright  redness, 
it  is  decomposed : half  its  carbon  is  deposited,  and  another  com- 
pound of  carbon  with  hydi'ogen  (light  carburetted  hydrogen)  is 
formed,  which  occupies  the  same  volume  as  that  of  the  olefiant 
gas  from  which  it  was  produced.  If  the  heat  to  which  the  gas  is 
subjected  be  extremely  intense,  all  the  carbon  is  deposited,  and 
for  each  volume  of  gas  decomposed  2 volumes  of  hydi*ogen  are 
liberated. 

The  composition  of  olefiant  gas  may  be  ascertained  by  deto- 
nation with  oxygen ; the  explosion,  however,  is  very  powerful, 
and  requires  care,  otherwise  tlie  eudiometer  will  be  broken.  One 
volume  of  the  gas  requires  for  its  complete  combustion  3 volumes 
of  oxygen  ; 2 volumes  of  carbonic  anhydride  remain  and  represent 
2 out  of  the  three  volumes  of  oxygen,  whilst  the  other  volume  of 
oxygen  combines  with  2 volumes  of  hydrogen,  furnishing  2 vol- 
umes of  steam,  which  immediately  become  condensed ; 2 volumes 
of  hydrogen  and  2 of  carbon  vapour  are  therefore  condensed  in 
olefiant  gas  into  the  space  of  1 volume.  -0,11, -h  3 0,=2  00, -f  2 
H.O.  Ihom  these  data  the  composition  of  the  gas  may  be  repre- 
sented in  the  following  manner  : — 


Olefiant  gaa. 

€h.. 


DUTCH  LIQUID PREPARATION. 


233 


Carbon O2 

Hydrogen. ..  H4 


By  ■weiffht  By  vol,  Sp,  g’*. 

24  or  85-71  4?  r=  2-0  = 0 829 
4 14-29  4 = 2-0  = 0-138 


Olefiant ) 
gas  f • • 


28  100  00  2 = 1-0  = 0-967 


Olefiant  gas  is  slightly  soluble  in  alcohol,  in  oil  of  turpentine, 
and  in  the  fixed  oils.  It  combines  with  sulphuric  anhydride, 
forming  with  it  a peculiar  compound  ; hence  it  is  completely  ab- 
sorbed by  fuming  sulphuric  acid,  and  it  is  somewhat  soluble  in 
ordinary  oil  of  vitriol ; the  latter  by  brisk  agitation  with  the  gas 
may  be  made  to  take  up  30  or  4-0  times  its  volume,  forming  ethyl- 
sulphuric  acid.  It  also  combines  with,  and  is  absorbed  by,  the 
perchloride  of  antimony.  Olefiant  gas,  when  mixed  over  water 
with  an  equal  volume  of  chlorine,  unites  with  it  and  becomes  con- 
densed to  a heavy,  sweetish,  aromatic  liquid : it  collects  into  oily- 
looking  drops,  which  sink  in  water  : it  was  owing  to  this  reaction 
that  the  name  of  olefiant  (or  oil-producing)  gas  was  given  to  it, 
and  the  oily  body  itself  is  commonly  known  as  Dutch  liquid^  from 
the  circumstance  of  its  discovery  in  Holland.  If  1 measure  of 
olefiant  gas  be  mixed  with  2 measures  of  chlorine,  the  mixture 
may  be  kindled  by  a lighted  taper,  and  will  burn  quietly,  deposit- 
ing the  whole  of  the  carbon  of  the  gas  in  the  form  of  a dense 
smoke,  whilst  the  hydrogen  unites  with  the  chlorine  to  form  hy- 
drochloric acid.  Olefiant  gas  will  be  referred  to  liereafter  among 
the  products  of  organic  chemistry  ; where,  as  a diatomic  radicle, 
it  performs  an  important  part. 

(488)  Dutch  Liquid,  or  Bichloride  of  Ethylene  (C  JL3CI,  II Cl) 
or  (0214,012)  = 99.  Sp.  Gr.  of  Liquid^  1*28  at  32°;  of  Vapour^ 


Theoretic^  3*42 ; Observed^  3*45  ; Boiling-pt.  184°*Y ; Mol.  Yol.  | |. 


This  is  a compound  of  considerable  interest,  as  it  is  the  sub- 
stance from  which  the  chlorides  of  carbon  were  originally  obtained 
by  Faraday;  and  the  careful  study  (since  made  by  Hegnault)  of 
the  stages  of  the  process  by  which  these  substances  are  formed, 
illustrates  in  a striking  manner  the  mode  in  which  compounds 
may  be  procured  by  a process  of  substitution  in  which  the  hydro- 
gen of  the  original  body  is  displaced  by  chlorine. 

Preparation. — 1. — Dutch  liquid  is  required  in  considerable 
quantity  for  these  experiments ; it  may  be  easily  obtained  by 
Limpricht’s  method  of  transmitting  the  olefiant  gas  through  a 
mixture  of  oxide  of  manganese  and  hydrochloric  acid,  from  which 
the  chlorine  is  generated.  The  olefiant  gas  is  conveyed  into  this 
mixture  by  means  of  a bent  tube  which  passes  through  the  tubu- 
lure  of  the  retort,  and  the  Dutch  liquid,  as  it  is  formed,  distils 
over  into  a receiver  connected  with  the  retort.  Formerly  it  was 
the  practice  to  allow  a current  of  chlorine  and  a current  of  olefiant 
gas,  both  in  a moist  state,  to  meet  in  a large  glass  globe,  where 
they  condensed  each  other  under  the  influence  of  difiused  day- 
light. 

2. — Another  method  by  which  Dutch  liquid  may  be  prepared 
consists  in  transmitting  olefiant  gas  through  perchloride  of  anti- 
mony so  long  as  it  is  absorbed.  The  product  is  submitted  to  dis- 


2^4:  ACTION  OF  CHLOKINE  UPON  DUTCH  LIQUID. 

tillation,  and  tlie  lieat  is  maintained  so  long  as  the  distillate  yields 
an  oily  liquid  on  the  addition  of  water. 

The  oil  which  is  obtained  by  either  of  these  processess  is  de- 
canted, agitated  with  successive  portions  of  oil  of  vitriol  so  long  as 
they  become  blackened,  and  the  product  purified  by  redistillation. 

Dutch  liquid  is  a colourless  aromatic  liquid  which  is  not 
soluble  in  water,  but  freely  soluble  in  ether  and  in  alcohol.  The 
simplest  supposition  respecting  the  composition  of  this  body,  since 
its  vapour  consists  of  equal  volumes  of  chlorine  and  of  olefiant  gas, 
condensed  into  half  their  bulk,  is  that  its  atomic  weight  should 
be  (OH^Cl)  or  one-half  of  that  which  has  been  given  above  (487). 
The  investigations  of  Regnault  have,  however,  shown  that  the 
composition  of  Dutch  liquid  is  not  correctly  represented  by  so 
simple  a formula ; that  its  molecular  formula  is  not  OHjCl,  but 
just  double.  The  usual  combining  volume  of  an  atom  of  such 
vapours  is  twice  that  of  the  atom  of  hydrogen,  and  the  density 
of  the  vapour,  as  obtained  by  experiment,  coincides  almost 
exactly  with  that  required  by  the  supposition  that  the  formula  is 


Chlorine 

...  CI2  - 

By  weight. 

71  or  71-68 

By  vol, 

2 or  1 

Sp.  gr. 
= 2*453 

Carbon 

24 

24-28 

4? 

2 

= 0 829 

Hydrogen 

...  H4 

4 

4-04 

4 

2 

= 0*138 

Dutch  liquid 

H2H4CI.2  = 

99 

100-00 

2 

1 

= 3-420 

The  formula  for  Dutch  liquid  is  sometimes  written  -0211301,1101. 

It  was  ascertained  by  Faraday  that  when  Dutch  hquid  is  ex- 
posed in  a glass  yessel  with  chlorine  to  the  direct  rays  of  the  sun, 
taking  care  to  renew  the  chlorine  as  long  as  it  is  absorbed,  the 
liquid  is  ultimately  conyerted  into  the  white  crystalline  and  vola- 
tile chloride  of  carbon  (OjOlg),  whilst  a very  copious  disengage- 
ment of  hydrochloric  acid  gas  takes  place  (p.  122). 

Degnault  has  shown  that  the  formation  of  this  chloride  of 
carbon  is  the  result  of  the  interchange  of  chlorine  for  hydrogen 
in  the  composition  of  the  Dutch  liquid ; so  that  the  chloride  of 
carbon  may  be  regarded  as  Dutch  liquid  in  which  the  place  of  the 
hydrogen  is  supplied  by  chlorine  : and  he  has  described  a series  of 
compounds  intermediate  between  this  liquid  and  Faraday’s  sesqui- 
chloride  of  carbon.  For  example : — if  chlorine  be  transmitted 
through  Dutch  liquid,  the  gas  is  rapidly  absorbed,  and  the  liquid 
acquires  a yellow  colour,  which  disappears  with  copious  evolution 
of  hydrochloric  acid  when  it  is  brought  into  the  sun’s  rays  : by 
carefully  adjusting  the  addition  of  chlorine  a new  liquid  is  ob- 
tained which  boils  at  239°,  and  has  a specific  gravity  of  1*422. 
Two  atoms  or  1 molecule  of  chlorine  act  upon  1 molecule  of  Dutch 
liquid,  1 atom  of  the  chlorine  combining  with  1 of  hydi’ogen  to 
form  the  disengaged  hydrochloric  acid,  while  the  second  atom  of 
chlorine  takes  the  position  of  the  displaced  hydrogen  : thus, 
OjH.Cl^  + Cl,  furnish  O^IIjClg, -f IICI.  This  new  liquid  maybe 
made  to  absorb  a fresh  quantity  of  chlorine,  and  in  the  sun’s 
rays  it  undergoes  a change  analogous  to  the  preceding  one  ; a 
liquid  is  formed  which  boils  at  275°,  and  has  a density  of  1*576 ; 


BIBROMIDE  AND  BINIODIDE  OF  ETHYLENE. 


235 


O2H3CI3  + CI2,  yielding  + HCl.  This  tliird  liquid,  if 

again  acted  upon  by  two  additional  atoms  of  chlorine,  undergoes 
a further  similar  decomposition  ; a still  heavier  liquid,  of  specific 
gravity  1*663,  boiling  at  307°,  is  produced,  O2II2CI4  + CI2  becom- 
ing -G^HClg  -f  IICl : and  finally,  this  fourth  liquid,  when  acted 
upon  by  an  excess  of  chlorine,  loses  the  remaining  atom  of  hydro- 
gen, and  becomes  Faraday’s  solid  chloride  of  carbon  ; for  O^HCl^ 
+ Cl2=02Cl6-|-HCl ; tlie  successive  products  having  the  composi- 
tion and  density  indicated  in  the  following  table : — 

Chlorinated  Compounds  derived  from  Dutch  Liquid. 


Name  of  compound. 

Boili  s- 

point®  F. 

Specific  gravity. 

Formula.  2 vols. 

Liquid. 

V apour. 

Dutch  liquid 

184 

1-280 

3-45 

^2H4Cl2 

Chlorinated  ditto 

239 

1-422 

4-613 

esHaCla 

Bichlorinated  ditto 

275 

1-576 

5-769 

Terchlorinated  ditto 

307 

1 -663 

7-08 

Solid  chloride  of  carbon  . . . 

356 

8-157 

e^Cle 

It  will  be  seen  that,  as  the  quantity  of  chlorine  increases,  the 
boiling-point  rises,  and  the  density  both  of  the  liquid  and  of  the 
vapour  increases : in  every  case  1 atom  of  the  compound  yields  2 
volumes  of  vapour, 

(489)  Bihromide  of  Ethylene  (O^H^Br^  = 188),  Gr.  of 
Liquid^  2*163 ; of  Vapour^  6*485  ; Boilingpt.  265°. — Cahours 
has  obtained  a series  of  compounds  from  olefiant  gas  containing 
bromine  : the  bibromide  of  ethylene,  or  brominated  compound 
corresponding  to  Dutch  liquid,  may  be  procured  by  placing  bro- 
mine in  a flask,  and  transmitting  into  it  a current  of  olefiant  gas 
as  fast  as  it  is  absorbed  ; a rapid  combination  occurs,  the  tempe- 
rature rising  sensibly.  The  bromine  is  gradually  decolorized,  and 
an  ethereal  liquid  of  aromatic  odour,  and  a pungent,  but  sweet 
taste,  is  obtained.  It  may  be  purified  by  agitating  it  with  caustic 
potash,  then  distilling  from  oil  of  vitriol  and  subsequently  from 
caustic  baryta. 

(490)  Biniodide  of  Ethylene  (O^HJ^  = 282  ; Sp.  Gr.  2*07 ; 
Eusing-pt.  163°),  or  the  compound  of  olefiant  gas  with  iodine, 
corresponding  to  Dutch  liquid,  is  a solid  which  crystallizes  in 
long,  colourless,  silky  needles,  or  in  flexible  plates  : it  has  a sweet- 
ish taste  and  an  ethereal  penetrating  odour,  which  causes  head- 
ache ; it  melts  at  163°,  and  forms  a crystalline  mass  on  cooling. 
It  may  be  sublimed  in  a current  of  olefiant  gas,  but  cannot  be 
sublimed  in  air  or  in  vacuo  without  being  decomposed  ; it  slowly 
undergoes  spontaneous  decomposition,  becoming  brown  at  ordinary 
temperatures,  especially  under  the  influence  of  light.  This  com- 
pound may  be  obtained  by  placing  iodine  in  a flask  with  a long 
neck,  heating  it  by  means  of  a water-bath  to  130°  or  140°,  and 
transmitting  a current  of  olefiant  gas.  The  iodine  melts  and  ab- 
sorbs the  gas,  whilst  the  new  compound  as  it  is  formed  undergoes 


236 


MAPtSH  GAS,  OE  LIGHT  CARELTSETTED  HTDROGEX. 

partial  siiblimatioH.  It  is  also  said  to  be  obtained  by  decomposing 
iodide  of  ethyl  by  transmission  through  a porcelain  tube  heated  to 
redness.  It  may  be  purified  by  washing  with  a weak  solution  of 
potash  and  recrystallization  from  boiling  alcohol. 

(491)  Light  Carberetted  Hydrogen  : Subcarhuretted  Hy- 
drogen / Hydride  of  Methyl : 2Iarsli  Gas  or  Fire-damj? 
or  C^H,  = 16)  ; Theoretic  Sj).  Gr.  0-5528  ; Observed^  0-5576  ; 
Mol.  Vol.  . 

Preymration. — 1. — This  gas  is  best  obtained  in  a state  of 
pirrity  by  a process  recommended  by  Persoz : lOf  parts  of  the 
hydrate  of  baryta  and  10^  of  anhydrous  acetate  of  sodimn  are 
very  intimately  mixed,  and  heated  over  a charcoal  fire  in  a Flo- 
rence flask,  coated  with  a luting  of  fire-clay  made  into  a paste 
with  a solution  of  borax.  The  flask  is  fitted  with  a cork  and  bent 
tube,  and  the  gas  is  collected  over  water  in  the  usual  way.'^  A 
mixture  of  2 parts  of  caustic  potash  and  3 of  quicklime  may  be 
substituted  for  the  hydrate  of  baryta. 

2.  — The  gas  is  also  easily  procured  (mingled  with  nitrogen  and 
carbonic  anhydride),  as  a result  of  the  decomposition  of  vegeta- 
ble matter  contained  in  the  mud  of  stagnant  pools ; and  hence  its 
name  of  marsh  gas.  In  order  to  collect  the  gas  fi’om  this  source 
a bottle  may  be  filled  with  water,  inverted  in  the  pool,  and  hav- 
ing fastened  a funnel  in  the  neck  of  the  bottle,  the  mud  beneath 
is  stirred  with  a stick ; the  gas  then  rises  into  the  bottle  in 
bubbles. 

3.  — Light  carbnretted  hydrogen  is  one  of  the  principal  con- 
stituents of  coal-gas:  it  also  occurs  abundantly  in  many  coal 
mines,  bursting  forth  unexpectedly  from  the  seams  of  coal,  and 
blowing  out  from  the  fissure  for  many  months  together,  as  though 
escaping  from  under  high  pressure.  These  natural  discharges  of 
the  gas  the  miners  term  ‘ blowers.’  Accordins^  to  the  experiments 
of  Graham,  the  gas  from  the  Newcastle  coal-field  is  free  from  ad- 
mixture with  olefiant  gas,  hydrogen,  carbonic  oxide,  and  carbonic 
anhydride. 

Properties. — Harsh  gas  is  a colourless,  inodorous,  and  tasteless 
gas,  scarcely  soluble  in  water,  but  soluble  in  alcohol  to  a small 
extent : not  injurious  to  life  if  diluted  with  air.  It  does  not  sup- 
port combustion,  but  it  is  itself  infiammable,  and  biuns  with  a yel- 
low luminous  fiame.  By  passing  through  it  a continued  succes- 
sion of  electric  sparks,  or  by  sending  it  through  tubes  heated  to 
whiteness,  it  is  decomposed ; its  carbon  is  deposited,  and  a vol- 
ume of  hydi-ogen,  double  that  of  the  gas  employed,  is  set  at  lib- 
erty. Chlorine  has  no  effect  upon  it  in  the  dark,  but  if  the  two 
gases  be  mixed  and  exposed  in  a moist  condition  to  diffused  light, 
hydrochloric  acid  and  carbonic  anhydride  are  formed;  -GH^-f 
d d^-f  2 HjO  = O02  + S ^ICl.  An  excess  of  chlorine  converts 
marsh  gas  into  hydrochloric  acid  and  tetrachloride  of  carbon, 
when  the  mixtm-e  is  exposed  to  light. 

* fodhim  ^arb.  sodiuto.  Marsh  gas. 

2 -f  BaOjHaO  = fia€^3  -i-  Xao^rOs  + 2 •GH4. 


EXPLOSION  OF  FIEE-DAMP  IN  COAL  MINES. 


237 


Marsh  gas  requires  twice  its  volume  of  oxygen  for  complete 
combustion.  The  3 volumes  of  the  mixed  gases  after  detonation, 
are  condensed  into  one  volume : they  yield  1 volume  of  carbonic 
anhydride,  and  2 volumes  of  steam  which  are  immediately  con- 
densed. i7ow  carbonic  anhydride  contains  its  own  bulk  of  oxy- 
gen ; it  therefore  represents  one  of  the  2 volumes  of  oxygen 
which  have  disappeared,  whilst  the  other  volume  of  oxygen  has 
united  with  2 volumes  of  hydrogen  and  formed  water.  Light 
carburetted  hydrogen  must  consequently  contain  twice  its  vol- 
ume of  hydrogen,  condensed  wdth  its  own  volume  of  carbon  va- 
pour into  the  space  of  1 volume,  and  its  composition  may  be  thus 
represented : — 


Carbon 

...H 

By  weight. 

= 12  or  75 

By  volume. 

2 ? or  1 ? 

Sp.  gr. 

= 0-4146 

Hydrogen  . 

...H4 

= 4 25 

4 

2 

0-1382 

Marsh  gas. 

..eH4 

= 16  100 

2 

1 

= 0-5528 

Wlien  marsh  gas  is  mixed  with  air,  an  explosive  mixture  is 
formed,  wliich  takes  fire  on  the  approach  of  a light,  and  often 
occasions  accidents  attended  with  loss  of  life  to  those  who  are 
engaged  in  coal  mines.  The  fatal  results  of  an  explosion  of  fire- 
damp in  the  mine  are  not,  however,  limited  to  the  mechanical 
violence  which  it  occasions  to  the  sufferers.  The  ^ after  damp,’  as 
the  miners  term  it,  or  vitiated  atmosphere  that  the  explosion  pro- 
duces, is  often  fatal  to  those  employed  in  other  parts  of  the  mine, 
or  to  the  generous  but  ignorant  and  rash  survivor  who  attempts 
to  descend  into  the  pit  before  it  has  been  properly  ventilated,  in 
order  to  succour  his  comrades,  or  to  ascertain  their  fate.  From 
the  composition  of  fire-damp  it  is  obvious  that  this  gas  in  explod- 
ing renders  ten  times  its  bulk  of  atmospheric  air  unfit  for  respir- 
ation ; the  2 volumes  of  oxygen  which  10  volumes  of  air  contain, 
producing  1 volume  of  carbonic  anhydride,  and  2 volumes  of 
steam  which  become  condensed,  leaving  8 volumes  of  nitrogen  at 
liberty. 

It  was  with  a view  of  discovering  some  means  of  preventing 
these  fatal  results  that  Davy  instituted  those  important  researches 
on  flame  which  led  him  to  the  invention  of  the  safety-lamp^  an 
instrument  wdiich  has  prevented  many  serious  accidents,  and  has 
enabled  many  coal-fields  to  be  worked  which  otherwise  must  have 
been  abandoned,  on  account  of  the  abundant  escape  of  fire-damp 
from  the  workings. 

(492)  Principle  of  the  Safety-Lamp. — The  temperature  re- 
quired for  the  combustion  of  different  bodies  varies  greatly : some 
take  fire  at  a very  low  temperature, — phosphorus,  for  instance, 
at  the  heat  of  the  body  ; bisulphide  of  carbon  at  about  420°  ; 
sulphur  at  about  480°  ; others,  as  olefiant  gas  and  hydrosulplmric 
acid,  need  a red  heat.  A high  temperature  is,  however,  essential 
to  the  existence  of  flames,  and  particularly  of  flames  produced  by 
the  combustion  of  the  hydrocarbons.  Subcarburetted  hydrogen, 
although  an  inflammable  gas,  requires  a much  liiglier  tempera- 
ture to  ignite  it  than  most  other  inflammable  bodies ; it  will  not 
explode  when  mixed  either  with  less  than  3 times  its  bulk  of  at- 


23S 


PPwDsCIPLE  OF  THE  SAFETY-LAMP. 


mosplieric  air,  or  with  more  than  18  times  its  voliime  ; the  gas  in 
the  latter  case  burns  only  in  immediate  contact  with  the  flame 
of  the  lamp,  for  the  large  volume  of  air  with  which  it  is  mixed 
prevents  the  temperature  from  rising  to  the  point  necessary  for 
the  general  conflagration  of  the  gas : the  most  powerful  explo- 
sion is  occasioned  when  the  gas  is  mixed  with  7 or  8 times  its 
bulk  of  air. 

Combustion  may  often  be  carried  on  below  the  point  of  in- 
flammation. The  smouldering  wick  of  a taper  recently  blown  out 
is  a case  in  point.  Again,  if  a glovdng  coil  of  platinum  wire,  or 
a hot  slip  of  platinum  foil,  be  suspended  in  a current  of  coal-gas 
mixed  with  atmospheric  air,  the  metal  will  be  maintained  at  a red 
heat  by  the  rapid  combination  of  the  oxygen  with  the  gas,  which, 
however,  does  not  take  Are  until  the  platinum  becomes  heated 
nearly  to  whiteness. 

Davy  found  that  no  exjflosion  could  be  produced  in  a mixture 
of  air  and  fire-damp,  through  a narrow  tube,  owing  to  the  cooling 
influence  which  the  tube  exerted  upon  the  gas ; and  the  narrower 
the  tube,  the  shorter  was  the  length  required  to  produce  this 
protective  eflect.  Hemming’s  safety  tube  for  the  oxyhydrogen 
blowpipe  (34:7)  depends  for  its  efficacy  upon  the  cooling  influence 
which  the  metallic  tubes  or  channels,  formed  by  the  interstices 
between  the  wires,  exert  upon  the  burning  jet  of  gas : the  heat 
of  the  flame  is  in  this  way  prevented  from  passing  backwards 
and  causing  the  explosion  of  the  mixed  gases  in  the  reser- 
voir. 

If  a stout  copper  wire  be  introduced  into  any  flame,  a dark 
space  will  be  observed  immediately  around  the  ^vire,  owing  to  the 
cooling  eflect  of  the  metal ; a second  wire  cools  the  flame  still 
further ; and  a small  flame  may  be  completely  extinguished  by 
the  reduction  of  temperature  produced  by  bringing  down  a coil 
of  wire  upon  it ; but  if  the  same  coil  be  previously  heated  to 
redness,  and,  whilst  still  hot,  be  placed  over  the  flame,  the  latter 
will  continue  to  bum. 

By  using  wire  gauze  we  may  easily  cut  ofi*  the  upper  part  of 
a flame,  the  unburnt  gases  being  cooled  by  its  means  below  the 
point  of  inflammation ; if  a piece  of  gauze  with  large  meshes  be 
employed  it  will  cut  ofi'  the  flame  so  long  as  it  remains  cold,  but 
the  flame  will  traverse  the  network  as  soon  as  the  wire  becomes 
red  hot : with  flner  meslies  (about  4:00  to  the  square  inch)  the  con- 
ducting power  of  the  metal  is  sufficient  to  cool  the  flame  below 
the  point  of  ignition,  even  though  the  wire  itself  be  red  hot.  In 
a similar  manner  the  gas  above  the  gauze  may  be  kindled,  and 
the  flame  will  not  pass  through  to  the  gas  below.  Advantage  is 
taken  of  this  circumstance  in  the  laboratory  to  obtain  a smoke- 
less flame  by  the  use  of  ordinary  coal-gas : — A metallic  chimney, 
five  or  six  inches  long,  open  below,  and  furnished  at  top  with  a 
cap  of  wire  gauze,  is  placed  over  any  convenient  form  of  burner  ; 
the  air  enters  at  the  bottom  and  mixes  with  the  gas : this  mix- 
ture burns  above  the  wire  gauze  with  a blue  flame,  which  emits 
scarcely  any  light,  and  deposits  no  smoke  upon  cold  objects,  pro- 


NATUKE  OF  FLAME. 


239 


Fig.  316. 


vided  that  the  supply  of  gas  be  duly  proportioned  to  that  of  the 
air  which  mixes  with  it.* 

These  principles  were  beautifully  applied  by  Davy  in  the  con- 
struction of  his  miner’s  lamp,  which  is 
merely  an  oil  lamp  (fig.  316)  inclosed 
within  a cylinder  of  fine  wire  gauze, 
provided  with  a double  top,  and  with  a 
crooked  wire,  w,  which  passes  up  tightly 
through  a tube  traversing  the  body  of  the 
lamp,  for  the  purpose  of  trimming  the 
wick  without  the  n ecessity  for  removing 
the  wire  covering.  When  such  a lamp  is 
introduced  into  an  explosive  atmosphere 
of  fire-damp,  the  flame  is  seen  to  enlarge 
gradually  as  the  proportion  of  carburet- 
ted  hydrogen  increases,  until  at  length  it 
fills  the  entire  gauze  cylinder ; when  the 
gas  is  in  sufficient  excess  the  lamp  is  en- 
tirely extinguished ; if  it  be  withdrawn 
from  the  explosive  mixture  while  the  cylinder  appears  to  be  full 
of  flame,  the  wick  is  generally  rekindled,  and  the  lamp  contin- 
ues to  burn  in  air  as  usual.  Whenever  this  pale,  enlarged  flame  is 
seen,  the  miner  must  withdraw  ; for  though  no  explosion  can  oc- 
cur while  the  gauze  is  sound,  yet  at  that  high  temperature  the 
metal  becomes  rapidly  oxidized,  and  might  easily  break  into  holes  ; 
a single  aperture  of  sufficient  size  would  then  determine  the 
fatal  explosion. 


The  wire  gauze  used  in  the  construction 
tains  from  YOO  to  800  meshes  in  the 


of  these  lamps 
square  inch.  In  a 


con- 
strong 


current  of  air  the  heated  gas  may  be  blown  through  the  apertures 
of  the  gauze  before  its  temperature  is  sufficiently  reduced  to  pre- 
vent the  explosion,  but  such  an  occurrence  may  be  easily  guarded 
against  by  the  use  of  a screen. 

(493)  Nature  of  Flame. — It  is  necessary  to  the  production  of 
flame,  that  the  combustible  be  of  such  a nature  as  to  be  conver- 
tible into  vapour  before  it  undergoes  combustion,  otherwise  no 
flame  is  produced.  Well-burned  charcoal  or  diamond  burns  with 
a steady  glow,  unattended  with  flame,  as  also  does  iron  wire. 
None  of  these  substances  are  susceptible  of  volatilization  at  the  tem- 
perature attending  their  combustion.  Sulphur,  phosphorus,  and 
zinc  pass  into  the  aeriform  condition  before  they  attain  a tempera- 
ture as  high  as  that  generated  by  their  combination  with  oxygen,  and 
they,  as  well  as  the  various  combustible  gases,  burn  with  flame. 

Flame  is,  in  fact,  produced  whenever  a continuous  supply  of 
combustible  vapour  or  gas  is  made  to  combine  at  a sufficiently 
elevated  temperature  with  atmospheric  oxygen,  or  with  some 


♦ Bunsen’s  burner  acts  upon  a similar  principle.  It  consists  of  a small  jet  for  the 
issue  of  the  gas ; this  jet  is  fitted  tightly  into  the  bottom  of  a brass  tube  4 or  5 
inches  long,  and  |ths  of  an  inch  in  diameter.  The  air  enters  by  holes  in  the  sides  of 
the  tube  near  the  bottom ; and  the  mixture  of  gas  and  air  is  kindled  at  the  top  of 
the  tube. 


240 


YAEIATIOX  IX  THE  LIGHT  OF  DIFFEEEXT  FLAMES. 


gaseous  supporter  of  combustion.  In  all  ordinary  cases,  therefore, 
name  is  a luminous  envelope  which  forms  a limiting  sm-face  be- 
tween the  unburned  combustible  within  and  the  supporter  of 
combustion  without.  This  hollow  structure  of  flame  may  be 
easily  shown  by  experiment.  If  a wooden  match  be  held  for  a 
few  seconds  across  the  middle  of  the  flame  of  a spirit-lamp  with  a 
large  wick,  the  match  will  become  charred  at  the  edges  of  the 
flame,  but  the  intermediate  portion  will  remain  uninjured.  If  a 
fragment  of  phosphorus  be  placed  in  a small  deflagrating  spoon, 
ignited,  and  then  introduced  into  the  middle  of  the  flame,  it  will 
be  extinguished ; but  it  will  burn  with  its  former  energy  the 
moment  that  the  spoon  is  withdrawn  from  the  flame.  The  taper- 
ing form  which  flames  assume,  is  due  to  the  ascending  current 
produced  in  the  atmosphere  by  the  heat  attendant  on  the  com- 
bustion. Within  the  burning  portion  of  the  flame  is  an  atmo- 
sphere of  unburned  combustible  matter ; by  inserting  into  a flame, 
such  as  that  of  a wax  candle,  just  above  the  wick,  the  lower  ex- 
tremity of  a glass  tube,  open  at  both  ends,  about  one-third  of  an 
inch  in  diameter,  and  flve  or  six  inches  long,  the  gases  in  the 
interior  may  be  drawn  off,  and  may  be  ignited  at  the  upper 
aperture  of  the  tube. 

It  is  important  to  remark  that  the  light  and  the  heat  emitted 
by  flames  are  by  no  means  proportioned  to  each  other.  The  heat 
is  due  solely  to  the  energy  of  the  chemical  action ; and  when  a 
pure  gaseous  matter,  without  solid  particles,  composes  both  the 
burning  body  and  the  product  of  the  combustion,  little  or  no  light 
is  emitted: — thus  the  flame  of  a jet  of  hydrogen  is  barely  visible 
in  clear  daylight ; and  that  of  the  oxy hydrogen  jet  itself,  although 
one  of  the  most  intense  sources  of  heat  at  our  command,  is  scarcely 
more  luminous  than  the  flame  of  hydrogen.  Tor  the  same  reason 
the  light  of  sulphur  burning  in  oxygen  is  feeble,  notwithstanding 
the  intense  energy  with  which  they  combine ; both  the  vapour  of 
sulphur  and  sulphurous  anhydride  are  gaseous  bodies.  Phosphorus 
and  chlorine,  though  they  unite  so  energetically  as  to  take  Are  at 
ordinary  temperatures  by  mere  contact,  yet  emit  but  little  light 
during  their  combustion ; the  chlorides  of  phosphorus,  as  well  as 
phosphorus  itself,  being  very  volatile  bodies. 

In  all  luminous  flames  the  light  is  emitted  from  solid  particles 
highly  ignited.  The  light  from  bodies  feebly  ignited  is  red ; as  the 
temperature  rises  the  light  becomes  yellow,  then  white,  and  when 
the  heat  is  very  intense,  the  more  refrangible  rays  of  the  spectrum 
predominate,  so  that  it  has  a shade  of  blue  or  violet  (89). 

By  introducing  a solid  object  into  a feebly  luminous  flame,  a 
platinum  wire,  for  example,  into  the  oxyhydrogen  jet,  or,  better 
still,  a body  which,  like  lime,  does  not  melt  at  that  temperature, 
the  light  becomes  so  intense  that  the  eye  can  scarcely  support  it. 
Such  bodies,  however,  since  they  do  not  contribute  to  the  chemical 
changes  occurring  in  the  flame,  necessarily  reduce  its  heat,  owing 
to  their  conducting  power.  It  is  immaterial  whether  the  bodies 
so  introduced  be  combustible,  or  have  already  undergone  perfect 
combustion : — the  flame  of  hydrogen  may  be  rendered  luminous 


MAXLMUM  OF  ILLUMINATION. 


241 


either  by  blowing  a little  powdered  charcoal  through  it,  or  by 
allowing  finely  powdered  magnesia,  oxide  of  zinc,  or  the  white 
fumes  of  phosphoric  anhydride  produced  by  the  combustion  of 
phosphorus,  to  traverse  it.  Indeed  no  better  illustration  of  this 
point  can  be  given  than  is  afforded  by  contrasting  the  painfully 
intense  light  produced,  by  the  combustion  of  phosphorus  in  oxy- 
gen, where  the  solid  scarcely  volatile  phosphoric  anhydride  is 
produced,  with  the  feeble  light  emitted  by  the  same  body  as  it 
burns  in  chlorine. 

The  fiames  used  for  illuminating  purposes  are  all  produced  by 
the  combustion  of  compounds  of  carbon  and  hydrogen.  All  of 
them,  notwithstanding  the  perfect  transparency  of  the  gas  before 
combustion,  contain  solid  particles  of  carbon  during  the  act  of 
combustion.  The  separation  of  carbon  during  the  process  of  com- 
bustion may  be  proved  by  the  simple  expedient  of  introducing  a 
cold  body,  such  as  a plate  of  metal,  or  a piece  of  glass,  into  a 
luminous  fiame ; it  becomes  speedily  blackened  from  the  deposi- 
tion of  carbon. 

The  fiame  of  a candle  is  sustained  by  the  decomposition  of  the 
melted  wax  or  tallow  absorbed  by  the  wick,  and  its  conversion 
into  gaseous  hydrocarbons  by  the  heat  of  the  combustion.  At  the 
lower  part  of  the  fiame,  <^,  fig.  317,  these  hydrocarbons  are  imme- 
diately mingled  with  atmospheric  air,  no  separation  of  carbon 
occurs  here,  and  they  burn  with  a pale  blue  light.  The  greater 
portion  of  the  combustible  gases  and  vapours,  however,  are  still 
unburned ; they  rise  above  the  wdck,  forming  the  central  dark 
part,  G,  of  the  fiame:  here  they  are  subjected  to  a high  tempe- 
rature from  the  combustion  of  the  blue  portion  already  men- 
tioned ; the  heat  now  causes  the  separation  of  the  carbon  in  the 
solid  form,  which  becomes  intensely  ignited  in  the 
burning  gas,  emitting  light  in  the  part  marked  h ; 
and  this  carbon  itself,  in  a properly  adjusted  fiame, 
gradually  burns  away  without  residue  or  smoke,  as  it 
comes  to  the  surface,  and  meets  with  oxygen. 

In  order  to  produce  the  maximum  amount  of  light, 
the  point  which  requires  the  greatest  attention  is  the 
due  adjustment  of  the  supply  of  air;  if  too  much  be 
given,  the  gas  burns  with  a blue,  feebly  luminous 
fiame ; an  enect  which  may  be  seen  by  blowing  upon 
a common  gas  fiame,  or  by  watching  the  effects  of  the 
wind  upon  the  exposed  gaslights  at  night : the  length- 
ening of  the  chimney  of  a lamp  produces  a similar 
effect.  In  these  cases  the  gas  becomes  immediately 
mixed  with  the  oxygen  of  the  air,  and  it  is  completely 
burned  before  it  has  been  exposed  to  an  elevated  tem- 
perature for  a time  sufficiently  long  to  allow  of  the  separation  of 
carbon.  The  supply  of  air,  however,  must  not  be  too  much 
limited;  otherwise,  as  may  be  seen  by  closing  the  central  tube 
which  admits  air  to  an  argand  burner,  the  light  becomes  red  from 
the  reduction  of  temperature,  the  carbon  passes  ofi  unburned, 
and  the  oxygen  being  insufficient  to  complete  ilie  combustion, 
16 


Fig.  317. 


242 


EFFECT  OF  VARYING  PRESSURE  ON  COMBUSTION. 


the  flame  becomes  smoky.  The  light  of  a flame  is  increased  by 
any  contrivance  which,  without  deranging  the  order  of  the  com- 
bustion, concentrates  it  into  a smaller  space,  so  as  to  raise  the 
temperature  of  the  deposited  carbon  to  the  maximum.  It  is  in 
this  way  that  an  argand  burner  produces  a far  greater  amount  of 
light  with  a given  consumption  of  gas,  than  if  the  same  quantity 
of  gas  were  burned  in  separate  jets. 

Frankland  {Phil.  Trans.  1861,  p.  631^  found  that  the  rate  at 
wdiich  candles  and  other  similar  combustibles  burn,  is  not  altered 
b}^  variations  in  the  atmospheric  pressure.  Candles  burned  at  the 
top  of  Mont  Blanc  at  the  same  rate  as  in  the  valley  of  Chamonix  ; 
but  the  luminosity  of  the  flame  is  greatly  affected  by  the  pressure, 
for  the  amount  of  light  emitted  by  the  same  candle  on  the  sum- 
mit of  Mont  Blanc  was  far  less  than  that  w’hich  it  produced  in 
the  valley  ; and  by  careful  experiments  conducted  under  regulat- 
ed pressures,  it  was  found  that  as  the  pressures  decreased  from 
30  to  14  inches  of  mercuiy,  the  illuminating  power  gradually 
diminished.  In  a series  of  experiments  upon  the  light  of  burning 
gas,  Frankland  found  that  taking  the  light  emitted  by  the  combus- 
tion of  a given  volume  of  gas,  in  a certain  burner,  under  the  ordin- 
ary pressure  of  30  inches  of  mercury,  at  1 00,  the  same  volume  of 
gas  for  each  diminution  of  1 inch  in  the  pressure  gave  5T  less 
light ; the  diminution  of  light  being  directly  as  the  diminution  of 
pressure ; so  that  at  14  inches,  the  light  emitted  instead  of 
amounting  to  100  was  reduced  to  18’4  ; and  this  rate  of  diminu- 
tion was  found  to  hold  good  with  the  light  of  hydro-carbon  flames 
generally. 

On  the  other  hand,  the  luminosity  of  a flame  may  be  pro- 
portionately increased  by  augmenting  the  atmospheric  pressure. 
So  rapidly  does  this  effect  increase,  that  an  ordinary  spirit-lamp 
which  burns  in  the  open  air  with  scarcely  any  measurable  amount 
of  light,  and  without  smoke,  becomes  powerfully  luminous  in  air 
at  a pressure  of  4 atmospheres,  and  when  supplied  wdth  air  com- 
pressed still  more,  even  burns  with  a smoky  flame.  The  result 
of  these  and  other  carefully  devised  experiments  led  to  the  un- 
expected conclusion  that  the  combustion  of  gaseous  matter  is  ren- 
dered less  perfect  in  proportion  as  the  density  of  the  atmosphere  is 
increased  ; and  on  the  other  hand,  within  certain  limits,  the  more 
rarefied  the  atmosphere  in  which  flame  burns,  the  more  com- 
plete is  its  combustion.  'No  reduction  in  the  temperature  of  the 
flame,  within  certain  limits  (as  low  as  14  inches  of  mercury),  is 
produced  by  a reduction  of  the  pressure  of  the  surrounding  air. 
The  decrease  in  illuminating  power  in  a rarefied  atmosphere  is 
attributed  by  Frankland,  and  with  strong  probability,  to  the 
greater  readiness  with  which  the  oxygen  of  the  atmosphere  finds 
access  to  the  interior  of  the  flame,  owing  to  the  greater  mobility 
of  the  particles  of  tlie  air  under  diminished  pressure. 

(494)  Theory  of  the  Blowpipe. — The  temperature  of  a flame 
may  be  very  materially  increased  by  augmenting  the  activity  of 
the  combustion,  and  concentrating  its  effect  by  diminishing  the 
extent  of  surface  over  which  it  would  otherwise  take  place.  It  is 


THEORY  OF  THE  BLOWPIPE. 


243 


upon  this  principle  that  all  blowpipes  act ; a jet  of  air  or  of  oxy- 
gen is  thrown  into  the  interior  of  a flame ; the  combustion  is  thus 
rendered  more  rapid,  it  is  limited  to  a much  smaller  s]3ace,  and  is 
entirely  changed  in  character. 

The  mouth  blowpipe  is  one  of  the  most  valuable  and  portable  ‘ 
instruments  of  research  which  the  chemist  possesses  : he  is  enabled 
by  its  means,  in  a few  minutes,  to  arrive  with  certainty  and  econ- 
omy at  results  which  without  its  aid  would  require  much  expen- 
diture both  of  fuel  and  of  time ; and  it  often  affords  information 
which  could  be  obtained  in  no  other  way. 

The  mouth  blowpipe  consists  essentially  of  a bent  tube,  ter- 
minating in  a fine  uniform  jet,  with  a chamber  for  the  condensa- 
tion of  moisture  from  the  breath.  A very  con- 
venient form  of  the  instrument  is  shown  at  fig.  318.  Fig.  318 
It  consists  of  a conical  tube  of  tin  plate,  about 
eight  inches  long,  open  at  the  narrow  end,  which 
is  rounded  off  so  as  to  adapt  itself  to  the  lips,  and 
closed  at  its  lower  end,  from  the  side  of  which  pro- 
jects a brass  tube,  5,  about  an  inch  in  length,  upon 
which  is  fitted  a small  brass  jet.  This  jet  is  in- 
serted to  a short  depth  into  the  flame  of  a candle, 
about  an  eighth  of  an  inch  above  the  wick  ; when 
a current  of  air  from  the  blowpipe  is  directed  hori- 
zontally along  the  surface  of  the  wick,  the  flame 
loses  its  luminosity,  and  is  projected  laterally  in  the 
form  of  a beautiful  pointed  cone,  in  -which  three 
parts  are  distinctly  discernible  (see  fig.  319).  In 
the  centre  is  a well-defined  blue  cone  ; outside  that 
is  the  brilliant  part  of  the  flame,  terminating  at  a,  and  exterior  to 
that  is  a pale  yellow  flame,  c.  The  different  parts  of  this  flame 
possess  very  different 

properties.  The  blue  Fkj,  319. 

cone  is  formed  by  the 
admixture  of  air  with 
the  combustible  gases 
rising  from  the  wick, 
and  it  corresponds  to 
the  blue  portion,  <x, 
of  an  ordinary  flame, 
fig.  317.  In  this  part  of  the  flame  combustion  is  complete,  and 
the  oxygen  introduced  by  the  jet  is  in  excess : the  points  where 
the  excess  of  oxygen  is  absorbed  by  combination  with  fresh  por- 
tions of  the  combustible  vapours  which  are  constantly  rising  from 
other  parts  of  the  wick,  are  clearly  defined  by  the  surface  which 
seems  to  limit  the  blue  cone.  In  front  of  this  blue  cone  is  the 
luminous  portion,  containing  unburnt  combustible  gases  at  a high 
temperature,  which  of  course  have  a powerful  tendency  to  com- 
bine with  oxygen. 

If  a fragment  of  some  metallic  oxide,  such  as  oxide  of  copper, 
sufficiently  small  to  be  completely  enveloped  by  the  luminous 
portion,  be  introduced  into  this  part  of  the  flame,  the  oxide  will 


244 


USE  OF  THE  MOUTH  BLOWPIPE. 


be  deprived  of  oxygen,  in  consequence  of  the  superior  attraction 
of  the  hot  gases  for  tliis  element,  and  the  oxide  will  he  reduced 
to  the  metallic  state : hence  this  portion  is  termed  tlie  reduciiig 
flame  of  the  blo^vpipe.  At  the  apex,  c,  of  the  iiame,  the  effects 
are  reversed.  Here,  atmospheric  oxygen  at  a high  temperature 
is  mechanically  carried  forward  along  with  the  completely  formed 
products  of  combustion,  and  a fragment  of  any  readily  oxidizable 
metal,  such  as  lead,  copper,  or  tin,  if  placed  at  this  point  will 
quickly  become  coated  with  oxide ; and  hence  this  spot  is  termed 
the  oxidating  flame  of  the  blovqDipe.  A good  illustra  tion  of  the 
opposite  actions  of  these  contiguous  portions  of  the  dame  is  af- 
forded by  the  effects  which  they  respectively  produce  on  a piece 
of  ffint-glass  tubing.  The  silicate  of  lead  contained  in  the  glass  is 
partially  decomposed  in  the  reducing  ffame,  and  the  glass  at  this 
point  becomes  black  and  opaque  from  the  reduction  of  the  oxide 
of  lead  to  the  metalhc  state ; but  by  placing  the  blackened  part 
for  a few  seconds  in  the  oxidating  ffame,  oxygen  is  again  absorbed 
by  the  metal,  and  the  transparency  of  the  glass  is  restored. 

(495)  Use  of  the  Mouth  Blowpipe. — The  art  of  maintaining  a 
continual  blast  by  the  mouth  blowpipe  is  not  easily  described,  but 
it  can  be  acquired  by  practice  without  much  difficulty.  When 
a substance  is  to  be  examined  by  the  blowpipe,  it  may  be  ffi'st 
heated  alone  in  a small  glass  tube,  in  order  to  observe  whether 
it  melts  or  decrepitates,  or  is  volatihzed  wholly  or  partially.  It 
may  next  be  heated  in  a narrow  tube  open  at  both  ends,  to  ascer- 
tain whether  it  burns,  or  changes  colour,  or  emits  any  odour.  It 
should  then  be  ascertained  whether  it  is  reduced  to  the  metallic 
state,  and  if  it  be  reduced,  what  is  the  colour  of  the  metal ; whether 
it  fuses  easily,  or  whether  it  is  brittle,  crystalline,  or  malleable. 
These  observations  upon  reduction  may  be  best  made  when  the 
globule  is  exposed  to  the  ffame  upon  a disk  of  char- 
coal, which  may  be  conveniently  supported,  as  pro- 
posed by  Mr.  Griffin,  in  the  manner  shown  at  1,  ffg. 
320,  which  represents  an  edge  view  of  a slip  of  tin 
plate,  about  8 inches  long  and  half  an  inch  wide, 
bent  at  one  end  so  as  to  hold  the  charcoal  disk. 
Ho.  2 shows  it  in  front.  The  charcoal  should  be 
sawn  into  slices  about  the  third  of  an  inch  in  thick- 
ness, so  as  to  present  a surface  across  the  grain.  A 
small  cavity  should  be  formed  upon  the  upper  sur- 
face of  each  disk  for  the  reception  of  the  fragment 
of  material  under  examination,  which  should  be 
about  the  size  of  a pin’s  head,  or  a grain  of  mustard-seed. 

Sometimes  when  the  sub- 
stance is  not  easily  reducible, 
a platinum  wire  bent  into  a 
hook  at  one  extremity  forms 
a more  convenient  support, 
as  shown  at  ffg.  321.  It  may 
by  this  means  be  ascertained 
whether  the  substance  im- 


Fig.  321. 


Fig.  320. 
/ 3 


OTHER  FORMS  OF  BLOWPIPE. 


245 


Fig.  322 


parts  any  colour  to  the  flame ; whether  the  body,  if  it  be  fusible, 
yields  a transparent,  an  opaque,  or  a coloured  bead ; whether  any 
change  be  produced  in  the  substance,  according  as  it  is  heated  iii 
the  reducing  or  in  the  oxidating  flame. 

The  employment  of  certain  fluxes  often  aids  the  judgment  of 
the  operator  by  the  colour  or  appearance  thus  produced.  The 
most  important  of  these  fluxes  are  borax  (592),  microcosmic 
salt  (621),  and  carbonate  of  sodium.  When  either  borax  or 
microcosmic  salt  is  used,  a platinum  wire  forms  the  best  sup- 
port; but  when  carbonate  of  sodium  is  employed,  especially 
for  the  purpose  of  reducing  the  metals,  a support  of  charcoal  is 
required. 

Different  forms  of  the  blowpipe  have  been  proposed,  according 
to  the  purposes  for  which  the  instrument  is  destined.  The  glass- 
worker  usually  requires  a large  supply  of  air  to  be  maintained 
uninterruptedly  for  long  periods,  and  he  commonly  employs  a pair 
of  double  bellows,  worked  by  the  foot. 

A portable  blowpipe 
for  glass- working  may  be 
made  as  follows : — A rect- 
angular box  of  zinc,  fig. 

322,  about  14  inches  high 
and  6 wide,  is  divided 
into  two  chambers,  c and 
by  a diaphragm  which 
passes  obliquely  nearly  to 
the  bottom  of  the  box; 
these  chambers  communi- 
cate with  each  other 
below ; one  of  them,  d^  is 
open  above,  and  is  cover- 
ed with  a loose  lid ; the 
other  chamber,  c,  is  closed 
at  the  top : a blowpipe  jet, 
passes  just  through  the 
covering  of  this  chamber, 
which  is  further  supplied 
with  a longer  pipe,  a 5, 
passing  down  to  within  a short  distance  of  the  botton,  covered  with 
a flap  of  silk  to  prevent  the  return  of  the  water  in  case  the  opera- 
tor should  suddenly  cease  to  blow  through  a.  If  the  box  l)e  now 
partially  filled  with  water,  the  pressure  of  the  column  of  liquid 
will  expel  the  air  through  the  jet,  e,  in  any  desired  direction.  By 
blowing  down  the  long  pipe,  the  operator  can  renew  tlie  supply 
of  air  as  often  as  may  be  necessary  ; it  bubbles  up  into  the  closed 
chamber,  c,  driving  the  water  back  into  the  open  one,  when  the 
column  of  liquid,  by  its  pressure,  renews  the  blast  as  before.  The 
gas-burner,/,  can  be  raised  or  lowered  as  may  be  necessary,  and 
by  means  of  a sliding  joint,  y,  can  be  made  to  approach  towards 
or  recede  from  the  jet,  as  may  be  required.  An  oil-lanq)  may 
be  used  when  gas  is  not  at  hand  ; it  has,  indeed,  the  advantage  of 


246 


OIL-GAS OXALIC  ACID. 


giving  a more  intense  heat  than  gas,  and  it  is  less  likely  to  reduce 
the  oxide  of  lead  contained  in  flint  glass. 

Where  a very  intense  heat  is  required,  a spirit-lamp,  or  gas- 
flame,  through  which  a current  of  oxygen  from  a gas-holder  is 
directed,  may  be  employed ; and  occasionally,  in  cases  where  a 
still  stronger  heat  is  requisite,  recourse  may  be  had  to  the  oxy- 
hydrogen  blowpipe,  in  which,  owing  to  the  complete  intermix- 
ture of  the  two  gases,  the  flame  is  solid,  and  therefore  of  small 
dimensions. 

(496)  Oil-Gas,  Tet'-rylene  or  Butylene  (O^Hg  or  CgHg  = 56) : 

Gr.  of  Gas^  1*854 ; of  Liquid  at  54°,  0*627 ; Mol.  Yol.  | | |. — 
This  compound  was  discovered  by  Faraday  to  be  one  of  the  con- 
stituents of  the  gases  obtained  by  the  destructive  distillation  of  oil. 
It  is  almost  insoluble  in  water,  but  is  taken  up  freely  by  alcohol, 
and  still  more  abundantly  by  oil  of  vitriol.  ()il-gas  is  condensed 
at  0°  F.  to  a colourless  liquid ; the  gas  itself  is  colourless,  and 
burns  with  a white,  powerfully  luminous  flame.  It  contains  the 
same  proportions  of  carbon  and  hydrogen  as  olefiant  gas,  but  the 
two  elements  are  condensed  in  oil-gas  into  half  the  bulk  which 
they  occupy  in  olefiant  gas.  One  volume  of  this  gas  requires  6 
times  its  bulk  of  oxygon  for  its  complete  combustion,  4 volumes  of 
steam  and  4 volumes  of  carbonic  anhydride  being  the  products. 
Consequently  its  composition  may  be  thus  represented  : — 


By  weight. 

Carbon -04  r=:  48  or  85‘71 

Hydrogen. ..  .Ha  = 8 14-29 


By  volume.  Sp.  gr. 
8?  or  4?  = 1-658 
8 4 = 0*276 


OU-gas ■e4H8  = 56  100*00  2 1 = 1*934 


§ III.  Compounds  of  Carbon  with  Oxygen 


(497)  Besides  carbonic  oxide  and  carbonic  anhydride,  carbon 
forms  several  other  oxides,  which  are  not  known  in  the  separate 
form,  but  which,  when  united  with  the  elements  of  water,  possess 
acid  characters  : viz.. 


Oxalic  acid II^O^O,  or  2 IIO,C,06  = 90 

Khodizonic  acid HgOgllOg  = 160 

Croconic  acid = 142 

Mellitic  acid or  2 HO,CgOg  = 114 


(498)  Oxalic  Acid:  H ,0,0,,  2 H.O,  or  2 HO,C,Og,4  Aq.= 
90  + 36  ; 8‘p.  Gr.  1*63. — This  important  and  powerful  acid  maybe 
usefully  introduced  here,  though  it  belongs  to  the  division  of 
organic  chemistry,  as  it  is  always  obtained  from  sugar,  starch,  or 
some  other  substance  of  organic  origin,  and  is  one  of  the  products 
of  the  oxidation  of  these  substances  under  the  influence  of  hot 
nitric  acid  or  cf  hydrate  of  potash  ; it  is  moreover  a frequent  con- 
stituent of  the  juices  of  plants.  Oxalic  acid  is  abundant  in  the 
le-aves  of  the  wood-sorrel  (Oxalis  acetosella)^  to  which  it  commu- 
nicates their  powerfully  acid  taste,  and  in  which  it  occurs  in  com- 
bination with  potassium  as  the  salt  commonly  known  as  binoxalate 
of  potash.  It  is  found  likewise  m the  Bumex  acetosa  and  in  the 


PROPERTIES  OF  OXALIC  ACID. 


247 


leaf-stalks  of  the  common  rhubarb.  Many  lichens  owe  their  solid- 
ity to  the  presence  of  oxalate  of  calcium,  and  have  been  employed 
as  a source  of  the  acid.  It  is  also  contained  abundantly  in  the 
barilla  plant,  in  the  form  of  neutral  oxalate  of  sodium. 

Preparation. — Oxalic  acid  may  be  procured  by  heating  tar- 
taric, citric,  or  malic  acid  with  an  excess  of  hydrate  of  potash  ; 
and  when  starch,  sugar,  or  ligneous  tissue  is  similarly  treated, 
hydi'ogen  is  evolved  and  oxalate  of  potassium  is  among  the  pro- 
ducts. Many  tons  of  oxalic  acid  are  indeed  now  made  weekly 
for  the  calico-printer  by  heating  sawdust  with  a mixture  of 
hydrate  of  potash.*  But  the  acid  is  still  commonly  prepared  by 
the  older  plan  of  oxidation  of  sugar  or  of  starch  by  nitric  acid  ; — 
1 part  of  dry  loaf  sugar  is  dissolved  in  8^1-  parts  of  nitric  acid,  of 
sp.  gr.  1*38,  and  heated  in  a flask  until  all  effervescence  has 
ceased ; a copious  evolution  of  carbonic  anhydride  and  of  nitric 
oxide  attends  the  reaction.  The  solution  is  then  evaporated  by  a 
water-bath  to  one-sixth  of  its  bulk,  and  the  acid  crystallizes  on 
cooling.  The  mother-liquor  may  be  further  concentrated  by  eva- 
poration : the  oxalic  acid  is  purified  by  recrystallization,  and 
amounts  to  more  than  half  the  weight  of  the  sugar  employed. 
(Schlesinger.)  Starch  may  be  substituted  for  the  sugar  in  this  pro- 
cess, with  results  nearly  as  good. 

Properties. — Oxalic  acid  as  thus  obtained  crystallizes  in  trans- 
parent four-sided  prisms,  which  are  represented  by  the  formula 
2 H^O).  This  acid  requires  about  9 times  its  weight 
of  cold  water  for  solution,  but  it  is  dissolved  much  more  freely  by 
boiling  water ; it  is  also  soluble  in  alcohol.  The  crystals  when 

* The  following  is  the  method  (Schunck,  Smith,  and  Roscoe,  Brit.  Assoc.  Report, 
1861,  p.  120)  employed  by  Messrs.  Roberts,  Dale,  and  Co,  for  manufacturing  oxalic 
acid  from  sawdust  on  a large  scale.  A concentrated  solution  of  mixed  caustic  soda 
and  potash  sp.  gr.  1-35  is  prepared,  containing  2 atoms  of  hydrate  of  soda  to  1 atom 
of  hydrate  of  potash.  Caustic  soda  alone  does  not  furnish  oxahc  acid  by  this  method, 
and  caustic  potash  singly  is  too  expensive,  hence  a mixture  of  the  two  is  necessary. 
Sawdust  is  introduced  so  as  to  form  a thick  paste.  The  pasty  mass  is  placed  in  thick 
layers  upon  heated  iron  plates,  and  stirred  constantly  whilst  the  temperatnre  is  gra- 
dually raised.  At  first  water  escapes  freely : as  the  decomposition  advances  the 
mass  swells  up  and  disengages  an  inflammable  gas,  containing  hydrogen  and  carbu- 
retted  hydrogen,  accompanied  with  an  aromatic  odour.  The  temperature  is  main- 
tained at  a point  between  400°  and  480°  for  a couple  of  hours,  when  a dark  brown 
mass,  wholly  soluble  in  water,  is  obtained.  The  exact  nature  of  this  mixture  is  not 
ascertained.  At  present,  however,  it  contains  only  from  one  to  four  per  cent,  of 
oxalic  acid,  and  a trace  of  formic,  but  no  acetic  acid ; the  application  of  heat  to  the 
mass  is  therefore  continued  for  3 or  4 hours  longer,  taking  care  to  avoid  charring. 
The  mass  becomes  thoroughly  dry,  and  finally  contains  from  28  to  30  per  cent,  of 
oxalic  acid ; hydrogen  appears  to  be  given  off’  continuously  during  the  process,  which 
is  quite  successful  in  closed  vessels. 

The  grey  mass  thus  procured  is  treated  with  water  at  60°,  which  dissolves  out 
everything  but  the  sparingly  soluble  oxalate  of  sodium.  The  mother-liquors  after  tho 
separation  of  the  oxalate  of  sodium  are  boiled  down  to  dryness,  ignited  to  destroy 
organic  matter,  and  the  alkalies  are  again  rendered  caustic,  and  after  tho  addition  of 
a suitable  quantity  of  soda,  arc  used  in  preparing  a fresh  charge. 

The  oxalate  of  sodium  is  decomposed  by  boiling  with  hydrate  of  lime,  oxalate  of 
calcium  is  formed,  and  separates  in  tho  insoluble  condition,  whilst  caustic  soda  enters 
into  the  solution,  and  may  be  used  over  again.  Meantime  the  oxalate  of  calcium  is 
decomposed  by  meanr.  of  sulphuric  acid,  and  the  liquor  decanted  from  the  sulphate 
of  calcium  furnishes  crystals  of  oxahc  acid  on  evaporation.  By  this  method  2 lb.  of 
sawdust  yield  about  1 lb.  of  crystallized  oxahc  acid. 


248 


PROPERTIES  OF  OXALIC  ACID OXALATES. 


heated  suddenly  to  212°  melt  in  their  water  of  crystallization;  hut 
if  slowly  raised  to  212°  they  become  opaque,  and  lose  28‘5  per 
cent,  of  water.  The  residue  then  consists  of  H2‘02O4.  If  these 
dried  crystals  be  placed  in  a retort,  and  heated  by  means  of  an 
oil-bath  to  between  300°  and  320°,  they  are  slowly  sublimed  and 
may  be  condensed  in  w^hite  needles  ; but  if  heated  above  320°  the 
acid  is  decomposed.  When  the  crystallized  oxalic  acid  is  heated 
quickly  without  previous  desiccation,  it  melts  in  its  water  of 
crystallization,  and  at  311°  is  resolved,  with  apparent  ebullition, 
into  a mixture  of  carbonic  anhydride,  formic  acid,  water,  and  car- 
bonic oxide : — 


Oxalic  acid. 


Formic  acid. 


2 H,e  eo,  + 2 H,e  -p  hoho,. 


the  carbonic  oxide  being  derived  from  the  formic  acid,  which  when 
decomposed  by  heat  yields  carbonic  oxide  and  water ; HOHO, 
becoming  H^O  + OO.  Berthelot  has  shown  that  the  conversion 
of  oxalic  acid  into  formic  acid  is  easily  effected  by  dissolving  the 
oxalic  acid  in  glycerin,  and  heating  to  about  300°,  when  formic 
acid  slowly  passes  over,  and  carbonic  anhydride  escapes  ; but  if 
the  temperature  be  raised  to  380°  carbonic  oxide  is  obtained  in 
abundance.  When  heated  with  oil  of  vitriol,  or  phosphoric 
anhydride,  it  breaks  up  into  equal  volumes  of  carbonic  oxide 
and  carbonic  anhydride.  JSTo  anhydride  of  oxalic  acid  appears  to 
exist. 

The  composition  of  oxalic  acid  is  as  follows : — 


Unknown  anhydride. 

Carbon -02  = 24  or  33-3 

Oxygen 03=48  66-7 

Water  


Hydrated. 
02=24  or  26-6 
03=48  53-4 

1120=18  20-0 


Crystallized. 

02  = 24  or  19-05 
03=48  38-10 

3H20=54  42-85 


H20204  = 9O  100-0 


H202O4,  2 020=126  100-00 


The  solution  of  oxalic  acid  has  an  intensely  sour  taste ; if 
swallowed,  the  acid  acts  as  a powerful  poison,  occasioning  death 
in  a very  few  hours.  The  best  antidote  in  such  a case  is  the  ad- 
ministration of  chalk  or  of  magnesia  suspended  in  water. 

It  is  a general  rule  that  when  an  elementary  body  forms  two  or 
more  acids  with  oxygen,  the  acid  which'  contains  the  largest  amount 
of  oxygen  is  the  most  energetic  in  its  action.  Thus  the  sulphuric 
acid  is  more  powerful  than  the  sulphurous  ; chloric  acid  is  stronger 
than  hypochlorous  acid,  and  the  perchloric  acid  is  stronger  than 
either.  It  is,  however,  otherwise  in  the  case  of  oxalic  acid  ; 
although  oxalic  acid  contains  a smaller  proportion  of  oxygen  than 
carbonic  acid,  its  attraction  for  bases  is  much  more  energetic,  and 
it  decomposes  all  the  carbonates  witli  effervescence.  It  even  libe- 
rates hydrochloric  acid  when  heated  wdth  dry  chloride  of  sodium. 
The  cause  of  this  remarkable  exception  to  the  general  rule  has 
not  hitherto  been  explained. 

Oxalates. — Until  lately  oxalic  acid  was  regarded  as  monobasic ; 
but  there  are  good  reasons  for  viewing  it  as  dibasic.  Besides  the 


OXALATES. 


249 


two  classes  of  salts  usually  formed  by  dibasic  acids,  the  oxalic 
furnishes  wdth  the  alkaline  metals  a group  of  super-acid  salts,  rep- 
resented by  the  so-called  quadroxalate  of  potash.  The  neuti^al 
oxalate  of  potassium  furnishes  efflorescent  very  soluble  prismatic 
crystals  : the  acid  oxalate  is  sparingly  soluble  in  cold  water,  and 
requires  about  14  parts  of  boiling  water  for  solution ; it  crystallizes 
in  large  prisms  which  are  unaltered  by  exposure  to  the  air ; and 
the  quadroxalate  furnishes  large  crystals  which  are  still  less  soluble. 
The  so-called  salt  of  lemons  is  one  of  these  acid  oxalates.  Oxalic 
acid  forms  a large  number  of  insoluble  salts.  The  insolubility  of 
oxalate  of  calcium  in  water  has  led  to  the  employment  of  oxalic 
acid  as  a reagent  for  indicating  the  existence  of  lime  in  solution, 
and  for  determining  its  amount.  On  adding  a neutral  oxalate  to 
a neutral  or  alkaline  solution  of  any  salt  of  calcium,  the  oxalate 
of  calcium  falls  as  a white  precipitate,  which  is  insoluble  in  acetic 
acid.  After  drying  at  100°  F.,  this  salt  consists  of  ■0aO2O4,  2 FI^O-, 
and  when  heated  to  bright  redness,  100  parts  leave  34T5  of  pure 
quicklime,  corresponding  to  43*9  of  oxalic  anhydride.  The  oxalates 
of  magnesium,  cadmium,  and  manganese  are  also  wdiite  and  nearly 
insoluble  : they  each,  wdien  dried  at  212°,  retain  2 Ilf}.  Oxalate 
of  zinc  is  white ; oxalate  of  cobalt  is  rose-coloured ; oxalate  of 
nickel  is  greenish  white,  and  ferrous  oxalate  is  yellow : they  are 
all  sparingly  soluble,  and  retain  2 at  100°  F.  The  oxalates 
of  barium  and  strontium  are  white,  and  that  of  copper  is  of  a pale 
blue : they  are  nearly  insoluble,  and  retain  at  212°.  The 

oxalates  of  lead  and  silver  are  white,  and  anhydrous.  All  the  in- 
soluble oxalates  are  readily  dissolved  by  diluted  nitric  acid. 

An  insoluble  basic  oxalate  of  lead  (Pb020-4,  2 PbO)  may  be 
obtained  by  precipitating  the  tribasic  acetate  of  lead  by  means  of 
a neutral  soluble  oxalate.  One  of  the  most  characteristic  salts  of 
this  acid  is  the  oxalate  of  silver,  which  when  heated  on  platinum 
foil  is  suddenly  reduced  to  the  metallic  state,  and  is  dispersed  with 
a slight  explosion,  owing  to  the  sudden  liberation  of  carbonic  an- 
hydride; Ag2-02O-4==2  Ag-1-2  OO^-  The  oxalates  of  many  other 
of  the  metals  which  have  but  small  attraction  for  oxygen,  those  of 
cobalt  and  nickel  among  the  number,  are  reduced  to  the  metallic 
state  if  heated  to  redness  in  a closed  vessel,  so  as  to  exclude  at- 
mospheric oxygen  ; 2 atoms  of  carbonic  anhydride  being  expelled, 
whilst  the  pure  metal  is  left  behind.  This  reducing  action  occurs 
in  the  case  of  gold,  when  a solution  of  a salt  of  this  metal  is  simply 
boiled  with  an  oxalate ; the  gold  is  precipitated,  either  in  flakes 
or  in  the  form  of  a very  finely  divided  powder.  The  oxalates  of 
the  metals  of  the  alkalies  and  the  alkaline  earths  are  converted 
by  a dull  red  heat  into  carbonates  of  these  metals ; the  carbonic 
oxide  burning  off  with  a pale  blue  flame,  whilst  the  salt  does  not 
exhibit  ariy  appearance  of  charring. 

The  general  formnlje  of  the  oxalates  are  the  following — the 
table  includes  some  of  the  principal  oxalates  : — 


Normal  oxalates M2O2O4 

Acid  oxalates MHO2O4 

Super-acid  oxalates MH3  2 O2O4 


250 


OXALATES KHODIZONIC  AND  CKOCONIC  ACID. 


Oxalate  of  potassium 

Binoxalate  of  potassium . , 
Quadroxalate  of  potassium 
Oxalate  of  ammonium .... 
Binoxalate  of  ammonium. . 

Oxalate  of  barium 

“ strontium 

“ calcium 

“ magnesium. . . . 

“ zinc 

‘‘  cadmium 

“ cobalt 

“ nickel 

“ iron 

“ copper  

“ lead 

“ silver 


. HaO 

KH3  2 ^204 . 2 HaO 
(04^)2  02O4 . 
H4NHe204  . H20 
fia0204  . H20 

Sr0204 . 020 

0a0204 . 2 020 
Mg0204  • 2 020 

2n0204 , 2 020 
ed0204 . 2 020 
000204 . 2 020 
?fi0204 . 2 020 
0e0204 . 2 020 

0U0204 . 020 

Pb0204 

Ag20204 


Oxalic  acid  forms  a large  number  of  double  salts, — such  as 
the  following : — 


Uranous  ammoniacal  oxalate  [W'  2 020^,1120]. 

Uranic  ammoniacal  oxalate  (UOH4]S^-02^45  2 HgO). 

Chromico-potassic  oxalate  (KgOr'''  3 020^,  3 H2O). 

(499)  Bhodizonic^  Croconic^  and  Mellitic  Acids. — Three 
other  acids  containing  carbon  and  oxygen  are  known  under  these 
names,  but  they  are  of  slight  importance. 

Bhodizonic  Acid  (HgOgHOg ; Will)  is  an  acid  w’hich  forms 
salts  of  a beautiful  red  or  scarlet  colour,  w^hence  it  derives  its 
name  (from  p6(iov,  a rose).  It  is  obtained  by  the  action  of  a moist 
atmosphere  on  the  dark  olive-green  compound  which  potassium 
yields  when  gently  heated  in  carbonic  oxide  gas,  and  which  is 
formed  abundantly  during  the  preparation  of  potassium. 

If  the  aqueous  solution  of  rhodizonate  of  potassium  (KgOgllgOg, 
HgO  V)  be  boiled  in  the  presence  of  free  alkali,  it  is  decomposed 
with  loss  of  w^ater  into  the  salt  of  a new  acid,  which  from  the  yel- 
low colour  of  its  compounds  is  termed  Croconic  Acid,  HgOgOg. 

Croconic  acid  is  obtained  by  decomposing  croconate  of  potas- 
sium wdth  silicofluoric  acid.  It  forms  yellow  crystals  soluble  both 
in  water  and  in  alcohol.  Croconic  acid  and  the  soluble  croco- 
nates  furnish  yellow  sparingly  soluble  crystalline  plates  when 
mixed  Avith  salts  of  barimn  or  of  lead  (Will,  Lieb.  Annal. 
cxviii.  187). 

(500)  Mellitic  Acid  (HgO^O^,  or  2 HO,  Cfi^)  has  hitherto 
been  found  only  in  Mellite,  a rare  mineral,  consisting  of  mellitate 
of  aluminum  (Alg  3 0^0^,  18 II2O),  which  is  now  and  then  met 
with  in  lignite,  and  occm’S  crystallized  in  honey-yellow  transpar- 
ent octohedra.  Mellitic  acid  is  extracted  from  mellite  by  boiling 
the  powdered  mineral  wdth  carbonate  of  ammonium.  Mellitate 
of  ammonium  is  obtained  in  solution : by  the  addition  of  acetate 
of  lead  to  the  liquid,  the  mellitate  of  lead  (PbO.O^HgO)  is  pre- 
cipitated. This  precipitate,  w'hen  washed,  is  suspended  in  water 
and  decomposed  by  a current  of  sulphuretted  hydrogen  ; sulphide 
of  lead  is  thus  formed,  and  is  separated  by  filtration  from  the  so- 
lution which  contains  the  liberated  mellitic  acid  : on  evaporating 


MELLITIC  ACID CYANOGEN. 


251 


tlie  liquid  the  acid  is  left  in  a state  of  purity.  Mellitic  acid  is 
soluble  in  water  and  in  alcohol ; it  may  be  obtained  crystallized 
in  groups  of  needles  by  the  spontaneous  evaporation  of  the  alco- 
holic solution.  Its  solution  reddens  litmus  strongly,  and  has  a 
strongly  sour  taste.  Mellitic  acid  is  unchanged  by  boiling  nitric 
or  sulphuric  acids.  The  acid  is  decomposed  by  heat  into  a vola- 
tile crystalline  sublimate,  and  into  carbon.  With  the  salts  of  lead 
the  mellitates  give  a voluminous  white  precipitate,  which  gradu- 
ally shrinks  in  bulk  and  becomes  crystalline. 

§ lY.  Compounds  of  Carbon  with  Hitjrogn. 

(501)  Cyanogen  ; OH  or  C^H,  or  Cy=26 : Theoretic  Sp.  Gr. 
1*800 ; Observed 1*8064 ; Atomic  Vol.  — This  substance  is 

one  of  the  most  interesting  compounds  ol  carbon,  and  its  discov- 
ery by  Gay-Lussac,  in  1814,  formed  an  epoch  in  the  history  of 
chemical  science.  It  was  the  first  compound  body  which  was 
distinctly  proved  to  enter  into  combination  with  elementary  sub- 
stances in  a manner  similar  to  that  in  which  the  elements  com- 
bine with  each  other.  Hew  views  of  chemical  composition  \vere 
thus  originated,  which  have  since  acquired  an  extensive  develop- 
ment, and  have  exercised  a most  material  infiuence  upon  the 
theory  of  organic  compounds  in  general.  The  name  of  Oyanogeii 
(fi’om  xoavog  blue,  yBvvdfji  to  produce),  is  derived  from  the  circum- 
stance tliat  this  body  forms  an  essential  ingredient  in  Prussian 
blue.  Ho  direct  union  of  its  constituent  elements  can  be  effected. 
If  a mixture  of  charcoal  and  carbonate  of  potassium  be  heated  to 
redness  in  a porcelain  tube,  and  nitrogen  be  passed  over  it,  car- 
bonic oxide  escapes  abundantly,  whilst  cyanogen  is  formed  and 
unites  with  the  potassium,  yielding  cyanide  of  potassium.f 

K,ee3  4-4e-h2H^2  koh + 3 ea 

Cyanogen  is  also  present  in  small  quantity  among  the  products 
obtained  during  the  distillation  of  pit  coal ; and  it  is  furnished 
during  the  decomposition  of  oxalate  of  ammonium  by  heat, 
2 llH  ,0^0^  becoming  2 GH-l-4  II^O.;]; 

The  compounds  of  cyanogen  are,  however,  almost  always  ob- 
tained from  the  double  cyanide  of  potassium  and  iron,  a salt  which 
crystallizes  in  transparent  yellow  tables,  and  is  commonly  known 

♦In  its  free  state  (CyCy=52;  Mol.  Vol.  | | |). 

f It  may  also  be  mentioned  as  a matter  of  theoretical  interest,  that  the  com- 
pounds of  ammonia  in  vapour  if  transmitted  over  glowing  charcoal  yield  cyanogen 
still  more  readily,  especially  when  carbonate  of  potassium  is  also  present.  The  oxi- 
dized compounds  of  nitrogen  such  as  the  nitrates,  likewise  readily  furnish  small 
quantities  of  the  compounds  of  cyanogen,  as  is  frequently  observed  in  deflagrating 
charcoal  with  nitre. 

X A sensitive  reaction  for  the  presence  of  nitrogen  in  organic  compounds  is 
founded  upon  the  facility  with  which  either  potassium  or  sodium  determines  the  for- 
mation of  cyanogen  from  azotised  compounds  of  carbon: — a small  globule  of  potas- 
sium (or  of  sodium)  is  introduced  into  a narrow  glass  tube  sealed  at  one  end,  and 
the  metal  is  heated  with  the  organic  body  under  examination.  The  residue  is  then 
dissolved  in  water  and  a small  quantity  of  a mixture  of  the  ferrous  and  ferric  sul- 
phates added,  then  a slight  excess  of  hydrochloric  acid ; a precipitate  of  Prussian 
blue  is  formed  if  nitrogen  be  present  in  the  compound. 


252 


LIQUEFACTION  OF  CYANOGEN. 


by  the  name  of  prussiate  of  j)otash,  or  ferrocyanide  of  potassiimi. 
This  salt  is  prepared  by  heating,  in  a covered  u-on  pot,  about  5 
parts  of  refuse  animal  matter,  such  as  the  parings  of  hoofs,  hides, 
homs,  ike.,  with  2 parts  of  peaiiash,  and  iron  filings  ; the  nitrogen 
and  carbon  of  the  animal  matters  react  upon  each  other  at  a high 
temperatiu-e,  and  combine  with  a portion  of  reduced  potassium 
and  with  iron.  On  digesting  the  mass,  when  cold,  with  water, 
the  ferrocyanide  of  potassimn  (K^FeCy6,3  H^O)  is  formed,  and  is 
deposited  li*om  the  solution  in  large  fom’-sided  tables.  When  10 
parts  of  this  salt  are  dissolved  in  4 times  their  weight  of  warm 
water,  and  distilled  with  7 parts  of  oil  of  vitriol  diluted  with  twice 
their  weight  of  water,  until  about  half  the  bulk  of  the  liquid  has 
passed  over,  a dilute  solution  of  hydrocyanic  acid  (HCy)  is  foimed  ;* 
this,  if  saturated  with  red  oxide  of  mercuiy,  furnishes,  on  evapo- 
ration, a crvstallizable  compound,  the  cyanide  of  mercury  (HgCy^). 
If  this  be  thoroughly  dined,  and  heated  in  a retort,  it  is  decom- 
posed into  mercury,  which  distils  over,  and  cyanogen,  which 
passes  ofi*  as  a permanent  gas. 

Cyanogen  is  a transparent  coloui’ess  gas,  of  a peculiar,  pene- 
trating odour : it  is  poisonous,  if  respired.  It  burns  with  a beau- 
tiful flame  edged  with  purple.  Cyanogen  is  soluble  in  one-fouith 
of  its  bulk  of  water,  and  still  more  fi’eely  so  in  alcohol ; hence  it 
must  be  collected  over  mercury.  In  porcelain  or  glass  vessels  it 
supports  a high  temperature  without  decomposition,  but  if  heated 
in  iron  tubes,  charcoal  is  deposited,  and  a volume  of  nitrogen, 
equal  to  that  of  the  cyanogen  used,  remains. 

The  composition  of  cyanogen  may  be  determined  by  detonation 
in  the  eudiometer  with  oxygen ; the  combustion  is  attended  with 
a powerful  explosion.  One  volume  of  cyanogen  with  2 volumes 
of  oxygen  yield  2 of  carbonic  anhydride  and  1 volume  of  nitro- 
gen ; 2 volumes  of  carbon  vapour  and  1 volume  of  nitrogen  must 
therefore  be  condensed  in  it  into  1 volume,  as  is  shown  in  the 
following  table : — 

By  weight.  Bv  vol.  Sp.  gr. 

Carbon -G  = 12  or  46T5  ' 2?  = 0*829 

Nitrogen N = 14  53-85  1 = 0-971 

Cyanogen GN  = 26  100*00  1 = 1*800 


Cyanogen  is  readily  reduced  to  the  liquid  state  by  a pressure  of 
its  own  vapom*  equal  to  about  4 atmospheres.  It  forms  a colour- 
less, limpid  liquid,  of  sp.  gr.  0-866  aft  63°,  which,  on  the  removal 
of  the  pressure,  rapidly  but  quietly  resumes  the  gaseous  state.  It 
fi-eezes  at  — 30°,  and  forms  a transparent  crystalline  solid,  which 
is  nearly  of  the  same  density  as  the  liquid. 

Fig.  323  shows  an  easy  method  of  liquefving  cyanogen  ; a tube 
of  hard  glass  is  bent  into  the  form  of  a,  t,  c.  Into  the  limb,  a, 
well-dried  cyanide  of  mercury  is  introduced ; heat  is  apphed  to 

* The  reaction  in  this  case  is  rather  less  simple  than  might  have  been  anticipated ; 
it  was  first  accurately  traced  by  Everitt ; 

K4FeCy«  + 3 H0SO4  = 3 HCy  + KFeCjs  + 3 KHSG4  ; 
half  the  cyanogen  only  is  expelled  as  hydrocyanic  acid,  the  other  half  remaining  be- 
hind in  the  form  of  a white,  insoluble,  double  cyanide  of  iron  and  potassium  (KFe"Cys) 


HYDEOCYAiaC  ACID. 


253 


the  cyanide  of  mercury  at  a ; the  bend,  5,  is  placed  in  a basin 
containing  a freezing  mixture  of  ice  and  salt ; as  soon  as  the  gas 
begins  to  escape,  the  stopcock  at  c is  closed,  and  liquid  cyanogen 
becomes  condensed  in  the  bend,  h. 


Fig.  323. 


If  potassium  be  heated  in  cyanogen  it  burns  and  combines  with 
it,  without  occasioning  the  decomposition  of  the  gas,  forming  a 
saline  body  analogous  to  common  salt.  This  experiment  shows 
the  existence  of  the  remarkable  property  possessed  by  cyanogen, 
of  combining  with  metals  and  other  bodies  like  an  element.  This 
peculiarity  in  the  mode  of  combination  of  cyanogen,  which  has 
given  rise  to  the  theory  of  compound  radicles  now  so  extensively 
applied  in  organic  chemistry,  will  be  better  traced  by  examining 
a few  of  the  numerous  compounds  which  cyanogen  forms  with  the 
elementary  bodies. 

(502)  Hydeocyanic  oe  Peussic  Acid  (HCy  = 27) : Sp.  Gr. 
of  Vapour^  Theoretic^  0*933;  Observed^  0*9476;  of  Liquid^ 
6*7058  at  45°  F.  ; Melting-pt.  5°;  Boiling-pt.^  80°;  Atomic  and 
Mol.  Vol.  I I ]. — Cyanogen  forms  with  hydrogen  a highly  import- 
ant compound,  though  the  two  bodies  cannot  be  made  to  unite 
directly  with  each  other.  If  a current  of  dried  sulphuretted  hy- 
drogen be  transmitted  through  a long  tube  filled  with  cyanide  of 
mercury  until  the  cyanide  has  become  blackened  nearly  through- 
out, sulphide  of  mercury  and  hydrocyanic  acid  are  formed ; but 
it  may  also  be  prepared  by  decomposing  any  of  the  cyanides  by  a 
strong  acid,  and  subjecting  them  to  distillation  ; for  example,  cyan- 
ide of  mercury  wdien  treated  with  hydrochloric  acid  yields  it 
readily.  The  most  economical  process  is  that  of  Wohler ; he  pre- 
pares a crude  cyanide  of  potassium  by  fusing  8 parts  of  the  dried 
yellow  ferrocyanide  of  potassium  with  3 of  carbonate  of  potassium 
and  1 part  of  charcoal.  This  decomposition  is  shown  in  the  fol- 
lowing equation : — 

K^PeCy,  -p  K,ee3  -P  = 6 KCy  + Pe  -P  3 OO. 

The  fused  mass  is  treated  w'ith  6 times  its  weight  of  water,  in  a 
well-closed  vessel ; the  clear  liquid  is  decanted  from  the  iron,  which 
it  is  the  object  of  this  operation  to  separate,  and  is  poured  into  a 
retort : sulphuric  acid,  diluted  with  an  equal  weight  of  water,  is 
gradually  added  in  the  proportion  of  1 part  of  oil  of  vitriol  to  2 
parts  of  the  cyanide.  At  first  the  distillation  proceeds  sponta- 


254 


HYDEOCYANIC  AGED. 


neoiisly  from  the  heat  developed  by  the  admixture  of  the  sulphuric 
acid  with  the  water.  In  order  to  condense  the  acid,  the  products 
are  made  to  pass  through  a long  U-shaped  tube,  immersed  in  cold 
water,  and  filled  with  chloride  of  calcium,  with  the  exception  of 
the  first  fourth  of  the  tube,  which  contains  fragments  of  the  crude 
cyanide  of  potassium ; to  the  bent  tube  is  attached  a second  de- 
livering tube,  which  passes  to  the  bottopa  of  a bottle  cooled  with 
ice  and  salt.  The  chloride  of  calcium  in  the  syphon  tube  retains 
the  moisture,  and  the  cyanide  of  potassium  any  sulphuric  acid 
that  might  chance  to  pass  over,  whilst  the  hydi'ocyanic  acid  col- 
lects in  an  anhydrous  state  in  the  cooled  receiver.  The  reaction 
of  sulphuric  acid  upon  cyanide  of  potassium  is  very  simple,  being 
exactly  analogous  to  its  action  upon  chloride  of  sodium  : — 

2 KCy  -p  2 H,SO,  = 2 HCy  -f  2 KHSO,. 

Anhydrous  hydrocyanic  acid  is  a colourless,  transparent,  and 
very  volatile  liquid ; so  rapidly  does  it  evaporate,  that  if  a drop  be 
allowed  to  fall  upon  a glass  plate,  part  of  the  acid  becomes  frozen 
by  the  cold  produced  by  its  own  evaporation.  Its  vapour  has  an 
odour  of  peach  blossoms,  causing  a peculiar  sense  of  oppression, 
and  of  constriction  in  the  fauces.  Owing  to  its  intensely  poisonous 
character,  the  greatest  care  is  requisite  in  conducting  experiments 
upon  this  substance ; the  apparatus  should  always  be  arranged  so 
that  the  vapours  are  carried  away  from  the  operator  by  a brisk 
current  of  air. 

Hydrocyanic  acid  is  very  infiammable ; it  burns  with  a flame 
resembling  that  of  cyanogen,  but  of  a whiter  colour.  In  con- 
formity with  its  analogy  with  the  hydrogen  acids  of  chlorine  and 
the  other  halogens,  it  is  composed  of  1 volume  of  hydrogen  and  1 
of  cyanogen  united  without  condensation.  When  potassium  is 
heated  in  hydi’ocyanic  acid  vapour,  cyanide  of  potassium  is  formed, 
and  a volume  of  hydrogen  equal  to  half  that  of  the  vapour  em- 
ployed is  liberated ; chlorine  and  bromine  decompose  it  immedi- 
ately ; hydrochloric  or  hydrobromic  acid  is  produced,  and  if  excess 
of  the  halogen  be  present,  chloride  or  bromide  of  cyanogen  is 
foi’med.  If  5 volumes  of  oxygen  be  mingled  with  4 volumes  of 
hydrocyanic  vapour,  a mixture  is  obtained  which  detonates  pow- 
erfully on  transmitting  the  electric  spark  through  it ; 4 volumes 
of  carbonic  anhydride  and  2 volumes  of  nitrogen  remain,  and  2 
volumes  of  steam  are  condensed.  The  composition  of  hydi’ocyanic 
acid  may  be  calculated  from  the  result  of  this  experiment,  and 
may  be  represented  as  follows : — 


Bv  •weight. 

By  volume. 

Sp.  gr. 

Carbon 

..  H 

= 12 

or  44‘45 

2 

or  1-0  = 

0-414 

Nitrogen 

..  N 

= 14 

51-85 

1 

0-5  = 

0-485 

Hydrogen 

..  H 

= 1 

3 70 

1 

0 5 = 

0-034 

Hydrocyanic  ) 
acid  ) 

H€N 

= 27 

100-00 

2 

1-0  = 

0-933 

The  acid  properties  of  this  compound  are  but  feeble ; it  reddens 
litmus  slightly,  dissolves  red  oxide  of  mercury  freely,  and  pre- 
cipitates nitrate  of  silver  in  white  flocculi  (AgCy).  Cyanide  of 


IIYDEOCYANTC  ACID CYANIDES. 


255 


potassium  always  has  an  alkaline  reaction  : its  solution  emits  the 
odour  of  the  acid.  Pure  hydrocyanic  acid  may  he  kept  unchanged 
if  excluded  from  light ; but  in  dilfused  light  it  becomes  decom- 
posed, and  a brown  matter,  consisting  chiefly  of  paracyanogen,  is 
formed.  Pelouze  has  pointed  out  a remarkable  decomposition 
which  furnishes  dilute  hydrocyanic  acid  almost  in  a state  of  purity  : 

1 atom  of  crystallized  formiate  of  ammonium  contains  the  elements 

of  1 atom  of  hydrocyanic  acid  and  2 atoms  of  water.  If  this  salt 
be  placed  in  a retort  and  heated,  it  melts  at  248°,  loses  a little 
ammonia  at  284°,  and  between  356°  and  392°  distils  over,  and  if 
the  vapour  be  transmitted  through  a red-hot  tube  it  is  wholly  con- 
verted into  hydrocyanic  acid  and  water : = HOIST  + 

2 II^O.  If  equal  measures  of  concentrated  hydrocyanic  and  hy- 
drochloric acids  be  mixed  together,  formic  acid  and  ammonia  are 
reproduced. 

Hydrocyanic  acid,  mixed  with  a peculiar  essential  oil,  is  ob- 
tained by  distillation  from  the  kernels  of  the  bitter  almond,  and 
from  those  of  many  varieties  of  stone  fruit : it  is  also  present  in 
the  water  which  is  distilled  off  the  leaves  of  the  laurel,  the  peach, 
and  some  other  slirubs : the  juice  of  the  tapioca  plant  {Jatrojpha 
mcmihot)  likewise  contains  it,  and  it  is  also  formed  under  various 
circumstances  during  the  oxidation  and  decomposition  of  some 
kinds  of  nitrogenized  substances. 

The  preparation  of  diluted  hydrocyanic  acid  by  distillation  of 
ferrocyanide  of  potassium  with  diluted  sulphuric  acid  has  been 
already  noticed,  but  as  the  acid  is  now  frequently  employed  in 
medicine,  it  is  higlily  important,  on  account  of  its  energetic 
action,  to  be  able  to  insure  its  preparation  of  an  uniform  strength. 
This  is  easily  attained  by  the  process  of  a former  Pharmacopoeia, 
which  directs  48-|-  grains  of  cyanide  of  silver  to  be  suspended  in 
an  ounce  of  water,  and  to  be  decomposed  by  39^  grains  of  hydro- 
chloric acid,  decanting  the  clear  liquid  from  the  chloride  of  silver ; 
this  acid  contains  2 per  cent,  of  the  anhydrous  acid.  The  acid 
when  dilute  is  less  prone  to  decomposition  than  when  concen- 
trated, especially  if  a little  free  sulphuric  acid  be  present : but  it 
should  always  be  excluded  from  the  light.  This  acid  is  extremely 
volatile,  and  if  a bottle  containing  the  diluted  acid  be  left  open 
for  a few  hours  it  will  be  found  to  have  suffered  a very  material 
reduction  in  strength  ; indeed  the  mere  opening  and  closing  the 
bottle  in  dispensing  the  medicine  always  reduces  its  strength. 
When  subjected  to  distillation  a large  quantity  is  usually  lost,  and 
tlie  greater  portion  of  the  acid  comes  over  in  the  first  fourth  of 
the  distillate.  What  is  called  Scheele's  acid  varies  greatly  in 
strength,  owing  to  the  difficulty  of  condensing  the  acid  vapour. 
It  is  directed  to  be  prepared  by  mixing  10  parts  of  ferrocyanide 
of  potassium  with  3*75  of  oil  of  vitriol  previously  diluted  with  40 
parts  of  water,  and  distilling  over  till  10  parts  are  collected.  It 
seldom  contains  more  than  5 per  cent,  of  the  acid,  and  the  pro- 
portion is  often  considerably  less. 

(503)  Cyanides. — The  cyanides  of  the  alkaline  metals  are 
freely  soluble  in  water.  Many  of  the  cyanides  of  the  heavier 


256 


TESTS  FOR  HTDROCYAI^IC  ACID. 


metals  are  insoluble  in  water,  but  most  of  them  are  decomposed 
with  evolution  of  hydrocyanic  acid  when  boiled  with  hydrochloric 
acid  ; those  of  silver  and  mercmy,  when  heated  to  redness,  yield 
cyanogen  gas.  Solutions  of  mercurous  salts  give  a grey  precipi- 
tate of  the  reduced  metal ; but  the  mercuric  salts  give  no  precipi- 
tate with  the  cyanides.  Most  of  the  cyanides  which  are  insoluble 
in  water  may  be  dissolved  by  means  of  a solution  of  the  cyanides 
of  the  metals  of  the  alkalies,  or  of  the  alkaline  earths : in  such 
cases  double  cyanides  are  generally  formed.  Liebig  has  given  a 
ready  method  for  the  exact  determination  of  the  strength  of  a 
solution  of  hydrocyanic  acid,  founded  upon  the  solubility  of  these 
double  cyanides : — The  acid  to  be  tested  is  supersaturated  with  a 
solution  of  caustic  potash,  and  a standard  solution  of  nitrate  of 
silver  (IT  grains  of  nitrate  in  1000  measured  grains  of  water)  is 
gradually  added,  agitating  the  mixture  after  each  addition ; as 
soon  as  the  precipitate  is  no  longer  redissolved,  the  number  of 
divisions  of  nitrate  added  must  be  read  ofl'.  17  grains  of  the  nitrate 
of  silver  represent  5 ’4  grains  of  hydrocyanic  acid.  The  reaction 
is  the  following  : — 

AgNe3  + 2 KCy  = KNO,  + KCy,AgCy. 

The  presence  of  chlorides  does  not  interfere  with  the  applica- 
tion of  the  test.  Sulphate  of  copper  may  be  substituted  for  the 
nitrate  of  silver,  if  the  hydrocyanic  solution  be  rendered  alkaline 
with  ammonia  instead  of  with  potash.  The  reaction  is  complete 
as  soon  as  the  liquid  acquires  a slight  blue  tinge : 14’5  grains  of 
the  crystallized  sulphate  represent  5*4  grains  of  hydrocyanic  acid. 

The  presence  of  the  soluble  cyanides,  or  of  hydi’ocyanic  acid 
in  solution,  may  be  determined  by  the  following  tests  : — 

1.  Mith  nitrate  of  silver  a white,  curdy  precipitate,  which 
does  not  blacken  by  exposure  to  light,  is  formed  ; it  is  nearly 
insoluble  in  cold  nitric  acid ; when  heated  to  redness  it  gives  off 
the  inflammable  vapour  of  cyanogen. — 2.  If  to  the  liquid  a slight 
excess  of  potash  be  added,  and  then  a mixture  of  ferrous  and 
ferric  sulphate,  a precipitate  of  hydrated  ferric  and  ferrous  oxide 
is  occasioned,  which  when  treated  with  excess  of  hydrochloric 
acid  leaves  Prussian  blue.  The  reaction,  omitting  the  water  of 
hvdration  of  the  oxide,  may  be  thus  represented  ; 18  KCv  -f- 
2 Pe A,  3 FeO  18  HCl  = 18  KCl  -f  9 + ¥e,,¥e,Cj,,.  This 

test  may  be  modifled  by  heating  gently  the  suspected  mixture 
with  sulphuric  acid,  and  suspending  in  the  flask  or  retort  for  a 
few  minutes,  a piece  of  paper  moistened  with  a solution  of  potash  ; 
on  dropping  a weak  solution  of  the  mixed  sulphates  of  iron  upon 
the  paper,  and  immersing  it  in  diluted  sulphuric  acid,  hydrocyanic 
acid  may  be  recognised  by  the  formation  of  Prussian  blue  when 
very  minute  traces  only  are  present.  — 3.  Let  the  liquid  be 
acidulated  with  a few  drops  of  hydrochloric  acid,  place  it  in  a 
watch-glass,  and  let  a second  watch-glass  be  inverted  over  it, 
moistened  with  a drop  of  a solution  of  sulphuretted  hydrosulphate 
of  sulphide  of  ammonium  (contaiDing  bisulphide  of  ammonium); 
after  a few  minutes  let  the  upper  watch-glass  be  removed,  and 


CYANIC  ACID. 


257 


the  liquid  be  evaporated  to  dryness  by  steam  heat ; 2 + 

HCy  = H^NCyS  + ; let  the  dry  residue  be  treated  with 

a drop  of  a weak  solution  of  ferric  chloride  ; a red  sulphocyanide 
of  iron  is  formed  under  these  circumstances. 

The  cyanides  of  iron,  cobalt,  chromium,  platinum,  and  some 
other  metals,  form,  with  the  cyanides  of  the  alkalies  and  the 
earths,  compounds  of  a peculiar  character,  in  which  the  presence 
of  the  iron,  or  the  cobalt,  &g.,  cannot  be  detected  by  the  usual 
tests  for  these  metals.  Some  of  these  compounds  are  of  consider- 
able importance,  and  will  be  noticed  at  a future  point. 

(504)  Cyanic  Acid  : HCyO,  or  HO,CyO=43. — If  cyanogen 
gas  be  passed  into  an  alkaline  solution,  a change  ensues  something 
analogous  to  that  which  occurs  when  chlorine  is  similarly  treated, 
cyanide  and  cyanate  of  the  metal  being  produced ; but  the  cyanic 
acid  contains  a smaller  proportion  of  oxygen  than  chloric  acid 
does  ; Cy2  + 2 KHO=KCy  + KCyO  -f-  If  carbonate  of  potas- 

sium be  heated  in  cyanogen  gas,  a mixture  of  cyanide  and  cyan- 
ate of  potassium  is  formed,  whilst  carbonic  anhydride  is  set  free  : 

K2ee3  + Cy2=KCy-f  KCyO  + ee2.  ^ 

Cyanate  of  potassium,  however,  is  better  prepared  in  a state 
of  purity,  by  fusing  the  cyanide  of  potassium  in  a crucible,  and 
adding  litharge  (oxide  of  lead)  in  small  quantities,  till  the  oxide 
ceases  to  be  decomposed;  KCy  + PbO=KCyO-f  Pb.  The  cyan- 
ate is  easily  separated  from  the  reduced  lead  and  the  excess  of 
oxide  of  lead,  which,  from  their  superior  density,  sink  through  the 
melted  mass  to  the  bottom.  Another  method  of  preparing  the 
cyanate  of  potassium  consists  in  heating  an  intimate  mixture  of 
2 parts  of  thoroughly  dried  ferrocyanide  of  potassium  with  1 part 
of  finely  powdered  anhydrous  black  oxide  of  manganese : the 
mixture  is  placed  upon  a sheet-iron  plate  and  heated  to  dull  red- 
ness, and  the  mass  is  kept  constantly  stirred.  The  oxidation  of 
the  cyanide  is  effected  partly  at  the  expense  of  the  oxyg^en  in  the 
oxide  of  manganese,  partly  of  that  in  the  atmosphere.  W^hen  the 
combustion  has  ceased,  cyanate  of  potassium  may  be  dissolved  out 
of  the  residue  with  hot  alcohol,  from  which  it  crystallizes  in  deli- 
quescent plates  as  the  solution  cools. 

Cyanate  of  potassium,  if  kept  dry,  may  be  preserved  without 
change ; but  so  unstable  is  the  cyanic  acid  when  uncombined  with 
a fixed  base,  that  on  attempting  to  separate  it  from  the  cyanate 
of  potassium  by  the  addition  of  sulphuric  or  any  other  strong  acid, 
traces  of  it  only  are  obtained  : a brisk  effervescence  ensues, — each 
atom  of  the  cyanic  acid  assimilates  the  elements  of  water,  and  is 
almost  entirely  resolved  into  1 atom  of  ammonia,  which  remains 
in  combination  with  the  acid  employed  in  decomposing  the  ^a- 
nate,  and  1 atom  of  carbonic  anhydride,  which  escapes  with  effer- 
vescence : — 

Sulnh.  acid.  Cyanate  of  Sulphate  of  Sulphate  of 

‘ ' potaesium.  anamonium.  potassium. 

2 H2SO4  + ^KONO  + 2 H,e  + '(H4N),S04'  + K,Se4  + 2 

Cyanic  acid  may  be  otherwise  procured ; viz.,  by  distilling 
17 


258 


FXJLMINIC  ACID. 


cyanuric  acid  (Hg-Ggl^gOg),  which  is  a crystallizahle  acid  sub- 
stance, 1 atom  of  which  contains  exactly  the  same  elements  as  3 
atoms  of  cyanic  acid.  When  this  compound  is  sealed  np  in  a 
bent  glass  tnhe,  one  limb  of  which  is  kept  cool  whilst  heat  is  ap- 
plied to  the  cyannric  acid  in  the  other  limb,  a limpid,  colonrless 
liqnid  distils  over  and  is  condensed.  The  cyannric  acid  is  thns 
wholly  converted  into  pnre  cyanic  acid.  Cyanic  acid  in  its  tnrn 
may  be  converted  into  the  cyannric,  for  if  cyanate  of  potassium 
he  decomposed  by  the  addition  of  half  its  equivalent  of  acetic  acid, 
an  acid  cyannrate  of  potassinm  is  formed. 

Cyanic  acid  has  an  extremely  pnngent  odonr,  and  is  very  vola- 
tile ; its  vaponr  attacks  the  eyes  powerfnlly,  and  when  liqnid  it 
acts  as  a powerful  canstic  if  incautionsly  dropped  npon  the  skin. 
It  is,  however,  impossible  to  preserve  this  compound,  for  in  the 
conrse  of  a few  hours  it  changes  spontaneously,  wdth  evolution  of 
heat,  into  a wliite  enamel-like  mass,  which  is  permanent  in  the 
air,  insolnble  in  water,  and  destitute  of  acid  properties.  To  this 
body  the  name  of  cyamelid  has  been  given : it  has  the  same  cen- 
tesimal composition  as  the  hydrated  cyannric  and  cyanic  acids. 
Cyamelid  may  also  be  obtained  by  triturating  cyanate  of  potas- 
sinm with  crystallized  oxalic  acid  and  washing  out  the  solnble 
oxalate  of  potassinm.  It  may  be  converted  by  heat  into  hydrated 
cyanic  acid ; and  if  boiled  with  a solution  of  potash,  gradually 
yields  cyannrate  of  the  base ; oil  of  vitriol  decomposes  it  into  car- 
bonate of  ammoninm.  A solntion  of  cyanic  acid  in  water  qnickly 
becomes  decomposed  into  carbonate  of  ammoninm  and  nrea. 

Urea. 

+ H2O  = -602  + H3N ; and  H0N0  + H3N  = 004^20. 

Solutions  of  the  solnble  cyanates  give  white  precipitates  with 
solutions  of  the  salts  of  lead,  of  silver,  or  of  snboxide  of  mercury ; 
they  yield  no  precipitate  with  solntion  of  corrosive  snblimate,  or 
with  the  solntions  of  salts  of  iron  or  of  tin.  With  nitrate  of  cop- 
per they  give  a greenish-brown  precipitate,  and  with  terchloride 
of  gold  a brown  precipitate. 

(505)  Fulminic  Acid. — Besides  the  remarkable  oxides  of  cy- 
anogen already  mentioned,  there  is  another  acid  which  yields  on 
analysis  the  same  per-centage  of  its  components  as  cyamelid,  and 
the  cyanic  and  cyannric  acids,  though  it  possesses  properties  to- 
tally different  from  any  of  them.  Its  compounds  explode  with 
fearfnl  violence.  By  dissolving  1 grain  of  silver  in  20  grains  of 
nitric  acid  diluted  with  abont  50  of  alcohol,  the  nevr  componnd  is 
deposited  in  crystals,  which,  when  dry,  detonate  with  the  slight- 
est friction : they  consist  of  (AggOglST^Og).  The  reaction  by  which 
this  salt  is  produced  is  complicated ; the  nitrogen,  however,  is  de- 
rived from  the  nitric  acid,  and  the  carbon  from  the  alcohol. 

Fnlminic  acid  has  not  been  obtained  in  an  isolated  form ; on 
attempting  to  separate  it  from  its  salts  by  a more  powerful  acid 
it  is  resolved  into  hydrocyanic  acid  and  other  bodies.  Allusion 
will  again  be  made  to  the  fulminates  when  other  compounds  of 
cyanogen  are  described  among  the  products  of  organic  chemistry. 


METAJ^IERIC  AND  POLYMERIC  COMPOUNDS. 


259 


"When  the  fulminates  are  boiled  with  a solution  of  chloride  of 
sodium,  or  of  chloride  of  potassium,  the  acid  is  converted  into 
another  isomeric  compound  termed  isocyanuric  or  fulminuric 
acid.  This  body  is  but  very  slightly  explosive. 

(506)  Isomerism. — The  properties  of  these  oxides  of  cyanogen 
serve  clearly  to  show  that  mere  identity  in  ultimate  composition 
is  not  sufficient  to  produce  identity  of  chemical  character  or  pro- 
perties ; they  place  the  doctrine  of  isomerism  (or  the  existence  of 
compounds  identical  in  ultimate  composition,  but  different  in 
chemical  properties)  in  a striking  point  of  view,  hlumerous 
other  instances  will  occur  as  we  pursue  further  the  study  of  the 
different  compounds,  not  only  of  cyanogen,  hut  of  other  bodies, 
and  particularly  of  those  which  form  the  subject  of  organic 
chemistry. 

There  are  various  forms  of  isomerism ; in  some  cases  we  have 
no  clue  to  the  probable  differences  of  molecular  arrangement : in 
others  there  is  every  reason  to  suppose  that  the  arrangement  of 
the  elementary  molecules  is  on  a totally  different  plan  in  the  two 
bodies  which  are  compared.  Hydrated  cyanic  acid,  for  instance, 
may  be  represented  as  hydrated  oxide  of  cyanogen ; whilst  it  is 
certain  that  in  c^^amelid,  which  is  insoluble,  and  presents  nothing 
of  the  acid  character,  the  arrangement  of  its  constituents  is  quite 
different.  Isomeric  compounds,  the  equivalent  numbers  of  which 
are  identical,  are  said  to  be  metameric.  In  other  cases,  the  differ- 
ences in  the  projperties  of  bodies  which  contain  equal  amounts  of 
their  constituents  in  100  parts,  may  be  simply  explained  upon  the 
supposition  that  in  the  different  compounds  the  state  of  conden- 
sation of  these  elements  is  different ; bodies  supposed  to  be  thus 
constituted  have  been  termed  ’polymeric. 

The  table  on  p.  260  contains  a list  of  several  different  poly- 
meric compounds  of  carbon  and  hydrogen  which  contain  these 
two  elements  in  the  proportion  of  1 atom  of  carbon  to  2 atoms 
of  hydrogen.  Each  of  these  bodies,  however,  possesses  proper- 
ties peculiar  to  itself : and  if  equal  volumes  of  the  vapour  of  each 
be  compared,  it  will  be  found  that  the  elements  have  undergone 
different  degrees  of  condensation  in  the  different  compounds.  As 
the  density  of  the  vapour  increases,  it  has  been  observed  that  the 
boiling-point  of  such  as  are  liquid  rises  proportionately.  Sup- 
posing that  one  molecule  of  each  compound  gives  off  2 volumes 
of  vapour,  the  formulae  will  be  such  as  are  contained  in  the 
table  on  the  following  page. 

In  this  series,  oil  gas  has  double  the  density  of  ethylene,  and 
lienee  it  must  contain  in  the  same  volume  of  vapour  twice  as 
many  elementary  atoms.  In  like  manner  naphthene  will  contain 
twice  as  many  atoms  as  oil-gas,  and  four  times  as  many  as  ethy- 
lene, and  cetylene  again  will  contain  double  the  number  of  atoms 
of  carbon  and  hydrogen  in  the  same  volume  of  vapour  as  naph- 
thene. 

(507)  Paracyanogen  (O3H3). — The  ordinary  operation  of 
preparing  cyanogen  gas  from  cyanide  of  mercury  affords  a good 
illustration  of  polymeric  isomerism.  After  the  mercury  and  the 


260 


PAEACYAXOGEX CHLOKIDES  OF  CYAXOGEX. 


Substances. 

Formula. 
Mol.  vol.  rT~ L 

Density  of  vapour. 

Boiling 
point,  ° F. 

Observed. 

Calculated. 

Olefiant  gas  (Ethylene) 

■O2H4 

0-978 

0-967 

Propylene  (Tritvlene) 

■GsHe 

1-498 

1-451 

Oil  gas  (Tetrylene) 

1-852 

1-934 

0 

Amylene 

2-386 

2-418 

102 

Caproylene  (Hexaline) 

2-875 

2-902 

131 

Heptvlene 

3-385 

122? 

Xaphithene  (Octylene) 

e.His 

3-90 

3-868 

257 

Eleene  (Nonylene) 

egHis 

4-48 

4-351 

Paramylene 

■OloHoo 

5-061 

4-836 

3-20 

Cetylene 

■016H32 

8-007 

7-736 

527 

Cerotylene 

•027054 

12-159 

Melissylene 

030060 

14-508 

cyanogen  have  been  expelled  from  the  glass  retort,  there  always 
remains  a certain  quantity  of  a brown  matter,  composed  of  nitro- 
gen and  carbon,  combined  in  the  same  proportions  as  in  cyanogen. 
Paracyanogen^  as  this  brown  body  is  called,  is  insoluble  in  water : 
it  is  neither  volatile  nor  fusible,  but  like  cyanogen  it  enters  into 
combination  with  other  elementary  bodies,  though  the  composi- 
tion of  these  compounds  has  been  as  yet  but  imperfectly  studied. 

In  paracyanogen  the  carbon  and  nitrogen  are  more  condensed 
than  in  cyanogen  ; so  that  if  we  regard  cyanogen  as  composed  of 
ON,  paracyanogen,  according  to  the  experiments  of  Johnston, 
wmuld  consist  of  O3N3,  its  combining  number  being  three  times 
that  of  cyanogen,  and  the  elements  which  compose  it  being  more 
compactly  united. 

(508)  Chlorides  of  Cyaxogex. — Chlorine  forms  with  cyano- 
gen three  polymeric  compounds,  all  of  which  are  highly  poisonous  : 
one  is  gaseous  at  the  ordinary  temperature  of  the  air ; the  second 
is  liquid,  and  the  third  is  solid. 

The  Gaseous  Chloride  of  Cyanogen  (CyCl=61-5  ; Sp.  Gr.  2-124 ; 
Mol.  Yol.  I J I)  is  colomless : it  has  an  intolerably  pungent 
odour,  and  irritates  the  eyes  powerfully ; at  0°  F.  it  condenses  in 
long  prismatic  needles,  which  fuse  at  5°.  Two  volumes  of  the 
gas  contain  1 volume  of  chlorine  and  1 of  cyanogen,  united 
wdthout  condensation,  so  that  its  composition  may  be  thus  repre- 
sented : — 

By  weight.  By  volume.  Sp.  gr. 

Cyanogen Cy  = 26  or  42-28  1 or  0'5  = 0-900 

Chlorine Cl  = 35*5  57-72  1 0 5 = 1-226 

°'cyano^n[-  - ^ I'O  = 2-126 

Gaseous  chloride  of  cyanogen  is  freely  soluble  in  water,  in  ether, 
and  in  alcohol ; the  solution  has  no  acid  reaction,  and  does  not 
precipitate  nitrate  of  silver.  It  is  obtained  readily  by  transmit- 
ting a current  of  chlorine  through  a retort  containing  a mixture  of 
powdered  cyanide  of  mercury  and  water  cooled  to  32°  by  immer- 
sion in  melting  ice  : the  chloride  of  cyanogen  is  dissolved  by  the 
w'ater  ; from  this  solution  it  may  be  expelled  by  the  apphcation  of 
a gentle  heat,  and  may  be  collected  over  mercury.  According  to 


COMPOUND  EADICLES  WHICH  CONTAIN  CYANOGEN.  261 

Persoz,  the  gaseous  chloride  of  cyanogen,  if  liquefied  under  the 
pressure  of  its  own  vapour,  and  preserved  in  tubes  hermetically 
sealed,  becomes  gradually  converted  into  a crystallized  mass  of  the 
solid  chloride. 

Liquid  Chloride  of  Cyanogen  (Cy2Cl2=123;  Melting-pi.  19°; 
Boiling -pi.  61°)  is  procured  by  exposing  diluted  hydrocyanic  acid 
cooled  to  32°,  to  a gentle  current  of  chlorine.  After  a while,  a 
stratum  of  a liquid  lighter  than  water  is  formed,  and  partially 
distils  over  into  the  receiver,  which  must  be  kept  at  32°.  This 
liquid  must  be  washed  with  ice-cold  water,  and  agitated  in  a freez- 
ing mixture  with  red  oxide  of  mercury  to  remove  the  excess  of 
chlorine  and  hydrocyanic  acid,  after  which  it  is  rectified  from 
chloride  of  calcium  (Wurtz).  A very  mobile  colourless  liquid, 
with  an  excessively  irritating  odour,  resembling  that  of  the  gase- 
ous chloride,  is  thus  obtained ; it  is  converted  into  a crystalline 
mass  at  19°.  Liquid  chloride  of  cyanogen  is  not  soluble  in  water, 
but  is  freely  soluble  in  alcohol. 

Solid  Chloride  of  Cyanogen  (CygClg^  184*5) ; Sp.  Gr.  of 
Vapour.^  6*39;  Melting-pi.  284°;  Boiling-pi.  314°;  Mol.  Yol. 

I I |. — This  substance  crystallizes  in  white  needles.  It  has  a 
disagreeable  odour  like  that  of  mice.  The  vapour  of  this  com- 
pound is  three  times  as  dense  as  that  of  the  gaseous  chloride ; it 
therefore  contains  3 volumes  of  chlorine  and  3 of  cyanogen  con- 
densed into  the  space  of  2 volumes.  This  chloride  is  but  sparingly 
soluble  in  water,  though  it  is  freely  taken  up  by  alcohol  and  by 
ether.  The  solid  chloride  of  cyanogen  may  be  prepared  by  decom- 
posing concentrated  hydrocyanic  acid  by  exposing  it  in  a glass 
vessel  with  an  excess  of  dry  chlorine  to  the  direct  rays  of  the  sun. 

(508  a)  Bromine  and  iodine  form  solid  crystalline  compounds 
with  cyanogen,  corresponding  in  composition  with  the  gaseous 
chloride  ; they  may  be  obtained  by  distilling  cyanide  of  mercury 
with  bromine  or  with  iodine. 

Cyanogen  combines  directly  with  sulphuretted  hydrogen  in 
two  proportions  if  the  two  gases  are  mixed  in  the  presence  of 
moisture;  tlie  first  2 -GJSTjH^S,  forms  yellow  crystals  soluble  in 
water,  alcohol,  and  ether ; the  second,  2 -0^,21128,  is  formed  when 
cyanogen  with  an  excess  of  sulphuretted  hydrogen  is  transmitted 
into  alcohol : it  forms  orange-red  crystals  sparingly  soluble  in  cold 
water,  but  freely  soluble  in  hot  water,  in  alcohol,  and  in  ether. 
When  these  compounds  are  boiled  with  dilute  alkalies,  water  is 
taken  up,  and  oxalic  acid,  ammonium,  and  sulphuretted  hydrogen 
are  formed ; the  second  compound  corresponding,  in  fact,  to  oxa- 
mide  in  which  sulphur  has  taken  the  place  of  oxygen  ; for  exam- 
ple, 02^211,82-1-  4 H20=/II,N)20A+  2 II28.  As  will  be  seen 
hereafter,  cyanogen  is  the  nitrile  of  oxalic  acid. 

(509)  There  are  other  important  compounds  of  cyanogen,  the 
consideration  of  which  will  be  more  advantageously  pursued  here- 
after ; it  will  be  sufficient  at  this  point  to  indicate  some  of  their 
leading  chemical  peculiarities. 

Cyanogen,  as  we  have  seen,  enters  into  combination  with  the 
non-rnetallic  elements  as  though  it  were  itself  an  elementary  body. 


262 


DISCEmiXATION  OF  THE  GASES. 


In  this  manner  bodies  siicli  as  the  chlorides,  the  bromides,  and  the 
iodides  of  cyanogen  may  be  obtained ; they  form  well-defined 
compounds,  which  do  not  exhibit  any  special  tendency  to  unite 
with  other  elements.  In  other  cases,  "however,  it  is  important  to 
observe  that  many  of  the  compounds  to  which  cyanogen  give  rise 
are  themselves  endowed  with  the  property  of  uniting  again,  as 
though  they  were  simple  bodies,  with  other  elements.  TVIth  sul- 
phur, for  example,  cyanogen  forms  a sulphide  (-0XS),  which,  in 
combination  with  the  metals,  performs  the  part  of  a compound 
radicle,  usually  termed  suJphocyanogen  (Scy),  and  which  produces 
a series  of  salts,  termed  sulphocyanides,  many  of  which  may  be 
crystallized ; of  this  the  sulphocyanide  of  potassium,  KOXS  or 
KjScy,  fimiishes  an  instance.  Similar  compound  radicles  are 
furnished  also  by  the  union  of  cyanogen  with  many  of  the  metals 
themselves  ; in  this  way  iron  in  f err ocyanides  and  cobalt  and 
chromium  in  the  cdbaJticyanides  and  chrcnnicyanides^  form  each  a 
compound  group,  or  salt-radicle,  which  when  it  unites  in  its  turn 
with  other  metals,  performs  the  functions  of  a simple  body,  such 
as  chlorine  or  iodine  : an  example  of  this  is  seen  in  the  well-known 
yellow  prussiate  of  potash,  or  ferrocyanide  of  potassium  (K^Fe-Gy^), 
in  which  the  compound  of  iron  and  cyanogen,  FeCyg,  is  considered 
as  a compound  radicle  known  as  ferrocyanogen  (Fey). 

§ Y.  Gexeeal  Eemakks  ox  the  Disceduxatiox  of  the 
Gases  feom  each  othee. 

(510)  Having  now  described  all  the  gaseous  compoimds  which 
are  of  any  considerable  importance,  with  the  exception  of  two — 
viz.,  arseniuretted  hydrogen  and  antimoniuretted  hydrogen, — it 
will  be  advantageous  to  take  a brief  review  of  their  general  char- 
acters before  passing  to  the  consideration  of  the  metals  and  their 
compounds.'^ 

There  are  about  30  bodies  which  are  permanently  gaseous  at 
the  mean  temperature  of  the  atmospliere.  Several  of  these  com- 
pounds are  met  with  in  the  uncombined  form  in  the  atmosphere, 
either  uniformly,  or  under  particular  circumstances  not  of  unlre- 
quent  occurrence : these  gases  are  oxygen,  nitrogen,  carbonic  and 
sulphurous  anhydrides,  hydrosulphuric  acid,  ammonia,  and  occa- 
sionally carbonic  oxide  and  light  carbrn-etted  hvch’ogen.  Gene- 
rally speaking,  the  different  gases,  when  pure,  are  readily  distin- 
guished from  each  other  by  some  well-marked  physical  or  chemical 
property.  The  few  gases  which  are  coloured  are  at  once  indicated 
by  the  peculiarity  of  their  tint,  conjoined  with  their  characteristic 
odour  : in  this  manner  peroxide  of  nitrogen,  chlorine,  h^’pochlor- 
ous  and  chlorous  anhydidde,  peroxide  of  chlorine,  and  vapour  of 
bromine,  are  at  once  recognised. 

* Methyl,  ethyl,  and  trityl,  with  their  hydrides,  as  well  as  tritylene  and  acetylene, 
are  occasionally  present  in  coM-gas.  but  they  will  not  here  be  specially  noticed,  be- 
cause these  hydrocarbons  cannot  be  distinguished  from  each  other  except  by  analysis. 
Acetylene  may  be  absorbed  by  passing  the  gas  which  contains  it  through  an  ammo- 
niacM  solution  of  subchloride  of  copper,  when  a flocculent  red  deposit  of  acetylide 
of  copper  is  gradually  formed. 


DISCRIMINATION  OF  THE  GASES. 


263 


Many  gases  have  a pecnliar  and  characteristic  odour.  Some 
of  the  most  important,  however,  including  oxygen,  nitrogen,  hy- 
di’ogen,  carbonic  anhydride,  carbonic  oxide,  light  carburetted 
hydrogen,  olefiant  gas,  and  nitrous  oxide,  possess  little  or  no  odour, 
and  require  other  means  for  discriminating  them  from  each 
other. 

(511)  In  order  to  aid  the  operator  in  distinguishing  the  differ- 
ent gases  from  each  other,  Thenard  divided  them  into  four  groups, 
the  arrangement  being  dependent  upon  the  action  of  a solution  of 
potash  upon  them,  conjoined  with  the  occurrence  or  the  absence  of 
combustion  on  the  application  of  a lighted  match  to  the  gas.  The 
action  of  potash  is  ascertained  by  admitting  a few  drops  of  a solu- 
tion of  potash  into  a test-tube  filled  with  the  gas,  and  standing 
over  mercury : on  agitating  the  contents  of  the  tube,  it  is  imme- 
diately obvious  whether  any  absorption  occurs.  The  application 
of  a lighted  match  to  another  small  tube  filled  with  the  gas  shows 
whether  it  be  inflammable,  or  whether  it  extinguishes  or  supports 
combustion. 

The  four  groups  of  gases  which  are  formed  by  the  application 
of  these  tests  are  the  following  : 

1.  Gases  which  are  absorbable  by  potash,  but  which  are 

not  inflammable. 

2.  Gases  absorbable  by  potash,  but  which  are  inflammable. 

3.  Gases  not  absorbable  by  potash,  and  not  inflammable. 

4.  Gases  not  absorbable  by  potash,  which  are  inflammable. 

We  proceed  to  point  out  briefly  the  characters  of  the  compo" 
nents  of  each  gi’oup. 

(512)  1. — &ases  which  are  dbsorhahle  hy  Potash^  l)ut  are 
not  inflammable'  these  are  15  in  number: — viz.. 


1.  Hydrochloric  acid 

2.  Hydrobromic  acid 

3.  Hydriodic  acid 

4.  Fluoride  of  silicon 

5.  Fluoride  of  boron 

6.  Chloride  of  boron 

7.  Oxychloride  of  carbon 

8.  Sulphurous  anhydride 


9.  Nitrous  anhydride 

10.  Peroxide  of  chlorine 

11.  Chlorous  anhydride 

12.  Hypochlorous  anhydride 

13.  Chlorine 

14.  Carbonic  anhydride 

15.  Chloride  of  cyanogen. 


Of  these  gases  each  of  the  first  eleven  reddens  litmus-paper 
when  moistened  and  plunged  into  it.  Hypochlorous  anhydride 
and  chlorine  destroy  its  colour,  and  bleach  it  entirely.  Carbonic 
anhydride  is  nearly  without  action,  and  chloride  of  cyanogen  pro- 
duces no  eflect  upon  its  colour.  The  first  six  gases  fume  sti*ongly 
when  mixed  with  the  air,  owing  to  their  action  on  the  moisture 
which  it  contains : the  solutions  in  water  of  hydrochloric,  hydro- 
lu’omic,  and  liydriodic  acids  are  immediately  distinguislied  by  tlie 
usual  tests  for  them.  Each  gas  also  presents  certain  ])eculiaritie8 
— viz.,  1.  A small  quantity  of  cldorine  pi*oduces  no  change  in  the 
hydrochloric  gas  ; 2.  In  hydrobromic  gas  it  occasions  tlie  separa- 
tion of  red  fumes  of  bromine  ; and  3.  In  the  hydi’iodic  gas  violent 


264 


DISCEDtllN’ATIOX  OF  THE  GASES. 


fumes  of  iodine  appear.  4.  Fluoride  of  silicon  is  recognised  bv 
tbe  gelatinous  deposit  of  silica  which  water  produces  when  the 
gas  is  dissolved  in  this  liquid.  5.  The  fluoride  of  boron  produces 
a gelatinous  precipitate  in  a solution  of  potash,  but  not  in  pui-e 
water.  6.  Cliloride  of  boron  is  decomposed  by  water  into  hydi’o- 
chloric  and  boracic  acids,  which  may  be  recognised  in  the  solution 
by  the  appropriate  tests.  7.  Oxychloride  of  cai’bon  has  a peculiar, 
pungent  odour,  and  is  decomposed  by  water  into  hydi-ochloric 
acid  and  carbonic  anhydidde,  8.  Sulphurous  anhydiude  is  imme- 
diately recognised  by  the  suflbcating  odour  of  a burning  sulphur 
match : it  is  absorbed  by  the  peroxide  of  lead,  and  a white  sul- 
phate of  lead  is  formed.  9.  Xitrous  anliydiide  is  sufiiciently 
characterized  by  its  colour  and  peculiar  odour  ; and  10,  the  same 
may  be  remarked  of  peroxide  of  chlorine.  11.  Chlorous  anhydilde 
has  a greener  tinge  than  the  peroxide  of  chlorine,  and  it  yields 
a bright  yellow  solution  when  dissolved  in  water.  12.  Hypochlo- 
rous  anliydride  has  the  odour  of  the  bleaching  compounds  of 
chlorine  with  the  alkalies  and  earths,  and  it  rapidly  destroys 
vegetable  colours  : these  three  oxides  of  chlorine  detonate  by 
the  application  of  a temperature  below  that  of  boiling  water. 
13.  Chlorine  is  distinguished  by  its  green  colour  and  remarkable 
odour,  by  its  bleaching  action  on  vegetable  colours,  and  by  its 
sparing  solubility  in  water,  which  takes  up  about  twice  its  bulk 
of  the  gas.  14.  Carbonic  anhydride  extinguishes  flame,  renders 
lime-water  turbid,  and  is  soluble  in  about  its  own  bulk  of  water. 
15.  Chloride  of  cyanogen  is  recognised  by  its  pungent  odour,  and 
its  peculiar  irritating  eflect  on  the  eyes. 

(513)  2. — Gases  ohsorhaMe  hy  Potash  and  inflammable;  these 
are  only  4 in  number  : — viz., 

1.  Sulphuretted  hydi’ogen  3.  Telluretted  hydrogen 

2.  Seleniuretted  hvdroo:en  4.  Cvanos^en. 

These  gases  are  recognised  with  orreat  facility.  1.  Sulphuret- 
ted hydrogen  has  a peculiar  odour  of  putrid  eggs  ; it  burns  with 
a blue  flame,  often  attended  with  a deposit  of  sulphur  : it  black- 
ens paper  soaked  in  a solution  of  acetate  of  lead,  and  is  decomposed 
by  moist  chlorine,  with  separation  of  sulphur ; water  dissolves 
about  twice  its  bulk  of  the  gas.  2.  Seleniuretted  hydrogen  has 
an  odour  analogous  to  that  of  the  preceding  gas  ; its  aqueous 
solution  gradually  deposits  selenium  in  the  form  of  a red  amor- 
phous precipitate  : it  precipitates  salts  of  zinc  of  a flesh-red  colour. 

3.  Telluretted  hydrogen  is  also  decomposed  by  chlorine,  tellurium 
being  set  free,  and  subsiding  as  a brown  powder.  4.  Cyanogen 
burns  with  a rose-edged  purple  flame  ; it  has  a penetrating  cha- 
racteristic odour.  If  mixed  with  an  equal  volume  of  oxygen,  and 
a red-hot  platinum  wire  be  suspended  in  the  mixture,  red  nitrous 
fumes  are  produced  by  the  oxidation  of  the  nitrogen  contained  in 
the  gas. 

(514)  3. — Ga^es  not  absorbable  by  Potash^  and  not  inflammahle  ; 
of  these  also  there  are  four — viz.. 


DISCEmiNATION  OF  THE  GASES. 


265 


1.  Oxygen 

2.  Mtrous  oxide 


3.  Mtrogen 

4.  I^itric  oxide. 


1.  Oxygen  is  at  once  distinguished  from  all  other  gases  by  its 
property  ol  kindling  a glowing  match,  by  its  power  of  producing 
red  fumes  when  mixed  with  nitric  oxide,  and  by  its  insolubility 
in  water  when  agitated  with  it.  It  is  absorbed  by  moistened 
phosphorus  ; by  a solution  of  suboxide  of  copper  in  ammonia, 
rendering  the  colourless  solution  deep  blue  ; and  by  a solution  of 
pyrogallic  acid  in  potash,  the  mixture  becoming  of  an  intense 
bistre  colour.  Solutions  of  the  sulphides  of  the  alkaline  metals 
also  absorb  oxygen  rapidly.  2.  Nitrous  oxide,  though  it  rekindles 
a glowing  match,  is  dissolved  when  agitated  with  water.  3.  Ni- 
trogen extinguishes  the  dame  of  burning  bodies  ; it  is  insoluble  in 
water,  and  does  not  render  lime-water  turbid.  4.  Nitric  oxide  is 
instantly  recognised  by  the  red  fumes  which  it  occasions  when 
mixed  with  air  or  free  oxygen  ; it  is  immediately  absorbed  by  a 
solution  of  ferrous  sulphate,  giving  the  liquid  a deep  brown  colour 
when  oxygen  is  present. 

(515)  4. — Gases  not  absorbable  by  Potash^  which  are  inflam- 
mablethese  gases  are  7 in  number: — viz., 


1.  Hydrogen 

2.  Light  carburetted  hydrogen 

3.  Oledant  gas 

4.  Oil  gas 


5.  Phosphuretted  hydrogen 

6.  Arseniuretted  hydrogen 

7.  Carbonic  oxide. 


1.  Hydrogen  is  inodorous,  if  pure ; it  burns  with  a feebly 
luminous  dame,  and  if  mixed  with  half  its  volume  of  oxygen  pro- 
duces water  either  by  the  transmission  of  an  electric  spark,  or  by 
the  action  of  a ball  of  spongy  platinum.  2.  Light  carburetted 
hydrogen  burns  with  a yellowish  dame ; it  is  not  acted  upon  if 
mixed  with  chlorine  over  water  and  screened  from  light,  and  is 
not  dissolved  by  fuming  sulphuric  acid.  3.  Oledant  gas,  when 
mixed  with  an  equal  volume  of  chlorine,  even  in  the  dark  be- 
comes condensed  to  an  oily  liquid  which  is  insoluble  in  water ; it 
is  also  absorbed  by  perchloride  of  antimony,  and  by  the  Nordhau- 
sen  sulphuric  acid  : it  burns  with  a brilliant  smoky  dame.  4.  Oil- 
gas is  soluble  in  oil  of  vitriol,  and  in  alcohol ; it  burns  with  a 
hrilliant  smoky  dame.  When  the  last  two  gases  are  mixed  to- 
gether, there  is  considerable  difficulty  in  identifying  the  existence 
of  each  in  such  a mixture,  and  a still  greater  difdculty  occurs 
when  methyl,  ethyl,  trityl,  or  their  hydrides,  are  present.  5.  Phos- 
phuretted hydrogen  is  distinguished  by  its  peculiar  alliacious 
odour ; it  burns  with  a luminous  dame,  producing  white  fumes  of 
phosphoric  anhydride;  solution  of  the  salts  of  copper,  silver,  and 
mercury  dissolve  it  and  form  brown  precipitates.  6.  Arseniuret- 
ted hydrogen  is  decomposed  if  passed  through  glass  tubes  heated 
nearly  to  redness,  a ring  of  metallic  arsenic  being  deposited  : it 
burns  with  a peculiar  white  dame,  and  deposits  a brown  stain  of 
metallic  arsenic  on  cold  bodies  introduced  into  the  burning  jet. 
It  is  extremely  poisonous,  and  has  a peculiar  odour  of  garlic.  It 


266 


ANALYSIS  OF  A MIXTURE  OF  GASES. 


may  be  distinguished  from  antimoniuretted  hydrogen  by  methods 
to  be  described  hereafter  (8d6).  7.  Carbonic  oxide  bmms  with  a 

pale  bine  flame,  producing  carbonic  anhydiide ; it  is  insoluble  in 
water,  and  is  dissolyed  by  a solution  of  cupreous  chloride  in  hy- 
di’ochloric  acid. 

(516)  General  Principles  of  the  Analysis  of  a Mixture  of 
Gases. — In  a mixture  of  gases  a qualitative  examination  must  be 
made  as  a preliminary  step,  in  order  to  ascertain  what  gases  are 
present.  It  is  of  course  needless  to  search  for  those  which  mu- 
tually condense  or  decompose  each  other.  Thus  ammonia  would 
not  be  found  in  a mixtime  which  contained  hydrochloric,  hydil- 
odic,  hydi’obromic  acid  gases,  nor  in  the  presence  of  sulphm-ous 
or  nitrous  anhydrides.  Oxygen  would  not  occur  in  a mixtiu-e  in 
which  nitric  oxide  was  present.  Xeither  could  free  chlorine  or 
its  oxides  co-exist  with  hydriodic  or  hydi-obromic  acid,  or  with 
olefiant  gas,  or  with  the  compounds  of  hydrogen  with  sulphm-, 
selenium,  tellmium,  phosphorus,  or  arsenic  : chlorine  and  its  ox- 
ides are  equally  incompatible  with  ammonia. 

The  complete  analysis  of  a mixtm’e  of  different  gases  is  one 
of  the  most  delicate  and  diflicult  branches  of  chemical  analysis, 
and  it  is  not  intended  on  the  present  occasion  to  attempt  to  give 
more  than  an  idea  of  the  principles  on  which  such  an  operation 
is  conducted,  and  of  the  apparatus  by  which  it  is  effected. 

As  an  illustration  of  the  method  of  proceeding  we  may  take 
a case  of  frequent  occurrence : viz.,  the  determination  of  the 
composition  of  a sample  of  coal-gas.  In  this  gas,  the  ingredi- 
ents which  may  be  present  are  numerous.  These  are — 1,  hydi’o- 
gen ; 2,  oleflant  gas  and  other  heavy  hydrocarbons ; 3,  light  car- 
buretted  hydi'ogen  ; 4,  carbonic  oxide  ; 5,  carbonic  anhydride ; 6, 
sulphiu’etted  hydi’ogen ; 7,  ammonia  ; 8,  oxygen  ; and  9,  nitrogen ; 
the  last  two  derived  from  the  atmosphere. 

A qualitative  examination  is  made  thus : — the  proportion  of 
ammonia  and  of  sulphuretted  hydrogen  is  usually  very  minute, 
and  in  most  cases  these  gases  must  be  sought  for  by  placing  the 
tests  for  their  presence  for  some  time  in  a current  of  the  coal-gas. 
In  searching  for  ammonia,  a piece  of  moistened  litmus-paper, 
feebly  reddened,  is  placed  for  a minute  in  a jet  of  the  issuing  gas ; 
if  the  blue  colour  be  restored,  ammonia  is  present.  Paper  soaked 
in  a solution  of  acetate  of  lead  may  be  subjected  to  a similar 
trial : if  it  turn  brown,  sulphuretted  hydrogen  is  present.  The 
presence  of  oxygen  is  detected  by  admitting  a bubble  of  the  nitric 
oxide  into  a tube  fllled  with  the  gas  under  trial,  and  looking 
through  the  tube  obliquely  upon  a sheet  of  white  paper ; very 
small  traces  of  oxygen  may  thus  be  detected  by  the  red  tinge 
produced,  owing  to  the  formation  of  peroxide  of  nitrogen.  Car- 
bonic anhydride  may  be  detected  by  the  tm’bidity  which  it  pro- 
duces in  lime-water  or  in  a solution  of  basic  acetate  of  lead,  if 
throvm  up  into  the  gas,  whilst  standing  in  a tube  over  mercury. 
The  existence  of  the  other  gases  may  be  assumed,  for  they  are 
certain  to  be  present,  in  greater  or  less  quantity.  The  sulphu- 
retted hydrogen  and  ammonia  are  too  small  in  amount  to  be 


ANALYSIS  OF  COAL-GAS. 


267 


quantitatively  determined  ; but  supposing  tliat  oxygen  and  car- 
bonic anhydride  are  found  to  be  present,  the  proportion  of  seven 
different  gases  will  remain  to  be  ascertained.  The  following 
method  may  be  adopted  for  their  quantitative  determination : — 

1.  Carbonic  Anhydride. — A volume  of  the  gas  is  confined  over 
mercury,  and  its  bulk  is  measured,  with  due  attention  to  tempe- 
rature and  pressure.  A piece  of  caustic  potash  which  has  been 
melted  upon  the  end  of  a long  platinum  wire,  to  serve  as  a handle, 
is  introduced  from  below,  through  the  mercury  into  the  tube. 
After  two  or  three  hours  the  potash  is  withdrawn  : the  amount  of 
the  absorption  indicates  the  proportion  of  carbonic  anhydride 
which  was  present. 

2.  Olefiant  Gas  and  Heavy  Hydrocarbons. — These  gases  are 
absorbed  by  introducing  another  ball,  consisting  of  porous  coke 
moistened  with  fuming  sulphuric  acid.  It  is  necessary,  however, 
before  reading  off  the  volume  of  the  gas,  to  introduce  a ball  of 
potash  a second  time,  in  order  to  withdraw  the  vapour  of  sulphuric 
anhydride,  which  possesses  sufficient  volatility  to  introduce  a 
serious  error  by  dilating  the  bulk  of  the  gas  unless  it  be  com- 
pletely removed.  The  total  amount  of  absorption  will  indicate  the 
proportion  of  olefiant  gas,  together  with  the  vapours  of  condensible 
hydrocarbons. 

3.  Oxygen. — This  gas  is  determined  in  a similar  manner,  by 
employing  a ball  of  moist  phosphorus,  which  must  be  left  in  the 
gas  for  twenty-four  hours  ; the  fresh  diminution  in  bulk,  shows 
the  proportion  of  oxygen.* 

i.  Carbonic  Oxide. — The  accurate  separation  of  carbonic 
oxide  from  the  other  gases  is  not  easily  effected.  The  gas  may  be 
divided  into  two  portions,  one  of  which  is  to  be  carefully  measured 
as  it  stands  over  mercury,  in  the  jar  A,  fig.  285,  p.  53  ; a small 
quantity  of  a solution  of  subchloride  of  copper  in  hydrochloric 
acid  is  next  added  by  means  of  the  syringe,  i^  and  the  mixture 
is  briskly  agitated ; the  gas  is  then  withdrawn  by  means  of  the 
gas  pipette,  also  shown  in  fig.  285,  and  transferred  by  its  means 
to  a second  graduated  tube,  also  standing  over  mercury;  into 
tliis  tube  a ball  of  hydrate  of  potash  on  the  end  of  a platinum 
wire  is  introduced,  for  the  purpose  of  absorbing  the  vapours  of 
hydrochloric  acid  with  which  the  gas  is  saturated ; its  bulk  may 
then  be  read  ofi‘,  and  the  volume  of  carbonic  oxide  may  be  known 
by  the  loss  in  bulk  which  it  has  experienced.f 

_ * A ball  of  coke  moistened  with  a concentrated  solution  of  potash  and  pyrogallic 
acid  maybe  employed  for  the  same  purpose:  the  absorption  in  this  case  is  much  more 
rapid. 

The  use  of  pellets  of  appropriate  materials  may  be  extended  to  other  gases : for 
example — Sulphurous  anhydride  may  be  absorbed  by  using  a ball  of  moistened  peroxide 
of  manganese,  or  of  peroxide  of  lead ; and  hydrochloric  acid  is  rapidly  absorbed  by  a 
ball  consisting  of  crystallized  rhombic  phosphate  of  sodium. 

f The  absorption  of  gases  by  liquid  reagents  is  much  more  rapid  than  when 
moistened  balls  are  employed,  and  provided  that  only  very  small  volumes  of  liquid  are 
used,  the  results  are  equally  accurate.  Thus  carbonic  anhydride  may  be  absorbed 
by  means  of  a concentrated  solution  of  caustic  potash,  one  or  two  drops  of  which 
will  suffice ; and  oxygen  may  be  withdrawn  by  a concentrated  mixture  of  pyrogallio 
acid  and  caustic  potash. 


268 


ANALYSIS  OF  GASEOrS  MIXTEHES. 


5,  6,  7.  Nitrogen^  Carburetted  Hydrogen^  and  Hydrogen. — 
The  determination  of  the  carbonic  oxide,  however,  may  be  effected 
along  with  the  carburetted  hydrogen  and  hydrogen  without  having 
recourse  to  absorption.  Let  a portion  of  the  gas  in  which  the 
carbonic  oxide  is  still  present  be  now  transferred  to  a siphon 
eudiometer  (fig.  281,  p.  14),  and  let  its  bulk,  Y,  be  accurately 
measured ; then  add  about  twice  its  volume  of  oxygen,  and 
measure  the  gas  a second  time  ; let  this  bulk  be  Y, ; Y^— Y will 
give  the  voliune  of  oxygen  which  has  been  added.  Let  Y^  be 
the  bulk  of  the  gas  after  the  mixture  has  been  exploded  by  the 
transmission  of  the  electric  spark  : Y^— Y^  indicates  the  dimi- 
nution in  bulk  which  it  has  experienced:  call  this  a.  Then 
inject  a small  quantity  of  a strong  solution  of  potash,  and  again 
note  the  volume,  Yj.  The  absorption,  Y^— Yg,  will  be  due  to 
the  quantity  of  carbonic  anhydride  which  has  been  fanned : call 
this  %.  The  remaining  gas,  Yg,  consists  of  oxygen  in  excess  and 
nitrogen.  The  quantity  of  oxygen  in  excess  is  ascertained  by 
mixing  the  residual  gas  with  about  twice  its  bulk  of  hydrogen, 
and  causing  the  electric  spark  to  pass  a second  time.  Let  the 
volume  of  the  mixture  before  firing  be  Y^  and  let  Yg  be  the 
bulk  after  firing  : Y^— Yg  will  represent  the  amount  of  con- 
densation : and  one-third  of  this,  or  ^j^g 

excess  of  oxygen.  On  deducting  this  from  the  residue  Yg,  the 
difference  gives  the  volume  of  nitrogen,  rh\  Yg— The 
difference  between  the  amount  of  the  oxygen  thus  found  to  be  in 
excess,  and  that  originally  introduced,  will  of  course  represent 
the  quantity  of  oxygen  consumed;  call  this  g\  thus  Y^— Y 

V4— Va  p 

3 

Assuming  that  the  temperature  of  the  gas  has  not  varied 
in  the  course  of  the  experiment,  which  may  be  ensured  by  due 
precautions,  we  have  now  all  the  data  for  calculating  the  propor-, 
tions  of  carburetted  hydi'ogen,  of  hydrogen,  and  of  carbonic  oxide, 
which  are  present  in  the  mixture. 

Let  X represent  the  quantity  of  light  carburetted  hydrogen ; 
this  gas  requires  twice  its  own  volume  of  oxygen  for  complete 
combustion,  and  furnishes  its  own  volume  of  carbonic  anhydride, 
which  requires  for  its  formation  an  equal  volume  of  oxygen,  or 
half  the  amount  consumed ; whilst  the  other  half  of  the  oxygen 
is  required  by  the  hydrogen  which  is  condensed  in  the  form  of 
water ; 2 x will  consequently  represent  the  diminution  in  bulk  of 
oxygen  which  occurs  on  detonation,  due  to  the  amount  of  car- 
buretted hydrogen  which  is  present. 

Again,  when  hydrogen  is  converted  into  water,  it  requires 
half  its  bulk  of  oxygen,  and  both  are  condensed  entirely.  If  y 
represent  the  bulk  of  the  hydrogen,  will  be  the  diminution  in 
bulk  of  the  mixed  gases  on  detonation,  which  is  occasioned  by  the 
hydrogen  in  the  mixture. 

Let  2 represent  the  volume  of  carbonic  oxide  present;  car- 
bonic oxide  for  its  conversion  into  carbonic  anhydride  requires 
lialf  its  bulk  of  oxygen,  the  carbonic  anhydride  produced  occu- 
pying the  same  bulk  as  the  carbonic  oxide,  will  therefore  indi- 


Al^ALYSIS  OF  GASEOUS  MIXTUEES. 


269 


cate  the  condensation  which  occurs  on  firing  the  mixture,  owing 
to  the  carbonic  oxide  present. 

The  total  condensation  in  bulk,  which  occurs  on  firing  a 
mixture  of  light  carburetted  hydrogen,  hydrogen,  and  carbonic 
oxide,  will  consequently  admit  of  being  thus  represented:— 

3 2/  5 

(1)  a—^  x-\ 1 — . 

2 2 

Further,  the  quantity  of  the  carbonic  anhydride,  5,  formed  by  the 
detonation,  is  composed  of  a volume  of  carbonic  anhydride  equal 
in  bulk  to  the  light  carburetted  hydrogen,  and  a volume  equal  to 
that  of  the  carbonic  oxide,  so  that  the  total  quantity  of  carbonic 
anhydride  may  be  thus  indicated : — 

(2) 

And  lastly,  the  oxygen  consumed,  c,  will  be  composed  of  the 
following  quantities : by  light  carburetted  hydrogen,  twice  its 
bulk,  2 a? ; by  hydrogen,  half  its  bulk,  f ; and  by  carbonic  oxide 
half  its  bulk,  f ; or  the  total  quantity  of  oxygen  consumed  will 
be  the  following : — 


y ^ 

(3)  c==2a?H 

2 2 


From  these  three  equations  the  values  of  a?,  y,  z are  deter- 
mined : — 

X = c ; 


y = a—G  ; 
z = 


0. 


Minute  directions  for  the  analysis  of  various  gaseous  mixtures 
are  given  by  Eegnault  in  the  fourth  volume  of  his  Cours  El'e- 
inentaire  de  Chimie^  which  contains  a description  of  a form  of 
eudiometer  well  adapted  for  accurate  experiments ; this  eudiometer 
has  been  advantageously  modified  by  Frankland  and  Ward  {Q.  J. 
Cherri'.  Soc,  vi.  197).  Bunsen  has  also  introduced  very  important 
improvements  into  the  manipulation  and  apparatus  required  for 
the  analysis  of  gases,  which  are  fully  detailed  in  his  Gasometry^ 
translated  by  Boscoe  {see  also  the  article  on  Eudiometry,  in  Liebig 
and  Poggendorff ’s  Ilandworterhuch  der  Chemie^  vol.  ii.) ; and  the 
inodes  o^*  manipulation  have  been  still  further  simplified  by 
Williamson  and  Kussell. 


270 


GENERAL  PROPERTIES  OF  THE  METALS. 


CHAPTEK  XI. 

SECOND  DIVISION. THE  METALS. 

§ I.  General  Properties  of  the  Metals. 

(517)  General  Characters  of  the  2fetals. — The  metals,  as  a 
class,  are  characterized  bv  a peculiar  lustre  termed  the  metallic 
lustre.  They  are  possessed  of  a high  degree  of  opacity,  and  are 
good  conductors  both  of  heat  and  electricity.  Some  of  them  are 
also  endowed  with  the  properties  of  ductility,  or  fitness  for  drawing 
into  wire,  and  of  malleability,  or  extensibility  under  the  hammer. 
Many  of  them  have  a high  specific  gra^fity.  When  separated 
from  their  compounds  by  electrohdic  action,  they  appear  at  the 
platinode,  or  negative  wire  of  the  voltaic  battery. 

These  properties  are  not  developed  equally  in  all  the  metals ; 
in  some  metals  one  or  more  of  them  may  be  wanting  altogether : 
and  there  are  other  substances,  not  metallic  in  their  nature,  in 
which  some  of  these  characters  are  strongly  displayed. 

(518)  Lustre^  Opacity^  and  Colour. — Although,  when  polished, 
all  metals  present  the  lustre  termed  metallic,  yet  most  of  them 
may  be  obtained  by  minute  subdivision  in  a form  devoid  of  lustre. 
Iron,  copper,  platinum,  gold,  silver,  and  even  mercury,  may  be 
thus  readily  procured  by  processes  to  be  mentioned  hereafter. 

If,  however,  these  metallic  powders  be  subjected  to  pressure 
under  the  burnisher,  a sufficient  approximation  of  their  particles 
is  produced  to  render  them  capable  of  refiecting  light,  and  the 
metallic  lustre  reappears.  This  property  admits  of  being  applied 
in  the  fine  arts  : for  instance,  it  is  possible  to  make  copies  of 
medals  or  ancient  coins,  by  employing  finely-divided  copper,  which 
is  introduced  with  the  medal  into  a mould : by  submitting  it  to 
pressure  an  exact  copy  of  the  medal,  with  a beautifully  polished 
surface,  is  obtained : the  copy  is  then  strongly  heated,  care  being 
taken  to  exclude  atmospheric  air : during  the  ignition  the  copy 
shrinks  a little  in  all  directions,  but  a fac-simile  is  formed,  which 
is  extremely  distinct,  though  reversed,  and  a little  smaller  than 
the  onginal. 

Bodies  which  are  not  metallic  occasionally  assume  a brilliant 
surface  like  the  metals.  Iodine,  which  in  all  its  chemical  relations 
is  directly  opposed  to  the  metals,  yet  possesses  a strong  lustre ; the 
same  thing  is  observable  in  a form  of  charcoal,  termed  by  the 
workmen  which  escapes  from  the  vent-holes  of  the  moulds 
during  the  process  of  casting  iron.  A native  form  of  carbon, 
graphite  or  plumbago,  has  received  its  popular  name  of  hlaclc-lead 
from  its  metallic  appearance. 

Metals  are  among  the  most  opaque  bodies  with  which  we  are 
acquainted : but  their  opacity  is  not  perfect.  When  reduced  to 
exceedingly  fine  leaves,  a portion  of  light  is  transmitted ; for 
example,  pure  gold,  of  not  more  than  -jTnrlinnr  thick,  allows 
a green  light  to  pass. 


HAEDNESS,  BRITTLENESS,  AND  TENACITY  OF  THE  METALS.  271 


The  colour  of  the  reflected  light  varies  with  the  nature  of  the 
metal.  In  most  cases  it  is  nearly  white,  with  a shade  peculiar  to 
each  metal : the  tints  of  silver,  platinum,  tin,  cadmium,  and 
palladium,  are  nearly  alike ; other  metals,  such  as  lead  and  zinc, 
havQ  a bluish  colour  ; others,  like  iron  and  arsenic,  have  a greyish 
hue ; calcium  and  barium  are  pale  yellow  ; gold  is  a full  yellow  ; 
and  copper  is  of  a red  colour.  By  repeated  reflections  from  the 
same  metal  a distinct  colour  is  often  rendered  obvious,  though  it 
is  not  seen  upon  looking  at  the  polished  surface.  A red  tint 
may  thus  be  made  evident  in  silver,  and  a violet  tinge  in  steel. 

Some  of  the  metals  possess  a characteristic  odour  / iron,  tin, 
and  copper  emit,  on  friction,  a smell  peculiar  to  themselves,  and 
arsenic,  when  volatilized,  evolves  a powerful  odour  of  garlic.  The 
taste  of  most  of  the  soluble  compounds  of  the  metals  is  astringent 
or  acrid,  and  of  the  peculiar  kind  termed  metallic. 

(519)  Hardness^  Brittleness^  and  Tenacity. — Great  differences 
are  observable  between  the  hardness  of  the  different  metals  ; steel 
may  be  rendered  hard  enough  to  scratch  glass,  while  lead  will 
take  impressions  from  the  finger-nail,  and  potassium  may  be 
spread  like  butter.  Many  of  the  harder  metals  are  very  elastic 
and  sonorous  when  struck ; but  these  properties  are  more  strik- 
ingly displayed  in  some  of  the  alloys,  or  compounds  of  the 
metals  wdth  each  other,  as  in  the  alloy  of  tin  and  copper  used  for 
bells,  and  in  the  combination  of  carbon  with  iron,  well  known 
as  steel,  which,  by  its  high  elasticity,  is  pre-eminently  qualified 
for  the  construction  of  the  springs  used  in  machinery. 

Closely  connected  with  the  hardness  are  the  brittleness  and 
the  tenacity  of  metals,  which  are  very  variable.  Some,  like  anti- 
mony, arsenic,  and  bismuth,  may  be  pulverized  without  difficulty 
in  a mortar,  while  others,  as  iron,  gold,  silver,  and  copper,  require 
great  force  to  effect  their  disintegration.  The  brittleness  of  some 
of  the  metals  is  materially  affected  by  temperature.  Zinc,  within 
the  ordinary  atmospheric  range,  is  so  brittle  that  it  cannot  be 
bent  at  a sharp  angle  without  danger  of  destroying  its  cohesion, 
while  if  heated  to  between  200°  and  300°,  it  may  be  wrought 
with  facility.  Brass,  an  alloy  of  copper  and  zinc,  on  the  con- 
trary, becomes  brittle  at  temperatures  approaching  to  redness, 
but  while  cold  it  possesses  consideralfle  malleability. 

Taking  the  tenacity  of  lead  = 1,  the  tenacity  of  the  different 
metals,  after  annealing,  will  be  represented  according  to  Wert- 
heim’s  experiments  as  follows  : — 


Lead 1 

Cadmium 1*2 

Tin 1-3 

Gold 5*6 

Zinc 8 


Silver  8*9 

Platinum  13 

Palladium 15 

Copper 17 

Iron  26 


The  tenacity  of  the  metals  has  been  measured  by  fixing  firmly 
in  a vice  one  end  of  a bar  or  wire  of  the  metal,  the  strength  of 
which  is  to  be  ascertained,  and  attaching  to  the  other  end  a con- 
venient support  for  weights  which  are  cautiously  increased  until 


272 


TENACITY  OF  THE  METALS. 


the  wire  breaks.  Bj  comparing  together  the  weights  required 
to  determine  the  rupture  of  the  different  metals  for  bars  of  equal 
section,  a comparative  table  of  tenacity  may  be  formed.  Y arious 
circmnstances  materially  influence  the  strength  of  the  same 
metal  such  as  its  purity,  the  mode  in  which  the  bar  has  been 
prepared  (whether  by  casting,  by  forging,  or  by  wire-drawing), 
the  temperature  at  which  the  comparisons  are  made,  the  applica- 
tion or  omission  of  the  process  of  annealing,  and  the  manner  in 
which  the  tension  has  been  exerted,  whether  gradually  or  sud- 
denly. Different  observers,  in  consequence  of  operating  differ- 
ently in  some  one  or  other  of  these  respects,  have  obtained 
results  which  vary  from  each  other  considerably.  The  necessity 
of  attention  to  these  points  will  be  evident  on  examining  the 
results  obtained  by  Wertheim  (Ann.  de  Chimie^  III.  xii.  MO), 
who  has  given  an  elaborate  series  of  experiments  upon  the  tenacity 
of  different  metals,  the  most  important  of  which  are  embodied  in 
the  following  table.  The  numbers  represent  the  weight  in  kilo- 
grammes which  a bar  of  each  metal  of  1 millimetre  square  would 
support  without  breaking,  both  when  the  strain  is  gradually 
increased,  and  when  suddenly  applied  : — 


60°  F. 

212°  F. 

392°  F. 

Gradual. 

Sudden. 

Cast  steel,  drawn 

83-8 

Do.  do.,  annealed 

65-7 

Piano  wire,  (steel) 

70-0 

99-1 

Do.,  annealed 

40-0 

53-9 

59-10 

50-90 

Iron  wire 

61-10 

65-1 

Do.,  annealed 

46-88 

50-25 

51-10 

46-9 

Copper  wire 

40-30 

41-0 

Do.,  annealed 

30-54 

31-68 

22-10 

Platinum  wire 

34-10 

35-0 

Do.,  annealed 

23-50 

27-70 

22-60 

19-70 

Palladium  wire 

27-2 

Do.,  annealed 

27-4 

Silver  wire 

29-0 

29-6 

Do.,  annealed 

16-02 

16-5 

14-00 

14-00 

Zinc,  commercial,  drawn 

12-80 

15-77 

Do.  do.,  annealed 

14-40 

12-20 

7-27 

Pure  zinc,  cast 

4-5 

Grold,  drawn 

27-0 

28-4 

Do.,  annealed 

10-08 

11-1 

12-60 

12-06 

Cadmium,  drawn 

2-24 

Do.,  annealed 

4-81 

2-60 

Lead,  cast 

1-25 

2-21 

Do.,  drawn 

2-07 

2-36 

Do.,  annealed 

1-80 

2-04 

0-54 

Tin,  drawn 

2-45 

3-0 

Do.  do.,  annealed 

1-70 

3-62 

0-85 

* Deville,  for  example,  by  melting  cobalt  in  a crucible  of  lime,  has  obtained  it 
free  from  carbon  and  other  impurities,  in  the  form  of  a ductile  mass  of  such  tenacity 
as  to  furnish  a wire  capable  of  supporting  twice  as  great  a weight  as  a wire  of  pure 
iron  of  similar  dimensions ; and  a wire  of  nickel  prepared  in  a similar  way,  though 
inferior  in  tenacity  to  one  of  cobalt,  surpassed  one  of  iron  in  the  ratio  of  3 to  2. 


MALLE  ABILITY  AND  DUCTILITY  OF  THE  METALS. 


273 


It  will  be  seen,  from  an  inspection  of  this  table,  that  the 
general  effect  of  heat  is  to  diminish  the  tenacity  of  the  metals, 
except  in  the  case  of  iron,  steel,  and  gold,  the  tenacity  of  which 
seems  to  be  somewhat  increased  by  a heat  of  212° ; this  is  par- 
ticularly so  with  iron  : by  a further  elevation  of  temperature  the 
tenacity  is  again  diminished.  The  influence  of  annealing,  or 
heating  the  bar  to  dull  redness,  and  allowing  it  to  cool  slowly,  is 
still  more  remarkable,  for  by  this  means  the  tenacity  of  gold  is 
reduced  more  than  half,  that  of  silver  nearly  as  much,  that  of 
platinum  about  one-third,  and  that  of  iron  and  copper  about  a 
fourth. 

(520)  Malleability  and  Ductility. — The  following  metals  are 
termed  malleable  metals,  i.  e.  metals  which  may  be  reduced  to 
thin  leaves  either  by  lamination  between  rollers,  or  by  hammer- 
ing 


Gold 

Silver 

Copper 

Platinum 


Palladium 

Iron 

Aluminum 

Tin 

Zinc 


Lead 

Cadmium 

Mckel 

Cobalt. 


Lithium,  potassium,  and  sodium,  as  well  as  mercury  when  in 
a frozen  state,  and  thallium,  likewise  admit  of  extension  under 
the  hammer.  Gold  far  surpasses  all  the  other  metals  in  mallea- 
bility, being  capable  of  reduction  into  leaves  so  thin  that  a 
square  foot  weighs  less  than  3 grains,  and  the  film  does  not 
exceed  the  200,000th  of  an  inch  in  thickness.  Silver  and  copper 
may  also  be  reduced  to  leaves  of  great  tenuity.  The  other 
metals  may  be  rolled  into  foil,  but  cannot  be  hammered  into  leaf. 
At  the  Industrial  Exhibition  of  Breslau,  1852,  an  album  of  leaf 
iron  was  exhibited,  the  sheets  of  which  did  not  exceed  the 
of  an  inch  in  thickness,  and  a square  inch  of  the  leaf  weighed 
only  three-fourths  of  a grain.  Nickel  and  cobalt  are  far  less 
malleable  than  the  other  metals  in  the  list.  The  metals  become 
denser  in  rolling,  and  are  often  rendered  so  hard  by  the  operation 
that  they  require  to  be  annealed  between  every  second  or  third 
rolling.  During  the  processes  of  hammering  and  rolling,  much 
heat  is  extricated. 

The  metals  may  be  arranged  in  the  following  order  of  duc- 
tility, tlie  propei-ty  being  possessed  to  a nearly  equal  extent  by 
the  first  five  upon  the  list : — 


Gold 

Silver 

Platinum 

Iron 

Copper 


Palladium 

Cadmium 

Cobalt 

Nickel 

Aluminum 


Zinc 

Tin 

Lead 

Thallium 

Magnesium 

Lithium. 


Ductility  is  peculiarly  displayed  by  the  first  7 inetals  on  the 
list.  Wollaston  procured  a wire  of  platinum,  the  diameter  of 
18 


274 


STEUCTTIiE  OF  METALS. 


which  did  not  exceed  the  3-0, Vro  inch,  hv  placing  a wire  of 

platinum  in  the  axis  of  a small  cylinder  of  silver  and  reducing  the 
compound  wire  to  the  utmost  practicable  tenuity  in  the  ordinary 
way,  by  drawing  it  through  holes  made  in  a hard  steel  plate, 
termed  a ch*aw-plate ; the  apertures  through  which  the  wire  was 
made  to  pass  diminishing  in  size  by  regular  gradation.  Both 
metals  were  thus  attenuated,  pari  passu,  and  the  silver  was  finally 
dissolved  OS’  bv  nitric  acid,  which  left  the  platinum  unacted  upon. 
Gold  wire  equally  fine  was  obtained  bv  a similar  process  {Phil. 
Trans.  1S13).  Steel  wires  of  extreme  fineness  have  been  produced 
in  a similar  manner,  the  silver  being,  in  this  case,  dissolved  by  the 
action  of  mercury.  Zinc,  tin,  lead,  magnesium,  and  even  litliimn, 
may  also  be  obtained  in  the  form  of  wire,  but  with  difficulty,  on 
account  of  their  feeble  tenacity.  Matthiessen  has  succeeded  in 
obtaining  many  of  the  softer  metals  such  as  sodium  and  lithium, 
in  the  form  of  wire,  by  forcing  them  under  strong  pressm’e  through 
an  aperture  in  a steel  die. 

The  malleability  of  a metal  is  bv  no  means  always  propor- 
tioned to  its  ductility ; iron,  though  it  may  be  reduced  to  wires 
of  extreme  fineness,  is  not  nearly  so  malleable  as  gold,  silver, 
copper,  and  some  other  metals  which  are  inferior  to  it  in  ductility. 
A few  substances  which  are  not  metallic  exhibit,  when  in  a state 
of  semifusion,  a very  perfect  ductility.  Half-melted  glass  shows 
this  property  in  a marked  degree  ; it  may  be  spun  into  very  fine 
threads,  which  have  even  been  woven  into  a species  of  cloth,  de- 
signed for  ornamental  purposes. 

It  is  obvious  that  the  properties  of  brittleness,  tenacity,  duc- 
tility, and  malleability,  must  be  materially  dependent  upon  the 
texture  of  the  metal.  This  is  strikingly  exemplified  in  the  vaiia- 
tion  in  tenacity  exhibited  by  the  same  metal  under  different  cir- 
cimistances.  Silver,  in  ordinary  cases,  is  tough,  ductile,  and  mal- 
leable ; by  repeated  heatings  and  coobngs,  however,  its  particles 
an'ange  themselves  in  a crystalline  manner,  and  it  then  becomes 
very  brittle.  Copper,  when  deposited  in  crystals  by  slow  voltaic 
action,  is  very  hard  and  brittle  ; but  when  the  action  is  more  rapid 
it  is  soft  and  tough,  and  the  metal  then  exhibits  a fibrous  charac- 
ter : and  it  may  be  stated,  as  a general  principle,  that  the  crystal- 
line metals,  such  as  zinc,  antimony,  bismuth,  and  arsenic,  are  the 
most  brittle  ; while  those  which,  like  iron,  have  a fibrous  struc- 
time,  are  possessed  of  a high  degree  of  tenacity. 

The  structure  of  a metal  is  easily  displayed  in  many  cases,  by 
placing  it  in  solvents  the  operation  of  which  is  very  gradual. 
Some  of  the  metals  which  fuse  readily  may  be  obtained  in  crys- 
tals without  difficulty,  by  allowing  a few  pounds  of  the  melted 
metal  to  cool  slowly,  and  pouring  out  the  interior  portions  before 
the  whole  has  had  time  to  solidify  ; the  inner  walls  of  the  cavity  are 
then  found  to  be  lined  with  crystals.  Bismuth  is  particularly 
well  adapted  to  this  process.  The  less  fusible  metals,  such  as 
copper,  iron,  gnd  silver,  may  often  be  crystallized  from  their  solu- 
tions by  slow  voltaic  actions.  Many  of  them — as,  for  example, 
gold,  silver,  and  copper — occur  native  in  crystals.  A large  pro- 


SPECIFIC  GRAVITY  A:N^D  FUSIBILITY  OF  THE  METALS.  275 

portion  of  the  metals  crystallize  in  forms  belonging  to  the  regular 
system. 

(521)  Specific  Gravity. — Wide  differences  are  observable  in 
the  specific  gravity  of  the  metals.  In  the  annexed  table,  varia- 
tions are  exhibited  between  the  extremes  of  iridium  and  platinum, 
the  heaviest  known  forms  of  matter,  on  the  one  hand,  and  lithium 
on  the  other,  which  has  little  more  than  half  the  density  of  water. 
The  lighter  metals  are  all  characterized  by  their  powerful  attrac- 
tion for  oxygen  ; those  which  are  least  oxidizable  possessing  gene- 
rally the  highest  specific  gravity.  In  a few  instances,  the  most 
marked  of  which  is  platinum,  the  density  may  be  somewhat  in- 
creased by  rolling  and  hammering  ; but  this  is  not  usually  the 
case. 


Specific  GroA^ity  of  the  Metals. 


Metal. 

Sp.  Gr. 

Observer. 

Platinum  ....... 

21-53  

Osmium 

21-4  

Iridium 

21-15  

Gold 

19-34  

Uranium 

18-4  

Timgsten 

....17-6 

D’Elhuyart. 

Mercury 

13-596  

Rhodium 

12-1  

Thallium 

11-91-11-81  

Palladium 

11-8  

Ruthenium 

....11-4 

Lead 

11-36  

Reich. 

Silver 

10-53  

Bismuth 

9-799 

Cobalt 

Copper 

8-95  to  8-92  

Nickel 

8-82  

Molybdenum.  . . . 

8-62  

Cadmium 

...  8 694  to  8-604 

Manganese 

8-013  

Iron 

7-844  

Tin 

7-292  

Zinc 

7-146  

Chromium 

6-81  

Antimony 

Tellurium 

6-25  

Arsenic 

5-969-5-7  

Aluminum 

Strontium 

. ...  2 54  

Glucinum 

2-1  

Magnesium 

1 743 

Calcium 

1-578  

Rubidium 

1-52  

Sodium 

0-972  

Potassium 

0-865  

Lithium 

(522)  Fusihility. — The  melting-points  of  the  different  metals 
differ  not  less  widely  than  their  densities.  Mercury,  for  instance, 
remains  fluid  as  low  as  — 39°  F. ; potassium  and  sodium  melt 
below  the  heat  of  boiling  water.  Tin,  cadmium,  bismuth,  thal- 
lium, lead,  and  zinc  melt  below  redness  ; antimony,  calcium,  and 
aluminum,  above  a red  heat.  Silver,  copper,  and  gold  require  a 
bright  cherry-red  heat ; iron,  nickel,  and  cobalt  a white  heat ; 


276 


rUSEBILITY  A^T)  VOLATILITY  OF  THE  METALS. 


while  platinum,  iridium,  rhodium,  and  several  othei-s,  require  the 
intense  heat  of  the  oxyhydrogen  blowpipe,  or  even  of  the  voltaic 
arc,  to  eifect  their  fusion. 


Mercury — 39 

Rubidium 101 

Potassium 144 

Sodium 207 

Lithium 356 

Tin 

Cadmium 442 

Bismuth 507 

Thallium 561 

Lead 

Tellurium 

Arsenic 

Zinc 

Antimony about  1150 

Calcium 


of  Fusihility  of  the  2fetals. 

°F. 

°C. 

..—39  

—39-4  

Hutchins. 

. . 101-3  

38-5  

Bunsen. 

. . 144-5  

62-5  

Bunsen. 

..  207-7  

97-6  

Regnault. 

..356  

180  

Bunsen. 

. . 442  

228  

Crichton. 

..442  

228  

Stromeyer. 

..507  

264  

Rudberg. 

..561  

294  

Crookes. 

..  617  

325  

Rudberg. 

1 undetermined. 

..773  

412  

Daniell. 

F. 


.1873 

1023 

.1996 

1091 

.2016 

1102 

.2786 

1503 

. . . . 

DanielL 


Aiummum \ ^ 

Silver 1873 

Copper 

Gold 

Cast  iron 2786 

Cobalt 

brought  tan  ;■ 

Manganese J 

Molybdenum 

Chroraiu^' I"  fuse  in  the  forge. 

Palladium J 

Platinum 

Rhodium | 

Va^ato'm f"  require  the  heat  of  the  oxyhydrogen  blovvpipe. 

Ruthenium 

Osmimn J 


Some  metals  near  their  melting-points,  before  undergoing  com- 
plete fusion,  pass  through  a soft  intermediate  stage,  in  which,  if 
two  clean  surfaces  be  presented  to  each  other,  and  strong  pressure 
or  hammering  be  employed,  they  unite,  or  weld  together,  so  as  to 
form  one  continuous  mass.  Iron,  thallium,  lithium,  and  potassium 
afford  the  most  striking  instances  of  this.  Palladium  is  also,  in  a 
minor  degree,  susceptible  of  it. 

(523)  Volatility. — Many  of  the  metals  admit  of  being  volatilized 
without  difficulty.  Mercury,  when  heated  under  ordinary  atmo- 
spheric pressure,  boils,  and  is  reduced  to  a perfectly  colourless, 
transparent  vapour,  at  about  662°.  It  is  important  to  observe 
that  this  dry  vapour,  though  metallic,  is  an  insulator  of  electricity, 
and  will  allow  the  transmission  of  distinct  electric  sparks  as  read- 
ily as  atmospheric  air.  The  insulating  power  of  mercurial  vapour, 
on  the  one  hand,  and  the  small  specific  gravity  of  potassium,  of 
sodium,  and  of  lithium,  on  the  other,  show  that  there  is  nothing 
inconsistent  with  facts  in  the  supposition  tliat  hydrogen  itselt. 


CONDUCTING  POWER  FOR  HEAT  AND  ELECTRICITY. 


2Y7 


although  the  lightest  known  form  of  matter,  and  though  gaseous, 
and  consequently  an  insulator  of  electricity,  may  possibly  be  a 
metal ; and  indeed,  in  its  chemical  properties,  it  approximates 
very  closely  to  this  class  of  bodies.  Eight  of  the  metals  are  suffi- 
ciently volatile  to  be  distilled  from  the  compounds  from  which 
they  are  obtained — viz.. 


Mercury 

Arsenic 

Tellurium 


Zinc 

Cadmium 

Potassium 


Sodium 

Rubidium, 


Arsenic  is  volatilized  below  redness,  and  even  before  it  has  assumed 
the  liquid  form  ; cadmium  requires  a full  red  heat,  and  zinc,  po- 
tassium, sodium  and  rubidium  a higher  temperature.  Those 
metals  which  are  generally  considered  fixed  in  the  fire  are  like- 
wise volatilizable  to  a certain  extent.  In  the  process  of  lead- 
smelting, one-seventh  of  the  lead  escapes  up  the  chimney,  and 
would  be  wasted  unless  means  for  collecting  it  were  adopted. 
Even  copper  is  not  absolutely  fixed  in  the  fire.  My  friend.  Dr. 
Percy,  some  years  ago,  showed  me  a remarkable  illustration  of 
this  fact : he  has  in  his  possession  part  of  a beam  which,  for  many 
years,  was  suspended  over  a furnace  in  a copper-smelting  house  in 
Rorway ; the  whole  beam,  of  which  this  is  a fragment,  contains 
minute  beads  of  metallic  copper  studded  through  its  texture  : the 
copper  must  have  been  raised  in  vapour  and  so  deposited  within 
its  fibres.  Gold  has  been  found  similarly  studding  the  beams  of 
refineries ; and  it  may  be  seen  to  undergo  volatilization  in  the 
focus  of  an  intensely  powerful  burning-glass.  Platinum  may  be 
converted  into  vapour  with  scintillation  in  the  oxyliydrogen  jet, 
and  silver  is  volatilized  rapidly  in  the  voltaic  arc.  Pine  wires  of 
the  most  refractory  metals  may  be  dispersed  in  vapour  by  trans- 
mitting the  discharge  of  a powerful  Leyden  battery  through  them. 

(521)  Conducting  Power  for  Heat  and  Electricity. — The 
great  differences  of  expansion  exhibited  by  different  metals  when 
exposed  to  equal  degrees  of  temperature,  have  already  been  pointed 
out  (132) ; and  it  may  be  stated  generally  that  each  metal  pos- 
sesses a specific  expansion : the  conducting  power  of  each  metal, 
both  for  heat  (149)  and  for  electricity  is  also  definite  (239,  276): 
in  general  it  is  found  that  the  best  conductors  of  heat  are  also  the 
best  conductors  of  electricity  : but  though  conductors  in  the  solid 
and  liquid  conditions,  the  metals  are  insulators  in  the  aeriform 
state. 

(525)  Alloys. — Metals  enter  into  combination  with  each 
other,  and  form  compounds  termed  alloys^  many  of  which  are 
most  extensively  used  in  the  arts.  Comparatively  few  of  the 
metals  possess  qualities  such  as  render  them  suitalile  to  be  em- 
ployed alone  by  the  manufacturer;  aluminum,  zinc,  iron,  tin, 
copper,  lead,  mercury,  silver,  gold,  and  platinum,  constitute  tlie 
entire  number  so  used.  Arsenic,  antimony,  and  bismuth  are  too 
brittle  to  be  used  alone,  but  are  employed  for  hardening  other 
metals.  Many  of  the  physical  properties  of  the  metals  are 
greatly  altered  by  combination  with  others ; the  combination  or 


278 


ALLOYS. 


alloy  being  often  adapted  to  purposes  for  which  either  metal 
separately  would  be  unfit.  Copper  alone  is  not  fit  for  castings, 
and  it  is  too  tough  to  be  conveniently  wrought  in  the  lathe  or 
by  the  file ; but  when  alloyed  with  zinc,  it  forms  a much  harder 
cu^mpound.  which  can  be  cast,  rolled,  or  turned,  and  which  con- 
stitutes the  different  kinds  of  brass,  the  qualities  of  which  can  be 
varied  by  vaiying  the  proportions  of  the  two  metals.  The  ad- 
dition of  nickel  to  brass  destroys  its  yellow  colour,  and  produces 
the  white  compound  metal  known  under  the  name  of  German 
silver.  Copper  and  tin  in  various  proportions  yield  the  hard, 
tough,  but  moderately  fusible  compounds  known  as  bronze  and 
bell-metal.  When  the  metals  combine  with  mercury,  the  result- 
ing body  is  called  an  amalgam. 

In  most  cases  these  compounds  of  metals  with  each  other  are 
united  by  weak  ties : for  it  appears  necessary,  in  order  to  pro- 
duce energetic  union  between  any  two  bodies,  that  the  substances 
when  separate  should  exhibit  great  dissimilarity  in  properties. 
It  has  sometimes  been  questioned  whether  alloys  are  true  chem- 
ical compounds : definite  compounds  of  the  metals  with  each 
Other,  do.  however,  certainly  exist,  and  some  have  been  found 
combined  in  definite  proportions  in  the  native  state.  Such  is  the 
case  with  silver  and  mercmw.  which  occur  crystallized  together 
in  the  proportion  of  an  atom  of  each  (AgHg) : and  that  the  al- 
loys are  undoubtedly  in  many  instances  true  chemical  compounds, 
is  fui*ther  shown  by  the  increase  or  diminution  in  density  which 
attends  the  act  of  combination  ; the  specific  gravity  of  the  alloy 
being  generally  either  above  or  below  that  of  the  two  metals  em- 
ployed. The  fusing  point  of  an  alloy  is  generally  much  lower 
than  the  mean  of  those  of  the  metals  which  compose  it.  This 
circumstance,  as  well  as  the  alteration  which  alloys  exhibit  in 
their  general  relations  to  heat  and  electricity,  are  also  further  evi- 
dences of  the  definite  character  of  these  compounds.  A remark- 
able illustration  of  the  infiuence  which  the  chemical  union  of  the 
metals  exerts  upon  their  fusing  point,  is  afforded  by  the  alloy 
called  fusible  metal,  which  is  a mixture  of  bismuth,  of  lead,  and 
of  tin.  in  the  proportions  represented  by  the  formula  (,Bi,Pb,Sn) : 
they  form  a compound  which  melts  at  212°,  a temperature  more 
than  200°  below  the  fusing-point  of  tin.  the  most  fusible  of  these 
metals,  and  100°  below  that  of  lead.  Most  frequently,  however, 
the  alloys  are  mixtures  of  definite  compounds  with  an  excess  of 
one  or  other  metal,  and  the  separation  of  their  components  fi*om 
each  other  is  generally  easily  efiected  by  simple  means.  For  in- 
stance. by  exposing  brass  to  a high  temperature,  the  zinc  is  vola- 
tilized. leaving  the  copper  behind : and  from  the  alloy  of  arsenic 
and  platinum,  a heat  sufliciently  long  continued  will  expel  abuost 
the  whole  of  the  arsenic.  Even  mere  mechanical  means  will 
s«3metimes  suflice  to  efiect  the  separation.  M^hen  silver,  for  ex- 
ample, is  amalgamated  with  mercury,  the  amalgam  formed  is  dis- 
solved by  an  excess  of  mercury : this  excess,  however,  may  be  al- 
most entirely  removed  by  squeezing  the  mass  through  chamois 
leather : the  amalgam  is  retained  in  the  solid  form,  while  the  su- 


CONDITION  IN  WHICH  THE  METALS  OCCUK  IN  NATURE.  2 T9 

perfliions  mercury,  nearly  freed  from  silver,  escapes  tlirougli  tlie 
pores  of  tlie  leather. 

The  chemical  properties  of  an  alloy  are  generally  such  as  might 
have  been  anticipated  from  those  of  its  components.  In  many 
instances,  however,  the  alloy  of  two  oxidizable  metals  is  much 
more  readily  oxidized  than  either  of  its  constituents.  An  alloy 
of  1 part  of  lead  and  3 parts  of  tin,  for  example,  burns  when 
heated  to  dull  redness  much  more  easily  than  its  components,  and 
becomes  converted  into  a white  ash,  used  in  the  preparation  of 
enamels  (600).  Sometimes  an  alloy  is  completely  soluble  in  an  acid 
which  is  without  action  upon  one  of  its  components : — German 
silver,  which  is  a combination  of  copper  with  zinc  and  nickel,  is 
readily  dissolved  by  diluted  sulphuric  acid,  though  the  acid  will 
not  attack  metallic  copper ; and  in  a similar  manner,  an  alloy  of 
platinum  with  ten  or  twelve  times  its  weight  of  silver  is  entirely 
dissolved  by  nitric  acid,  although  platinum  alone  resists  the  action 
of  the  acid  completely. 

The  ductility  of  metals  is  usually  impaired  by  combination  with 
one  another.  Alloys  of  two  brittle  metals  are  invariably  brittle : 
such  is  the  case  with  the  compound  of  arsenic  and  bismuth. 
Alloys  of  a brittle  with  a malleable  metal  are  also  brittle.  Even 
when  two  malleable  metals  are  united,  the  compound  is  sometimes 
brittle ; gold,  for  example,  when  alloyed  with  a minute  portion 
of  lead,  splits  under  the  hammer.  Generally  speaking,  the  hard- 
ness of  metals  is  increased  by  alloying  them ; of  this  a familiar 
instance  is  afforded  by  the  standard  coin  of  the  realm : neither 
gold  nor  silver,  when  unalloyed,  is  sufficiently  hard  to  resist  attri- 
tion to  the  degree  required  for  the  currency,  but  the  addition  of 
tV  iV  weight  of  copper  to  either  metal  increases  its  hard- 
ness to  the  requisite  extent. 

The  more  important  alloys  will,  however,  be  best  considered 
separately,  when  the  individual  metals  which  enter  into  their 
composition  are  described. 

(526)  Condition  in  which  the  Metals  occur  in  Nature. — The 
ties  which  unite  the  components  of  an  alloy  are  feeble,  and  are 
easily  severed  ; but  the  compounds  formed  by  the  metals  with  the 
class  of  substances  known  as  non-metallic,  are  for  the  most  part 
held  together  by  attractions  of  a very  powerful  order,  and  these 
compounds  are  in  a chemical  point  of  view  much  more  interesting 
and  important  than  the  alloys.  With  some  of  the  metals  carbon 
and  silicon  combine  in  small  proportion  without  appearing  to 
destroy  the  metallic  character ; and,  in  fact,  these  compounds 
more  resemble  alloys  than  any  other  class  of  combinations ; the 
most  remarkable  instances  of  carbides  and  silicides  are  furnished 
by  iron,  which,  in  its  modifications  of  steel  and  cast  iron,  is  com- 
bined with  variable  quantities  of  these  elements.  Many  of  the 
compounds  of  the  metals  with  sulphur  preserve  their  metallic 
lustre,  as  is  seen  in  galena  and  pyrites,  yet  lose  nearly  all  the 
other  physical  properties  by  which  the  metals  are  recognised ; 
ductility,  malleability,  and  power  of  conducting  electricity  are 
extremely  impaired.  The  metallic  character  is  still  more  com- 


280 


DISTFJBUTION  OF  THE  METALS. 


pletely  destroyed  by  oxygen,  wbicli  converts  the  metals  into  bodies 
apparently  earthy,  as  in  the  familiar  cases  of  lime,  magnesia, 
alumina,  and  oxide  of  zinc  ; whilst  chlorine  and  its  , allied  group 
of  elements  form  compounds  'which  are  most  of  them  soluble,  and 
possess  all  the  cpialities  of  true  salts.  The  energy  with  which 
iron,  zinc,  and  many  other  metals  combine  with  oxygen  is  very 
remarkable : and  the  attraction  of  chlorine  for  these  metals  is  still 
more  powerful. 

The  more  common  metals,  on  account  of  their  powerful  attrac- 
tion for  oxygen  and  sulphur,  are  very  rarely  met  with  in  the 
uncombined  form.  Some  of  those  which  are  less  abundant  are, 
however,  found  naturally  in  the  metallic  condition  : such  is  the 
case  wnth  gold,  silver,  mercury,  platinum,  and  copper.  They  are 
then  said  to  occur  in  the  natwe  state.  Many  are  found  alloyed 
with  each  other : gold,  for  instance,  forms  native  alloys  with  palla- 
dium and  with  silver ; silver  with  mercury ; antimony  with  arsen- 
icum.  The  occurrence  of  native  metals  or  natural  alloys  is, 
however,  an  exceptional  circumstance,  for  the  majority  of  the 
metals  are  found  in  combination  with  other  elements.  Oxygen 
and  sulphur,  in  particular,  from  their  powerful  chemical  attrac- 
tions and  the  abundance  in  which  they  occur,  are  the  bodies  most 
frequently  associated  with  the  metals  ; at  other  times  arsenicum, 
and  more  rarely  chlorine,  are  the  mineralizing  agents.  These 
compounds,  whether  oxides,  sulphides,  arsenides,  or  chlorides, 
constitute  what  are  termed  the  ores  of  the  metals. 

(527)  Distribution  of  the  Metals. — Next  to  silica  in  its  various 
forms,  the  most  abundant  components  of  the  rocks  and  superficial 
portions  of  the  globe,  are  the  compounds  of  lime,  alumina,  and 
magnesia.  These  earths  are  themselves  oxides  of  metallic  bodies, 
the  attraction  of  which  for  oxygen  is  so  intense  that  tliey  are 
rarely  isolated  from  it  except  for  scientific  purposes  in  the  labora- 
tory of  the  chemist.  In  their  oxidized  form  they  are  everywhere 
scattered  in  abundance  over  the  face  of  the  globe.  It  is  not  so 
with  those  metals  which  man  is  in  the  habit  of  separating  from 
their  ores  upon  the  large  scale,  and  of  employing  for  the  various 
requirements  of  civilized  society  in  the  metallic  state.  Most  of 
the  ores  of  the  highest  importance  and  utility  constitute  but  a 
comparatively  small  portion  of  the  components  of  the  earth’s 
crust ; but  this  deficiency  in  their  relative  proportion  is  more  than 
compensated  by  the  mode  of  their  distribution,  for  they  are  not 
dispersed  at  random,  or  diffused  in  minute  quantity  uniformly 
throughout  the  mass  of  the  earth,  but  are  collected  into  thin 
seams  or  beds,  which  form  mineral  veins. 

Man  has  hitherto  been  able  to  penetrate  but  to  a very  small 
depth  into  the  body  of  the  earth,  the  deepest  excavation  which  he 
has  been  enabled  to  make  being  not  greater,  in  proportion  to  the 
diameter  of  the  earth,  than  the  thickness  of  an  ordinary  sheet  of 
writing-paper  to  a globe  of  two  feet  in  diameter.  Geological  ob- 
servations have  shown,  and  any  person  who  has  traversed  a rail- 
way cutting  has  had  a partial  opportunity  of  convincing  himself, 
of  the  fact,  that  a great  part  of  the  superficial  portions  of  the 


DIRECTION  OF  MINERAL  VEINS. 


281 


globe  consists  of  a succession  of  beds  or  layers  — strata^  as  they 
are  commonly  termed,  which  rest  one  above  another  : these  beds 
in  some  places  retain  nearly  their  original  horizontal  direction  ; 
but  usually  they  have  assumed  a position  more  or  less  inclined,  so 
as  to  form  a considerable  angle  with  the  surface.  The  same  stra- 
tum is  liable  to  great  variations  in  thickness  in  different  parts,  but 
each  bed  is  found  to  occur  in  a uniform  position  in  the  series,  the 
successive  strata  following  each  other  in  regular  order,  the  upper- 
most being  those  of  most  recent  formation.  In  this  way  the  Lon- 
don clay  rests  upon  the  chalk,  the  chalk  upon  what  is  termed  the 
green-sand,  the  green-sand  upon  the  gault,  and  so  on.  The  stra- 
tified or  sedimentary  rocks  rest  upon  others,  which,  like  granite, 
porphyry,  and  basalt,  show  no  appearance  of  stratification,  but 
bear  marks,  more  or  less  evident,  of  having  undergone  igneous 
fusion. 

Occasionally  it  happens  that  a thin  bed  of  metallic  ore  forms 
a part  of  the  regular  succession  of  the  strata  ; in  Staffordshire, 
for  instance,  over  many  square  miles  of  country,  thin  bands  or 
seams  of  the  ore  termed  clay  iron-stone,  varying  in  thickness  from 
2 to  8 inches,  are  found  lying  between  the  beds  of  coal.  Usually, 
however,  the  metalliferous  masses  occur  in  still  older  formations ; 
such  as  in  the  mountain  limestone  of  Cumberland  and  Derbyshire, 
or  in  the  granite  and  clay-slate,  as  in  Cornwall : they  are  then 
found  in  fissures  which  traverse  the  ordinary  strata  of  the  district, 
and  assume  a direction  which,  though  it  never  becomes  quite  ver- 
tical, still  approaches  more  or  less  towards  this  position.  These 
fissures  vary  in  thickness  from  a few  inches  to  as  many  feet ; they  are 
often  filled  with  masses  of  basalt,  granite,  or  trachyte  (which  have 
been  injected  from  below,  whilst  the  materials  were  in  the  molt- 
en state  under  the  effects  of  subterranean  heat),  and  then  consti- 
tute what  the  miner  terms  dykes  ; but  in  other  cases  they  are  filled 
with  metallic  ores,  and  form  mineral  veins  or  lodes.  The  ore 
sometimes  occurs  nearly  pure ; at  others  mingled  with  quartz, 
fluor-spar,  and  various  crystallized  minerals,  or  else  with  earthy 
impurities  of  different  descriptions.  These  veins  extend  from  the 
surface  downwards,  often  to  a depth  greater  than  can  be  followed 
even  in  the  deepest  mines.  The  veins  which  occur  in  the  same 
district  usually  run  in  two  directions,  nearly  at  right  angles  to 
each  other,  the  principal  or  original  veins  being  traversed  by  the 
others.  In  Cornwall,  for  example,  the  metalliferous  veins  run 
nearly  east  and  west,  but  they  are  occasionally  intersected  more 
or  less  obliquely  by  other  lodes,  to  which  the  term  of  cannier 
(contrary)  lodes ^ or  cross  courses,  has  been  given. 

These  cross  courses,  however,  are  by  no  means  always  metallif- 
erous ; they  often  appear  to  have  been  occasioned  by  the  action 
of  a force  emanating  from  below,  which,  after  bending  and  s])lit- 
ting  the  original  strata,  produced  the  fissures  which  were  subse- 
quently filled  with  quartz,  clay,  and  various  minerals.  Such  cross 
courses  as  these  not  seldom  occasion  the  miner  much  trouble  and 
perplexity,  since  the  subterranean  force  necessary  to  ])roducethem 
is  often  attended  with  great  displacement  of  the  original  sti-ata.  A 


282 


MINING  OPERATIONS. 


valuable  vein  of  ore  is  from  this  cause  frequently  interrupted,  and 
is  sometimes  lost  altogether  for  want  of  knowing  in  what  dh*ec- 
tion  to  seek  for  it.  This  sudden  break  in  a vein  and  its  displace- 
ment is,  in  mining  language,  termed  a fault.  It  is  very  rarely 
that  a single  mineral  vein  occurs  alone ; usually  several  are  found 
together. 

The  thickness  of  the  same  vein,  as  might  be  expected,  is  sub- 
ject to  great  variations  ; at  one  time  it  dwindles  to  a mere  thread, 
at  others  it  attains  considerable  expansion.  The  most  productive 
veins  usually  occur  near  the  junction  of  two  dissimilar  kinds  of 
rock — the  metallic  ores  having  probably  accumulated  there  in 
consequence  of  slow  voltaic  actions  which  have  been  going  on 
through  uncounted  ages,  and  which  have  been  occasioned  by  dif- 
ferences in  chemical  composition  of  the  two  contiguous  rocks : 
in  Cornwall,  for  example,  where  so  large  a proportion  of  the  min- 
eral wealth  of  Great  Britain  is  accumulated,  the  most  important 
mines  occur  upon  the  junction  of  the  granite  with  the  clay-slate 
or  killas. 


(528)  Mining  Operations. — The  existence  of  a vein  having 
been  ascertained,  and  its  dip  and  general  direction  having  been 
determined,  the  miner  commences  by  sinking  a vertical  pit,  or 
shaft.,  in  such  a manner  that  he  calculates  upon  cutting  thi*ough 
the  lode  at  some  30  or  40  fathoms  below  the  surface.  When  he 
has  reached  the  lode,  he  drives  a gallery,  or  level.,  horizontally 
into  it,  right  and  left,  raising  the  ore  to  the  surface  through  the 
shaft.  If  the  produce  be  such  as  to  encourage  him  to  proceed,  a 
second  shaft  is  sunk  in  the  course  of  the  lode,  at  the  distance  of 
about  100  yards  from  the  first,  and  into  this  the  gallery  or  level 
is  driven,  so  as  to  facilitate  the  ventilation  of  the  mine  and  the 
extraction  of  the  ore.  In  order  to  be  able  to  remove  the  ore  from 
other  parts  of  the  lode  above  and  below  the  point  at  which  the 
first  level  is  made,  the  shaft  is  continued  downwards,  and  other 
galleries,  or  cross  cuts.,  as  they  are  termed,  are  made,  both  above 
and  below  the  first  level,  at  intervals  of  ten  fathoms,  to  meet  the 
lode  at  different  points  ; these  cross  cuts  are  at  right  angles  to 
the  levels.  Fig.  324  shows  a vertical  cross  section  of  the  lode 
at  the  Callington  Mine,  e s represents  the  engine  shaft,  v v the 
vein  or  lode,  and  c,  <?,  the  cross  cuts.  The  levels  cannot  be  shown 
in  this  view  ; but  whenever  a cross  cut  meets  the  lode,  a level  is 
driven  east  and  west,  in  the  direction  of  the  lode  itself. 

Fig.  325  shows  the  arrangement  of  the  levels  in  the  same 
mine  ; e s represents  the  engine  shaft,  w,  a second  smaller  shaft, 
and  L,  L,  L,  the  different  levels,  the  depths  of  which  in  fathoms 
are  indicated  by  the  numbers  attached  to  them  ; these  levels  com- 
municate at  different  points  by  short  cuts,  or  winzes.,  as  the 
Cornish  miners  term  them  ; they  are  shown  at  u^  in  various 
parts,  and  are  needed  to  facilitate  the  extraction  of  the  ore  from 
different  parts  of  the  lode.  The  different  levels  are  not  imme- 
diately over,  or  parallel  to  each  other,  but  their  direction  and 
position  varies  with  that  of  the  inclination  and  direction  of  the 
lode.  This  is  explained  by  fig.  326,  in  which  the  direction  of 


PLAN  AND  SECTION  OF  A MINE. 


283 


these  galleries  is  exhibited  ; it  represents  a jplan  of  the  mine,  sup- 
posing the  figures  to  refer  to  the  levels  shown  in  325  : the  lode,  it 
will  be  seen,  does  not  preserve  the  same  dip  at  all  points,  being 
much  more  nearly  vertical  at  the  right  than  at  the  left  extremity 
of  the  plan.  The  cross  cuts  cannot  be  shown  in  fig.  325.  The 


Fig.  324.  Fig.  326. 


Fig.  326. 


shaded  parts  in  this  figure  indicate  the  portions  of  the  lode  which 
have  been  already  worked  away.  The  galleries  in  the  mine  are 
supported  by  strong  timbering,  the  object  of  which  is  to  prevent 
the  rubbish  from  falling  in  and  overwhelming  the  men  w'hile  en- 
gaged in  their  work. 

One  of  the  principal  difficulties  which  the  miner  has  to  contend 
with  is  tlie  continual  oozing  of  water  into  the  mine  in  all  direc- 
tions. Where  the  mine,  as  very  often  happens,  is  situated  upon 
the  side  of  a hill,  an  adit  levels  or  watercourse,  shown  at  a a,  fig. 
325,  is  carried  from  the  shaft  to  the  lowest  accessible  point  of  the 
surface  ; and  through  this  the  waters  of  the  upper  part  of  the  mine 
readily  escape  ; but  when  the  workings  extend  below  this  point, 
it  becomes  necessary  to  pump  more  or  less  constantly,  and  for 
this  purpose  powerful  steam-engines  are  required.  The  galleries 
and  levels  are  so  constructed  that  the  water  shall  flow  from  them 
into  the  principal  shaft  of  the  mine,  so  that  by  pum])ing  from  the 
sump^  or  lowest  part  of  this  shaft,  the  whole  mine  is  freed  from 
water.  The  greater  part  of  the  water  is  lifted  only  to  tlie  adit 
level,  but  a considerable  quantity  is  raised  to  the  surface  for  the 
purpose  of  washing  the  ore. 

Much  of  the  excavation  is  done  by  hand,  with  the  pickaxe  and 


£S4  l^CHiJN'ICAL  TEEA’nrE^'T  OF  THE  OEES. 

wedges  ; but  after  judicious  cleai*ing,  gunpowder  properly  applied 
facilitates  the  progress  greatly.  The  quantities  of  powder  used 
for  blasting  in  the  mines  are  small,  usually  about  two  oimces. 
The  process  of  blasting  consists  in  boring  a hole  to  the  depth  of 
IS  inches  or  2 feet,  somewhat  obliquely,  under  the  portion  of  rock 
which  is  to  be  raised  ; the  powder  is  then  introduced,  and  the  hole 
is  closed  by  ramming  in  clay  or  friable  rock.  A copper  wire  runs 
from  the  surface  down  to  the  charge,  and  when  the  ramming  or 
tamping  is  finished,  the  wire  is  withdrawn  and  its  place  supplied 
with  a hollow  rush  charged  with  powder,  and  the  train  is  fired  by 
means  of  a fusee.  A safety  fusee  is  now  commonly  substituted 
for  the  copper  wii’e  and  pithed  reed  filled  with  powder.  The  ore 
that  is  detached  is  raised  to  the  surface  of  the  mine  in  large 
wrought-iron  buckets,  or  kibbles^  which  are  capable  of  containing 
about  3 cwt.  of  ore. 

(529)  ^fe^hanical  Treatment  of  the  Ores. — The  extraction  of 
metals  from  their  ores  is  effected  by  two  classes  of  operations  ; 
those  of  the  first  class  are  mechanical ; by  theii’  means  the  earthy 
parts  contained  in  the  matrix  or  vein-stone  are  to  a certain  extent 
separated  : the  operations  of  the  second  class  are  chemical,  by 
which  the  metal  itself  is  procm-ed.  The  mechanical  treatment  is 
influenced  not  only  by  the  nature  and  composition  of  the  ore,  but 
also  by  its  market  value  : an  ore  of  tin,  of  copper,  or  of  lead,  from 
the  higher  price  which  the  metal  bears,  will  be  worth  a more  elabo- 
rate treatment  than  an  ore  of  non  or  of  zinc. 

The  ores  of  zinc  and  of  non  are  occasionally  subjected  to  the 
operation  of  w ashing  ; for  when  they  are  accompanied  by  a loose 
friable  clay,  the  clay  admits  of  being  readily  diftiised  in  a finely 
divided  state  through  the  water,  and  is  easily  removed  by  its  means. 
The  specific  gravity  of  clay  is  not  much  more  than  2'0,  whilst  that 
of  carbonate  of  iron  and  hydrated  oxide  of  non  varies  from  B’S  to 
4'0,  and  that  of  calamine  is  about  4‘2 ; consequently  particles  of 
these  materials  of  equal  size  expose  a smaller  surface  in  propor- 
tion to  their  weight  to  the  action  of  water  than  the  clay,  and 
when  agitated  with  water  they  subside  more  rapidly ; and  "if  sub- 
jected to  the  action  of  a current  of  water,  they  are  held  for  a 
shorter  time  in  suspension,  and  are  therefore  canded  by  it  to  a 
smaller  distance. 

The  same  principles  apply  to  the  more  elaborate  processes  of 
washing  adopted  with  the  ores  of  lead  and  tin.  Galena  has  a 
specific  gravity  of  7‘6  ; tin-stone  of  about  7.  Sulphate  of  barimn 
has  a density  of  4*6  ; fluor-spar  of  3T  ; and  quartz  of  2'65.  'When 
reduced  to  particles  tolerably  uniform  in  size,  the  earthy  portions 
may  therefore  to  a considerable  extent  be  separated,  by  the  action 
of  water,  from  the  ores  of  lead  and  tin. 

The  following  is  an  outline  of  the  mechanical  operations  pur- 
sued in  dressing  the  ores  of  lead  and  tin ; and  the  same  method  is 
to  a certain  extent  adopted  with  the  copper  ores : — 

The  ore  haviug  been  brought  to  the  surface,  if  a lead  or  cop- 
per ore,  is  first  sorted  by  hand  : the  purest  portions,  or  prills.,  as 
the  Cornish  miners  term  them,  are  set  aside,  and  are  ready  for 


WASHING  THE  OKES — THE  HUDDLE. 


285 


smelting  without  further  preparation ; hut  the  hulk  of  the  ore  is 
broken  by  hammers  into  lumps  of  about  the  size  of  a walnut,  and 
the  best  pieces  are  again  picked  out  by  hand.  The  rougher  por- 
tions go  to  the  crushing  mill,  which  consists  of  a pair  of  horizontal 
cylinders  placed  parallel  to  each  other  at  a little  distance  apart : 
the  cylinders  may  be  either  grooved  or  plain.  The  ore  is  supplied 
to  them  by  a hopper  from  above.  After  passing  through  the  mill, 
the  crushed  ore  is  sifted  through  coarse  sieves  ; the  coarser  parts 
are  set  aside  for  the  stampers,  and  the  finer  portion  is  subjected  to 
the  operation  oi  jigging.  This  consists  in  plunging  the  ore  con- 
tained in  a sieve  into  a pit,  through  which  water  is  constantly 
flowing;  the  workman  keeps  the  ore  in  continual  agitation,  alter- 
nately raising  and  lowering  the  sieve,  to  which  he  also  gives  an 
alternate  rotatory  motion,  taking  care  always  to  keep  it  beneath 
the  surface  of  the  water.  By  this  means,  the  contents  of  the  sieve 
are  separated  into  layers  of  different  quality.  If  it  be  a lead  ore 
which  is  undergoing  treatment,  the  galena,  from  its  friable  charac- 
ter, is  easily  reduced  to  small  fragments : most  of  the  galena, 
therefore,  passes  through  the  sieve  and  subsides  to  the  bottom  of 
the  pit,  whilst  what  is  left  upon  the  sieve  consists  chiefly  of  the 
less  friable  fluor-spar  and  quartz.  This  residue  is  mixed  with  the 
inferior  qualities  of  ore,  and  is  transferred  to  the  stamping  mill, 
whilst  the  richer  part  is  set  aside  for  smelting. 

Tin  ore  is  usually  disseminated  through  a compact  hard 
matrix,  and  passes  at  once  to  the  stampers. 

The  stamping  mill  consists  of  five  or  six  upright  wooden  beams, 
tlie  lower  ends  of  which  are  shod  with  iron,  each  beam  weighing 
about  2^  cwt.  These  are  placed  in  a wooden  frame,  and  are 
alternately  lifted  up  and  allowed  to  fall  back  upon  the  ore  by  the 
action  of  arms  projecting  from  a horizontal  axle,  which  is  turned 
by  water  or  steam  power.  The  ore  is  placed  on  an  inclined  plane 
behind  the  stampers,  and  slides  down  under  them,  and  is  crushed. 
The  crushed  particles,  when  reduced  to  a sufficient  degree  of  fine- 
ness, are  washed  out  through  a grating  in  front,  by  the  action  of 
a current  of  water  which  is  constantly  flowing  through  the  mill ; 
the  washed  ore  is  carried  into  a channel  in  which  two  pits  are 
formed  ; in  the  one  nearest  the  mill  the  purer  and  heavier  part 
of  the  ore,  or  cvop^  is  deposited ; whilst  the  more  finely  divided 
portion,  technically  termed  slime  or  schlich^  accumulates  in  the 
second. 

The  crushed  ore  now  undergoes  a series  of  washings,  the  object 
of  which  is  to  separate  the  impurities  from  the  valuable  part  of 
the  ore. 

The  crop  is  first  subjected  to  wasliing  in  the  huddle  j tliis  is 
a wooden  trough,  fig.  327,  about  8 feet  long,  3 wide,  and  2 dee}>, 
fixed  in  the  ground,  with  one  end  somewhat  elevated.  At  the 
upper  end,  a small  stream  of  water  enters,  and  is  reduced  to  a 
uniform  thin  sheet  by  means  of  a distributing  board,  a,  on  which 
a number  of  small  pieces  of  wood  are  fastened  to  break  the 
stream.  The  ore  to  be  washed  is  placed  in  small  quantities 
at  a time  upon  a board,  b,  somewhat  more  inclined  tlian  the  body 


286 


WASHING  THE  ORES VANNING. 


of  the  huddle,  and  it  is  spread  ont  into  a thin  layer ; the  water 


carries  it  forward : the  richer 
portions  subside  near  the 
head  of  the  trough,  and 
the  lighter  ones  are  carried 
further  down.  ‘ The  heads  ’ 
are  then  tossed  in  the  Meve^ 
or  tub,  shovTi  at  c,  which  is 
filled  with  water,  and  ore 
added  by  a workman,  who 
keeps  the  contents  of  the 
kieve  in  continual  agitation 
by  turning  the  paddle  or 
agitator,  the  handle  of  which 
is  seen  projecting  at  the  top. 
When  the  vessel  is  nearly 
full,  the  agitation  is  stopped 
— the  kieve  is  struck  smart- 


Fig.  32*7. 


^ ly  upon  the  side  several 
times,  and  its  contents  are 
allowed  to  subside ; the  up- 


per half  of  the  sediment  is  again  passed  through  the  huddle. 
Various  modifications  of  the  washing  process  are  resorted  to,  but 
they  are  all  the  same  in  principle. 

A rough  estimate  of  the  value  of  any  sample  of  dressed  ore  is 
obtained  b^y  the  process  called  vanning : — A small  quantity  of  the 
ore  is  placed  on  a shovel,  and  agitated  gently  with  a peculiar  cir- 
cular movement  in  water,  then,  by  giving  it  a dexterous  lateral 
shake,  the  different  constituents  arrange  themselves  according  to 
their  density — the  galena,  or  the  tin-stone,  at  the  bottom ; above 
this  are  iron  pyrites  and  blende ; and  at  the  top  are  the  fluor-spar 
and  quartz.  The  eye  then  at  a glance  rouglily  estimates  the 
quantity  of  each. 

The  water  employed  in  the  various  washings  is  not  allowed  at 
once  to  run  to  waste,  but  is  made  to  pass  through  a long  shallow 
channel,  in  which  the  slime  and  mud  which  have  been  carried 
away  in  the  different  operations  may  subside.  This  slime  still 
retains  some  portion  of  ore ; and  in  order  to  recover  this  as  far  as 
possible,  it  is  again  subjected  to  the  action  of  a fine  stream  of 
water,  either  upon  an  inclined  table,  which  acts  in  a manner 
similar  to  the  huddle, — or  it  is  washed  upon  a swinging  table,  the 
bed  of  which  is  also  inclined,  but  moveable,  and  is  suspended  by 
Ciiains  from  supports  at  the  four  corners ; the  bed  is  alternately 
thrust  forward  two  or  three  inches  by  the  revolution  of  a cam- 
wheel,  and  is  then  allowed  to  fall  back  against  solid  wooden 
bearings  with  a sudden  jar.  The  ore  is  spread  upon  a board 
which  overhangs  the  upper  part  of  this  table,  and  carried  forward 
by  a gentle  stream  of  water ; the  heavier  particles  of  the  ore, 
owing  to  the  superior  momentum  which  their  density  gives  them, 
are  by  this  jarring  movement  of  the  table  carried  back  to  the 
upper  part  of  it,  whilst  the  lighter  impurities  are  washed  away. 


ROASTING,  OR  OXIDATION. 


287 


(530)  Roasting^  or  Oxidation. — The  chemical  operations  are 
divisible  into  two  main  branches,  one  dependent  on  the  addition, 
the  other  on  the  removal,  of  oxygen.  If  the  mineral  contain 
volatile  ingredients,  such  as  snlphnr  or  arsenic,  the  process  of 
roasting^  or  oxidation,  is  first  resorted  to.  In  principle  it  is  very 
simple ; the  mode  of  effecting  it  varies,  however,  in  difierent  cases. 
In  the  most  common  method,  a furnace  of  particular  construction, 
termed  a reverl)eratory.^  is  employed.  Fig.  328  shows  a section  of 


Fig.  328. 


a reverberatory  furnace,  such  as  is  employed  for  roasting  copper 
ores ; t is  the  platform,  from  which  the  hoppers,  h,  h,  are  charged 
with  the  ore,  which  at  proper  intervals  is  allowed  to  fall  upon  the 
bed,  c G : the  fuel  is  consumed  upon  a distinct  hearth,  a,  and  does 
not  come  into  contact  with  the  ore,  from  which  it  is  separated  by 
the  bridge,  h : the  heated  gases,  as  they  arise  from  the  burning 
mass,  are,  from  the  construction  of  the  arched  roof,  reverberateil, 
or  driven  down  upon  the  ore  to  be  roasted,  and  then  pass  off 
through  the  flue  f\  when  sufficiently  roasted,  the  ore  is  allowed 
to  fall  into  the  arched  recess,  e,  beneath  the  bed  of  the  furnace 
through  openings,  <^,  which  are  kept  closed  by  sliding  plates  till 
the  roasting  is  complete.  After  the  fire  has  been  lighted,  a con- 
stant supply  of  air  to  the  mineral  is  maintained,  and  care  is  taken 
to  prevent  the  heat  from  rising  so  high  as  to  melt  the  ore,  which 
is  stirred  at  intervals  to  expose  fresh  surfaces  to  the  action  of  the 
air : the  sulphur  burns  off  in  the  shape  of  sulphurous  anhydride, 
which  escapes  into  the  atmosphere ; whilst  the  arsenicum  forms 
arsenious  anhydride,  which,  though  volatile,  speedily  becomes  con- 
densed, and  is  collected  on  the  sides  of  the  chimney,  or  else  in 
chambers  constructed  for  its  reception,  whence  it  is  removed  at 
intervals,  and  subsequently  purified.  In  metallurgic  operations 
where  sulphides  of  metals  of  different  degrees  of  oxidability  are 
present,  it  may  happen  that  the  sulpliide  of  the  more  oxidizable 
metal  is  completely  converted  into  a metallic  oxide,  wliilst  sul- 
phurous anhydride  escapes,  and  that  the  sulphide  of  the  less  oxi- 
dizable metal  is  reduced  to  the  metallic  state.  For  example,  in 
roasting  copper  pyrites  (the  mixed  sulphides  of  copper  and  iron), 
the  iron  is  wholly  converted  into  oxide,  whilst  the  copper  is  ex- 
tracted at  once  in  the  metallic  state,  by  a series  of  careful  roast 


288 


EEDUCTION,  OK  SMELTIXG. 

ings  (870).  In  the  case  of  sulphide  of  lead,  where  the  metal 
possesses  but  a moderate  degree  of  oxidability,  it  is  also  the  prac- 
tice so  to  regulate  the  supply  of  air  in  the  furnace  that  the 
sulphur  is  wholly  expelled  in  the  oxidized  condition,  whilst  the 
greater  part  of  the  lead  is  extracted  in  the  form  of  metal  dm-ing 
a single  roasting  in  the  reverberatory  (890).  Where  the  metal 
possesses  a high  degree  of  oxidability,  as  is  the  case  with  zinc,  it 
is  not  practicable  to  limit  the  degree  of  oxidation  in  this  manner 
during  the  roasting : the  metal  itself  passes  into  a state  of  oxide, 
simultaneously  with  the  expulsion  of  the  sulphur  as  sulphurous 
anhydi’ide  (702). 

(531)  Reduction^  or  Smelting. — The  second  chemical  process 
for  the  extraction  of  the  metals,  that  of  reduction.^  is  applicable  to 
most  metallic  oxides,  whether  of  natural  or  of  artificial  origin. 
The  object  in  this  case  is  to  remove  the  oxygen,  by  presenting  to 
the  mineral  some  body  which,  at  a high  temperature,  has  a stronger 
attraction  for  oxygen  than  the  metal  itself  possesses.  The  fur- 
naces employed  in  this  operation  are  often  of  great  size,  and  vary 
in  form  with  the  nature  of  the  metal : in  them  the  ore  is  heated 
intensely,  in  contact  with  carbon ; carbonic  oxide  and  carbonic 
anhydride  are  thus  produced,  and  from  their  gaseous  nature  are 
quickly  removed  from  the  sphere  of  action.  It  becomes  necessary 
at  this  stage  to  get  rid  completely  of  the  earthy  and  other  impuri- 
ties of  the  ore,  which  the  mechanical  operations  never  succeed  in 
removing  entirely,  and  which  often  form  a large  proportion  of  the 
ore.  In  order  to  effect  this,  certain  fluxes,  or  substances  which 
are  capable  of  forming  fusible  compounds  with  the  earthy  mat- 
ters, are  added  at  the  same  time  with  the  carbon ; these  melt  and 
form  a kind  of  glass,  through  which  the  reduced  metal,  from 
superior  density,  sinks,  and  is  thus  completely  defended  from  con- 
tact with  the  air : the  metal  is  at  suitable  intervals  drawn  off*  fr*om 
the  bottom  of  the  furnace,  while  the  melted  glass — or  slag.,  as  it 
is  termed — runs  off  at  an  aperture  left  in  the  side  for  the  purpose. 
Limestone  is  in  some  cases  added  to  the  ore,  with  the  view  of 
aiding  the  fusion  of  the  siliceous  impurities : in  other  instances 
fluor-spar  or  some  other  readily  fusible  material  is  added,  for  the 
purpose  of  increasing  the  fluidity  of  the  slag.  Much  judgment  is 
required  in  the  selection  of  the  flux,  and  in  deciding  upon  the 
proper  proportion  to  be  added : frequently  this  object  is  economi- 
cally eftected  by  a judicious  mixture  of  different  ores  of  the  same 
metal,  each  of  which  aids  the  other  by  supplying  some  compound 
which  was  wanting  to  render  the  slag  sufficiently  fusible. 

The  various  modiflcations  of  these  processes  will  be  described 
as  they  present  themselves  in  connexion  with  the  different  metals 
which  require  these  modiflcations.  Other  modes  of  separating 
indi\ddual  metals  are  employed,  which  will  be  alluded  to  in  their 
respective  places.  For  details  upon  metallurgic  processes,  Percy’s 
Jfetallurgy,  or  the  fourth  volume  of  Dumas’  valuable  work,  Traite 
de  Chimie  applignee  aux  Arts.,  may  be  consulted  ; and  the  second 
and  third  volumes  of  the  same  work  contain  many  excellent  de- 
scriptions of  processes  in  which  metallic  chemistry  is  applied  to 


CLASSIFICATION^  OF  THE  METALS. 


289 


the  purposes  of  industry  and  commerce.  Phillips’s  Metallurgy 
is  a smaller  and  more  compendious  treatise  on  this  subject. 

(532)  Classification  of  the  Metals. — The  metals  may  be  divided 
into  eight  groups  (page  8),  regard  being  principally  had  in  this 
arrangement  to  the  convenience  of  indicating  the  method  of  test- 
ing for  the  presence  of  the  metal,  in  the  ordinary  processes  of 
analysis,  in  consequence  of  which  it  is  sometimes  necessary  to 
depart  from  the  strictly  natural  order. 

In  treating  of  the  groups  of  the  non-metallic  and  electro- 
negative elements,  it  has  been  remarked  that  the  electronegative 
character  of  those  belonging  to  the  same  group  is  most  strongly 
marked  in  those  which  have  the  lowest  combining  number ; chlo- 
rine, for  example,  being  more  active  than  bromine,  and  bromine 
than  iodine.  With  the  basylous  or  electropositive  elements,  the 
reverse  generally  holds  good ; the  basic  power  of  rubidium,  for 
example,  being  greater  than  that  of  potassium,  that  of  potassium 
greater  than  that  of  sodium,  and  that  of  sodium  being  superior 
to  the  basic  power  of  lithium. 

I.  The  metals  of  the  alkalies ; these  are  five  in  number — viz., 

1.  Potassium  2.  Sodium  3.  Lithium 

4.  Coesium  5.  Rubidium. 

These  metals  present  a close  analogy  in  properties : sodium, 
which  is  intermediate  in  properties  between  potassium  and  lithi- 
um, possesses  a combining  number  which  is  the  arithmetic  mean 
of  the  two  for  In  like  manner  the  atomic  weight  of 

rubidium  (85 ’3)  is  intermediate  between  that  of  coesium  and 
potassium  1 3_3^+.3.9. — §0^  similar  remark  is  applicable  to  the 
intermediate  member  of  some  of  the  other  groups. 

The  corresponding  salts  formed  by  the  metals  of  the  alkaline 
group  are  isomorphous  only  when  they  contain  equal  atomic  pro- 
portions of  water  of  crystallization.  With  these  metals  will  be 
described  the  salts  of  ammonium  ; they  are  isomorphous  with  the 
salts  of  potassium,  and  indeed  present  the  closest  analogy  with 
them.  r 

The  metals  of  the  alkalies  are  distinguished  by  the  following 
characters  : — They  are  monad  or  uniequivalent,  and  displace 
therefore  1 atom  of  hydrogen  from  the  acids.  They  are  soft, 
easily  fusible,  and  volatile  at  high  temperatures  ; they  have  an 
intense  attraction  for  oxygen,  and  become  tarnished  immediately 
tliat  they  are  exposed  to  the  air  : when  thrown  upon  water  they 
decompose  it  at  all  temperatures  with  rapid  disengagement  of 
hydrogen  : they  each  form  at  least  two  oxides,  but  only  one  of 
these,  that  with  tlie  smallest  proportion  of  oxygen,  forms  salts : 
the  general  formula  of  this  basic  oxide  is  These  liasic 

oxides  combine  with  water  with  great  avidity,  yielding  soluble 
hydrates  of  the  general  formula  !MIIO ; their  aqueous  solutions 
are  powerfully  caustic  and  alkaline.  When  they  have  once  com- 
bined with  water,  the  compound  thus  obtained  cannot  be  rendered' 
anhydrous  by  heat  alone.  In  these  metals  the  basylous  quality, 
or  their  capacity  for  saturating  the  acids,  is  developed  to  the* 
19 


290 


CLASSIFICATIOX  OF  THE  METALS. 


highest  degree.  The  hydrated  alkalies,  when  exposed  to  the  air, 
either  in  the  solid  form  or  in  solution,  absorb  carbonic  acid 
rapidly : each  alkali  forms  with  this  acid  two  salts,  a normal 
carbonate  and  an  acid  carbonate  commonly  known  as  the  bicar- 
bonate, both  of  which  are  freely  soluble  in  water.  The  metals  of 
the  alkalies  combine  with  sulphur  in  several  proportions  ; all  of 
these  compounds,  also,  are  soluble.  With  chlorine  they  form  but 
a single  chloride  ; but  their  oxides  have  the  power  of  combining 
with  chlorine,  and  forming  compounds  possessed  of  bleaching 
properties.  Lithium,  from  the  sparing  solubility  of  its  carbonate, 
forms  the  connecting  link  between  this  group  and  the  one  which 
follows  it. 

II.  The  metals  of  the  alkaline  earths  are  three  in  number — 
yiz., 

1.  Barium  | 2.  Strontium  | 3.  Calcium. 

These  metals  are  dyad,  or  biequivalent,  1 atom  usually  displacing 
2 atoms  of  hydrogen  from  its  combinations.  They  decompose 
water  at  all  temperatures  with  great  rapidity  ; with  the  exception 
of  barium,  they  each  form  but  one  oxide,  and  this  oxide  combines 
with  water  with  avidity,  but  the  hydrate  may  be  decomposed  by 
ignition.  The  hydrated  oxide  is  soluble  to  a certain  extent  in 
water,  and  is  capable  of  forming  salts  by  its  reaction  upon  acids. 
They  each  furnish  but  one  chloride,  which  assumes  the  form  of 
Is  "Clj.  The  metals  of  this  group  are  also  powerfully  basylous. 
They  form  several  sulphides  which  are  soluble  in  water  ; the  pro- 
tosulphides being  less  so  than  those  which  contain  higher  propor- 
tions of  sulphur.  With  chlorine  their  oxides  form  bleaching 
compounds.  Their  carbonates  are  insoluble  in  pure  water,  but 
are  soluble  to  a small  extent  in  water  charged  with  carbonic  acid. 
They  form  insoluble  phosphates  and  oxalates.  The  corresponding 
salts  of  these  metals  are  in  many  cases  isomorphous. 

III.  Metals  of  the  eaidhs ; ten  in  number — viz., 


1.  Aluminum 

2.  Glucinum 

3.  Zirconimn 

4.  Thorinum 


I 5.  Yttrium 

I 6.  Erbium 

' 7.  Terbium 


8.  Cerium 

9.  Lanthanum 
10.  Didymium. 


The  oxides  of  this  class  are  insoluble  in  water  ; several  of  them 
are  dissolved  by  solutions  either  of  the  caustic  alkalies  or  of  their 
carbonates.  The  phosphates  of  this  group  are  insoluble  in  water. 
Aluminum  and  glucinum  do  not  decompose  water  at  ordinary 
temperatures  unless  the  metals  are  in  a very  finely  divided  state  : 
the  other  metals  of  this  group  are  scarcely  known  in  an  isolated 
form.  The  basylous  character  of  this  group  of  metals  is  much 
less  marked  than  that  of  the  preceding  ones.  When  salts  of  these 
metals  in  solution  are  mixed  with  sulphide  of  ammonium,  preci- 
pitates consisting  of  hydrated  oxides  instead  of  sulphides  are 
formed,  whilst  sulphuretted  hydrogen  escapes.  Many  of  these 
metals  are  very  rare,  and  their  properties  have  been  but  imper- 
fectly examined.  Zirconium  is  closely  allied  to  silicon.  Alunii- 


CLASSIFICATION  OF  THE  METALS. 


291 


niim,  by  the  isomorphism  of  its  oxide  with  sesqiiioxide  of  iron, 
the  volatility  of  its  chloride,  its  slight  attraction  for  carbonic  acid, 
and  other  peculiarities,  connects  this  group  with  the  group  of  iron 
metals. 

TY.  Magnesian  metals,  three  in  number : — 

1.  Magnesium  | 2.  Zinc  | 3.  Cadmium. 

Magnesium  is  usually  reckoned  as  one  of  the  metals  of  the 
alkaline  earths  ; but  from  its  power  of  resisting  oxidation  at  the 
ordinary  temperature  of  the  air,  its  volatility  at  high  tempera- 
tures, the  isomorphism  of  its  salts  with  those  of  zinc,  the  sparing 
solubility  of  its  oxide  and  its  sulphide,  the  solubility  of  its  sulphate, 
and  several  other  particulars,  it  stands  in  closer  relation  to  zinc 
and  cadmium.  Magnesium,  zinc,  and  cadmium  are  dyads ; they 
all  burn  with  dame  when  heated  in  air  to  a sufficiently  high  tem- 
perature, and  each  of  these  metals  forms  but  a single  oxide,  chlo- 
ride, and  sulphide,  as  well  as  but  a single  class  of  salts  with  the 
radicles  of  the  acids. 

Y.  Metals  more  or  less  analogous  to  iron ; six  in  number : — 


1.  Cobalt 

2.  Nickel 

3.  Uranium 


4.  Iron 

5.  Chromium 

6.  Manganese. 


They  are  all  dyads  or  biequivalent  metals.  These  metals,  when 
heated  to  dull  redness,  decompose  the  vapour  of  water  if  it  be 
transmitted  over  them,  and  become  converted  into  oxides,  whilst 
hydrogen  escapes : they  are  also  soluble  with  effervescence  and 
evolution  of  hydrogen  in  diluted  sulphuric  or  in  hydrochloric 
acid.  The  protoxides  of  these  metals  are  powerful  bases : they 
have  the  general  formula  N'^O.  They  yield  hydrates,  usually  of 
the  form  N'^0,H20-,  and  lose  their  water  readily  when  heated. 
These  protoxides,  with  the  exception  of  that  of  uranium,  are 
dissolved  more  or  less  freely  by  ammonia,  especially  if  chloride 
of  ammonium  be  present  in  the  solution.  Each  of  the  metals  of 
this  group  forms  a sesquioxide,  which,  excepting  in  the  case 
of  those  of  cobalt  and  nickel,  reacts  with  acids  and  forms  corre- 
sponding salts : they  also  form  an  oxide  of  the  form  N0,N203 
corresponding  with  the  magnetic  oxide  of  iron  (Ee0,Ee203). 
Several  of  the  metals  of  this  group — viz.,  iron,  chromium,  and 
manganese — form  teroxides  or  even  higher  oxides,  which  are 
very  soluble  in  water,  and  furnish  powerful  metallic  acids.  Hy- 
drated sulphides  of  these  metals  are  produced  by  the  addition  of 
a solution  of  sulphide  of  potassium  or  of  ammonium  to  a solution 
of  their  salts  ; the  precipitate  so  occasioned  is  insoluble  in  excess 
of  the  alkaline  sulphide.  The  chromic  salts,  however,  are  preci- 
pitated as  hydrated  oxide  of  chromium,  not  as  sulphide.  Sul- 
phuretted hydrogen  gas,  when  transmitted  through  the  solutions 
of  these  metals  acidulated  with  sulphuric  acid,  occasions  no  pre- 
cipitate of  sulphide,  excepting  in  the  case  of  the  salts  of  cadmium. 
Corresponding  salts  of  the  protoxides  of  this  group  are  isomor- 
phous : and  the  salts  formed  by  the  sesquioxides  with  the  same 


292 


CLASSIFICATION  OF  THE  METALS. 


acid  are  likewise  isomorphous  with  eacli  other.  Chromimn  and 
manganese  also  exhibit  an  isomorphous  relation  to  the  sulphur 
group,  inasmuch  as  the  corresponding  sulphates,  chromates,  and 
manganates  have  the  same  crystalline  form.  In  the  case  of  man- 
ganese a singular  connexion  with  the  halogens  is  exhibited  in  the 
isomorphism  of  the  permanganates  with  the  corresponding  per- 
chlorates and  periodates. 

YI.  Metals  which  yield  powerful  acids  when  their  higher 
oxides  are  combined  with  water ; of  these  there  are  ten,  as  fol- 
low : — viz.. 


1.  Tin 

2.  Titanium 

3.  niobium 

4.  Tantalum 


5.  Molybdenum 

6.  Tungsten 

7.  Yanadium 


8.  Arsenic 

9.  Antimony 

10.  Bismuth. 


The  first  four  of  these  metals  are  biequivalent  or  dyads  under 
certain  circumstances,  but  tetrad  or  quadrequi valent  in  other 
more  usual  cases  ; the  next  three  are  sometimes  tetrads,  but  often 
liexads,  or  equivalent  to  six  atoms  of  hydrogen  ; whilst  the  last 
three,  though  usually  triads,  are  occasionally,  as  in  pentachloride 
of  antimony,  pentad  or  quinquequivalent. 

A close  parallelism  in  properties  exists  between  tin  and  tita- 
nium, corresponding  compounds  such  as  tinstone  (Sn02)  and 
rutile  (TiO^)  being  isomorphous ; they  each  yield  a liquid  volatile 
perchloride,  and  in  this  particular,  as  well  as  in  their  powerful 
attraction  for  fiuorine,  they  exhibit  considerable  analogy  with 
silicon : columbium  and  tantalum  also  a're  similarly  related  to 
each  other,  and  to  silicon  ; they  both  furnish  an  anhydride  with 
2 atoms  of  oxygen,  form  a volatile  tetrachloride,  and  yield  definite 
compounds  with  fiuorine.  Molybdenum,  vanadium,  and  tungsten, 
have  likewise  certain  analogies  with  each  other,  but  they  are  less 
strongly  marked ; and  the  properties  of  vanadium  are  not  truly 
intermediate  between  those  of  molybdenum  and  tungsten. 

Protoxide  of  tin  is  a powerful  base,  but  basic  qualities  are 
nearly  wanting  in  the  oxides  of  the  other  metals  in  this  group. 
The  metals  included  in  this  class  decompose  water  when  its 
vapour  is  driven  over  them  at  a red  heat  (with  the  exception  of 
arsenic,  which  is  more  allied  in  character  to  phosphorus  than  to  the 
metals),  but  they  do  not  evolve  hydrogen  when  treated  with 
diluted  sulphuric  acid,  owing  to  their  want  of  basylous  power. 
Many  of  them,  owing  to  this  tendency  to  form  acids,  decompose 
water  with  evolution  of  hydrogen  in  the  presence  of  a powerful 
base,  such  as  potash.  The  metallic  acids  formed  by  these  metals 
are,  with  the  exception  of  arsenic  acid,  nearly  insoluble  in  water. 
The  persulphides  of  this  group  of  metals  are  soluble  in  the  sul- 
phides of  the  alkaline  metals,  and  in  many  cases  form  crystalliza- 
ble  compounds  with  them. 

YII.  The  next  group  contains  but  three  metals : — viz., 

1.  Copper  I 2.  Lead  | 3.  Thallium. 


THE  OXIDES. 


293 


They  are  not  related  to  each  other  by  any  strong  chemical  resem- 
blances ; copper  and  lead  exert  no  decomposing  action  npon 
water,  even  at  a full  red  heat ; all  form  powerfully  basic  oxides. 
Copper  and  lead  exhibit  a considerable  tendency  to  the  formation 
of  subsalts  ; they  are  not  dissolved  by  either  diluted  sulphuric  or 
hydrochloric  acid ; they  are  precipitated  from  acid  solutions  by 
sulphuretted  hydrogen,  and  their  sulphides  do  not  combine  with 
the  sulphides  of  the  alkaline  metals.  In  the  case  of  thallium  the 
precipitation  is  incomplete  ; copper  forms  salts  which  are  isomor- 
phous  with  those  derived  from  the  protoxides  of  the  metals  in  the 
iron  group,  and  in  the  compounds  which  it  forms  Avith  carbonic 
' acid  displays  a close  correspondence  with  magnesium  and  zinc,  as 
Avell  as  with  cobalt  and  nickel ; and  lead  in  some  of  its  compounds 
is  isomorphous  with  those  of  the  alkaline  earths,  but  in  chemical 
properties  it  is  more  allied  to  mercury  and  silver.  Thallium  is 
uniequivalent,  copper  is  so  occasionally,  as  in  the  subchloride,  but 
in  the  majority  of  cases,  it,  like  lead,  is  biequivalent. 

YIII.  The  last  group  consists  of  the  noble  metals,  of  which 
there  are  nine — viz.. 


1.  Mercury 

2.  Silver 

3.  Gold 


4.  Platinum 

5.  Palladium 

6.  Phodium 


7.  Puthenium 

8.  Osmium 

9.  Iridium. 


These  metals  are  unable  to  decompose  water  at  any  temperature. 
They  have  but  a feeble  attraction  for  oxygen  ; the  oxides  of  the 
first  five  being  decomposed  below  a red  heat,  the  metal  remaining 
in  an  uncombined  form  ; and  in  many  cases  simple  exposure  to  a 
strong  light  produces  a similar  decomposition  : all  of  them  yield 
more  than  one  series  of  salts.  Mercury  and  silver  are  often  found 
mineralized  in  the  form  of  sulphides,  but  the  other  metals  of  this 
group  usually  occur  in  the  native  state,  several  of  them  being  fre- 
quently associated  together.  Their  attraction  for  sulphur  and  for 
chlorine  is  much  stronger  than  for  oxygen.  All  of  them  form  at 
least  two  chlorides,  and  some  three  or  even  four  : the  chlorides  of 
the  noble  metals  have  a strong  tendency  to  form  double  chlorides 
with  the  chlorides  of  the  metals  of  the  alkalies. 

Silver  exhibits  considerable  analogy  with  lead  : it  is  powerfully 
basylous  ; palladium  is  somewhat  allied  to  copper. 


§ II.  General  Properties  of  the  Compounds  of  the  Metals 

WITH  THE  NON-METALLIC  ElEMENTS. 


(533)  The  Oxides. — The  most  important  compounds  of  the 
metals  with  the  non-metallic  bodies  are  those  Avhich  tliey  form 
with  oxygen.  The  oxides  in  many  cases  constitute  abundant  and 
valuable  metallic  ores ; such  as  the  different  forms  of  haematite, 
the  specular  and  magnetic  iron  ores,  and  tinstone,  the  ordinary 
ore  of  tin. 

The  metallic  oxides  may  be  subdivided  according  to  their 
chemical  function  into  3 classes  : — viz.,  1,  basic  oxides  ; 2,  saline 
or  indifferent  oxides ; and  3,  metallic  anhydrides,  which  when 
hydrated  form  the  metallic  acids. 


294 


THE  OXroES. 


The  atomic  proportions  in  which  the  constituents  of  the  prin- 
cipal varieties  of  metallic  oxides  are  united  are  exhibited  in  the 
following  table : — 

1.  Suboxides,  of  Ijpo  5 feebly  basic,  such  as — 

Suboxide  of  copper  ^^Ou^O. 

2.  Monoxides,^  M'^O  or  ^”"0,  of  the  type  H^O ; strongly 
basic,  such  as — 

Oxide  of  silver  Ag'^O  | Lime  Oa^O. 

3.  Sesquioxides,  of  the  type  HgOg ; feebly  basic,  neutral, 

or  even  acid,  such  as — 

Alumina,  AL^'^^g 
Sesquioxide  of  uranium,  L-aOg 
Sesquioxide  of  cobalt,  Oo'^gOg 
Arsenious  anhydride,  As'^gOg. 

4.  Three-fourths  oxides,  of  the  type  HgO^ ; saline  oxides, 

such  as — 

Magnetic  oxide  of  iron,  Fe''(Fe''^)204,  or  Fe''0,Fe'"20g 
Chrome  ironstone,  Pe'^0,0r'"2^3- 

5.  Binoxides,  of  the  type  ; rarely  basic,  but 

generally  neutral  or  acid,  such  as — 

Binoxide  of  platinum, 

Binoxide  of  barium,  fiaO, 

Binoxide  of  tin,  Sn^^O^. 

6.  Teroxides,  E’^'^Og,  of  the  type  H^Og ; metallic  anhydrides, 
such  as — 

Molybdic  anhydride,  Mo'^Og 
Tungstic  anhydride,  W'^'Og. 

7.  Anhydrides,  B^O^,  of  the  type  HjgOg 

Arsenic  anhydride,  As^Og 
Antimonic  anhydride,  SbgOg. 

* These  oxides  may.  in  fact,  be  regarded  as  compounds  formed  upon  the  type  of 
a single  atom  of  water,  HHO,  if  each  atom  of  hydrogen  in  the  molecule  is  displaced 
by  an  atom  of  a metallic  monad,  such  as  potassium ; or  if  both  atoms  of  hydrogen  be 
displaced  by  a single  atom  of  a metallic  dyad,  such  as  barium,  we  have  an  analogous 
oxide ; for  example : — 

HHO,  water, 

KKO,  anhydrous  potash, 

Ba"0,  anhydrous  baryta ; 

but  if  only  one  atom  of  hydrogen  be  displaced  by  the  metallic  monad  we  have  a 
hydrate  of  the  metallic  oxide.  If  the  metallic  dyad  displaces  half  the  hydrogen  of  two 
atoms  of  water,  we  have  a hydrate  of  the  oxide  of  the  metallic  dyad,  as  for  instance 

V ) ^ lo 

^ O,  hydrate  of  potash  ; fia  , hydrate  of  baryta. 

^ ) H 

In  the  sesquioxides  and  teroxides  the  molecular  type  is  a group  consisting  of  three 
atoms  of  water,  each  atom  of  the  metal  representing  3 or  6 atoms  of  hydrogen  in  the 
combination ; alumina  being  and  its  normal  hydrate  (Ar")H303. 

The  binoxides  correspond  in  composition  to  a group  containing  2 atoms  of  water ; 
the  f oxides  to  a group  containing  4 atoms  of  water,  and  so  on,  as  indicated  in  the 
table. 


VAEIETIES  OF  THE  METALLIC  OXIDES. 


295 


The  oxides  constitute  so  important  a series  of  compounds,  that 
it  will  be  necessary  to  consider  their  relations,  particularly  to 
water  and  to  the  acids,  somewhat  more  in  detail,  classifying  them 
in  the  order  just  indicated. 

1.  Suboxides ^ of  the  type  — A few  of  the  dyad  metals, 

such  as  copper,  lead,  and  mercury,  form  oxides  in  which  1 atom 
of  the  metal,  which  usually  is  equivalent  to  two  atoms  of  hydro- 
gen, becomes  for  the  time  equivalent  only  to  a single  atom  of 
hydrogen.  Thus  we  have  the  cupreous  oxide,  or  red  oxide  of  cop- 
per (-Gu^O) ; mercurous  oxide,  or  black  oxide  of  mercury  (Hg^O) ; 
and  a suhoxide  of  lead  (Pb^O).  Though  each  of  these  oxides  gives 
rise  to  an  unstable  series  of  salts,  it  frequently  becomes  decom- 
posed into  the  normal  oxide  and  free  metal ; suboxide  of  copper, 
for  instance,  becomiim  converted  into  metallic  copper  and  the 
black  oxide,  Ou^O^^Ou-f-GuO ; but  with  hydrochloric  acid  the 
reaction  is  as  follows : Gu^G  -f-  2 IT  Cl  = H^G  + 2 GuCl.  Ho 
normal  hydrates  of  these  oxides  appear  to  exist,  the  suboxides  of 
mercury  and  lead  being  anhydrous,  and  the  yellow  hydrate  of 
cupreous  oxide  being  4 Gu2G,IT2G,  instead  of  GuTIG. 

2.  Monoxides^  of  the  type  M'^G,  or  H''G. — This  class  of  oxides 
includes  all  the  most  powerful  bases  : they  are  formed  by  the  union 
either  of  2 atoms  of  a metallic  monad  with  1 atom  of  oxygen,  or 
by  the  union  of  1 atom  of  a metallic  dyad  and  1 of  oxygen.  The 
first  subdivision  includes  the  five  alkalies  and  the  oxides  of  thal- 
lium and  silver.  Among  the  members  of  the  second  subdivision 
are  included  the  alkaline  earths,  the  oxides  of  lanthanum,  didy- 
mium,  magnesium,  zinc,  and  cadmium,  and  the  protoxides  of 
cerium,  uranium,  cobalt,  nickel,  iron,  chromium,  manganese,  tin, 
copper,  lead,  mercury,  and  palladium.  The  anhydrous  oxides  of 
the  alkali-metals  become  converted  into  hydrates  with  extrication 
of  intense  heat  on  the  addition  of  water,  which  dissolves  them 
rapidly  and  in  large  quantity,  one  atom  of  water  and  one  of  alkali 
yielding  two  atoms  of  the  hydrate  : e.g.^  KKG-1-HHG=:  2 KHG. 
The  hydrates  of  the  alkalies  cannot  be  again  decomposed  by  ex- 
posure to  heat,  but  are  slowly  volatilized  without  decomposition 
by  a prolonged  elevation  of  temperature.  Ho  definite  hydrate  of 
oxide  of  silver  is  as  yet  known,  though  it  is  soluble  in  a very  slight 
degree. 

The  action  of  water  upon  anhydrous  baryta,  strontia,  and  lime 
is  also  very  energetic,  a single  atom  of  the  hydrate  being  in  each 
case  formed  by  the  combination  of  single  atoms  of  water  and  the 
earth;  as,  for  instance,  GaG-f- IlaG^-fealTG^.  The  hydrate  of 
lime  requires  a full  red  heat  for  its  decomposition,  but  the  liydrates 
of  baryta  and  strontia  fuse  at  an  elevated  temperature,  and  do  not 
part  with  their  water  even  by  prolonged  ignition.  Tliese  hydrates 
are  soluble  in  water,  though  that  of  lime  is  but  sparingly  so. 
Magnesia  combines  very  slowly  with  water.  It  is  very  sparingly 
soluble ; the  oxides  of  lead  and  mercury  are  somewliat  more  solu- 
ble. The  other  oxides  above  enumerated  do  not,  wlien  anhydrous, 
combine  with  water  when  mixed  with  it.  Their  monohydrates 
may  usually  be  obtained  by  precipitating  a solution  of  one  of  their 


296 


VAKIETIES  OF  THE  METALLIC  OXIDES. 


salts  by  the  addition  of  a solution  of  one  of  the  alkalies  in  slight 
excess.  The  hydrated  oxide  of  copper  has  the  formula  OuO, 
2 H^O ; those  of  lead  and  tin  consist  of  2 PbOjH^O,  and  2 SnO, 
H,0. 

Most  of  the  monoxides,  by  their  reaction  with  the  ordinary 
acids,  form  salts  which  are  neutral  in  their  action  upon  test-paper. 
The  following  equations  may  be  taken  as  exemplifying  some  ordi- 
nary cases  of  the  action  of  acids  upon  these  oxides  and  their 
hydrates : — 

Ag,e  -}-  2 im03=  H3O  -f  2 AgNO, 

KHO  -f  HCl  = + KCl 

T1,0  -f-  2 HI  = + 2 Til 

■0aO  -f  HjSO^  = HjO  + OaSO^. 

3.  Sesquioxides,  of  the  type  — Most  of  the  oxides  of 

this  class  are  feeble  bases  ; among  them  are  included  alumina,  and 
the  sesquioxides  of  cerium,  uranium,  iron,  manganese,  chromium, 
antimony,  and  bismuth.  They  furnish  salts  when  acted  upon  by 
acids,  but  all  these  salts  redden  litmus : usually  3 atoms  of  water 
are  separated  by  the  reaction  of  the  base  upon  the  acid  ; as,  for 
instance, 

OrgOg  + 6 HCl  =3  HgO  -f  OrgClg 
FegOg  + 3 HgSO^^  3 HgO  -f-  Fe23  SOy 

The  oxides  of  iron,  antimony,  and  aluminum,  occasionally,  and 
the  oxide  of  uranium  invariably,  however,  form  salts,  with  the 
elimination  of  1 atom  of  water  only,  two-thirds  of  the  oxygen  re- 
maining in  a state  apparently  of  intimate  combination  with  the 
metal : for  instance  : — 

HgOg  + 2 HCl=Hge  -f-  (H,e)Cly 

Sesquioxides  of  cobalt  and  nickel  exhibit  no  tendency  to  form 
salts  by  reaction  either  with  acids  or  bases.  When  heated  with 
hydrochloric  acid,  they  evolve  chlorine  and  furnish  a lower  chlo- 
ride ; no  chloride  corresponding  to  these  sesquioxides  is  known  : — 

eoA+6,nci=2  Oocig+cig-f  3 ha 

Sesquioxide  of  arsenic  possesses  no  basic  properties,  but  when  dis- 
solved in  water  is  feebly  but  decidedly  acid  ; the  sesquioxide  of 
gold  is  insoluble  in  water,  but  its  hydrate  (H^O, AuA?  or  AuHOg) 
presents  the  properties  of  an  acid,  though  they  are  but  feebly 
marked. 

The  basic  sesquioxides  have  but  a feeble  attraction  for  water ; 
when  precipitated  by  alkaline  solutions  from  the  solutions  of  their 
salts,  they  furnish  very  bulky  gelatinous  precipitates,  which  easily 
lose  water  during  drying. 

4.  Three-fourths  '^Oxides^  of  the  type  HgO^  or  As- — 

These  oxides  do  not  form  salts  with  acids,  being  probably  com- 
pounds of  a protoxide  with  a sesquioxide,  into  the  compounds 
corresponding  to  which  they  are  resolved  by  the  action  of  acids  ; 
as  for  instance:  PegO,-f8  HCl=FeClg  + Fe2Clg-t-4  HgO.  Mag- 
netic oxide  of  iron  FogO^  or  FeO,FegOg,  is  the  best  representative 


VARIETIES  OF  THE  METALLIC  OXIDES. 


297 


of  tlie  class,  which  is  rather  numerous,  and  includes  correspond- 
ing oxides  of  chromium,  uranium,  manganese,  nickel,  and  cobalt, 
besides  the  double  oxides,  chrome  ironstone,  FeO,-0r2O3 ; spinelle, 
MgOAl^Og ; gahnite,  Zn0,Al203. 

5.  B inoxides  of  the  type  or 

Of  these  there  are  three  distinct  varieties. 

The  first  variety  comprises  the  basic  oxides,  of  winch  the  bin- 
oxides  of  platinum  (PtO^)  and  palladium  are  the  most  important : 
they  are  feeble  bases,  and  with  water  form  hydrates,  such  as  (Ft 
2 H,0). 

The  second  variety  is  represented  by  the  peroxides  of  sodium 
(Na^O^)  and  silver  (Ag^O^),  and  those  of  barium  (fiaO^),  mangan- 
ese, and  lead.  These  oxides  do  not  form  corresponding  salts  with 
acids,  nor  do  the}^  yield  corresponding  chlorides : they  retain  the 
second  atom  of  oxygen  but  feebly.  When  heated  with  oil  of  vit- 
riol they  give  off  oxygen,  and  form  a sulphate  corresponding  to 
the  protoxide  ; 2 Mn*^2  -f  2 = 2 MnSO^  -f  + 2 H^O.  When 

treated  with  hydrochloric  acid  they  either  furnish  peroxide  of  hy- 
di’ogen  or  liberate  chlorine  and  form  water ; for  example 

1.  Bae3  + 2HCl=BaCl,  + HA; 

2.  MnO^-f^  HCl=MnCl3  + 2 K.O+Cl,. 

Of  these  oxides  some,  as  those  of  potassium  and  sodium,  are  de- 
composed with  evolution  of  oxygen  when  thrown  into  water ; per- 
oxide of  barium  forms  the  hydrate  (BaO^,  6 H^O)  ; whilst  the  per- 
oxides of  manganese,  lead,  and  silver  do  not  become  hydrated, 
the  three  oxides  last  mentioned  conduct  the  voltaic  current : 
peroxide  of  lead,  indeed,  exhibits  some  properties  of  a metallic 
anhydride,  and  when  fused  with  the  hydrated  alkalies  furnishes 
compounds  known  as  plumbates,  whilst  water  is  evolved ; 2 KHO 
+Pbe,=rK,Pb^3-t-HA 

In  the  third  variety  of  binoxides  the  character  of  the  metal- 
lic anhydrides  is  distinctly  marked  ; such,  for  example,  as  the 
stannic  anhydride  SnO^,  and  the  titanic,  niobic,  and  tantalic 
anhydrides,  with  which  silica  and  zirconia  ought  also  to  be 
classed  ; these  oxides  do  not  unite  with  water  when  placed  in  con- 
tact with  it,  but  yield  hydrates  possessed  of  feebly  marked  acid 
characters  when  precipitated  with  due  precautions  from  their  com- 
binations. For  each  of  these  binoxides  a corresponding  chloride, 
containing  4 atoms  of  chlorine,  may  be  obtained. 

6.  Ter  oxides^  of  the  type 

This  class  includes  the  metallic  anhydrides  in  which  the  acid 
property  is  most  strongly  developed ; such,  for  example,  as  chromic, 
vanadic,  molybdic,  tungstic,  and  ruthenic  anhydrides.  Although 
the  ferric  and  manganic  anhydrides  have  not  been  isolated,  their 
place  is  obviously  in  this  group.  The  molybdic,  tungstic,  and 
ruthenic  anhydrides  are  insoluble  in  water. 

7.  A nhydrides^  of  the  type  B''203. 

Arsenic  and  antirnonic  anhydrides,  AsA  SbA  the 
representatives  of  this  group  of  oxides  : when  combined  with  water 
they  furnish  well-marked  metallic  acids.  Arsenic  anhydride  is 


298 


GENERAL  PROPERTIES  OF  THE  OXIDES. 


deliquescent  and  fi^eely  soluble ; the  antimonic  compound  does 
not  combine  with  water  when  mixed  with  it. 

The  properties  of  the  metallic  acids  or  hydrated  compounds 
obtained  by  the  action  of  these  binoxides,  teroxides,  and  peroxides 
upon  water,  directly  or  indirectly,  will  be  referred  to  again  here- 
after, when  the  bodies  themselves  are  described. 

The  compounds  of  the  same  metal  with  oxygen  are  often 
numerous ; and  the  extremes,  or  the  oxide  with  the  maximum  of 
oxygen,  and  the  oxide  with  the  minimum  of  oxygen,  frequently 
jiresent  chemical  qualities  of  opposite  kinds;  the  former  being 
electronegative,  and  possessing  acid  properties,  whilst  the  lower 
oxides  are  electropositive,  or  basic  in  their  nature. 

An  excellent  instance  of  this  kind  is  afforded  in  the  various 
oxides  of  manganese  : the  protoxide  (MnO)  is  a powerful  base ; 
the  sesquioxide  (Mn^Og)  is  a much  weaker  base ; the  red  oxide 
(Mn0,Mn203)  is  a saline  or  indifferent  oxide,  and  shows  little  dis- 
position to  furnish  corresponding  salts  by  reaction  either  upon 
acids  or  alkalies,  and  the  same  may  be  said  of  the  black  oxide 
(MnOJ ; while  the  two  higher  oxides,  which,  however,  are  only 
known  in  combination  either  with  hydrogen  or  the  metals,  are 
soluble  in  water,  when  they  constitute  the  manganic  and  per- 
manganic acids  (H^MnO^,  and  HkfnO^).  As  a general  rule,  the 
greater  the  number  of  atoms  of  oxygen  which  an  oxide  contains, 
the  less  is  it  disposed  to  form  salts  hj  reaction  with  the  acids : on 
the  contrary,  its  hydrate  frequently  possesses  acid  properties,  and 
then  it  reacts  upon  bases  to  form  salts. 

The  basic  oxides  in  general  are  devoid  of  all  metallic  appear- 
ance, and  present  par  excellence  the  characters  of  earthy  matter. 
The  protoxides,  when  solid,  are  all  insulators  of  the  voltaic  cur- 
rent ; but  some  of  the  higher  oxides,  such  as  the  peroxides  of  silver, 
lead,  and  manganese,  allow  it  to  pass  with  facility.  It  is  singular 
that  all  these  conducting  peroxides  may  be  formed  in  solutions  of 
salts  of  their  respective  metals  by  the  action  of  the  current  itself. 

These  oxides,  when  found  crystallized  in  the  native  state,  are 
much  harder  than  the  metals  that  furnish  them,  and  they  gene- 
rally have  a specific  gravity  considerably  less  than  that  of  the 
metals  themselves.  All  the  oxides  are  solid  at  ordinary  tempera- 
tures ; many  of  them  are  fusible  at  a red  heat,  such,  for  example, 
as  the  protoxides  of  potassium,  sodium,  and  lead,  and  the  sesqui- 
oxide of  bismuth : but  the  oxide  of  copper,  molybdic  anhydride, 
sesquioxide  of  chromium,  and  black  oxide  of  iron,  require  a much 
higher  temperature  to  effect  their  fusion.  Baryta,  strontia,  and 
alumina  require  the  heat  of  the  oxy hydrogen  jet ; while  some 
oxides,  such  as  lime  and  yttria,  exhibit  no  appearance  of  fusion, 
even  after  the  application  of  this  intense  heat. 

As  a general  rule,  the  addition  of  oxygen  to  a metal  renders 
it  much  less  fusible  and  volatile.  The  protoxide  of  iron,  the  sesqui- 
oxide of  chromium,  and  molybdic  anhydride,  are  the  only  oxides 
which  melt  at  a temperature  below  that  of  the  metal  from  which 
they  are  produced.  A few  of  tlie  oxides  are  volatile  at  moderate 
temperatures;  among  these  arsenious  anhydride,  sesquioxide  of 


PKEPAKATION  OF  THE  METALLIC  OXIDES. 


299 


antimony,  and  tessaroxide  of  osmium.  Mne  only  of  the  basic 
oxides  are  soluble  in  water  to  any  considerable  extent — viz.,  the 
five  alkalies,  and  baryta,  strontia,  lime,  and  oxide  of  thallium. 
The  insolubility  of  the  oxides,  however,  is  far  from  being  so  com- 
plete in  general  as  that  of  the  corresponding  sulphides,  and  con- 
sequently, except  in  particular  cases,  it  is  less  advisable  in  analy- 
tical operations  to  separate  the  metals  in  the  form  of  oxides  than 
in  that  of  sulphides ; the  oxides  of  lead,  silver,  and  mercury  in 
particular,  are  perceptibly  soluble  in  pure  water. 

Those  hydrated  compounds  of  oxygen  with  the  metals  which 
possess  acid  characters — such  as  the  chromic,  manganic,  and 
arsenic  acids — are  often  freely  soluble  in  water ; but  even  those 
acids,  which,  like  the  tantalic,  molybdic,  and  tungstic,  are  nearly 
insoluble,  usually  redden  litmus-paper,  though  their  anhydrides 
have  no  such  effect. 

Preparation. — Most  of  the  oxides  may  be  procured  in  combi- 
nation with  water  ; generally  speaking,  these  hydrated  oxides  are 
obtained  by  double  decomposition,  on  the  addition  of  the  solution 
of  an  alkali  to  one  of  their  soluble  salts  : in  this  manner  sulphate 
of  zinc  yields  hydrated  oxide  of  the  metal  on  adding  hydrate  of 
potash  to  its  solution  ; ZnS04  4-2  KHO=K2SO,-f  ZnH^O^.  The 
metals  which  form  powerful  bases,  like  those  of  the  alkalies  and 
alkaline  earths,  retain  the  water  with  great  obstinacy ; while 
others,  which  are  less  powerful  bases,  such  as  the  hydrated  oxide 
of  copper,  are  decomposed  at  a temperature  below  that  of  boiling 
water. 

The  anhydrous  oxides  may  be  obtained  in  several  ways : — 
1. — They  may  often  be  formed  directly,  by  burning  the  metal  in 
air,  or  in  oxygen  gas.  This  process  is  best  adapted  to  metals 
which,  like  zinc  or  arsenic,  are  volatile,  or  which  produce  fusible 
oxides,  like  iron  or  lead ; in  such  cases  the  oxide  is  removed  as 
fast  as  it  is  formed,  and  fresh  surfaces  of  the  metal  are  continually 
exposed  to  the  action  of  the  gas.  Anhydrous  potash  and  soda  are 
obtained  by  this  method  ; and  it  is  resorted  to  on  the  large  scale 
in  the  preparation  of  arsenious  anhydride,  and  of  the  oxides  of 
zinc  and  lead.  Several  of  the  metallic  protoxides,  if  roasted  at  a 
low  red  heat  in  a current  of  air  or  of  oxygen,  absorb  an  additional 
quantity  of  oxygen.  Litharge,  or  protoxide  of  lead,  is  thus  con- 
verted into  red  lead,  2 PbOjPbO^ ; and  peroxide  of  barium,  BaOj? 
may  in  this  way  be  obtained  from  baryta.  2. — Another  method 
consists  in  the  formation  of  a nitrate  of  the  metal  by  means  of 
nitric  acid ; the  nitrate  is  then  decomposed  by  heat,  which  expels 
the  elements  of  the  anhydride  and  leaves  the  oxide : in  this  way 
the  oxides  of  mercury,  bismuth,  antimony,  copper,  barium,  and 
strontium  are  prepared.  3. — In  some  cases  it  is  found  advanta- 
geous to  prepare  the  oxide  by  the  decomposition  of  the  carbonate 
of  the  metal  by  heat.  All  the  carbonates,  with  the  exception  of 
tliose  of  coesium,  rubidium,  sodium,  potassium,  and  i)ariuin,  are 
decomposed  at  a red  heat.  Lime  is  thus  commonly  obtained  from 
limestone,  which  is  an  impure  carbonate.  4. — Sometimes  tlie 
hydi’ated  oxide  is  first  precipitated,  as  already  mentioned,  and 


300 


DECOMPOSITIONS  OF  THE  I^IETALLIC  OXIDES. 


then  rendered  anhydrous  by  heat ; in  this  manner  the  sesqnioxides 
of  iron  and  nraninm  are  often  prepared.  5. — Occasionally  the 
ignition  of  a sulphate  is  resorted  to,  as  in  preparing  alumina  and 
sesquioxide  of  iron.  6. — All  the  acid  oxides  may  be  obtained  by 
deflagrating  the  metal  or  its  sulphide  with  nitre ; the  tendency  of 
the  metallic  acid  to  unite  with  the  alkali  favours  the  oxidation 
of  the  metal : the  higher  oxides  of  osmium,  titanium,  manganese, 
and  chromium,  as  well  as  of  some  other  metals,  may  be  obtained 
in  this  way. 

Decwnpositions. — 1.  By  the  action  of  a red  heat  many  of  the 
oxides  lose  their  oxygen,  either  partially  or  entirely.  The  oxides 
of  gold,  silver,  mercury,  platinum,  and  palladium  may  thus  be 
completely  reduced ; the  peroxides  of  lead,  cobalt,  nickel,  and 
barium,  return  to  the  state  of  protoxide ; and  the  metallic  anhy- 
drides lose  a portion  of  their  oxygen ; for  example,  arsenic  and 
chromic  anhydrides  are  thus  converted  respectively  into  arsenious 
anhydride  and  sesquioxide  of  chromium.  The  higher  oxides  of 
iron  and  manganese  furnish  the  magnetic  oxide,  FegO^,  and  the 
red  oxide  MngO^.  It  may  be  stated  as  a general  rule,  liable  how- 
ever to  exception,  especially  in  the  case  of  the  acidifiable  metals, 
that  the  attraction  of  a metal  for  oxygen  increases  in  the  inverse 
proportion  of  its  speciflc  gravity ; the  lightest  metals,  such  as  po- 
tassium and  sodium,  being  the  most  readily  oxidized,  while  pla- 
tinum, iridium,  and  gold,  which  are  the  densest  metals,  are  also 
those  which  show  the  smallest  tendency  to  combine  with  oxy- 
gen. 

2.  — The  oxides  are, not  aflfected  by  hydrogen  gas  at  the  ordi- 
nary temperature  of  the  air.  All  the  higher  oxides  of  the  metals 
are  readily  reduced  to  protoxides  by  hydrogen  at  a low  red  heat, 
whilst  water  is  formed ; and  at  a full  red  heat  a large  number  of 
them  are  reduced  to  the  metallic  state.  This  reduction  goes  on 
most  readily  when  the  current  of  hydrogen  is  brisk,  so  that  the 
vapour  of  water  is  carried  away  as  fast  as  it  is  formed.  The  oxides 
of  many  of  the  metals  which  decompose  water  at  a red  heat  may 
nevertheless  be  deprived  of  their  oxygen  in  a brisk  current  of 
hydrogen ; this  is  the  case,  for  example,  with  the  oxides  of  iron, 
zinc,  and  cadmium ; but  not  with  chromium  or  manganese.  The 
alkalies  and  the  earths  are  not  reducible  by  hydrogen. 

3.  — The  reducing  action  of  carhon  at  a high  temperature  is 
still  more  important ; all  the  metals  which  yield  their  oxygen  to 
hydrogen  do  so  to  carbon,  and  potassium  and  sodium  are  obtain- 
able from  their  compounds  by  its  agency.  This  arises  in  part 
from  the  volatility  of  these  two  metals,  which  is  sufficient  to  enable 
them  to  be  distilled  from  the  carbonaceous  mixture.  Lithium  and 
the  metals  of  the  earths  are  not  sufficiently  volatile  to  pass  over 
in  vapour,  and  though  their  attraction  for  oxygen  is  less  intense 
than  that  of  potassium  or  of  sodium,  they  cannot  be  obtained 
from  their  oxides  by  the  action  of  carbon.  It  depends  upon  the 
nature  of  the  metal,  and  upon  the  temperature  employed,  whether 
the  gas  that  is  formed  during  the  reduction  be  carbonic  oxide  or 
carbonic  anhydride.  The  more  readily  oxidizable  metals,  such  as 


ESTIMATION  OF  OXYGEN  IN  METALLIC  OXIDES. 


301 


potassium,  zinc,  and  iron,  at  a high  temperature  decompose  car- 
bonic anhydride,  so  that  carbonic  oxide  only  is  formed  when  they 
are  reduced ; while  if  the  reduction  takes  place  readily,  as  is  the 
case  with  copper  and  lead,  carbonic  anhydride  is  obtained. 

4.  — Dry  chlorine  sometimes,  even  without  the  application  of 
heat,  decomposes  the  basic  metallic  oxides,  such  as  oxide  of  silver 
and  the  red  oxide  of  mercury,  expelling  their  oxygen,  and  con- 
verting them  into  chlorides.  At  an  elevated  temperature,  few  of 
them,  excepting  those  of  magnesium  and  of  the  earths  in  the 
third  group,  resist  its  action : the  oxides  of  gold  and  platinum 
are  simply  reduced  to  the  metallic  state,  but  chlorides  of  the 
metals  are  formed  in  other  cases. 

If  the  oxides  be  hydrated  and  suspended  in  water,  the  action 
of  chlorine  is  quite  ditferent ; the  metals  of  the  first  two  groups 
yield  bleaching  compounds,  and  by  heat  are  converted  into  chlo- 
rates and  chlorides,  in  the  manner  already  explained  (3Y9).  The 
oxides  of  the  third  group,  the  earths  proper,  experience  no  par- 
ticular change,  hut  those  in  the  ferric  group  are  converted  into 
a mixture  of  chloride  and  hydrated  sesquioxide.  The  sesquioxides 
of  cobalt  and  of  nickel  are  usually  prepared  in  this  manner ; for 
example,  3 ■0oH2O2  + Cl2=DoOl2-i-Do2O-3,  3 H^O. 

If  the  liquid  be  strongly  alkaline,  the  whole  of  the  metal  may 
be  converted  into  sesquioxide;  2 •0oIl2O-2  + 2 KHO-f-Cl^ =-00203, 
3 11^0  + 2 KCl.  The  potash  in  this  case  parts  with  its  oxygen, 
which  is  transferred  to  the  cobalt,  whilst  the  chlorine  combines 
with  the  potassium.  The  protoxide  of  manganese,  under  these 
circumstances,  yields  the  hydrated  peroxide,  Mn02,  2 H2O. 

If  the  metal  be  capable  of  forming  an  acid  with  3 atoms  of 
oxygen,  the  process  of  oxidation  may  even  proceed  further,  and 
the  sesquioxide  may,  in  the  presence  of  a large  quantity  of  potash, 
become  converted  into  the  metallic  acid,  which  reacts  upon  a 
portion  of  the  excess  of  alkali  and  forms  a salt,  as  in  the  case  of 
sesquioxide  of  iron,  wlien  ferrate  of  potassium  is  produced ; De203, 
3 1120  + 10  KIie  + 3 02=2  K2DeO,  + 6 KCl + 8 H2O. 

5.  — Most  of  the  oxides  are  decomposed  more  or  less  completely 
when  heated  with  sulphur ; the  alkalies  and  alkaline  earths  are 
converted  into  a mixture  of  sulphate  and  sulphide,  but  magnesia, 
oxide  of  chromium  (?),  stannic  and  titanic  anhydrides,  as  well  as 
the  metals  of  the  earths,  or  those  of  the  third  group,  are  unaltered. 
Most  of  the  other  oxides  are  converted  into  sulphides,  with  escape 
of  sulphurous  anhydride.  The  oxides  are  more  readily  decom- 
posed by  sulphur  if  they  be  previously  mixed  with  carbon. 

(534)  Estimation  of  Oxygen  in  Metallic  Oxides. — The  compo- 
sition of  a metallic  oxide  may  be  ascertained,  if  it  l^e  decom- 
posable by  hydrogen,  by  lieating  the  compound  in  a current  of 
this  gas,  collecting  and  weighing  the  water  produced,  and  deter- 
mining the  amount  of  reduced  metal  which  a given  weight  of  the 
oxide  has  yielded.  In  other  cases  their  composition  is  determined 
synthetically,  a given  weight  of  the  metal  being  converted  into 
oxide,  either  by  heating  the  metal  in  a current  of  air,  or  by  con- 
verting it  into  a nitrate,  and  afterwards  expelling  the  elements  of 


302 


PKOPEKTIES  OF  THE  METALLIC  SULPHIDES. 


nitric  anhydride  by  the  application  of  heat,  and  weighing  the 
quantity  of  oxide  which  is  left. 

(535)  Sulphides.  — The  combinations  of  sulphur  with  the 
metals  are  numerous  ; they  are  in  many  instances  of  great  value, 
and  form  important  ores.  A large  number  of  the  native  sulphides 
often  exhibit  a high  metallic  lustre,  as  is  shown  by  the  sulphides 
of  iron,  copper,  lead,  and  antimony. 

Sulpliur  frequently  combines  with  the  same  metal  in  several 
proportions,  and  it  usually  happens  that  for  each  oxide  a corre- 
sponding sulphide  may  be  formed.  Sometimes,  as  in  the  case  of 
the  metals  of  the  alkalies  and  alkaline  earths,  the  sulphides  are 
more  numerous  than  the  oxides  : for  instance,  three  oxides  of 
potassium  and  sodium,  and  two  only  of  barium  are  known,  but 
there  are  not  fewer  than  five  sulphides  of  each  of  these  metals. 

All  the  metallic  sulphides  are  solid  at  ordinary  temperatures. 
Most  of  them  may  be  fused  at  a heat  a little  above  redness,  and 
if  the  air  be  excluded,  the  protosulphides  undergo  no  change  in 
composition  ; but  many  of  the  higher  sulphides,  such  as  the  bisul- 
phide of  iron  and  bisulphide  of  tin,  are  decomposed,  and  give  off 
the  second  atom  of  sulphur,  whilst  a lower  sulphide  of  the 
metal  is  left.  Sesquisulphide  of  arsenic,  or  orpiment  (As^Sg), 
and  sulphide  of  mercury,  or  cinnabar  (HgS),  may  be  sublimed 
if  excluded  from  the  air ; that  is  to  say,  they  may  be  converted 
into  vapour,  and  recondensed  in  the  solid  form  ; indeed,  these 
sulphides  are  usually  purified  by  this  operation. 

The  sulphides  of  all  the  metals  are  insoluble  in  water  with 
the  exception  of  those  of  the  alkali-metals  and  of  strontium  and 
barium.  Sulphides  of  calcium  and  magnesium,  however,  are 
sparingly  soluble. 

If  solutions  of  the  sulphides  of  the  metals  of  the  alkalies  and 
alkaline  earths  be  subjected  to  a current  of  gaseous  sulphuretted 
hydrogen,  they  combine  with  it,  and  form  soluble  compounds 
which  correspond  to  the  hydrates  of  the  oxides  ; for  example : — 

K,S-hHgS=2  KHS 
eaS-fH,S=:eaS,H,S. 

The  compounds  thus  formed  have  been  termed  sulph-hydrates. 
Those  of  calcium  and  magnesium  are  decomposed  into  hydrates 
by  boiling  with  water ; for  example  : — 

MgS,H,S  + 2 H,e=:Mge,H,0-|-2  H,S. 

Several  of  the  sulph-hydrates  may  be  obtained  in  crystals,  if 
evaporated  in  vessels  from  which  air  is  excluded. 

Tlie  sulpliides,  like  the  oxides,  may  be  subdivided  into  basic 
and  acid  sulphides,  according  to  the  nature  of  the  metal  and  the 
number  of  atoms  of  sulphur  with  which  each  atom  of  metal  is 
combined.  These  may  be  supposed  to  be  formed  on  the  type  of 
one  or  more  atoms  of  sulphuretted  hydrogen,  as  the  oxides  are 
upon  the  type  of  one  or  more  atoms  of  water.  The  protosulphides 
of  the  alkaline  metals  afford  illustrations  of  basic  sulphides,  and 
they  enter  into  combination  with  the  higher  sulphides  of  metals 


METALLIC  SULPHIDES. 


303 


which,  like  antimony  and  arsenic,  form  acids  with  oxygen.  Per- 
sulphide of  arsenic,  or  arsenic  sulphanhydride  (AS2S5),  in  this  way 
combines  with  sulphide  of  sodium,  and  forms  a crystalline  soluble 
compound  (3  ^^a2S,As2S5, 15  H^O) ; and  in  like  manner  persulphide 
of  antimony,  or  antimonic  sulphanhydride  (•Sb2S5),  forms  a soluble 
compound  with  sulphide  of  sodium  (3  Na^S,  SbjSg,  18  HaO,  or 
NagSbS^,  9 H^O),  which  crystallizes  in  beautiful  transparent  tetra- 
hedra.  A large  number  of  similar  compounds  may  be  formed 
with  the  sulphides  of  other  metals,  and  these  compounds  are  for 
the  most  part  soluble  in  water. 

In  consequence  of  the  tendency  to  the  formation  of  these 
double  sulphur  salts,  many  of  the  sulphides  which  are  insoluble  in 
water  are  dissolved  freely  by  solutions  of  sulphide  of  potassium 
or  of  sulphide  of  ammonium  ; and  this  circumstance  is  frequently 
taken  advantage  of  in  the  laboratory  during  the  progress  of  an 
analysis,  for  the  purpose  of  separating  certain  metals  the  sulphides 
of  which  are  soluble  in  solutions  of  the  sulphides  of  the  alkalifi- 
able  metals,  from  others  which  are  not  soluble  in  these  com- 
pounds. The  following  sulphides  may  be  dissolved  by  a solution 
of  sulphide  of  ammonium,  and  by  a solution  of  sulphide  of  potas- 
sium : — 


Persulphide  of  gold AU2S3 

Bisulphide  of  platinum PtS2 

Sesquisulphide  of  rhodium. . . .^0283 

Sesquisulphide  of  arsenic AS2S3 

Persulphide  of  arsenic AS285 

Sesquisulphide  of  antimony, . . . SbSs 

Persulphide  of  antimony Sb-Aa 

Bisulphide  of  vanadium ^¥^2 


Tersulphide  of  vanadium ¥83 

Tersulphide  of  tungsten WS3 

Tersulphide  of  molybdenum. . .M0S3 
Quadrisulphido  of  molybdenum . M0S4 

Protosulphide  of  tin SnS 

Bisulphide  of  tin 8082 

The  sulphides  of  tellurium. 

The  sulphides  of  iridium. 


The  double  salts  thus  obtained  are  decomposed  by  the  addition 
of  an  acid,  such  as  the  sulphuric  or  the  hydrochloric,  sulphuretted 
hydrogen  being  evolved,  whilst  the  sulphide  of  the  electronegative 
metal  is  precipitated  ; for  example,  3 l^a2S,Sb2S5  + 6 HCl  become 
6NaCl  + SbA  + 3n,S. 

These  electro-negative  sulphides  are  often  soluble  in  solutions 
of  the  alkalies,  forming  a mixture  of  a sulpho-salt  with  an  oxy-salt. 
Sesquisulphide  of  antimony,  for  instance,  when  dissolved  in  caustic 
potash,  gives  the  following  result : — 

sbA+6  Kiie=K3Sbe3+K3SbS3+3  H^e. 


Decompositions. — If  free  oxygen  or  atmospheric  air  be  allowed 
access  to  the  heated  sulphides,  they  are  all  decomposed  ; the  sul- 
phur becomes  oxidized,  and  passes  off  as  sulphurous  anhydride, 
whilst  the  metal,  in  most  cases,  as  occurs  with  tin,  antimony,  and 
molybdenum,  remains  in  combination  with  oxygen.  Tlie  sul- 
phides of  the  metals  of  the  alkalies  and  of  the  alkaline  earths  be- 
come converted  into  sulphates  of  the  metal,  and  the  same  thing 
occurs  less  completely  with  many  of  the  metals  which  have  a 
strong  attraction  for  ox^^gen ; the  sulphides  of  iron,  lead,  and 
copper,  are  partially  converted  into  sulphates,  but  by  a stronger 
heat  these  sulphates  afterwards  lose  their  acid,  and  the  oxide  of 
the  metal  only  is  left.  The  sulphides  of  the  noble  metals,  when 


304: 


DECOMPOSITIOX  A^"D  PKEPAEATIOX  OF  THE  SULPHIDES. 


roasted  in  a current  of  air,  lose  tlieir  sulphur,  which  burns  off  in 
the  form  of  sulphurous  anhydride,  while  the  pure  metal  remains 
behind,  though  in  the  case  of  silver  a portion  of  sulphate  of  silver 
is  commonly  formed. 

Many  of  the  hydrated  sulphides  become  oxidized  by  exposure 
to  the  air,  and  generally  are  converted  into  sulphates.  Hydi’ated 
sulphide  of  iron,  however,  furnishes  hydrated  sesquioxide  of  the 
metal,  whilst  sulphur  is  liberated : whilst  the  sulphides  of  the 
metals  of  the  alkalies  and  alkaline  earths  become  converted  into 
hyposulphites ; for  instance,  2 OaS  + H2O  + + 2 =-0aS2H2O^ 

+ OaOOg. 

A large  number  of  the  sulphides,  especially  those  of  the  more 
oxidizable  metals,  such  as  those  of  iron,  zinc,  and  manganese,  are 
dissolved  by  diluted  hydrochloric  acid  when  cold,  and  still  more 
readily  when  heated, — a chloride  of  the  metal  and  hydrosulphuric 
acid  being  formed.  Others,  such  as  those  of  nickel,  cobalt,  and 
lead,  require  boiling  with  the  concentrated  acid : it  is  in  this  way 
that  hydrochloric  acid  acts  upon  the  sesquisulphide  of  antimony ; 
Sb^Sg  + 6 HCl  becoming  2 SbClg  + 3 H^S.  Sulphuric  acid,  when 
diluted,  acts  in  a similar  manner  upon  the  sulphides  of  the  more 
oxidizable  metals,  though  less  readily  than  hydi’ochloric  acid. 
The  sulphides  are  all  decomposed  when  heated  in  a current  of 
chlorine  gas,  chloride  of  sulphur  and  chloride  of  the  metal  being 
formed.  This  property  is  sometimes  made  use  of  in  the  analysis 
of  ores  consisting  chiefly  of  sulphides,  or  of  sulphides  and  arsenides 
of  the  metals  ; the  volatile  metallic  chlorides  are  in  this  way  sepa- 
rated from  the  more  flxed  ones.  Aqua  regia  attacks  and  decom- 
poses the  sulphides  as  readily  as  gaseous  chlorine  ; and  a mixture 
of  hydrochloric  acid  and  chlorate  of  potassium  is  equally  efiectual 
in  decomposing  them.  With  the  exception  of  sulphide  of  mercury, 
they  are  also  decomposed  by  nitric  acid,  sulphuric  acid  and  nitrate 
of  the  metal  being  formed  ; during  this  operation  part  of  the 
sulphur  is  often  separated  in  the  form  of  tough  elastic  masses, 
which,  if  the  heat  be  continued,  collect  into  yellow  globules,  and 
can  be  oxidized  only  by  prolonged  digestion  in  the  acid.  When 
the  sulphides  are  fused  with  the  alkaline  carbonates  or  with  th« 
hydrated  alkalies,  they  are  partially  decomposed,  and  the  mar-s 
contains  a variable  mixture  of  alkaline  sulphide  with  oxide  of  the 
metal,  and  different  oxysalts  of  sulphur. 

Before  the  blowpipe  the  sulphides  are  easily  recognised  by  the 
odour  of  sulphurous  anhydride  which  they  emit,  either  when 
heated  in  a glass  tube  open  at  both  ends,  or  when  roasted  upon 
charcoal.  Some  other  particulars  relating  to  the  sulphides  have 
been  already  mentioned  (4:28). 

Preparation. — Many  methods  for  preparing  the  sulphides  may 
be  adopted.  1. — Sulphur  may  be  heated  with  the  metallic  oxides, 
many  of  which  it  decomposes : with  the  alkalies  and  alkaline 
earths,  a sulphate,  and  a sulphide  with  variable  proportions  of 
sulphur,  are  obtained : but  when  definite  and  pure  sulphides  are 
required,  other  means  should  be  adopted.  2. — The  lowest  sul- 
phides of  the  metals  of  the  alkalies  and  alkaline  earths  may  be 


PEEPAKATION  AND  ESTESIATION  OF  METALLIC  SULPHIDES.  305 

procured  bj  decomposing  their  sulphates  by  igniting  them  in 
closed  vessels  with  charcoal ; oxygen  is  removed,  carbonic  oxide 
formed,  and  the  remaining  sulphide  may  be  dissolved  in  water  and 
freed  from  the  excess  of  charcoal ; + 4 + 4 -60. 

3. — Hydrogen  is  sometimes  employed  for  preparing  the  sulphides 
from  the  sulphates,  which  are  to  be  placed  in  a tube  and  ignited 
in  a current  of  the  gas.  In  tliis  manner  the  protosulphides  of  the 
alkalifiable  metals  are  easily  obtained,  but  the  sulphates  of  the 
other  metals  frequently  lose  a portion  of  the  sulphur,  as  well  as 
all  their  oxygen,  and  subsulphides  are  procured.  4. — Many  of  the 
metals  combine  directly  with  sulphur,  if  heated  with  it,  and  form 
sulphides  ; but  the  compounds  thus  obtained  often  contain  sulphur 
dissolved  in,  or  disseminated  through,  the  mass.  Sulphide  of  iron 
is  usually  prepared  in  this  manner.  Indeed,  sulphur,  though 
itself  combustible,  supports  the  combustion  of  many  metallic 
bodies,  which  burn  vividly  when  heated  in  its  vapour.  5. — In 
other  cases  the  sulphides  may  be  formed  by  heating  the  metal  in 
a current  of  sulphuretted  hydrogen,  or  in  the  vapour  of  bisulphide 
of  carbon.  This  latter  method  is  the  plan  commonly  adopted  in 
procuring  sulphide  of  titanium  from  titanic  acid;  Ti02  + -^2=^Ti 
+ — Hydrated  sulphides  of  the  metals  of  the  last  three 

groups  may  also  be  procured  by  passing  a stream  of  sulphuretted 
hydrogen  through  neutral  or  acid  solutions  of  their  salts,  when 
they  are  precipitated  in  the  insoluble  form.  7. — The  hydrated 
sulphides  of  zinc,  iron,  manganese,  cobalt,  and  nickel,  which  are 
not  thrown  down  by  sulphuretted  hydrogen,  may  be  prepared  by 
double  decomposition,  by  mixing  a solution  of  the  salts  of  any  of 
these  metals  with  that  of  a sulphide  of  one  of  the  alkalifiable 
metals : thus  sulphate  of  manganese  if  mixed  with  sulphide  of 
potassium  yields  sulphate  of  potassium  and  sulphide  of  manganese  ; 
MnSO4+Ml2O,K,S=K2S04  + Hl2O-,MnS.  In  many  cases  the 

colours  of  these  hydrated  sulphides  are  characteristic  of  the  metal : 
— for  example,  the  hydrated  sulphide  of  zinc  is  white ; that  of 
manganese  tlesh-red ; those  of  cadmium,  arsenic,  and  persulphide 
of  tin  are  yellow  ; and  that  of  the  hydrated  protosulphide  of  tin  is 
chocolate-brown.  The  sulphides  of  molybdenum,  rhodium,  iridi- 
um, and  osmium  are  brown,  each  with  its  peculiar  shade ; whilst 
in  a large  number  of  instances — including  the  sulphides  of  iron, 
cobalt,  nickel,  uranium,  vanadium,  bismuth,  copper,  lead,  silver, 
mercury,  gold,  platinum,  and  palladium — the  precipitated  sul- 
phides are  of  a black,  more  or  less  pure. 

(536)  Estimation  of  Sulphur  in  Metallic  Sulphides. — Sulphur 
is  always  estimated  in  the  form  either  of  sulphuric  acid  or  of  free 
sulphur.  The  sulphur  in  a sulphide  is  easily  converted  into  sul- 
phuric acid  by  the  agency  either  of  gaseous  chlorine  or  of  acpia 
regia ; and  the  soluble  sulphates,  when  mixed  in  sliglitly  acid  solu- 
tion with  a salt  of  barium,  yield  an  insoluble  sulphate  of  barium, 
the  amount  of  which,  after  it  has  been  well  waslied  with  boiling 
water  and  ignited,  furnishes  data  for  the  calculation  of  thesul])hur ; 
100  parts  of  sulphate  of  barium  representing  34'34  of  sulphuric 
anhydride,  or  13*74  of  sulphur.  If  a salt  of  silver  be  present, 
20 


306 


SELEJsTDES TELLmroES CHLORIDES. 


nitrate  of  barium  must  be  employed  to  precipitate  the  sulphuric 
acid. 

If,  during  the  solution  of  a sulphide  in  aqua  regia,  the  sulphur 
have  collected  into  clear  yellow  balls,  and  the  action  upon  the 
ore  appears  to  be  complete,  it  is  not  necessary  to  wait  till  the 
whole  of  the  sulphur  is  dissolved : the  undissolved  portion  may  be 
collected  on  a small  counterpoised  filter,  and  weighed,  and  its 
amount  must  be  added  to  that  which  has  been  converted  into  sul- 
phuric acid,  the  proportion  of  which  is  to  be  ascertained  by  means 
of  a barium  salt  in  the  manner  above  described. 

(537)  The  selexides  and  tellurides  are  closely  analogous 
to  the  sulphides  in  general  characters,  but  they  are  too  rare  to 
need  particular  description.  The  presence  of  selenium  in  a com- 
pound is  readily  ascertained  by  the  peculiar  odour  which  it  emits 
when  heated  in  the  reducing  fiame  of  the  blowpipe. 

(538)  Chlorides. — Just  as  the  difierent  classes  of  oxides  may 
be  conceived  to  be  formed  from  one  or  more  atoms  of  water  in 
which  the  hydrogen  is  displaced  by  metal,  so  the  different  varie- 
ties of  chlorides  may  be  referred  to  one  or  more  atoms  of  hydro- 
chloric acid,  in  which  the  place  of  the  hydrogen  is  supplied  by  a 
metal. 

The  principal  groups  of  chlorides  are  the  following : — 

1st.  Subchlorides^  or  XCl,  on  the  type  of  HCl;  as 

Subchloride  of  silver ^g-jCl 

Calomel SgCl. 

2nd.  Monochlorides ^ M'Cl,  formed  on  the  type  of  HCl ; as 
Chloride  of  potassium KCl. 

3rd.  Bichlorides^  on  the  type  of  H2CI2 ; such  as 

Chloride  of  calcium -CaClj. 

Ith.  Terchlorides,  H'^'Clg,  on  the  type  of  H^Clg ; such  as 
Terchloride  of  antimony SbClg. 

5th.  Hexachlorides,  H^Clg,  or  on  the  type  6 HCl ; 

such  as 

Molybdic  chloride HoClg ; 

Chloride  of  aluminum i^lgCle- 

6th.  Tetrachlorides,  K'^Cl^,  on  the  type  of  H,C1, ; such  as 
Perchloride  of  platinum PtCl^. 

7th.  Pentachlorides^  H^'Clg,  on  the  type  of  HgCl^, ; such  as 
Pentachloride  of  antimony SbCl^. 

1.  The  basic  chlorides,  or  suhchlorides^  are  few  in  number 
and  of  small  importance  ; they  are  insoluble  in  water,  subchloride 
of  silver,  subchloride  of  copper,  and  calomel,  comprising  all  that 
are  of  interest. 

2.  The  Protochlorides  form  an  important  group  including 
the  chlorides  of  the  alkali-metals,  and  those  of  silver  and  thallium, 
as  well  as  aurous  chloride.  The  chlorides  of  gold  and  silver  are 
insoluble  in  water;  that  of  thallium  is  but  sparingly  soluble. 


VARIETIES  OF  METALLIC  CHLORIDES. 


307 


Aurons  chloride  is  decomposed  by  a heat  below  redness,  but  the 
other  chlorides  fuse  readily  when  heated,  and  may  even  be  slowly 
volatilized  without  decomposition.  They  are  conductors  of  the 
voltaic  current  when  fused. 

3.  Bichlorides. — The  compounds  contained  in  this  group  are 
formed  by  the  union  of  1 atom  of  a metallic  dyad  with  2 atoms 
of  chlorine.  They  present  characters  which  are  similar  to  those 
of  the  foregoing  group,  to  which,  indeed,  they  bear  the  closest 
resemblance : they  were  till  quite  recently  considered  to  form  part 
of  it;  these  chlorides  being,  in  fact,  usually  described  as  proto- 
chlorides. 

Amongst  the  members  of  this  group  are  the  chlorides  of 
many  highly  basylous  metals,  such  as  barium  and  calcium.  The 
chlorides  of  the  electronegative  dyads,  like  that  of  mercury,  are 
strongly  opposed  to  tliese  basylous  chlorides  in  properties.  All 
the  chlorides  of  this  group,  when  anhydrous,  are  solid  at  common 
temperatures;  but  when  heated  in  vessels  from  which  air  is  ex- 
cluded, they  may  all  be  melted  without  undergoing  decomposition, 
except  those  of  copper,  platinum,  and  palladium.  Chloride  of 
copper  loses  half  its  chlorine  and  becomes  converted  into  sub- 
chloride, whilst  platinous  chloride,  PtCl^,  and  palladious  chloride 
are  decomposed  into  free  chlorine,  and  a residue  of  the  pure 
metal.  Several  of  the  chlorides  remain  semi-transparent  after 
fusion  ; in  general  these  are  soft  and  sectile  compounds,  somewhat 
horny  in  aspect.  Many  of  these  chlorides,  such  as  those  of  zinc 
and  mercury,  may  be  distilled  without  decomposition.  Chloride 
of  lead  is  but  sparingly  soluble ; platinous  chloride,  in  one  of  its 
modifications,  is  quite  insoluble.  The  other  members  of  the 
group  are  freely  soluble  in  water. 

4.  The  next  group  comprises  those  known  as  ter  chlorides.^ 
of  which  the  following  are  the  most  important : — 


Terchloride  of  arsenic AsCls 

“ antimony SbCla 

“ bismuth Bids 

“ gold AuCU 


The  terchloride  of  gold  is  decomposed  into  the  protochloride  by  a 
moderate  heat,  and  at  a higher  temperature  loses  all  its  chlorine ; 
the  other  three  chlorides  are  volatilized  unchanged  by  a moderate 
elevation  of  temperature.  They  are  decomposed  by  the  addition 
of  water ; chloride  of  arsenic  into  arsenious  acid  and  hydrochloric 
acid,  AsCl3-h3  1120=3  HCl -h  AsIIgOg ; whilst  the  chlorides  of  anti- 
mony and  bismuth  furnish  oxychlorides  ; 3 SbClg-f  3 Il20=SbCl3, 

Sb2e3  + 6IIC1. 

5.  Parallel  with  these  volatile  terchlorides  in  properties  are 
the  hexcbchlorides  of  three  other  acidifiable  metals : — 


Perchloride  of  molybdenum MoClo 

“ vanadium VClo 

“ tungsten WClo. 


These  chlorides  are  all  volatile,  and  are  decomposed  by  water. 

The  substances,  formerly  called  Sesquichlorides^  constitute  a 
remarkable  group,  of  which  the  most  important  are  the  chloride 


308 


PEOPEKTIES  OF  METALLIC  CHLOEIDES. 


of  aluminum,  per  chloride  of  iron,  and  chloride  of  chromium. 
Each  of  these  compounds  contains  1 atom  of  the  metallic  element 
united  with  3 atoms  of  chlorine,  hut  each  may  be  volatilized  at  a 
high  temperature  without  decomposition ; the  vapour  density  has 
indeed  been  taken  for  the  chlorides  of  aluminum  and  iron,  and  the 
result  is  remarkable,  since  if  HII=2  vols.,  rzkl^Clg  is  also  = 2 vols., 
and  hence  shows  that  the  formulse  should  be  doubled,  as  follows : 


Chloride  of  aluminum AlsCle 

Perchloride  of  iron FeaCle 

Chloride  of  chromium  (judging  by  analogy) ■Gr2Cl6. 


The  aqueous  solutions  of  these  chlorides  undergo  partial  de- 
composition when  evaporated,  hydrochloric  acid  escapes,  and  a 
considerable  portion  of  oxide  of  the  metal  is  formed. 

6.  Xext  we  have  a group  of  chlorides  formerly  described  by 
chemists  as  the  bichlorides,  but  now  considered  as  tetrachlorides. 
Several  of  these  are  volatile  liquids — viz. : — 


Chloride  of  silicon 

..  SiCU 

Molvhdous  chloride 

Moa4 

Perchloride  of  titanium  . . . . 

TiCb 

Tungstous 

U 

wcu 

U 

tin 

...  SnCh 

Platinic 

(( 

PtCU 

(( 

tantalum  . . . 

...  TaCh 

PaUadic 

u 

PdCU 

(( 

niobium  . . . . 

^hCU 

Iridic 

it 

IrCq 

u 

zirconium  . ... 

...  ZrCU 

Euthenic 

ii 

PuCh 

The  first  three  compounds  are  liquid  at  ordinary  temperatures  : 
they  are  densely  fuming  when  exposed  to  the  air ; they  may  be 
distilled  unaltered.  With  the  exception  of  the  chlorides  of  plati- 
num, palladium,  iridium,  and  ruthenium,  which  by  a high  tem- 
perature are  decomposed  into  metal  and  free  chlorine,  the  remain- 
ing compounds  are  fusible  volatile  solids,  and  may  be  sublimed 
unaltered  in  vessels  from  which  air  is  excluded.  The  perchlorides 
of  tin,  titanium,  and  the  noble  metals,  form  crystallizable  double 
salts  with  the  chlorides  of  the  alkali-metals. 

T.  The  Pentachlorides  are  represented  by  pentachloride  of 
antimony,  which  corresponds  with  pentachloride  of  phosphorus. 
It  is  fuming  and  volatile,  is  decomposed  by  water,  forming  an 
oxychloride  if  the  proportion  of  water  is  small,  but  yielding 
hydrated  metantimonic  acid,  with  separation  of  all  its  chlorine 
as  hydrochloric  acid,  if  the  quantity  of  water  be  large. 

The  action  of  chlorine  upon  the  metals  is  generally  stronger 
than  that  of  oxygen  upon  them ; but  if  a metallic  chloride  be 
heated  in  a current  of  oxygen  or  of  atmospheric  air,  the  chlorine 
is  expelled,  and  an  oxide  of  the  metal  is  produced.  The  only 
instances  in  which  this  decomposition  does  not  take  place,  occur 
in  the  case  of  the  chlorides  of  the  noble  metals  and  in  those 
belonging  to  the  first  and  second  groups.  Chloride  of  magnesium 
is,  however,  readily  decomposed  in  tliis  manner. 

In  the  case  of  the  metals  which  have  but  slight  attraction  for 
oxygen,  the  chlorides  generally  correspond  in  number  with  the 
oxides  ; and  for  every  chloride  an  analogous  oxide  is  always 
obtainable,  one  atom  of  oxygen  occupying  the  position  of  two 
atoms  of  chlorine  in  the  compound.  For  example,  the  corre- 


PREPAEATION  OF  METALLIC  CHLORIDES. 


309 


sponding  chlorides  and  oxides  of  iron,  tin,  and  gold  are  the 
following : — 

FeCla  ; FeO  I SnCls ; SnO  1 AuCl  ; AuaO 

Fe2Cl6;  FeaOs  | SnCU;  SnOa  1 AuCU;  AuaOa. 

Yet  it  is  easy  to  obtain  the  oxides  from  solutions  of  the  chlorides 
by  precipitation ; for  example,  in  the  case  of  the  compounds  of 
iron,  the  following  reactions  may  be  observed : — 

FeCl,  +2  KHO  2 KCl  + Fee,H,e 
Fe,Cl,  + 6 KHO  = 6 KCl  + FeA,  3 H.O 
FejClfi  + B BaHA  ==  3 BaCl^  + FeA?  3 H^O. 

When  the  metal  exhibits  a strong  attraction  for  oxygen,  and 
forms  a powerful  base,  the  number  of  oxides  frequently  exceeds 
that  of  the  chlorides. 

In  many  cases  chlorine  unites  with  the  oxides  of  the  metals. 
If  the  oxide  of  the  metal  be  soluble  in  water,  the  oxychloride 
which  is  formed  is  soluble  likewise,  and  the  compound  is  remark- 
able for  its  bleaching_  properties.  Chloride  of  lime  (■0aOCl2),  and 
chloride  of  potash  (K2OCI2),  furnish  instances  of  this  kind.  Some- 
times the  chloride  of  a metal  combines  with  its  oxide  and  forms 
an  insoluble  oxychloride,  as  is  the  case  with  the  oxychloride  of 
mercury  (3  IIgO-,iIgCl2).  It  is  a still  more  frequent  occurrence 
that  a chloride  of  one  of  the  alkalitiable  metals  combines  with  a 
chloride  of  one  of  those  metals  which  have  a feebler  attraction  for 
oxygen,  and  the  oxides  of  which  partake  rather  of  the  character 
of  acids  than  of  bases.  Thus  we  have  a double  chloride  of  plati- 
num and  potassium  (2  KCl,PtCh)  and  a double  chloride  of  gold 
and  sodium  (ISTaChAuCh,  2 H2O).  Indeed,  the  higher  chlorides 
of  the  noble  metals  generally  form  double  salts  of  this  nature  : the 
same  thing  holds  true  in  very  many  cases  with  the  corresponding 
bromides  and  iodides. 

Preparation. — 1.  Many  of  the  metallic  chlorides  may  be  formed 
by  heating  the  metal  in  a current  of  dry  chlorine  : in  this  way  the 
perchlorides  of  antimony  and  iron  are  procured.  2. — If  the  basic 
oxides  be  heated  to  redness  in  a current  of  dry  chlorine,  oxygen  is 
expelled  and  a chloride  of  the  metal  remains ; but  this  process  is 
never  adopted  for  procuring  the  chlorides.  3. — The  sulphides  are 
generally  more  readily  decomposed  by  a current  of  gaseous  chlo- 
rine than  the  oxides : owing  to  the  strong  attraction  of  chlorine 
for  sulpliur,  both  the  sulphur  and  the  metal  combine  with  the  gas, 
chloride  of  sulphur,  and  a metallic  cliloride  being  produced.  This 
process,  however,  is  seldom  employed  except  in  the  course  of  an 
analysis.  4. — In  cases  where  the  chloride  is  volatile,  like  that  of 
aluminum,  of  glucinum,  and  of  titanium,  the  oxide  of  the  metal  is 
mixed  with  charcoal,  and  a current  of  dry  chlorine  is  transmitted- 
over  the  mixture  ; the  charcoal  removes  the  oxygen  in  tlie  form 
of  carbonic  oxide,  and  the  chlorine,  uniting  with  the  metal,  forms 
a chloride  which  volatilizes  and  becomes  condensed  in  the  cool 
part  of  the  apparatus.  5. — In  many  cases  the  chloride  may  be 
obtained  by  transmitting  dry  hydrochloric  acid  gas  over  the  oxide 
or  the  sulphide  of  the  metal  heated  to  low  redness,  the  attraction 


310  PKEPAEATIOX  AOT)  DECOMPOSITIONS  OF  METALLIC  CHLOEIDES. 


of  liydrogen  for  oxygen  and  for  snlphnr  greatly  facilitating  tlie 
progress  of  the  decomposition.  6. — An  easier  method,  in  cases 
where  it  is  applicable,  particularly  in  cases  where  the  hydra- 
ted chlorides  are  required,  consists  in  dissolving  the  metal 
itself,  its  oxide,  or  its  carbonate,  in  hydrochloric  acid,  and 
evaporating  the  solution  till  crystallization  commences.  Chlo- 
ride of  cobalt,  of  nickel,  and  of  calcium  may  be  thus  obtained. 
This  process,  however,  fails  in  many  cases,  if  it  be  attempted  to 
render  the  chloride  anliyckous,  particularly  in  the  class  to  which 
the  earths  belong;  chlorides  of  magnesium  and  almninum,  for 
example,  lose  their  chlorine  as  hydrochloric  acid  when  their  solu- 
tions are  evaporated ; MgCl^  -f  AEgO  -f-  2 ITCl.  7. — In 

some  cases  chlorides  of  the  metals,  such  as  those  of  gold  and  pla- 
tinum, are  obtained  by  dissolving  the  metal  in  aqua  regia,  and 
decomposing  any  excess  of  nitric  acid  by  evaporation  to  dryness 
with  an  excess  of  hydrochloric  acid ; a pure  chloride  of  the  metal 
may  be  obtained  on  re-dissohung  the  residue  in  water.  8. — Many 
of  the  chlorides  of  the  more  electronegative  metals  are  decomposed 
when  heated  with  the  more  basylous  metals.  Perchloride  of  tin 
may  thus  be  obtained  by  heating  metallic  tin  with  an  excess  of 
corrosive  sublimate;  and  terchlorides  of  antimony  and  bismuth 
may  be  obtained  in  a similar  manner.  Sometimes  this  process  is 
employed  for  the  purpose  of  isolating  those  metals  the  oxides  of 
which  resist  decomposition  by  the  usual  means.  In  this  way 
sodium  is  employed  to  decompose  the  chloride  of  aluminum  or  of 
magnesium  for  the  purpose  of  procuring  the  aluminum  or  magne- 
sium in  an  uncombined  form  ; and  in  a similar  manner  potassium 
is  employed  to  obtain  uranium  from  uranous  chloride.  9. — The 
insoluble  chlorides,  such  as  those  of  silver  and  lead,  and  mercm-ous 
chloride,  may  be  formed  by  the  addition  of  hydi’ochloric  acid,  or 
of  a soluble  chloride,  to  a solution  of  the  corresponding  salts  of 
these  metals. 

Decomposittons. — All  the  metallic  chlorides,  excepting  those 
of  the  metals  of  the  alkalies  and  earths,  are  reduced  when  suffi- 
ciently heated  in  a brisk  current  of  hydi’ogen.  In  many  cases  the 
reduction  is  easily  effected,  and  this  process  is  occasionally  resorted 
to  as  a means  of  procuring  certain  metals  in  a state  of  purity. 
Iron,  for  example,  may  be  obtained  in  ffne  cubic  crystals  by  reduc- 
ing ferrous  chloride  in  this  manner.  It  is  necessary,  however,  to 
maintain  a current  of  hydrogen  of  sufficient  rapidity  to  carry 
away  the  hydrochloric  acid  from  the  reduced  metal,  as  otherwise, 
in  most  cases,  the  chloride  would  be  reproduced  by  the  decompo- 
sition of  the  acid.  All  the  chlorides,  except  those  of  the  alkaline 
metals,  and  of  barium  and  mercury,  are  decomposed  when  heated 
•in  a current  of  steam,  generally  leaving  corresponding  oxides,  but 
chloride  of  bismuth  leaves  an  oxychloride  (Kunheim).  All  the 
soluble  chlorides,  when  heated  with  sulphuric  acid  and  black  oxide 
of  manganese,  evolve  chlorine  gas.  Other  particulars  relating  to 
the  chlorides  have  been  already  mentioned  (373,  376). 

(539)  Estimation  of  Chlorine  in  ^Metallic  Chlomdes. — Chlorine 
is  almost  always  estimated  in  the  form  of  chloride  of  silver,  100 


METALLIC  BKOMIDES IODIDES. 


311 


parts  of  which  represent  24:'74  of  chlorine.  The  solution  should 
be  acidulated  with  nitric  acid,  and  gently  warmed,  and  then  the 
nitrate  of  silver  should  be  added.  If  iodine  or  bromine  be  pres- 
ent, it  will  be  precipitated  with  the  chlorine,  and  must  be  deter- 
mined separately,  and  the  corresponding  weight  of  iodide  or  bro- 
mide of  silver  deducted. 

The  composition  of  an  insoluble  chloride  or  of  a basic  chloride 
may  be  ascertained,  except  in  the  case  of  chloride  of  silver,  by 
boiling  a given  weight  of  the  compound  with  a pure  solution  of 
potash,  and  then  determining  the  quantity  of  chlorine  in  the 
alkaline  solution  by  means  of  nitrate  of  silver : before  adding  the 
solution  of  silver,  the  alkaline  liquid  must  be  filtered  from  the 
undissolved  metallic  oxide,  and  acidulated  with  nitric  acid. 

(540)  The  Bromides  (389,  391)  closely  resemble  the  chlorides 
in  chemical  characters,  and  may  be  arranged  in  corresponding 
groups ; the  bromides  of  the  metals  of  the  alkalies  and  alkaline 
earths  may  be  prepraed  by  digesting  a solution  of  the  alkali  or  of 
the  earth  with  bromine  in  slight  excess  ; a bromide  and  a bro- 
mate  of  the  metal  are  thus  formed,  and  by  gentle  ignition  the  bro- 
mate  is  decomposed,  leaving  a pure  bromide : a small  quantity  of 
charcoal  may  be  added  previously  to  the  ignition,  by  which  the 
decomposition  of  the  bromate  is  more  easily  effected.  The  bromide 
is  removed  from  the  excess  of  charcoal  by  solution  in  water.  The 
other  bromides  may  be  procured  by  acting  upon  the  metals  by 
bromine,  either  in  a dry  state  or  in  the  presence  of  water.  They 
are  also  easily  formed  by  dissolving  the  oxides  or  the  carbonates 
in  hydrobromic  acid. 

Bromine  may  be  precipitated  from  its  solutions,  and,  in  the 
absence  of  chlorine,  its  quantity  may  be  estimated  by  means  of 
nitrate  of  silver,  which  occasions  a white  precipitate  of  bromide 
of  silver,  100  parts  of  which  indicate  41 ‘47  of  bromine.  If  chlorine 
be  present  the  precipitate  will  consist  of  a mixture  of  the  bromide 
and  chloride  of  silver  : it  must  be  collected  and  weighed  then, 
digested  with  metallic  zinc  and  a drop  or  two  of  sulphuric  acid ; 
in  a day  or  two  the  zinc  will  have  reduced  the  bromide  and 
chloride  to  metallic  silver ; this  must  be  well  washed,  dried,  and 
weighed.  It  should  be  wholly  soluble  in  nitric  acid,  since  if  it  be 
not,  a portion  of  the  precipitate  has  escaped  decomposition. 

From  the  above  data  the  relative  proportions  of  the  bromide 
and  chloride  of  silver  may  be  calculated : — let  m be  the  weight  of 
the  mixed  bromide  and  cliloride,  and  let  s be  the  weight  of  the 
reduced  silver ; then  if  x represent  the  proportion  of  bromide,  and 
y that  of  chloride  of  silver,  it  will  be  found  that 

108  108 

m = a?  -f  y,  and  s H x — y ; 

143-5  188 

consequently  a?,  or  the  bromide  of  silver  in  the  mixture,  = m —y\ 
and  y,  or  the  chloride  of  silver  in  the  mixture,  = 5-6134  s — 
3-2247  m. 

(541)  The  Iodides  (396)  may  be  formed  by  processes  analo- 


312 


METALLIC  FLEOEIDES  A^’D  XITKIDES. 


goiis  to  those  employed  for  the  bromides : the  insoluble  iodides, 
such  as  those  of  mercury,  silver,  and  lead,  may  be  obtained  from 
a solution  of  iodide  of  potassium,  by  mixing  it  vdth  a solution  of 
the  metallic  salt. 

The  iodides  exhibit  a strong  tendency  to  form  double  salts,  the 
iodides  of  the  strongly  basylous  metals  combining  readily  to  form 
crystallizable  double  iodides  with  those  of  the  electronegative 
mkals,  such  as  those  of  silver,  mercury,  and  lead.  The  iodides 
also  foim  double  compounds  with  the  oxides  and  chlorides  : for 
example,  there  are  several  compounds  of  the  iodide  with  the  oxide 
of  lead ; and  a combination  of  perchloride  of  tin  with  the  stannous 
iodide  (Snlj.SnCl^)  may  be  obtained  in  orange-coloui’ed  crystals 
(Kane). 

The  quantity  of  iodine  in  a solution  which  contains  iodides,  if 
chlorides  be  absent,  may  be  estimated  by  the  addition  of  nitrate 
of  silver  slightly  acidulated  with  nitric  acid : the  resultiug  buff- 
coloured  iodide  of  silver,  when  collected  and  di’ied,  contains  od’O 
per  cent,  of  iodine.  If  chlorine  or  bromine  be  present,  the  iodine 
must  be  precipitated  by  means  of  nitrate  of  palladium ; the  pre- 
cipitate must  be  allowed  to  subside  dmlng  ten  or  twelve  hours, 
and  it  may  then  be  collected  on  a filter  and  dried  at  a temperature 
not  exceeding  160° ; this  precipitate  is  insoluble  in  cold  diluted 
nitric  or  hydrochloric  acid,  but  soluble  in  ammonia.  It  contains 
70*0  per  cent,  of  iodine.  Iodine  may  also  be  separated  from  bro- 
mine and  chlorine,  but  less  perfectly  by  a mixture  of  green  sul- 
phate of  iron  and  sulphate  of  copper  (883). 

(512)  Tleoeedes. — The  general  properties  of  these  compounds 
have  been  already  stated  (103).  The  fiuorides  are  usually  pre- 
pared by  the  direct  action  of  hydrofiuoric  acid  either  upon  the 
metal  or  more  usually  upon  the  oxide  of  the  metal.  Those  which 
are  insoluble  may  be  procured  by  mixing  a solution  of  the  metal- 
lic salt  with  one  of  fiuoride  of  potassium  or  of  sodium. 

Estimation  of  Fluorine. — A simple  method  of  detecting  and 
of  approximatively  estimating  fluorine,  when  present,  even  in 
very  small  quantities,  has  been  proposed  by  Dr.  G.  TTilson.  The 
following  is  the  process,  shghtly  modified : — the  substance,  if  it 
does  not  ah’eady  contain  silica,  is  mixed  with  poimded  glass,  placed 
in  a retort,  and  made  into  a thin  cream  with  oil  of  Gtriol ; the 
mixture  is  next  heated,  and  distilled  into  a flask  containing  a 
solution  of  ammonia ; the  fluoride  of  silicon  comes  over,  and  is 
immediately  decomposed  : on  evaporating  the  liquid  in  the  flask 
to  di*ynes3  on  a water-bath,  the  silica  is  rendered  insoluble,  and 
can  be  collected  and  weighed,  whilst  the  fluoride  of  ammonium 
may  be  dissolved  out  with  a little  water,  and  the  presence  of 
fluorine  shown  by  mixing  it  with  oil  of  vitriol  ; tlie  vapour  which 
is  evolved  produces  the  usual  corrosive  action  of  hydrofluoric  acid 
on  glass  (103)  : the  proportion  of  silica  in  the  insoluble  residue 
to  the  fluorine,  however,  is  not  very  uniform. 

(543)  Kitrides. — It  is  not  improbable  that  the  fulminating 
compounds,  obtained  by  digesting  the  hydrated  oxides  of  gold,  of 
silver,  and  of  platinum,  in  a solution  of  ammonia,  may  owe  their 


PHOSPHIDES CAEBIDES HYDEIDES THEORY  OF  SALTS.  313 

explosive  character  to  tlie  formation  of  a nitride  : the  composition 
of  these  bodies  has,  however,  been  but  imperfectly  investigated, 
on  account  of  the  ease  with  wdiich  they  explode.  So  weak  is  the 
chemical  attraction  of  nitrogen  for  most  metallic  bodies,  that  a 
slight  alteration  of  circumstances  often  suffices  to  restore  it  sud- 
denly to  the  gaseous  state,  hsitride  of  copper  is  formed  by  pass- 
ing dry  ammonia  over  oxide  of  copper,  at  a temperature  not  ex- 
ceeding 480°,  in  which  case  water  is  formed  at  the  expense  of  the 
hydrogen  of  the  ammonia  and  the  oxygen  of  the  oxide,  and  part 
of  the  nitrogen  escapes ; thus,  6 -GuO  + 4 HgN  = 2 Gugh^  -f  6 
HgG  -f  bTg.  Strides  of  mercury  and  iron  may  be  prepared  by 
passing  ammonia  over  oxide  of  mercury  and  oxide  of  iron  in  a 
similar  manner.  Titanium,  molybdenum,  and  vanadium  absorb 
nitrogen  rapidly  at  a red  heat ; and  crystalline  nitrides  of  chromium 
and  magnesium  have  also  been  obtained. 

(544)  The  Phosphides  of  the  metals  are  of  comparatively  small 
importance : they  are  never  met  with  in  the  native  state.  The 
phosphides  of  the  metals  of  the  alkalies  and  alkaline  earths  de- 
compose water  when  thrown  into  it ; self-lighting  phosphuretted 
hydi’ogen  is  disengaged,  and  a hypophosphite  of  the  metal  is  re- 
tained in  solution.  In  some  cases,  as  for  example  in  that  of 
phosphide  of  calcium,  the  phosphide  is  formed  by  heating  the  oxide 
strongly,  and  driving  the  vapour  of  phosphorus  over  it ; in  this 
case  it  is  mixed  with  a large  proportion  of  phosphate  of  calcium. 
The  insoluble  phosphides  may  often  be  obtained  by  transmitting 
a current  of  phosjjhuretted  hydrogen  through  a solution  of  the 
salt  of  the  metal  in  water  : phosphides  of  copper  and  silver  may 
be  thus  obtained. 

When  heated  in  air,  phosphide  sare  converted  into  phosphates, 
or  into  phosphoric  anhydride,  while  the  metal  is  liberated. 

(545)  Carbides. — The  only  carbides  of  importance  are  those 
of  iron,  which  will  be  considered  in  detail  when  treating  of  that 
metal.  Manganese,  palladium,  iridium,  and  a few  other  metals, 
also  combine  with  carbon ; generally  speaking,  these  carbides  are 
more  fusible  than  the  metals  which  enter  into  their  formation. 

Silicon  and  boron  form  with  the  metals  analogous  compounds 
of  small  importance.  Amongst  the  most  interesting  of  the  sili- 
cides  are  those  of  calcium,  aluminum,  magnesium,  iron,  and  copper. 

(546)  Hydrides. — Hydrogen  is  not  known  to  combine  with 
more  than  five  metals: — viz.,  arsenic,  antimony,  copper,  iron,  and 
potassium.  The  first  two  of  these  compounds  are  gaseous,  and 
are  decomposed  by  a red  heat  into  metal  and  hydrogen  gas.  A 
solid  hydride  of  arsenic  is  also  said  to  exist.  A few  metals,  such 
as  zinc  and  potassium,  appear  under  peculiar  circumstances  to 
undergo  partial  volatilization  along  with  the  hydrogen  at  the  mo- 
ment that  this  gas  is  evolved. 

§ III.  Hypotheses  on  the  Constitution  of  Salts. 

(54Y)  Acids  and  Bases. — It  has  already  lieen  stated  (6)  that 
any  substance  which  is  produced  by  the  action  of  an  acid  upon  a 


314: 


THEORY  OF  SALTS OXYACIDS  AND  HYDRACIDS. 


base  is  termed  a salt.  It  is,  however,  necessary  to  examine  more 
minutely  into  the  nature  both  of  bases  and  acids,  and  into  that  of 
the  compounds  formed  by  their  combination  wdth  each  other. 

By  the  word  hase^  is  meant  a body  always  of  a compound 
nature,  very  frequently  an  oxide  of  a metal,  which  is  capable  of 
eftecting  a double  decomposition  with  an  acid,  whilst  a salt  and 
water  are  formed,  and  the  distinctive  characters  of  the  acid  are 
more  or  less  completely  neutralized.  A base,  how'ever,  is  not 
necessarily  a metallic  oxide ; the  hydrates  of  ammonia,  quinia,  and 
morphia,  for  example,  are  powerful  bases,  but  they  contain  no 
metallic  substance. 

(518)  Oxy acids  and  Hydradds. — When  Lavoisier  imposed  the 
name  of  oxygen  upon  one  of  the  constituents  of  the  atmosphere, 
he  supposed  that  the  presence  of  that  energetic  body  was  essential 
to  the  existence  of  an  acid ; and  this  view  was  supported  by  the 
known  composition  of  the  principal  acids,  such  as  the  sulphuric, 
the  sulphurous,  the  nitric,  the  carbonic,  the  j)hosphoric,  and  the 
boracic  acids.  The  term  acid  was  indifferently  applied  to  the 
anhydrides  and  to  the  compounds  produced  by  the  action  of  anhy- 
dildes  upon  water  ; to  which  latter  class  of  compounds  the  term 
is  more  properly  restricted  by  many  later  writers,  and  to  which 
it  is  limited  in  this  work.  Lavoisier  considered  an  acid  to  be  an 
oxidized  body  more  or  less  soluble  in  water,  with  a sour  taste, 
capable  of  reddening  vegetable  blues,  and  entering  into  combina- 
tion with  the  alkalies,  the  distinctive  properties  of  which  it 
neutralized. 

By  degrees,  however,  acids  were  discovered  in  which  no  oxy- 
gen could  be  detected : such,  for  example,  as  the  hydrochloric,  the 
hydriodic,  and  the  hydrobromic,  into  the  composition  of  which 
hydrogen  enters ; yet  these  bodies  were  found  in  other  respects  to 
correspond  perfectly  with  the  above  definition,  and  to  possess  all 
the  characters  of  powerful  acids.  To  meet  this  objection,  the 
theory  was  modified,  and  the  acids  were  divided  into  two  great 
classes,  the  first  of  which  comprised  the  oxyacids^  such  as  the  sul- 
phuric, nitric,  and  others  of  analogous  composition,  in  which  it 
was  supposed  that  the  acid  properties  depended  on  the  presence 
of  oxygen ; the  second  class  was  formed  by  the  hydradds^  such 
as  the  hydrochloric  and  hydriodic  acids,  in  which  hydrogen  was 
an  essential  component.  It  was  noticed,  that  when  bodies  belong- 
ing to  either  of  these  classes  combine  with  metallic  compounds, 
and  form  neutral  combinations,  the  acids  do  not  unite  directly 
with  the  metals  without  evolution  of  gas ; with  their  oxides^  on 
the  contrary,  combination  appears  to  take  place  directly : diluted 
sulphuric  acid,  for  example,  has  no  action  upon  metallic  copper, 
but  it  quickly  dissolves  its  oxide,  forming  the  blue  solution  of  sul- 
phate of  copper.  On  applying  heat  so  as  to  render  the  salt  anhy- 
drous, it  was  found  that  the  salts  of  the  oxyacids  (of  which  sulphate 
of  potash,  K0,S03,  may  be  taken  as  the  type,  adopting  for  the 
present  the  equivalents  O = 8,  S = 16,  and  the  old  notation) 
might  be  represented  under  the  form  M0,S03,  which  supposes  the 
union  of  1 equivalent  of  the  anhydilde  with  1 equivalent  of  a 


BINARY  HYPOTHESIS  OF  SALTS. 


315 


metallic  oxide  ; while  a liydracid  (such  for  instance  as  hydrochloric 
acid)  if  made  to  act  upon  a base  such  as  soda,  yields  a body  like 
common  salt  (NaCl),  which  when  dry  contains  neither  hydrochloric 
acid  nor  soda,  the  radicle  of  the  acid  being  left  in  combination 
with  the  metal  itself:  NaO,HO  + HCl  yielding  IsTaCl  + 2 HO. 
Thus,  in  the  case  of  the  salts  of  the  hydracids,  it  wdll  be  observed 
that  the  oxygen  of  the  oxide  is  precisely  sufficient  to  convert  the 
hydrogen  of  the  acid  into  water : this  union,  indeed,  actually 
takes  place,  and  the  water  so  formed  is  expelled  on  the  applica- 
tion of  heat.  When,  therefore,  a hydracid  acts  upon  a base,  a true 
double  decomposition  occurs. 

In  consequence  of  this  supposed  difference  in  constitution,  it 
was  proposed  to  subdivide  salts  into  two  classes, — the  first,  like 
nitrate  of  potash,  K0,N05,  being  formed  by  the  union  of  an  ox- 
ide, such  as  potash,  with  an  oxyacid,  or  anhydride  as  we  now  term 
it,  such  as  the  nitric  ; these  were  termed  oxysalts : the  other  class 
being  produced  by  the  combination  of  a metal  with  the  charac- 
teristic element  in  a hydrogen  acid.  The  salts  of  the  second 
class,  being  composed  upon  the  same  plan  or  type  as  sea-salt,  were 
termed  haloid  salts  (from  aX^,  sea-salt).  This  distinction  is  still 
recognised  by  many  chemical  writers.  The  supposition  that  a 
salt  consists  of  an  anhydride  united  to  a base  still  in  many  cases 
affords  the  simplest  explanation  of  many  chemical  decompositions. 

(5 49)  Binary  Hypothesis  of  Salts. — The  foregoing  observa- 
tions seem  to  prove  that  there  is  a marked  difference  between  the 
composition  of  the  oxyacid  and  the  hydracid  series  of  salts.  The 
separation  of  salts  into  two  classes,  one  consisting  of  the  salts  of 
the  oxy acids,  and  the  other  of  those  of  the  hydracids,  is  not,  how- 
ever, indispensable.  A hypothesis  was  advanced  by  Davy  and  by 
Dulong,  which  reduces  all  salts  to  the  hydracid  type.  Upon  this 
view — frequently  termed  the  binary  theory  of  salts — all  the 
hydrated  acids  are  regarded  as  salts  containing  hydrogen  in  the 
place  of  a metal,  so  that  hydrogen  acts  the  part  of  a feeble  basyl 
towards  a group  of  elements,  or  a single  element,  which  forms  tiie 
radicle  of  the  salt.  It  has  already  been  shown  that  those  of  the 
oxy  acids  which  can  be  obtained  as  anhydrides,  such  for  example 
as  the  sulphuric,  the  nitric,  the  phosphoric,  the  carbonic,  and  the 
boracic,  do  not  as  anhydrides  possess  the  properties  generally 
admitted  to  constitute  the  true  acid  character.  Sulphuric  anhy- 
dride, for  instance,  does  not  redden  dry  litmus  ; it  may  be  moulded 
in  the  fingers  without  injury;  but  when  once  it  has  passed  into 
tlie  hydrated  form,  which  it  speedily  does  by  absorbing  moisture 
from  the  air,  it  corrodes  all  organized  substances  with  great 
activity.  Carbonic  anhydride  is  also  without  action  on  litmus. 
When  such  compounds  have  entered  into  combination  with  water 
they  may  be  represented  as  liydracids,  by  a slight  modification  of 
the  ordinary  formula : e.  g.,  nitric  acid  (IIO,  HO,)  maybe  ex- 
])ressed  as  (rI,]SrOg),  corresponding  with  hydrocldoric  acid  (11,01) : 
each  atom  of  these  bodies,  when  heated  in  contact  with  a base  or 
a metallic  oxide,  gives  off  1 atom  of  water,  in  a manner  precisely 
analogous  to  the  hydracids  already  examined.  One  equivalent  of 


316 


BmAHT  THEOET  OF  SALTS. 


oil  of  vitriol  treated  with  1 equivalent  of  oxide  of  lead  would  thus 
produce  an  equivalent  of  sulphate  of  lead  and  an  equivalent  of 
water  ; HjSO^  + PbO  becoming  Pb,SO,  + HO. 

Many  chemists  indeed  now  regard  the  compounds  which 
were  previously  considered  as  hydrated  acids  as  salts  composed  of 
a compound  radicle  (consisting  of  the  anhydidde  + an  equivalent 
of  oxygen)  united  with  an  equivalent  of  hydrogen.  The  other 
salts  of  the  acid  would  he  formed  from  these  hydrogen  compounds 
by  the  displacement  of  the  hydrogen  by  an  equivalent  amount  of 
each  of  the  dilferent  metals  which  enter  into  the  composition  of 
the  various  salts,  and  which  are  indicated  by  their  respective 
names.  In  accordance  with  this  view,  we  have  already  given  a 
simple  explanation  of  the  liberation  of  hych’ogen  when  diluted 
sulphuric  acid  is  acted  upon  by  zinc ; the  zinc  merely  entering 
into  combination  with  the  radicle  of  the  acid,  and  displacing  the 
hydrogen ; so  that  (resuming  the  notation  which  regards  0=16 
and  water  H^O)  HjSO^-l-Zn  become  ^nSO^  + H^ ; and  the  reaction 
is,  upon  this  view,  analogous  to  that  of  the  same  metal  upon 
hydrochloric  acid;  2 HCl4-Zn=ZnCl2  + H2. 

A comparison  of  a few  of  the  so-called  hydracids  with  some 
of  the  hydrated  oxyacids  will  show  the  similarity  between  them ; 
whilst  the  corresponding  anhydrides  will  be  at  once  seen  to  belong 
to  an  entirely  distinct  group  of  compounds  : — 


Hydracids. 

Hydrated  oxyacids. 

Anhydrides. 

HF 

Nitric  acid 

. HN03 

HCl 

Iodic  “ 

. HIO3 

l205 

HBr 

Hypochlorous  acid 

. Hcie 

ClaO 

HI 

Sulphuric  “ 

. H2S04 

S03 

A few  reactions  between  certain  bases  on  the  one  hand  with  some 
of  the  hydracids,  and  on  the  other  with  certain  hydrated  oxyacids, 
will  enable  us  to  complete  theparallel : — 

2HC1  -f  Ag^e  = 2 AgCl  -f 

2HF  -f  Oa'^e  = ea'T^  4-  H^O 

HI  -f  KHO  = KI  -f  H^O 

2 msO,  -f  Tl^e  = 2 11X03  -f  H2O 

H2SO,  + XaHO  = XaHSO,  -f  H^O 
H^se,  -h  Pb"0  = Pb"SO,  4-  H2O. 

In  each  case  the  salt  is  formed  by  the  substitution  of  an  equi- 
valent amount  of  metal  for  hydrogen,  whilst  a corresponding 
quantity  of  water  is  liberated  and  occupies  the  place  of  the 
metallic  oxide  originally  employed. 

Binary  compounds  are  such  as  consist  of  single  atoms  of  two 
elements  only;  chloride  of  sodium  (XaCl),  therefore,  is  a binary 
compound  ; and  if  all  salts  be  assimilated  to  this  t\q)e,  it  is  assumed 
that  the  grouping  of  their  molecules  resembles  that  which  occurs 
in  this  binary  compound.  It  has  indeed  been  supposed  that  all 
salts  consist  of  two  portions ; one  comprising  the  distinctive  con- 
stituents of  the  acid,  and  consisting  either  of  a non-metallic  ele- 


BINAKr  THEOKY  OF  SALTS. 


317 


meiitary  substance  (chlorine,  Cl,  for  example),  or  else  an  equiva- 
lent compound  body  (such  as  sulphion,  SO^),  which  is  termed  the 
radicle  of  the  salt ; the  other  is  either  a metal  (sodium,  l^a,  for 
instance),  or  else  a compound  like  ammonium  (H^N),  equivalent 
to  a metal,  termed  the  hasyl  of  the  salt.  Attention  has  already 
been  directed  to  the  bearing  of  the  electrolysis  of  saline  com- 
pounds (286),  upon  this  theory  of  their  constitution. 

(550)  Objections  to  the  Binary  Hypothesis. — ^Notwithstanding 
the  ingenuity  of  the  foregoing  hypothesis,  and  the  advantages 
which  it  offers  in  the  explanation  of  certain  modes  of  decomposi- 
tion, it  is  open  to  many  serious  objections  ; and  indeed  it  cannot 
be  regarded  as  a correct  representation  of  the  composition  of  a 
salt  under  all  circumstances.  In  fact,  none  of  the  compound 
radicles,  SO^,  NO3,  OOg,  have  been  obtained  in  an  isolated  form, 
nor  is  it  probable  that  they  ever  will  be. 

It  also  appears  to  be  highly  improbable  that  a body  of  such 
powerful  chemical  attractions  as  potash  should,  in  carbonate  of 
potassium  for  example,  part  with  its  oxygen  to  a substance  which, 
like  carbonic  anhydride,  exliibits  no  tendency  to  further  oxidation, 
so  that  K2O,O02  should  become  K^OOg. 

The  conclusion  which  is  most  probable  is  this : viz.,  that  a 
salt,  when  once  formed,  must  be  regarded  as  a whole ; it  can  no 
longer  be  looked  upon  as  consisting  of  two  distinct  parts,  but  as  a 
new  substance,  maintained  in  its  existing  condition  by  the  mutual 
actions  of  all  the  elements  which  compose  it.  These  different 
elements  are  not  all  united  with  each  other  in  every  direction  with 
an  equal  amount  of  force.  As  in  a crystal  there  are  certain  direc- 
tions in  which  the  mass  admits  of  cleavage  with  greater  facility 
than  in  others,  and  as  two  or  three  different  directions  of  cleavage 
may  be  found  in  the  same  crystal  by  varying  the  direction  in 
which  the  force  is  applied,  so  in  the  same  salt  there  are  directions 
in  which  it  yields  to  the  application  of  chemical  force  more 
readily  than  in  others ; and  according  as  that  chemical  force  is 
applied  in  one  way  or  in  another,  the  compound  splits  up  into 
simpler  substances,  the  nature  of  which  will  vary  according  to  the 
mode  which  has  been  selected  for  effecting  its  decomposition. 

For  example,  if  the  solution  of  a powerful  acid,  such  as  nitric 
acid,  be  poured  upon  carbonate  of  potassium,  carbonic  anhydride 
is  liberated  abundantly,  and  nitrate  of  potassium  is  produced ; 
KgOOg  -f  2 IINOg  ^ ^ ^ , A OO,  -f  ; but  if  another 

portion  of  the  same  carbonate  of  potassium  be  mixed  with  char- 
coal, and  heated  in  an  iron  retort  to  whiteness,  metallic  potassium 
and  carbonic  oxide  are  the  results ; -|-  2 O = + 3 O0. 

Again,  if  a solution  of  carbonate  of  potassium  be  subjected  to 
electrolysis  by  tlie  aid  of  the  voltaic  battery,  the  salt  splits  up 
into  potassium  (wliich  is  immediately  oxidized  by  tlie  water  in 
the  midst  of  which  it  is  liberated),  and  into  OO3,  wliich  is  as 
instantly  resolved  into  oxygen  gas  and  carbonic  anhydride ; 
2 KgOOg  becoming  2 + 2 003,  and  2 -f  4 1130, 

4 KII0  -f-  2 IIj,  whilst  2 00,  becomes  2 00^  -f  0,.  Tlie 
probability  therefore  is,  that  neither  the  old  nor  the  new  view  is 


318 


SULPHO-SAI.TS TAPrETIES  OF  SALTS. 


absolutely  coiTect,  but  that  eacb  may  in  turn  well  represent  the 
salt  when  subjected  to  the  influence  of  particular  circumstances. 
It  may  therefore  readily  be  conceded  that  the  binary  theory  may 
in  certain  cases  elucidate  the  decompositions  observed,  not’svith- 
standing  the  difficulties  which  prevent  its  adoption  as  a correct 
representation  of  the  molecular  arrangement  of  saline  compounds 
in  general  when  in  a quiescent  state.  On  the  other  hand,  it  may 
often  be  convenient  to  represent  certain  salts  as  compounds  of 
the  anhydride  and  the  base ; carbonate  of  calcium,  for  example, 
may  sometimes  be  written  CaO,-0O2  although  the  empirical  for- 
mula -GaOOg  may  generally  be  preferred.  So,  again,  in  the  case 
of  the  sulphates.  Sulphate  of  magnesium  may,  for  instance,  be 
often  written  MgO.SOg.  although  we  may  generally  adopt  the 
form  MgSO^  which  involves  no  theory  of  its  constitution. 

(551)  Siilpho-Salts. — The  preceding  remarks  have  been  made 
with  almost  exclusive  reference  to  those  salts  into  the  composition 
of  which  oxygen  enters.  There  is,  however,  a numerous  series  of 
compounds  parallel  to  these  oxy-compounds,  but  in  which  sulphur 
enters  into  combination  ivith  the  metal ; and  for  each  atom  of 
oxygen  in  the  series  of  the  oxy-salts  an  equivalent  of  sulphur  is 
substituted  in  the  corresponding  compound  in  the  sulphiu’  series. 
Generally  speaking,  the  sulphur-salts  are  of  subordinate  impor- 
tance to  the  oxy-compounds ; many  of  them  are  decomposed  by 
admixture  with  water,  and  they  have  been  the  subject  of  much 
less  study  and  research  than  the  oxy-salts.  Many  chemists  regard 
these  compounds  as  salts  in  which  the  electropositive  sulphides, 
such  as  the  protosulphides  of  potassiimi,  (kc.,  act  the  part  of  bases ; 
and  the  electronegative  sulphides,  such  as  the  higher  sulphides  of 
arsenic  and  antimony,  act  as  acids.  Xo  doubt  their  molecular 
constitution  is  analogous  to  that  of  the  oxy-salts. 

(552)  Varieties  of  Salts. — Salts  are  usually  spoken  of  as  neu- 
tral., acid,  or  basic  ‘ but  though  these  terms  are  in  general  use, 
there  is  some  ambiguity  in  the  manner  in  which  they  are  applied. 

(553)  JVeutral,  or  jVormal  Salts. — The  idea  of  neutrality  im- 
plies that  the  peculiar  characters  of  the  acid  and  of  the  alkali  have 
each  disappeared  as  a result  of  chemical  combination,  and  one 
of  the  usual  means  by  which  this  neutralization  in  properties  is 
judged  of,  consists  in  observing  the  eflect  which  is  produced  upon 
certain  vegetable  colours  when  mixed  with  a solution  of  the  salt. 

The  blue  colour  of  litmus,  for  example,  is  changed  to  red  by 
the  action  of  an  acid,  whilst  the  colour  of  litmus  reddened  by  an 
acid  becomes  blue  if  it  be  mixed  with  an  alkali.  The  yellow 
colour  of  turmeric  is  changed  to  brown  when  mixed  with  an 
alkali,  but  the  yellow  is  restored  if  the  alkali  be  caused  to  com- 
bine with  an  acid.  A salt  which  affects  neither  the  blue  of  litmus 
nor  the  yellow  of  turmeric  is  said  to  have  a neutral  reaction.  But 
chemists  are  in  the  habit  of  regarding  many  salts  as  neutral  in 
composition  which  are  not  neutral  in  their  action  upon  coloured 
tests.  The  basic  properties  of  different  metallic  oxides  vary  con- 
siderable in  intensity.  Equal  quantities  of  the  same  acid,  accord- 
ing as  it  is  neutralized  by  equivalent  quantities  of  a weak  base  or 


319 


NEUTRAL,  OR  NORMAL  SALTS. 

of  a strong  one,  will  differ  considerably  in  tbeir  action  upon 
coloured  tests  : for  example,  62  parts  of  nitric  acid  radicle  in 
combination  with  39  parts  of  potassium  furnish  nitrate  of  potas- 
sium (KNO3),  which,  when  dissolved  in  water,  does  not  affect  the 
colour  either  of  blue  or  of  reddened  litmus-paper.  It  is  therefore 
neutral  in  its  reactions  upon  coloured  tests. 

Salts  of  nitric  acid  in  which  1 atom  of  a monad  or  uniequiva- 
lent metal  like  potassium,  sodium,  or  silver  displaces  the  hydrogen 
in  1 atom  of  the  acid  HHOg,  or  in  which  1 atom  of  a dyad  or 
biequivalent  metal  such  as  lead  or  copper  displaces  the  hydrogen 
of  2 atoms  of  nitric  acid  (2  HNO3)  are  regarded  as  neutral  in 
composition  whatever  may  be  their  action  upon  vegetable  colours. 
If,  for  instance,  223  parts  of  oxide  of  lead  be  made  to  act  upon 
1 26  parts  of  nitric  acid,  nitrate  of  lead  and  water  will  be  formed  ; 
Pb''0  + 2 H^I03=H20+Pb"  2 NO3,  and  the  salt  is  neutral  in 
composition,  though  if  dissolved  in  water  it  reddens  litmus,  and 
has  an  acid  reaction.  The  same  thing  is  true,  also,  in  the  case  of 
nitrate  of  copper. 

The  change  in  the  tint  of  the  coloured  test  is  therefore  not  to 
be  regarded  as  an  absolute  proof  of  neutrality  or  acidity  in  a salt. 
The  change  of  colour  which  the  litmus  experiences,  even  from  a 
salt  of  neutral  composition,  is  readily  explained.  Blue  litmus  is 
itself  a species  of  salt,  formed  by  the  combination  of  the  metals 
of  one  of  the  alkalies  or  earths  with  the  radicle  of  a feeble  vege- 
table acid  which  is  naturally  of  a red  colour,  but  which  becomes 
blue  when  it  is  neutralized  by  an  alkali.  When  a powerful  acid, 
such  as  the  nitric  or  the  sulphuric,  is  mixed  with  this  blue  colour- 
ing matter,  the  radicle  of  the  strong  acid  seizes  upon  the  basyl 
which  the  litmus  contains,  and  sets  free  the  litmus  acid  which 
appears  of  its  natural  red  hue ; but  on  the  addition  of  an  alkali 
the  blue  is  restored  by  the  reaction  of  the  newly  added  base  upon 
the  litmus  acid  and  the  formation  of  the  litmus  salt  of  the  alkaline 
metal.  Again,  if  a salt  with  a strong  acid  radicle  and  a compa- 
ratively feeble  basyl  be  mixed  with  the  blue  litmus,  the  strong 
radicle  of  the  salt  seizes  upon  the  part  of  the  basyl  which  is  in 
combination  with  the  litmus,  and  liberates  the  litmus  acid,  which 
appears  of  a more  or  less  intense  red,  according  as  the  basyl  of  the 
neutral  salt  has  given  up  more  or  less  of  its  acid  radicle. 

For  analogous  reasons  it  sometimes  happens  that  a salt  which 
is  neutral  in  composition  may  exhibit  characters  in  which  the 
basyl  preponderates  to  a greater  or  less  extent.  Carbonate  of 
potassium  (K^OOg)  is  neutral  in  composition,  but  it  appears  to  be 
basic  in  its  action  upon  the  yellow  colour  of  turmeric-paper, 
which  it  renders  powerfully  brown,  and  it  immediately  restores 
the  blue  tinge  to  reddened  litmus.  This  ambiguity  in  the  use  of 
the  word  neutral,  may,  however,  be  entirely  obviated  by  describ- 
ing as  normal  salts  the  salts  above-mentioned  as  neutral  in  com- 
position ; employing  the  term  neutral  solely  with  reference  to  the 
action  of  the  body  upon  coloured  tests;  and  in  this  sense  we  shall 
hereafter  use  these  terms. 

(554)  Polyhasic  Acids — Acid  Salts. — If  a quantity  of  oxalic 


320 


POLYBASIC  SALTS. 


acid  be  divided  into  two  equal  portions,  one  of  which  is  dissolved 
in  water,  and  mixed  with  a solution  of  hydrate  of  potash  until  the 
liquid  becomes  neutral  in  its  reaction  upon  litmus,  a salt  is  formed 
which,  on  evaporation,  may  be  obtained  ciystallized  in  six-sided 
prisms,  which  consist  of  the  normal  oxalate  of  potassium, 

HjO).  If  this  salt  be  redissolved  in  water,  and  the  second  portion 
of  oxalic  acid  be  added  to  it,  chemical  union  of  the  two  bodies 
wiU  occm’ ; the  liquid  so  * obtained  will  be  found  to  have  a sour 
taste,  to  redden  htmus  powerfully,  and  on  evaporation  to  }deld  a 
new  salt,  which  crystallizes  in  rhomboidal  prisms,  containing 
exactly  half  as  much  potassium  in  proportion  to  the  acid  as  the 
first  salt ; this  is  the  binoxalate,  or  acid  oxalate,  of  potassium 
(KHGA^H.O)  ; for  K.GA,  H,e  H.GA,  H,e=2  (KHGA, 
H,0). 

Again,  if  the  normal  sulphate  of  potassium  (K^SOJ  be  dis 
solved  in  hot  sulphuric  acid,  tabular  plates  of  a new,  fusible,  and 
strongly  acid  salt,  will  crystallize  out  as  the  liquid  cools,  and  the 
bisulphate  or  acid  sulphate  of  potassium  wiU  be  foiTned  (XHSO^)  ; 
for,  K3S0^  + H2S0^=2  KHSO^.  This  salt  contains  only  half  the 
amount  of  potassium  which  is  present  in  the  nomial  sulphate. 
If  an  attempt  be  made  to  form  a similar  salt  by  dissolving  nitrate 
of  potassium  in  nitiic  acid,  the  experiment  will  fail,  for  the  nitre 
will  be  found  to  crystallize  out  unchanged. 

It  is  thus  apparent  that  there  are  certain  acids  which  furnish 
salts  containing  only  one  proportion  of  the  metallic  basyl  united 
with  the  radicle  of  the  acid,  whilst  there  are  other  acids  in  which 
the  radicle  has  the  power  of  combining  with  the  basyl  in  two 
proportions,  forming  two  classes  of  salts,  one  of  which  is  neutral 
in  its  reaction,  the  other  is  acid. 

It  usually  happens  that  such  acid  salts  contain,  in  addition  to 
the  salt  radicle  and  basyl,  a certain  quantity  of  hydrogen,  as 
occurs,  for  instance,  in  the  acid  sulphate  and  the  acid  oxalate  of 
potassium.  This  hych’ogen  is  not  to  be  regarded  as  present  in  the 
form  of  water  of  crystallization  : it  discharges  a more  important 
function,  for  it  takes  the  place  of  one  of  the  atoms  of  the  metal 
on  these  occasions ; and  it  is  because  the  basic  properties  of  hydi'o- 
gen  are  so  feeble,  that  the  acid  character  predominates  to  so  great 
a degree  in  such  salts. 

Acids  in  the  molecule  of  which  a single  atom  of  hydrogen 
admits  of  displacement  by  a single  atom  of  a metallic  monad  such 
as  potassium,  are  said  to  be  mcmobasic.  Of  this  description  the 
hydrochloric  acid  HCl,  the  nitric,  IIAO3,  and  the  acetic, 
acids  are  examples. 

If,  however,  the  molecule  of  the  acid  contains  2 atoms  of 
hydrogen,  susce])tible  of  displacement  by  two  atoms  of  a monad 
like  potassium,  or  by  one  atom  of  a dyad  like  zinc,  the  acid  is  said 
to  be  dihasic.  like  the  sulphiulc,  II^SO^,  the  oxalic,  and 

the  tartaric,  acids.  ^lany  of  the  vegetable  acids  belong 

to  this  class. 

Again,  if  the  molecule  of  the  acid  contains  3 atoms  of  hydro- 
gen susceptible  of  displacement  by  3 atoms  of  a monad  like  potas- 


SALTS  FORMED  FROM  SESQUIOXIDES. 


321 


sium  or  silver,  or  by  one  atom  of  a triad  like  bismuth,  such  an 
acid  is  said  to  be  trihasic.  Common  phosphoric  acid,  HgPO^,  is 
a good  instance  of  this  kind ; and  among  the  organic  acids  the 
citric,  1 IgOgHgO,,  may  be  mentioned. 

Acids  which  allow  the  substitution  of  more  than  one  atom  of 
hydrogen  by  a corresponding  number  of  atoms  of  a metallic  monad 
(whether  2,  3,  or  4 atoms)  are  said  to  jpol/yhasio. 

Nitrate  of  potassium  (KNO3)  affords  an  instance  of  the  forma- 
tion of  a normal  salt  by  the  action  of  the  oxide  of  a monad  or 
uniequivalent  metal  upon  a monobasic  acid ; whilst  nitrate  of  lead 
(Pb"  2 NOg)  illustrates  the  case  of  a normal  salt  formed  by  the 
reaction  of  the  protoxide  of  a biequivalent  or  dyad  metal  upon  a 
monobasic  acid ; and  carbonate  of  potassium  affords  an 

example  of  the  formation  of  a normal  salt  by  the  reaction  of  the 
oxide  of  a monad  metal  with  a dibasic  acid.  These  three  varieties 
include  the  most  common  forms  of  normal  salt.  When  a dibasic 
acid  acts  upon  the  protoxide  of  a metallic  dyad,  a salt  is  formed 
similar  to  that  obtained  by  the  reaction  of  sulphuric  acid  upon 
hydrate  of  lime,  where  two  atoms  of  hydrogen  in  the  acid  are  re- 
placed by  1 atom  of  the  dyad  or  biequivalent  metal  calcium ; 

But  numerous  salts  are  known  which  are  formed  by  the  action 
of  sesquioxides  upon  the  acids.  In  certain  cases  the  sesquioxides 
act  upon  the  acids  just  as  the  protoxides  do.  Thus  the  sesqui- 
oxide  of  antimony  and  uranium,  as  well  as  those  of  bismuth,  iron, 
and  aluminum,  in  certain  circumstances  yield  a sulphate  by  the 
action  of  the  two  bodies  in  the  proportions  indicated  in  the  fol- 
lowing equations  : — 

HA  -p  Ase,=:(HA)''  AO 

Sb  A + i-i.SA= (Sb  A)''^4 + 

Bi  A + H3se,= (Bi  A)"  -so,  -f- 11,0 

FeA  + (Pe  A)''se,  -h  HA 

Ai  As + = (Ai  AsX  + ha 

These  sulphates,  however,  with  the  exception  of  the  first,  are  all 
insoluble ; the  oxide  of  uranium  (HAs)^^  {umnyl,  as  Peligot  has 
termed  it)  has  been  isolated ; indeed  it  was  for  some  years  mis- 
taken for  metallic  uranium,  till  Peligot  showed  it  to  be  a com- 
pound, and  obtained  the  metal  itself.  The  other  oxides  of  the 
formulae  corresponding  to  uranyl  have  not  been  isolated.  The 
foregoing  salts  are  generally  regarded  as  basic  salts,  derived  from 
the  sesquioxides.  Many  of  them  retain  water  (not  shown  in  the 
formulae),  and  may  be  conveniently  represented  either  by  the 
general  formula  MA35SO3,  or  they  may,  by  trebling  the  formulae 
just  given  above,  be  represented  in  the  following  manner : — 

Basic  sulphate  of  antimony  Sb^  3 SO4,  2 Sb^Oa 

“ “ bismuth  Bia  3 SO4,  2 BiaOs 

“ “ iron  Fea  3 HO4,  2 FejOs 

“ “ aluminum  Ala  3 SO4,  2 APOa 

In  the  majority  of  instances,  when  a dibasic  acid,  such  as  the 
sulphuric,  acts  upon  a sesquioxide,  such  as  alumina  or  ferric  oxide, 
21 


322 


METALS  WITH  YAHIABLE  EQEIYALEXTS. 


three  atoms  of  the  dibasic  acid  are  required  to  form  a normal 
soluble  salt,  in  which  case  the  metal  becomes  ter  equivalent,  and 
two  atoms  of  the  metal  are  therefore  equivalent  to  6 atoms  of 
hydrogen.  For  example,  (2tl'")203  + 3 H^SO,  yield  3 H3O  + 
3 SO4,  and  under  these  particular  circumstances  iron  itself, 
instead  of  being  biequivalent,  as  in  the  ferrous  salts,  becomes  ter- 
equivalent  in  these  ferric  salts.  (Fe'")203  + 3 H^SO,  yield  3 
O + (Fe"')2  3 SO^ ; thus  affording  an  example  of  the  remarkable 
fact  of  a metal  possessing  two  different  equivalents. 

Other  metals  besides  iron  exhibit  this  power  of  assuming  two 
different  equivalents  : chromium  and  cerium,  for  example,  in  par- 
ticular cases  may  be  biequivalent,  whilst  in  other  cases  they  are 
undoubtedly  terequivalent  metals  ; for  instance,  they  are  biequi- 
valent in — 

Chromous  chloride  and  sulphate  •0r"Cl2 ; •0r''SO4 

Cerous  chloride  and  sulphate ■Ge''Cl2 ; ■0e"SO4 

and  terequivalent  in 

Chromic  chloride  and  sulphate •0r"'Cl3;  •0r’''2  3 SO4 

Ceric  chloride  and  sulphate  ■6e'''Cl3 ; •0e'''2  3 SO4. 

In  the  protoxides  and  salts  corresponding  to  them,  these  metals 
are  biequivalent ; whilst  in  the  sesquioxides  and  the  salts  corre- 
sponding to  them  the  metals  are  terequivalent.  Tin,  platinum, 
and  palladium,  again,  in  certain  cases  are  biequivalent,  in  others 
quadrequivalent. 

The  normal  salts  derived  from  these  different  sesquioxides  by 
the  action  of  acids  upon  them,  have  usually  an  acid  taste,  and 
redden  litmus  powerfully.  This  is  well  seen  in  the  ferric  and 
aluminic  sulphates. 

It  is  not  necessary  that  the  two  or  three  atoms  of  basyl  which 
the  salts  of  the  dibasic  or  tribasic  acids  contain  should  consist 
of  the  same  metal.  Indeed,  it  has  already  been  shown,  in  the 
case  of  the  various  phosphates,  that  several  basyls  may  coexist  in 
the  same  salt,  in  definite  proportions.  There  is,  for  example,  a 
pyrophosphate  of  sodium  and  hydrogen,  composed  of  Xa^H^P, 
O^,  in  which  two  atoms  of  hydrogen  supply  the  place  of  their 
equivalent  of  sodium  ; and  in  the  microcosmic  salt  (^a,II^X,II, 
PO^ . 4 II2O),  we  have  a tribasic  phosphate  of  sodium,  ammonium, 
and  hydrogen,  where  each  of  the  three  atoms  of  basyl  differs  from 
the  others. 

Xow  it  frequently  happens  that  hydrogen  is  one  of  the  basyls 
present  in  the  salt,  and  when  such  is  the  case,  the  salt,  when 
dissolved  in  water,  often  has  a sour  taste,  and  reddens  litmus- 
paper  strongly.  It  is  in  this  way  that  the  most  common  variety 
of  acid  salts  is  formed.  Cream  of  tartar,  or,  as  it  is  often  called, 
bitartrate  of  potash,  offers  a good  illustration  of  this  kind  of 
salt. 

Cream  of  tartar  is  a sparingly  soluble  crystallizable  compound, 
of  an  agreeable  acidulous  taste ; it  consists  of  KHO^H^Og,  and 
is,  in  fact,  a dibasic  tartrate  of  potassium  and  hydrogen : if  now 
it  be  dissolved  in  hot  water,  and  another  equivalent  proportion 


POLYBASIC  ACIDS DOUBLE  SALTS. 


323 


of  caustic  potash  be  added,  the  hydrogen  is  displaced  by  tlie 
second  atom  of  potassium,  all  the  acid  taste  disappears,  and  nor- 
mal tartrate  of  potassium  (K20^H40e),  a salt  which  no  longer 
affects  the  colour  either  of  litmus  or  of  turmeric  paper,  is  jiroduced. 
An  equivalent  quantity  of  carbonate  of  potassium  may  be  sub- 
stituted for  caustic  potash  with  equal  effect,  as  it  will  be  decom- 
posed, and  the  carbonic  anhydride  will  be  expelled  with  efferves- 
cence. Carbonate  of  sodium  may  be  substituted  for  the  carbon- 
ate of  potassium,  but  in  this  case  a different  salt,  known  as  Ro- 
chelle salt,  the  tartrate  of  sodium  and  potassium  (KRaOJI.O^, 
4 H^O)  will  be  formed  by  the  following  reaction;  fSTall-GOa-f 

KHO.H  A = H,e  + ce,  4-  KRaO  a. 

Acid  salts,  however,  though  generally  formed,  like  cream  of 
tartar,  from  a dibasic  acid  which  has  reacted  with  1 atom  only 
of  a powerful  base,  the  place  of  the  second  atom  of  metal  being 
supplied  by  an  atom  of  hydrogen,  are  not  always  so  produced : 
an  acid  sulphate  of  potassium,  which  is  anhydrous,  may  be  ob- 
tained (K2S04,S03)  ; and  the  acid  chromate  or  bichromate  of 
potash  always  occurs  in  the  anhydrous  form.  Such  salts  have 
been  distinguished  from  ordinary  acid  salts  by  the  term  anhydro- 
salts^  or  salts  containing  an  anhydride. 

(555)  Double  Salts. — The  foregoing  description  of  the  poly- 
basic  acids  has  presented  us  with  certain  cases  in  which  double 
salts  are  formed.  There  are  several  varieties  of  double  salts.  The 
most  common  are  those  which  are  produced  by  the  union  of  two 
dissimilar  metals  with  the  same  acid  radicle.  These  varieties, 
however,  are  confined  within  certain  limits.  It  is  not  possible  to 
form  double  salts  ad  libitum^  by  bringing  2 equivalents  of  any 
acid  in  contact  with  1 equivalent  each  of  any  two  bases.  Chemists 
assume  tliat  when  two  different  metallic  monads,  such  as  sodium 
and  potassium,  combine  wdth  the  same  acid  radicle  in  the  propor- 
tion of  1 atom  of  each  metal  to  form  a double  salt  (like  Rochelle 
salt),  the  acid  in  question  is  dibasic.  The  larger  number  of  double 
salts  which  have  been  produced  are  thus  formed  by  the  combina- 
tion of  different  metals  with  polybasic  acid  radicles.  The  so- 
called  bicarbonates,  binoxalates,  and  many  other  similar  com- 
pounds, prove,  on  examination  to  be,  as  we  have  already  shown, 
true  double  salts  of  tliis  class,  analogous  to  normal  or  neutral  salts 
in  composition.  Some  other  considerations  relating  to  the  basicity 
of  acids  and  to  the  polybasic  acids  will  be  more  conveniently 
deferred  until  tlie  nature  of  the  organic  acids  has  been  discussecl. 

The  formation  of  another  remarkable  series  of  doul)le  salts,  par- 
ticularly investigated  by  Graham,  appears  to  be  directly  connected 
with  the  mode  in  which  water  attaches  itself  to  certain  salts.  In 
most  cases  the  water  of  crystallization  may  be  expelled  from  a salt 
by  exposing  it  to  a temperature  not  exceeding  212°.  This,  how- 
ever, does  not  always  happen  : sometimes  all  the  water  of  crystal- 
lization may  thus  be  expelled  with  the  exception  of  a single  atom, 
which  requires  a much  higher  heat  for  its  expulsion,  although  in 
these  cases  it  does  not  appear  to  act  in  any  degree  as  a base. 
Under  these  circumstances  it  was  found  that  this  last  atom  of 


324 


DOUBLE  SALTS. 


water  might  readily  be  displaced  by  adding  to  the  salt  an  equiva- 
lent of  certain  anhydrous  salts.  An  excellent  illustration  of  such 
a method  of  the  formation  of  double  salts  is  afforded  in  the  case 
of  a certain  class  of  the  sulphates.  All  the  sulphates  of  metals 
isomorphous  with  magnesium  are  capable  of  forming  double  salts 
of  this  nature  with  some  anhydrous  sulphate  not  isomorphous  with 
this  class — such,  for  instance,  as  the  sulphate  of  potassium. 

When  sulphate  of  magnesium  (MgS04,H20 . 6 H^O)  is  heated 
to  212°,  six  out  of  the  seven  atoms  of  water  are  expelled,  but  the 
seventh  atom  is  retained  until  the  temjDerature  is  raised  consider- 
ably. If,  however,  sulphate  of  magnesium  and  sulphate  of  potas- 
sium be  separately  dissolved  in  water  in  equivalent  proportions, 
mixed  while  hot,  and  allowed  to  crystallize,  a new  double  salt 
(MgS04,K2SO-4 . 6 H^O)  is  deposited  ; having  the  same  crystalline 
form  as  sulphate  of  magnesium,  but  it  contains  only  6 atoms  of 
water  of  crystallization.  The  seventh  atom  has  been  displaced  by 
the  sulphate  of  potassium,  and  this  portion  of  water  has  hence 
been  termed  by  Graham,  constitutional,  or  saline  water. 

There  is  another  well-known  variety  of  double  salts,  in  which 
it  is  not  necessary  that  the  component  salts  should  be  formed 
from  oxides  of  the  same  class,  or  even  contain  a similar  number 
of  equivalents  of  the  radicle  of  the  acid.  In  this  way  sulphates 
of  sesquioxides  often  unite  with  the  sulphates  of  protoxides  to 
form  well-characterized  double  salts : a striking  example  of  this 
kind  is  afforded  in  the  important  tribe  of  alums.  Common  alum 
consists  of  a combination  of  sulphate  of  potassium  with  sulphate 
of  aluminum  and  water  of  crystallization  (KAl  2 SO^,  12  Il2^) : 
numerous  other  salts,  having  the  same  crystalline  form,  and  of 
similar  composition,  might  be  mentioned. 

There  are  a few  instances  of  two  different  acid  radicles  being 
united  to  one  basyl,  but  they  are  neither  sufficiently  numerous  nor 
important  to  merit  lengthened  notice,  and  are  more  frequently 
met  with  among  natural  than  artificial  combinations. 

Instances  are  common  in  Avhich  two  different  haloid  salts 
unite  with  each  other ; compounds  of  this  description  are  most 
usual  between  the  chlorides,  iodides,  and  bromides  of  the  less  oxi- 
dizable  metals  with  those  of  the  metals  contained  in  the  alkalies 
and  earths : the  double  chloride  of  platinum  and  potassium 
(2  KCl,PtCl4)  and  the  double  iodide  of  mercury  and  potassium 
(2  Kl,IIgl2)  are  good  instances  of  such  compounds.  Bonsdorff 
proposed  to  consider  these  compounds  in  the  light  of  salts  in 
which  the  chloride  and  iodide  of  the  electronegative  metal  (pla- 
tinum, gold,  &c.)  acted  the  part  of  an  acid  towards  the  electro- 
positive chloride  (cliloride  of  potassium,  sodium,  Ac.) ; but  this 
view  is  not  tenable.  Such  salts  are  never  resolved  by  electric 
action  into  their  constituent  chlorides,  and  the  acid  reaction  of 
the  higher  chlorides  is  not  neutralized  or  modified  by  combination 
with  the  chlorides  of  the  alkaline  metals  ; in  fact,  the  constituent 
chlorides  themselves  are  salts. 

Many  double  salts  may  be  formed  by  fusion  with  each  other, 
though  tliey  cannot  be  procured  by  the  usual  method  of  crystal- 


STIBSALTS. 


325 


lization  from  a solution  containing  equivalent  quantities  of  the 
two  salts.  Chloride  of  sodium,  for  example,  may  he  melted  with 
an  equivalent  amount  of  chloride  of  calcium,  of  strontium,  or  of 
barium ; and  in  each  case  a compound  salt  is  obtained,  which  has 
a much  lower  fiising-point  than  either  of  its  component  chlorides 
in  a separate  form ; but  the  double  salt  is  decomposed  when  it  is 
dissolved  in  water. 

(556)  Subsalts. — A very  different  series  of  saline  compounds 
still  remains  for  consideration,  and  in  these  the  proportion  of  base 
predominates  over  that  of  the  acid ; they  are  usually  designated 
basic  salts^  or  subsalts.  The  theory  of  the  formation  of  these 
compounds  is  very  imperfect.  In  many  cases  subsalts  may  be 
compared  to  salts  which  contain  water  of  crystallization,  the  atoms 
of  base  in  excess  being  assumed  to  be  attached  to  the  normal  salt 
in  a manner  analogous  to  that  by  which  the  water  of  crystalliza- 
tion is  retained  in  ordinary  instances. 

The  tendency  to  the  formation  of  subsalts  is  limited  to  certain 
acids  and  bases.  It  is  indeed  one  of  the  peculiarities  of  the 
monad  bases,  such  as  the  alkalies,  and  the  oxides  of  silver  and 
thallium,  that  they  do  not  form  basic  salts  ; whilst  the  dyads,  such 
as  the  oxides  of  copper,  lead,  mercury,  and  zinc,  have  a strong 
tendency  to  do  so,  while  the  oxides  of  the  triads,  when  basic,  such 
as  oxide  of  antimony  and  bismuth,  have  a still  greater  propensity 
to  form  basic  salts : no  general  rule  can  be  laid  down  for  the  acids, 
but  among  the  common  acids,  those  which  most  frequently  form 
basic  salts  are  the  sulphuric,  nitric,  carbonic,  and  acetic  acids. 
Among  basic  sulphates,  for  example,  are  the  following : — 

Brochantite -GUSO4,  3 -GuO,  4 H2O 

Tribasic  sulphate  of  copper GUSG4,  2 GUOH2O 

Turpeth  mineral HgS04,  2 HgO. 

Among  basic  nitrates  are. 

Dibasic  nitrate  of  lead Pb  2 5fO3,PbO,H20 

Tribasic  nitrate  of  copper Gu  2 NO3  3 GUOH2G 

Subnitrate  of  mercury 3 (Hg2  2 NG3),  HgoGjHaG 

De  Marignac’s  do 3 (iig2  2 NG3),  2 Hg20H20. 

The  following  are  instances  of  basic  acetates : — 

Dibasic  acetate  of  copper  (verdigris) Gu  2 G2H3G2,  GuG  6 H2G 

Tribasic  acetate  of  copper 2 (Gu  2 G2H3G2),  4 GuG,  3 H2G 

Tribasic  acetate  of  lead Pb  2 G2H3G2,  2 PbGjHaG 

Hexabasic  acetate  of  lead Pb  2 G2H3G2,  5 PbG,H2G. 

As  examples  of  basic  carbonates,  we  give. 

Malachite GuGG3,GuGIl2G 

Blue  carbonate  of  copper 2 GuGG3,GuGH2G 

White  lead 2 PbGG3,PbGH2G. 

Just  as  we  liave  polybasic  acids,  so  are  there  polyacid  basyls — 
basyls,  that  is,  which  require  more  than  one  atom  of  a monobasic 
acid  for  their  saturation.  This  is  the  case,  for  example,  with  the 
metals  of  the  alkaline  earths;  but  as  yet  the  class  of  double  salts, 
which  they  no  doubt  compose,  has  been  scarcely  examined. 

(557)  Oxychlorides.,  <&c. — A class  of  compounds  which  resemble 
the  subsalts  more  than  any  others,  is  presented  to  us  in  the  bodies 


326  SYilBOLS  OF  MIXTURES  OF  ISOMOEPHOUS  COMPOUNDS. 

termed  oxyclilorides,  oxjiodides,  and  oxycyanides.  In  these  com- 
pounds, one  atom  of  the  chloride,  of  the  iodide,  or  of  the  cyanide 
of  a metal  is  united  with  one  or  more  atoms  of  the  oxide  of  the 
same  metal.  Turner's  yellow,  which  is  an  oxychloride  of  lead 
(PbClj  7 PbO),  is  a well-known  commercial  article  belonging  to 
this  class.  Such  combinations  usually  occur  between  oxides  and 
chlorides  or  iodides  of  metals  the  pure  chlorides  or  iodides  of 
which  never  form  any  hut  anhydrous  crystals. 

Some  salts  enter  into  combination  with  other  bodies,  and  form 
compounds  which  are  in  many  respects  anomalous  ; such  for 
instance  are  the  compounds  of  ammonia  with  many  dry  salts  : 
2 atoms  of  chloride  of  silver  will  in  this  manner  absorb  3 atoms  of 
ammonia.  !\[any  of  the  salts  of  copper  exhibit  a similar  power  (622). 


CHAPTEK  XII. 

GEOUP  I. METALS  OF  THE  ALKALIES. 


MetaL 

Sym- 

bol. 

Atomic 

weight. 

Atomic 

volume. 

Specific 

heat. 

1 Fusing 
j point  F°. 

Specific 

gravity. 

Electric 

conduc- 

tivity. 

6S— 71  F®. 

Coesiura 

1 Cs 

133 

1 

Rubidium 

1 Eb 

85-3 

1 101-3 

1-52 

Potassium  . . . 

K 

391 

44-96 

0-16956 

! 144  5 

0-865 

20  85 

Sodium 

Xa 

23 

23  60 

0-29340 

1 207-7 

0 972 

37  43 

Lithium 

L 

•7 

n-80 

0-94080 

356  0 

0 593 

19-00 

The  metals  of  this  class  are  soft,  easily  fusible,  and  volatile  at 
high  temperatures  ; they  furnish  several  oxides,  of  which  only  one 
is  basic.  This  oxide  is  caustic,  and  extremely  deliquescent : the 
hydrate  cannot  be  decomposed  by  ignition  ; it  absorbs  carbonic 
acid  with  avidity.  The  carbonates  are  soluble,  so  are  the  sulphides 
and  hydrosulphates  of  the  sulphides  (see  p.  289). 

§ I.  Potassil’m:  K'=39T.  Sp.  Gr.  0.865;  Fusing-pt.  144°‘5. 

Native  Compounds  which  contain  Potassium. 


Alum (KAl  2 SO,,  12  H.O 

Felspar KXa)'20,Al203,  6 SiO,. 

Biaxal  mica [(AlPe)'"A,Siej. 


(558)  SyiTibols  of  2Iixtures  of  Isomoiphous  Compounds. — The 
formulge  employed  above  for  felspar  and  mica  require  explanation, 
as  the  principle  of  notation  adopted  in  these  cases  will  be  applied 
hereafter  to  the  formulae  of  a large  number  of  minerals.* 

* The  fonnuljE  of  the  silicates  are  so  complex,  and  the  true  function  of  sdica  in 
combination  is  at  present  so  ill  defined,  that  I have  throughout  formulated  silica  as 
present  in  combination  with  the  bases,  in  accordance  with  the  older  view,  retaining, 
however,  the  new  atomic  weights. 


NOTATION  OF  MIXTURES  OF  ISOMORPHOUS  COMPOUNDS. 


327 


It  often  happens  that  isomorphons  bases  displace  each  otlier 
in  the  same  mineral  without  altering  its  form  or  mineralogical 
characters,  or  even  Avithout  altering  its  general  chemical  formula. 
Mica,  for  example,  may  be  regarded  as  a compound  of  1 atom  of 
a silicate  of  a protoxide  of  a metal  with  3 atoms  of  a different 
silicate  of  a sesquioxlde  of  a different  metal.  Let  M stand  for 
the  metallic  base  of  the  protoxide,  H for  the  metallic  base  of  the 
sesquioxide ; the  general  formula  for  mica  may  then  be  expressed 
thus : — 

Mica  = [M,0,3  Sie„  3 (bTA^SiO,)]. 

JSTow  the  components  of  potash-mica  are  principally  silicate  of 
potash  and  silicate  of  alumina,  the  potash  being  the  metallic  prot- 
oxide and  the  alumina  being  the  metallic  sesquioxide  ; but  sesqui- 
oxide of  iron,  sesquioxide  of  manganese,  and  sesquioxide  of 
chromium  are  also  isomorphous  with  alumina  : these  compounds 
frequently  displace  a portion  of  the  alumina  from  its  combinations, 
and  this  is  especially  the  case  with  the  sesquioxide  of  iron.  The 
peculiarity  of  isomorphous  metals,  when  they  displace  each  other, 
is  this — that  the  displacement  is  liable  to  occur  in  any  possible 
proportion  ; for  example,  in  different  specimens  of  mica  the  re- 
lative proportions  of  iron  and  aluminum  are  liable  to  great 
variations ; this  arises  from  the  fact  that  the  ferric  silicate  and 
silicate  of  aluminum  which  are  isomorphous,  may  be  mixed  in 
any  conceivable  proportion,  and  will  crystallize  together  without 
altering  the  form  of  the  mineral.  The  same  fact  may  also  be 
represented  by  stating  that  they  may  vary  indefinitely  in  amount 
provided  only  that  the  quantity  of  the  two  metals  taken  together 
in  any  one  specimen  furnishes  such  a proportion  of  a metallic 
sesquioxide  as  is  equivalent  to  the  silica  in  that  portion  of  the 
mineral ; that  is  to  say,  that  the  two  proportionals  of  metal 
required  for  combination  with  the  3 proportionals  of  oxygen  in 
the  sesquioxide,  may  either  consist  wholly  of  aluminum,  or  a small 
hut  indefinite  proportion  of  the  aluminum  may  have  its  place 
supplied  by  a small  hut  equivalent  quantity  of  iron,  or  a large 
proportion  of  the  aluminum  may  have  its  place  supplied  by  a 
corresponding  and  equivalent  proportion  of  iron. 

Kow  the  method  of  notation  adopted  in  the  preceding  for- 
mulae is  employed  to  indicate  precisely  this — that  the  proportions 
of  the  two  or  more  metals,  the  symbols  of  which  are  bracketed 
together,  thus,  (AlFeMn)'^'203,  are  liable  to  vary  Avithin  any  con- 
ceivable limits,  provided  that  the  united  amount  of  all  the  metals 
so  bracketed  be  exactly  sufficient  to  form  a true  sesquioxide  Avith 
the  three  proportionals  of  oxygen. 

In  like  manner,  in  the  case  of  the  potash  in  felspar,  tlie  })lace 
of  part  of  the  potassium  may  be  supplied  by  sodium ; but  the 
proportions  of  the  two  taken  togetlier  require  exactly  tlie  same 
amount  of  oxygen,  and  consequently  saturate  the  same  ])roportion 
of  silica,  that  I atom  of  potash  alone  would  havm  re<piirod. 

This  frequent  partial  displacement  of  one  isomorplious  metal 
by  another  in  native  crystallized  minerals  renders  much  caution 


328 


POTASsniM — ^rrs  pkopeeties. 


necessary  in  interpreting  the  results  of  an  analysis.  The  difficulty 
of  fixing  the  formula  of  a mineral  of  course  increases  with  the 
complexity  of  its  composition,  and  it  is  with  the  silicates  especially 
that  these  difficulties  are  experienced.  It  is  usual,  when  the  ana- 
lytical operations  are  completed,  to  ascertain  the  proportion  of 
oxygen  in  the  silica,  then  the  proportion  of  oxygen  contained 
in  the  sesquioxides,  and  lastly  the  quantity  of  oxygen  in  the  prot- 
oxides ; because,  however  much  the  proportions  of  the  difierent 
metals  may  vary  in  difi’erent  specimens  of  the  same  mineral, 
the  ratio  of  the  oxygen  in  both  sets  of  bases  to  the  oxygen  in 
the  silica  remains  uniform.  In  felspar,  for  instance,  if  the 
proportion  of  oxygen  in  the  silica  be  taken  as  12,  that  in  the 
sesquioxide  of  aluminum  is  3,  and  that  in  the  protoxide  of  potas- 
sium or  sodium  is  1. 

(559)  PoTASsioi. — This  remarkable  metal  was  discovered  by 
Da\y,  in  the  year  1807,  and  its  isolation  marks  an  important  era 
in  the  progress  of  philosophical  chemistry.  The  alkalies  and  the 
earths  had  long  been  suspected  to  be  compound  bodies,  but  up  to 
that  period  they  had  resisted  all  attempts  to  decompose  them. 
When  once  potassium,  however,  had  been  separated  from  its  com- 
pounds, and  potash  had  been  proved  to  be  an  oxide  of  this  metal, 
the  decomposition  of  the  other  alkalies  and  earths  followed  as  a 
necessary  consequence : more  correct  ideas  upon  fundamental 
points  of  chemical  theory  were  introduced ; new  methods  of  re- 
search were  placed  within  reach  of  the  analytical  chemist,  and 
potassium  itself,  from  its  powerful  attraction  for  oxygen,  became 
an  important  addition  to  the  reagents  of  the  laboratory. 

Properties. — Potassium  is  a bluish- white  metal,  which  is  brittle, 
and  has  a crystalline  fracture  at  32°  ; at  temperatures  a little  above 
this  it  is  malleable  ; at  60°  it  is  soft ; as  the  temperature  rises  it 
becomes  pasty,  and  at  111° ’5  it  is  completely  liquid.  Whilst  in 
the  soft  condition,  two  clean  surfaces  of  the  metal  admit  of  being 
welded  together  like  iron ; at  a red  heat  it  may  be  distilled,  and 
it  yields  a beautiful  green  vapour.  Potassium  is  light  enough  to 
fioat  in  water,  haffing  a specific  gravity  of  only  0-865.  If  ex- 
posed to  the  air,  even  for  a few  minutes  only,  it  becomes  covered 
with  a film  of  oxide  : when  heated  to  its  point  of  volatilization  it 
bursts  into  fiame,  and  burns  with  great  \fiolence.  The  powerful 
attraction  of  potassium  for  oxygen  is  seen  on  throwing  the  metal 
into  water,  in  which  case  part  of  the  water  is  immediately  decom- 
posed ; half  the  hydrogen  of  the  water  is  displaced  by  the  potas- 
sium andhydi-ate  of  potash  is  formed,  2 Il20  + K2=2  KHO  + 
while  the  escaping  hydrogen  carries  with  it  a small  portion  of  the 
volatilized  metal,  and  taking  fire  from  the  heat  evolved,  burns 
with  a beautiful  rose-red  fiame  ; the  metal  melts  and  swims  about 
rapidly  upon  the  water,  and  finally  disappears  with  an  explosive 
burst  of  steam,  as  the  globule  of  melted  hydrate  of  potash  which 
is  formed  during  its  oxidation  becomes  sufficiently  cool  to  come 
into  contact  with  the  water.  Potassium  decomposes  nearly  all 
gases  which  contain  oxygen,  if  it  be  heated  in  contact  with  them ; 
and  at  a high  temperature  it  will  remove  oxygen  from  almost  all 


PEEPAHATION  OF  POTASSIUM. 


329 


bodies  into  the  constitution  of  which  that  element  enters.  It 
becomes  necessary  therefore  to  preserve  the  metal  either  in  ex- 
hausted hermetically  sealed  glass  tubes,  or  under  the  surface  of 
some  liquid,  like  naphtha,  which  does  not  contain  oxygen.  At  a 
heat  short  of  redness  potassium  absorbs  hydrogen  and  becomes 
converted  into  a greyish  mass  (HK^  ?) ; but  if  more  strongly 
heated,  the  hydi’ogen  is  again  expelled.  Potassium  enters  directly 
into  combination  with  the  halogens  and  with  sulphur,  selenium, 
and  tellurium,  burning  vividly  when  heated  with  them.  It  likewise 
absorbs  carbonic  oxide  wdth  facility  when  heated  moderately  in 
it,  or  when  the  vapour  of  potassium  is  allowed  to  condense  slowly 
in  an  atmosphere  of  the  gas  ; a black  mass  is  thus  formed  from 
which  the  metal  cannot  be  recovered.  ' It  furnishes  rhodizonate 
of  potassium  when  treated  with  water,  and  occasions  considerable 
waste  in  the  ordinary  method  of  preparing  potassium. 

(560)  Preparation. — 1.  Davy  originally  obtained  potassium  by 
decomposing  a fragment  of  hydrate  of  potash  (which  had  become 
dightly  moistened  upon  its  surface  by  exposure  to  the  air  for  a 
few  minutes)  by  the  current  of  a voltaic  battery  of  200  or  250 
pairs  of  six-inch  plates,  on  Wollaston’s  construction.  The  dry 
hydrate  is  an  insulator,  but  a trace  of  moisture  confers  upon  it  a 
sufficient  degree  of  conducting  power : under  such  circumstances, 
globules  of  metallic  potassium  are  separated  at  the  negative  wire, 
and  may  be  preserved  under  naphtha.  They  burn  vividly  in  air, 
leaving  an  intensely  alkaline  residue.  This  method  of  procuring 
the  metal,  however,  furnishes  it  only  in  very  small  quantity,  and 
is  difficult  and  expensive. 

2.  — Gay-Lussac  and  Thenard,  in  1808,  invented  a method  by 
which  potassium  may  be  obtained  by  purely  chemical  means  in 
greater  abundance.  Iron  turnings  were  heated  to  whiteness  in  a 
curved  gun-barrel,  which  was  covered  with  a clay  lute,  to  preserve 
it  from  the  action  of  the  air  at  a high  temperature,  and  melted 
hydrate  of  potash  was  allowed  to  pass  slowly  over  the  ignited  iron  ; 
decomposition  ensued,  the  iron  combined  with  the  oxygen,  and 
potassium  along  with  hydrogen  passed  forwards,  the  potassium  con- 
densing in  a copper  receiver  which  was  kept  cool. 

3.  — The  process  by  which  potassium  is  now  obtained  consists 
in  decomposing  the  carbonate  of  potassium  by  charcoal,  a plan 
originally  invented  by  Curaudau,  and  improved  by  Brunner. 
This  operation  has  been  carefully  studied  by  Mareska  and  Donny 
{Ann.  de  Chimie^  III.  xxxv.  147).  In  order  to  ensure  a successful 
result,  attention  to  a number  of  minute  precautions  is  requisite. 
The  material  which  is  best  adapted  to  its  preparation  is  the  potas- 
sium salt  of  some  vegetable  acid,  which,  when  decomposed  by 
heat  in  a vessel  from  which  air  is  excluded,  leaves  a large  quantity 
of  carbon.  Bor  this  purpose  the  acid  tartrate  of  potassium,  or 
crude  tartar,  is  preferred.  About  6 lb.  of  this  substance  is  placed 
in  a capacious  iron  crucible  furnished  with  a cover,  and  ignited 
till  it  ceases  to  emit  combustible  vapours.  A porous  mass  of  car- 
bonate of  potassium,  intimately  mixed  with  very  finely  divided 
carbon,  is  thus  obtained  : this  is  rapidly  cooled  by  moistening  the 


330 


EXTRACTION  OF  POTASSIOI. 


exterior  of  the  crucible  with  cold  water  ; the  charred  mass,  when 
cold,  is  broken  up  into  lumps  about  the  size  of  a hazel-nut,  and 
quickly  introduced  into  a wrought-iron  retort.  This  retort  is 
usually  made  of  one  of  the  iron  bottles  in  which  mercury  is  im- 
ported ; it  is  introduced  into  a tiirnace,  a,  as  sho\^Ti  at  h,  fig.  329, 


Fia.  329. 


Fig.  330. 


and  placed  horizontally  upon  supports  of  fire-brick,  yy*;  a wrought- 
iron  tube,  4 inches  long,  serves  to  convey  the  vapours  of  potas- 
sium produced  during  the  distillation  into  a receiver,  which  it 
is  found  most  advantageous  to  construct  of  the  form  shown  on  an 
enlarged  scale  in  fig.  330.  It  consists  of  two  pieces  of  wrought 
iron,  (2,  J,  which  are  fitted  closely  to  each  other,  so  as  to  form  a 
shallow  box  only  a quarter  of  an  inch  deep,  and  are  confined  in 
their  places  by  clamp  screws  : the  iron  plate  should  be  one-sixth 
of  an  inch  thick,  12  inches  long,  and  5 inches  wide  ; the  receiver 
is  open  at  both  ends,  the  socket  fitting  upon  the  neck  of  the  iron 
retort.  The  object  of  preparing  the  receiver  of  this  particular 
form  is  to  ensure  the  rapid  cooling  of  the  potassium,  and  so  to 
withdraw  it  from  the  action  of  the  carbonic  oxide  which  is  disen- 
gaged during  the  whole  process.  Before  this  receiver  is  connected 
with  the  tube,  the  fire  is  slowly  raised  until  the  retort  attains  a 
dull  red  heat ; powdered  vitrified  borax  is  then  sprinkled  over  its 
exterior ; the  borax  melts,  and  forms  a coating  which  protects 
the  metal  from  oxidation.  The  heat  is  then  urged  until  it  becomes 
very  intense.  A mixture  of  coke  and  charcoal  forms  a fuel  well 
adapted  to  this  puiq)ose ; care  should  be  taken  that  the  tempera- 
ture of  the  furnace  be  raised  as  equally  throughout  every  part  as 
possible.  When  a full  reddish- white  is  attained,  vapours  of  potas- 
sium begin  to  appear,  and  burn  with  a brilliant  fiame  : the 
receiver  is  now  adjusted  to  the  iron  neck  of  the  retort,  which  is 
not  allowed  to  project  more  than  a quarter  of  an  inch  through  the 
iron  plate  which  forms  part  of  the  front  wall,  <?,  of  the  furnace, 
lest  the  tube  should  become  obstructed  by  the  accumulation  of 
solid  potassium.  Should  any  obstruction  occur,  it  must  be  re- 
moved by  thrusting  in  an  iron  rod  ; if  this  fails,  the  fire  must  be 
immediately  withdrawn  ; this  is  readily  eflected  by  removing  the 
fire-bars,  from  the  furnace,  with  the  exception  of  two  which 


OXIDES  OF  POTASSIUM. 


331 


support  the  retort ; the  fuel  thus  falls  into  the  ashpit.  The  re- 
ceiver is  kept  cool  by  the  application  of  a wet  cloth  upon  its 
exterior.  When  the  operation  is  complete,  the  receiver  with  the 
potassium  is  removed,  and  instantly  plunged  into  a vessel  of 
rectified  Persian  naphtha,  provided  with  a cover.  The  vessel  is 
kept  cool  by  immersion  in  water.  When  this  apparatus  is 
sufficiently  cold,  the  potassium  is  detached,  and  preserved  under 
naphtha. 

In  order  to  obtain  the  maximum  produce  of  potassium,  it  is 
necessary  that  the  mixture  of  carbonate  of  potassium  and  carbon 
should  contain  1 atom  of  the  carbonate  to  2 of  carbon,  or  138 
parts  of  the  carbonate  by  weight  to  24  of  carbon.  Upon  the 
application  of  heat  the  mixture  is  wholly  converted  into  carbonic 
oxide  and  potassium;  K2003+02=K2 -f- 3 UO.  The  charge 
usually  yields  about  one-fourth  of  its  weight  of  crude  potassium, 
some  loss  during  the  process  being  inevitable.  Donny  and 
Mareska  found  this  loss  to  amount  to  about  one-third  of  the  entire 
quantity  of  the  metal  contained  in  the  charge. 

The  potassium  so  obtained  is  not  pure  ; it  is  necessary  to 
subject  it  to  a second  distillation  in  an  iron  retort.  This  precau- 
tion is  essential  / for,  if  it  be  neglected,  a black  detonating  com- 
pound is  speedily  formed  by  exposure  to  the  atmosphere,  and  is 
even  produced  spontaneously,  although  the  metal  be  kept  under 
naphtha ; this  subtance  explodes  violently  upon  the  slightest 
friction.  The  purified  metal  amounts  to  about  two-thirds  of  the 
quantity  operated  on.  A third  distillation  may  be  necessary  if 
the  potassium  be  required  in  a state  of  perfect  purity.  A little 
impure  potassium  almost  always  remains  in  the  tube  attached 
to  the  retort ; and  in  order  to  prevent  the  possibility  of  the  for- 
mation of  the  detonating  compound  already  mentioned,  it  is  best 
to  detach  this  tube  as  soon  as  it  is  cold,  and  to  immerse  it  in 
water. 

(561)  Oxides  of  Potassium. — ^Potassium  forms  three  well- 
established  compounds  with  oxygen  : a protoxide,  which  consti- 
tutes potash,  the  basis  of  the  salts  of  the  alkali ; and  two  other 
oxides  which  do  not  form  corresponding  salts  with  acids.  A blue 
suboxide  appears  also  to  be  formed  upon  the  surface  of  the  metal 
during  its  gradual  oxidation  in  dry  air. 

K.  O. 

Potash K2O  = 94-2,  or  82-9'7  + 1P03  = 100 

Deutoxido  of  potassium  K2O2  = 110-2  “ TO'OS  + 29'02  = 100 

Peroxide  of  potassium.  K2O4  = 142-2  “ 54-93  + 45-07  = 100 

Tetroxide  of  Potassium  = 142*2  ; Ilarcourt,  Q.J.  Chenn. 

SoG.  xiv.  267). — This  substance  is  formed  when  potassium  is 
heated  gently  in  a current  of  dry  air  ; the  operation  must  be  com- 
pleted m a current  of  dry  oxygen  gas : if  formed  at  a tempera- 
ture of  536°,  it  slowly  cakes  together,  but  below  that  temperature 
it  famishes  a powder  of  a chrome-yellow  colour.  It  absor])s 
moisture  rapidly  when  exposed  to  the  air,  and  is  decomposed  by 
water  with  extrication  of  oxygen  and  formation  of  a solution  of 
binoxide  of  potassimn. 


332 


HYDEATE  OF  POTASH. 


(562)  Potash  (K^O  = 94-2,  or  KO  = 47*1). — This  compound 
can  be  procured  in  an  anhydrous  form  by  oxidating  potassium  in 
thin  slices,  in  air  perfectly  free  from  moisture  and  carbonic  anhy- 
dride ; or  by  heating  potassium  with  an  equivalent  quantity  of 
the  hydrate,  when  hydrogen  is  expelled  and  pure  potash  is  formed, 
2 KHO  + Kj  = 2 KKO  + H2.  It  is  white,  very  deliquescent, 
and  caustic ; wdien  moistened  with  water  it  becomes  incandes- 
cent : after  it  has  thus  become  hydrated,  no  degree  of  heat  is 
sufficient  to  expel  the  water.  Anhydrous  potash  fuses  at  a red 
heat,  and  is  volatilized  at  a high  temperature.  For  most  purposes 
the  presence  of  water  is  immaterial,  potash  is  therefore  generally 
procured  in  the  state  of  hydrate,  in  which  form  it  may  be  obtained 
without  difficulty. 

Hydrate  of  Potash^  or  Caustic  Potash  (KHO,  or  KO,HO  = 
56-1  ; Sp.  Gr.  2‘2)  is  prepared  by  dissolving  carbonate  of  potas- 
simn,  of  which  the  jpearlash  of  commerce  is  an  impure  variety, 
in  10  or  12  times  its  weight  of  water,  and  adding  to  the  boiling 
solution  a quantity  of  caustic  lime  equal  in  weight  to  half  the  car- 
bonate of  potassium  used ; the  lime  should  be  slaked,  madein  to 
a thin  paste  with  water,  and  added  in  small  portions  at  a time, 
so  that  the  liquid  may  be  maintained  at  the  boiling  point : a crys- 
talline carbonate  of  calcium  is  precipitated,  and  hydrate  of  pot- 
ash remains  in  solution  ; K^OBg  + -GaHgOg  giving  2 KHO  -}- 
OaOOg.  After  decantation  from  the  precipitate  the  liquid  is 
evaporated  rapidly  in  a clean  iron  or  silver  basin,  till,  when  the 
heat  is  raised  nearly  to  redness,  it  flows  without  ebullition,  like 
oil : it  is  then  either  cast  into  cylinders  in  a metallic  mould,  or 
is  poured  upon  a cold  stone  slab,  and  solidifies  on  cooling.  Hy- 
drate of  potash  may  be  obtained  crystallized  in  acute  rhombo- 
hedrons  (KHO,  2 H^O),  from  a hot  concentrated  aqueous  solu- 
tion. 

Hydrate  of  potash  is  one  of  the  most  indispensable  reagents 
to  the  chemist.  It  is  therefore  necessary  that  he  should  be  able 
readily  to  ascertain  its  purity,  and  if  needful  prepare  it  for  him- 
self: when  required  pure,  acid-carbonate  of  potassium,  in  crystals, 
may  be  decomposed  in  the  manner  above  described  by  means  of 
lime  obtained  from  black  marble.  The  impurities  which  occur 
most  frequently  in  ordinary  caustic  potash  are  carbonates,  sul- 
phates, chlorides,  and  silicates  of  calcium,  aluminum,  iron,  and 
lead,  and  peroxide  of  potassium.  If  pure,  it  is  perfectly  soluble 
in  water  without  efi*ervescence ; a diluted  solution  gives  no  precipi- 
tate with  baryta-water,  showing  the  absence  of  carbonates  and 
sulphates  ; it  yields  no  precipitate  wdth  oxalate  of  ammonium, 
showing  the  absence  of  salts  of  calcium.  On  neutralizing  it  with 
nitric  acid,  nitrate  of  silver  gives  no  precipitate,  showing  the  ab- 
sence of  chlorine.  Freedom  from  iron  or  metallic  impurities  is 
shown  by  the  absence  of  any  precipitate  on  the  addition  of  sul- 
phide of  ammonium.  Caustic  potash,  when  pure,  is  wholly  solu- 
ble in  alcohol,  the  impurities  above  mentioned  remaining  undis- 
solved. Common  potash  is  therefore  often  purified  by  forming  a 
solution  of  it  in  alcohol,  and  boiling  down  to  dryness  in  a silver 


HYDKATE  OF  POTASH. 


333 


vessel,  till  it  flows  tranquilly;  the  alcohol  is  thus  expelled,  the 
melted  hydrate  is  poured  off  upon  a silver  plate  from  the  black 
crust  which  forms  over  its  surface,  and  when  cold  it  is  broken  up 
and  placed  in  a well-closed  bottle. 

A dilute  solution  of  pure  potash  may  be  readily  obtained  by 
adding  a hot  solution  oi  hydrate  of  baryta  to  a solution  of  sul- 
phate of  potassium,  until  the  liquid  gives  no  further  precipitate, 
either  with  baryta  or  with  the  sulphate  of  potassium ; K2S0-4  -h 
BaH  A = + 2 KHO. 

Hydrate  of  potash,  after  fusion,  is  a hard,  greyish- white  sub- 
stance : it  rapidly  absorbs  both  moisture  and  carbonic  anhydride 
from  the  air ; it  is  soluble  in  about  half  its  weight  of  water,  with 
the  extrication  of  considerable  heat ; it  is  likewise  soluble  in  alco- 
hol to  an  almost  equal  extent.  . Hydrate  of  potash  has  a peculiar 
nauseous  odour,  and  an  acrid  taste ; it  is  a powerful  cautery,  and 
quickly  destroys  both  animal  and  vegetable  matters;  for  this 
reason  its  solution  cannot  be  filtered  except  through  pounded  glass 
or  sand,  and  is  always  best  clarified  by  allowing  the  impurities  to 
subside,  and  then  decanting  the  clear  liquid.  The  solution  should 
be  preserved  in  glass  bottles  into  the  composition  of  which  no  oxide 
of  lead  enters,  as  the  solution  gradually  dissolves  this  oxide  out  of 
the  glass.  It  also  attacks  vessels  even  of  green  glass  and  of  porce- 
lain when  heated  in  them. 

The  following  table  gives  approximatively  the  proportion  of 
anhydrous  potash  contained  in  100  parts  by  weight  of  solutions  of 
the  alkali  of  various  densities : — 

Strength  of  Solutions  of  Potash  {Dalton). 


Sp.  gr. 

KiO  in  100 
parts. 

Sp.  gr. 

K20  in  100 
parts. 

1-60 

46-7 

1-33 

26*3 

1*52 

42-9 

1*28 

23*4 

1-47 

1-23 

19-5 

1-44 

36-8 

1-19 

16-2 

1-42 

34-4 

1*15 

13-0 

1-39 

32-4 

Ml 

9-5 

1 36 

29-4 

1-06 

4-7 

The  Liquor  Potasses  of  the  Pharmacopoeia  contains  nearly  6 
per  cent,  of  the  solid  hydrate,  and  has  a sp.  gr.  of  1*058.  The 
concentrated  solution  used  for  organic  analysis  may  be  obtained 
by  dissolving  1 part  of  the  hydrate  in  3 parts  of  water. 

At  a high  temperature  hydrate  of  potash  is  wholly  volatilized  ; 
consequently  the  water  cannot  be  expelled  from  this  hydrate  by 
the  mere  application  of  heat.  Its  chemical  attractions  are  so  })ow- 
erful  that  few  vessels  are  found  capable  of  resisting  its  action ; 
those  which  contain  silica  are  decomposed  by  it,  and  platinum 
itself  is  oxidized  when  heated  in  contact  with  it : gold  and  silver 
resist  it  better.  Caustic  potash  decomposes  the  fixed  oils,  and 
converts  them  into  soluble  soaps : when  fused  with  siliceous  min- 


334 


NATURAL  SOURCES  OF  POTASH. 


erals  it  displaces  tlie  bases,  and  combines  with  the  silica,  forming 
silicate  of  potassium.  Potash  is  extensively  employed  in  the  arts : 
to  the  soap-boiler  and  the  glass-maker  it  is  indispensable ; in  com- 
bination in  the  form  of  nitre,  it  enters  largely  into  the  manufac- 
ture of  gunpowder ; and  in  greater  or  less  quantity  it  furnishes 
important  aids  to  a variety  of  processes  employed  in  the  manufac- 
tures of  the  country.  In  the  laboratory,  potash  is  in  constant  use 
for  absorbing  acid  gases,  such  as  carbonic  acid,  and  for  separating 
the  metallic  oxides  from  solutions  of  their  salts,  since,  owing  to  the 
powerful  attraction  of  the  alkali  for  acids,  it  readily  decomposes 
the  salts  of  all  the  metals  which  produce  oxides  insoluble  in 
water. 

Potash  is  present  in  small  proportion  in  all  fertile  soils,  the 
grand  reservoirs  of  this  alkali  being  the  different  varieties  of  clay, 
which  contain  2 or  3 per  cent,  of  it,  derived  from  the  disintegra- 
tion of  felspar,  in  which  it  exists  in  the  proportion  of  from  10  to 
12  per  cent.,  and  certain  kinds  of  mica,  which  yield  5 or  6 per 
cent.  By  exposure  to  the  air  and  atmospheric  vicissitudes,  these 
rocks  become  gradually  disintegrated ; their  soluble  constituents, 
potash  amongst  the  number,  are  taken  up  by  the  water  which  falls 
upon  the  earth’s  surface,  and  are  assimilated  by  the  plants  which 
spring  from  its  bosom;  they  accumulate  it,  especially  in  the  leaves, 
young  shoots,  and  succulent  parts.  Owing  to  this  circumstance, 
large  quantities  of  potash  may  be  obtained  with  facility : dried 
brushwood  is  incinerated,  and  the  remaining  ash,  which  seldom 
constitutes  more  than  1 per  cent,  of  the  diy  wood,  contains  the 
potash  in  the  form  of  carbonate : the  salt  is  extracted  by  water 
from  the  insoluble  portions.  M.  Merle  now  extracts  consider- 
able quantities  of  chloride  of  potassium  fr’om  the  mother-liquors 
of  sea-water  by  a modification  of  the  method  of  Balard  {note^ 
p.  355).-^ 

(563)  SuLPHmEs  of  Potassium. — Potassium  takes  fire  readily 
and  burns  with  brilliancy  when  heated  in  the  vapour  of  sulphur. 
It  combines  with  this  element  in  not  less  than  4 and  possibly  in 
5 difierent  proportions,  K^S  ?,  K^S^,  K.Sg,  Iv^S,,  and  Owing 

to  this  circumstance,  the  reactions  which  occur  when  sulphur  is 

* Much  potash  accumulates  as  an  organic  salt  in  the  fleece  of  the  sheep  and  is 
wasted.  Maumene  and  Rogelet  collected  this  potash  salt  by  simply  washing  and  eva- 
porating the  wash  water.  A fleece  weighing  9 lb.  contains  about  7 ounces  of  pure 
potash,  of  which  they  consider  nearly  6 is  recoverable.  A good  deal  of  the  potash 
which  is  carried  off  the  land  cultivated  for  beet-root  is  now  recovered  by  suitable 
treatment  of  the  waste  after  the  sugar  has  been  extracted. 

Messrs.  Ward  & Wynants  have  recently  contrived  a method  of  extracting  potash 
from  felspar  in  the  form  of  carbonated  or  of  caustic  alkali,  which,  if  commercially  suc- 
cessful, will  materially  alter  the  source  of  supply  of  this  alkali.  In  this  process  the 
felspar  is  ground  to  a flne  powder  and  mixed  with  a suitable  quantity  of  chalk,  slaked 
lime,  and  fluor-spar.  The  materials  are  fritted  in  a furnace,  at  a heat  about  suflBcient 
to  fuse  silver,  the  mixture  not  being  allowed  reaUy  to  melt.  The  chalk  during  igni- 
tion evolves  carbonic  anhydride ; it  thus  mechanically  preserves  the  porosity  of  the 
mass,  and  facilitates  the  extraction  of  the  soluble  products.  The  mass  obtained  is 
then  lixiviated,  and  rendered  caustic  by  the  addition  of  slaked  lime.  The  propor- 
tion of  lime  required  is  indicated  by  the  following  formulae,  supposing  the  materials 
to  be  employed  in  a pure  state: — (KjO,  3 SiOa,  AI2O3  3 SiOa)  -I-  T^^raO  -t-  -GaFa. — 
{Hofmann's  Jury  R^ort,  1862.) 


SULPHIDES  OF  POTASSIUM. 


335 


heated  with  caustic  or  carbonated  potash  are  somewhat  compli- 
cated ; but  they  are  now  well  understood,  and  may  be  traced  with- 
out dithculty. 

Protosidphide  of  Potassium  (K^S,  or  KS). — Some  doubt  exists 
as  to  the  possibility  of  forming  this  compound.  The  usual  direc- 
tions are  to  heat  sulphate  of  potassium  in  a current  of  dry  hydro- 
gen, or  to  mix  the  sulphate  intimately  with  finely  powdered 
charcoal  and  ignite  in  covered  vessels.  Bauer,  however  {Chem. 
Gaz.  1858,  468),  finds  that  the  result  is  not  that  usually  repre- 
sented by  the  equation,  K^SO^-f  4H2=K2S-1-4H20-,  but  that  a 
mixture  of  free  alkali  and  a variable  amount  of  one  of  the  higher 
sulphides  of  potassium  is  the  result.  The  residue  obtained  has  a 
reddish-yellow  colour ; it  is  deliquescent,  and  acts  powerfully 
upon  the  skin  as  a caustic.  When  a current  of  sulphuretted 
hydrogen  is  transmitted  through  a solution  of  caustic  potash  it  is 
rapidly  absorbed ; and  if  the  gas  be  allowed  to  pass  till  the  liquid 
is  completely  saturated,  the  compound  KHS  will  be  obtained  in 
solution.  This  solution  is  colourless  when  first  prepared,  but  if 
exposed  to  the  air  it  quickly  absorbs  oxygen,  and  acquires  a ^^ellow 
colour,  owing  to  the  formation  of  bisulphide  of  potassium ; 4 KHS 
-1-02=2  K2&2  + 2 H2O.  It  is  usually  stated,  and  probably  with 
truth,  that  if  a solution  of  potash  be  divided  into  two  equal  por- 
tions and  one  be  converted  into  the  suljfiiide  of  potassium  and 
hydrogen  (KHS),  and  be  then  mixed  with  the  other  half  of  the 
solution  of  potash,  a solution  of  pure  protosulphide  will  be  obtained, 
KHS  + KIIO  becoming  K2S-f  H2O.  It  is  possible,  however,  that 
this  is  not  so  ; but  that  both  the  caustic  and  potash  and  the  double 
sulphide  remain  unaltered  in  the  liquid.  On  the  addition  of  a 
stronger  acid,  sulphuretted  hydrogen  is  given  off  abundantly  ; and 
this  would  occur  whichever  view  were  correct,  no  sulphur  l3eing 
deposited;  for  K2S-f  112^0,= 1128  + K2SO4,  and  KIIS-fKHO-f 
11280, = H2S -fl^e -f  K28e,. 

If  sulphate  of  potassium  be  mixed  in  fine  powder  with  half  its 
weight  of  lampblack,  and  heated  in  a covered  crucible,  the  sulphate 
is  reduced  to  sulphide  of  potassium,  which  remains  in  a finely 
divided  state  mixed  with  the  excess  of  charcoal,  and  yields  a 
phorus^  or  compound  which  takes  fire  spontaneously  in  the  air, 
owing  to  the  heat  emitted  by  its  rapid  absorption  of  oxygen. 

The  bisulphide  (K282,  or  KS2)  may  be  formed  by  exposing  an 
alcoholic  solution  of  KII8  to  the  air  till  it  begins  to  become  turbid, 
and  evaporating  to  dryness  in  vacuo.  It  fuses  easily,  and  is  of  an 
orange  colour. 

Tlie  tersulphide  (K283,  or  KS3)  is  obtained  pure  by  passing  the 
vapour  of  bisulphide  of  carbon  over  ignited  carbonate  of  potassium 
so  long  as  any  gas  makes  its  escape  ; carbonic  anhydride  and  car- 
bonic oxide  are  produced  as  follows  : 2 K2003-f  3 082=2  1^283^- 
4 00-1- 002*  the  old  process  of  making  liver  of  sulphur^  61) 
parts  of  dry  carbonate  of  potassium  are  fused  with  40  parts  of 
sulphur ; the  resulting  yellowish-brown  mass  consists  of  3 atoms 
of  tersulphide  and  1 atom  of  sulphate  of  potassium  : part  of  the 
carbonate  in  this  case  yields  oxygen  to  one  portion  of  the  sulphur, 


336 


SULPHIDES  OF  POTASSIUM. 


and  forms  sulphuric  acid,  ns  shown  in  the  annexed  equation : 
4 KjOOg  + S §2— I^2^^4  + 3 K2S3  + 4 ■002- 

A tetrasuljpliide  (KaS^,  or  KS^)  may  be  formed  by  reducing 
sulphate  of  potassium  by  the  vapour  of  bisulphide  of  carbon. 

T\\q  2)entasulphide  (K2S5,  or  KS^)  is  formed  by  boiling  a solu- 
tion of  any  of  the  preceding  sulphides  with  excess  of  sulphur 
till  saturated  : or  by  fusing  any  of  the  dry  sulphides  with  an  excess 
of  sulphur ; the  excess  of  sulphur  separates  and  floats  above  the 
sulphide,  which  has  a dark  liver-brown  colour ; it  is  deliquescent, 
and  forms  a deep  yellow  solution  in  water. 

All  these  sulphides  have  an  alkaline  reaction  to  test-paper, 
and  an  odour  of  sulphuretted  hydrogen  more  or  less  distinct.  On 
the  addition  of  a stronger  acid  they  are  decomposed  with  extrica- 
tion of  sulphuretted  hydrogen,  attended,  in  the  case  of  all  but 
the  protosulphide,  by  the  precipitation  of  white,  finely  divided 
sulphur.  On  adding  the  persulphide  to  an  excess  of  hydrochloric 
acid  of  sp.  gr.  about  1*1,  the  persulphide  of  hydrogen  (429)  is 
separated  as  an  oily  liquid.  By  exposing  solutions  of  the  higher 
sulphides  to  air,  they  become  colourless,  hyposulphite  of  potassium 
is  formed,  and  the  excess  of  sulphur  is  separated.  When  a solu- 
tion of  caustic  potash  is  boiled  with  sulphur,  a decomposition 
ensues  similar  to  that  which  occurs  when  hydrate  of  potash  and 
sulphur  are  fused  together ; a deep  reddish-yellow  liquid  is  formed, 
which  contains  hyposulphite  of  potassium,  and  one  of  the  higher 
sulphides  of  the  metal ; 6 atoms  of  hydrate  of  potash  and  12  of 
sulphur  would  thus  furnish  1 atom  of  hyposulphite  and  2 of  penta- 
sulphide  of  potassium  ; 6 KHO  -|-  6 62  = K2S2H2O4  -f  2 K2S5  + 
2 1120. 

(564)  Chloride  of  Potassiuivi  (KCl  = 74*6) ; Sp.  Gr.  1*994 
(Filhol) : Comp,  in  100  parts  ’ K,  52*35  ; 01,47*65. — This  salt  is 
extracted  in  considerable  quantity  from  Icelp.,  the  ashes  of  burnt 
sea-weed,  and  is  used  largely  as  a source  of  the  potash  required 
in  the  manufacture  of  alum.  It  may  be  prepared  pure  by  directly 
neutralizing  either  the  acid  or  the  normal  carbonate  of  potassium 
with  hydrochloric  acid,  and  evaporating.  It  crystallizes  in  cubes, 
and  is  very  readily  soluble  in  cold  water,  which  takes  up  about  a 
third  of  its  weight,  attended  with  great  depression  of  temperature. 
It  is  remarkable  that  this  salt  possesses  the  property  of  absorbing 
the  vapours  of  sulphuric  anhydride,  forming  a hard  translucent 
mass  (K 01,803),  which  is  instantly  decomposed  by  water.  With 
chromic  acid  it  forms  a corresponding  compound  (KCl,0r03),  which 
is  also  decomposed  by  water : it  is  obtained  in  needles  when  a 
solution  of  acid  chromate  of  potassium  in  hydrochloric  acid  is 
allowed  to  crystallize. 

According  to  Bunsen,  a blue  subchloride  of  potassium  also 
exists. 

A native  compound  of  chloride  of  potassium  and  magnesium 
has  recently  been  discovered  in  a bed  of  clay  in  the  neighbour- 
hood of  Stassfurt,  near  Magdeburg,  which  is  immediately  above 
a bed  of  rock-salt,  100  feet  in  thickness.  This  is  precisely  the 
position  which  it  would  occupy,  supposing  the  deposit  to  have 


BROMIDE  AND  IODIDE  OF  rOTASSITM. 


337 


been  formed  by  tlie  gradual  drying-up  of  an  inland  sea,  where  the 
common  salt  would  crystallize  out  first,  and  the  salts  of  magnesium 
and  potassium  afterwards.  This  bed  of  clay  contains  the  sulphates 
and  chlorides  of  potassium  and  sodium,  and  magnesium,  and  the 
upper  part  of  the  deposit  consists  chiefly  of  a hydrated  double 
chloride  of  magnesium  and  potassium,  (KCl,  MgCl,,  6 H2O),  re- 
sembling rock-salt  in  appearance,  but  with  a more  pearly  lustre, 
and  extremely  deliquescent.  It  has  been  worked  for  the  sake  of 
the  chloride  of  potassium,  which  amounts  to  nearly  one-fourth  of 
its  weight. 

(565)  Bromide  of  Potassium  (KBr  = 119T);  Sj?.  Gr.  2*672: 
Com^j).  m 100  parts  ; K,  32*78  ; Br,  67*22. — This  is  a very  soluble 
salt,  which  crystallizes  in  cubes.  It  may  be  obtained  by  adding 
bromine  to  a solution  of  caustic  potash  until  the  liquid  acquires 
a slight  permanent  yellow  colour : bromide  and  bromate  of  potas- 
sium are  formed.  Lowig  dissolves  the  mixed  salts  in  water, 
decomposes  the  bromate  by  a current  of  sulphuretted  hydrogen, 
warms  gently  to  expel  the  excess  of  tlie  gas,  filters  from  the 
deposited  sulphur,  and  evaporates  till  the  solution  crystallizes : 
2 KBre3  + 6 II,S=2  KBr-f6  IBO  + 3 

(566)  Iodide  of  Potassium,  or  Ilydriodate  of  Potash  (KI  = 
166);  Sp.  Gr.  3*056:  Comp,  in  100  p>arts  I,  76*5;  K,  23*5. — 
This  valuable  medicine  may  be  procured  in  several  ways.  A 
simple  method  consists  in  adding  iodine  to  a solution  of  caustic 
potash  gently  warmed,  until  the  solution  begins  to  assume  a brown 
tint.  Iodide  and  iodate  of  potassium  are  formed;  3 I^-f  6 KITO 
= 5 KI-fKI03-|-3  II2O.  By  gentle  ignition  of  tlie  residue  ob- 
tained on  evaporation,  the  iodate  is  decomposed,  and  the  remain- 
ing iodide  fuses.  The  salt  must  not  be  strongly  heated,  as  iodide 
of  potassium  is  volatilized  by  a red  heat.  A better  plan  is  to 
digest  2 parts  of  iodine  and  1 part  of  iron,  in  a stoppered  vessel, 
with  10  parts  of  water,  the  iron  being  purposely  added  in  excess ; 
under  these  circumstances  iodide  of  iron  is  formed  by  the  direct 
union  of  the  metal  with  the  iodine  : the  solution  is  decanted,  and 
a quantity  of  iodine  equal  to  one-third  of  that  which  it  already 
contains  is  added.  The  liquid  is  then  boiled,  and  a solution  of 
carbonate  of  potassium  is  added  in  small  quantities  so  long  as 
effervescence  is  produced  and  a precipitate  occurs  ; the  solution  is 
next  filtered  from  the  dense  magnetic  oxide  of  iron,  and  on  evapo- 
ration it  yields  crystals  of  iodide  of  potassium ; Pog  -|-4 1,  -f  4 
=8Ki-fPe3e,-f4ee3. 

Iodide  of  potassium  crystallizes  in  anhydrous  cubes,  which  in 
a dry  air  are  not  deliquescent.  It  is  very  soluble  in  water,  and 
to  a smaller  extent  in  alcohol ; it  has  a cooling,  bitterish  taste. 
Its  solution  has  the  property  of  dissolving  an  additional  equivalent 
of  iodine,  with  which  it  forms  a deep  brown  liquid. 

Iodide  of  potassium,  if  pure,  should  be  completely  soluble  in 
six  times  its  weight  of  alcohol  (sp.  gr.  0*83) ; it  should  not  effer- 
vesce when  moistened  with  hydrochloric  acid  (carbonate  of  j)otas- 
sium  would  be  indicated  by  effervescence),  and  it  should  not  turn 
brown  by  the  action  of  the  acid  ; if  iodate  of  potassium  were  mixed 
22 


338 


ACID  SULPHATE,  AXD  XITEATE  OF  POTASSIUM. 


with  it  free  iodine  would  be  shown  by  the  brown  colour  developed 
on  adding  the  acid. 

(567)  Fluoelde  of  Potassium:  (IaF=58-1  ; Sp.  Gr.  2-4:5d)  is  a 
very  deliquescent  salt  obtained  by  neutralizing  hydrofluoric  acid 
vdth  a solution  of  caustic  potash.  Its  solution  has  an  alkaline 
reaction  and  corrodes  glass. 

(568)  SiLicoFLuoKiDE  OF  PoTAssiuM  (2  KF.SiF^  = 220,  or 
KF,SiF2=110). — This  salt  is  one  of  the  most  insoluble  compounds 
of  potassium ; it  falls  as  a transparent  gelatinous  precipitate  when- 
ever hydrosilicofluoric  acid  is  added  to  a salt  of  potassium ; it  dries 
to  a white  earthy-looking  powder.  Advantage  is  occasionally 
taken  of  its  insolubility  to  separate  potassium  from  some  of  its 
salts : in  this  way  chloric  acid  is  sometimes  prepared  from  chlorate 
of  potassium. 

(569)  Sulphate  of  Potassium  (K,S0^=1TI:,  or  K0,S03=8T); 
Sp.  Gr.  2-6I ; Composition  in  parts K„O,5-I'02  ; SO3, 45-98. — 
This  salt  crystallizes  either  in  anhydrous  six-sided  prisms,  termi- 
nating in  six-sided  pyramids,  or  in  four-sided  oblique  rhombic 
prisms  ; it  requires  about  16  parts  of  cold  water  for  solution.  The 
crystals  decrepitate  strongly  when  heated.  Sulphate  of  potassium 
forms  a series  of  double  salts  with  sulphates  of  the  metals  isomor- 
phous  with  magnesium,  and  another  class  of  salts  (the  varieties  of 
alum)  with  the  sulphates  of  the  metals  isomorphous  with  alumi- 
num. Jacquelain  flnds  that  if  normal  sulphate  of  potassium  be 
dissolved  in  nitric  acid,  a little  nitre  and  acid  sulphate  of  potassium 
are  formed,  whilst  a salt  consisting  of  (IIX03,K3S0^)  crystallizes 
in  oblique  prisms.  An  analogous  compound  may  be  formed  with 
phosphoric  acid  (Il3PO^,K2SO^). 

Aero  Sulphate,  or  Bisulphate  of  Potassium:  KHS0^=136; 
Sp.  Gr.  2-475. — This  salt  is  formed  on  a large  scale  as  a residuary 
product  in  the  preparation  of  nitric  acid  from  nitrate  of  potassium. 
It  crystallizes  from  a strongly  acid  solution  in  rhomboidal  tables, 
which  fuse  at  a heat  below  redness,  and  by  prolonged  ignition 
lose  half  their  acid ; they  are  very  soluble  in  water  and  have  a sour 
bitterish  taste.  If  redissolved  in  water,  the  normal  sulphate  crys- 
talhzes  flrst,  and  afterwards,  when  the  liquid  has  become  strongly 
acid,  the  bisulphate  is  deposited.  This  salt  is  sometimes  used  as 
a flux  in  cases  where  the  action  of  an  acid  is  required  at  a high 
temperature  upon  salts  or  metallic  oxides  with  which  it  may  be 
fused.  The  bisulphate  occasionally  ciwstallizes  in  anhydrous 
needles,  K3S0,SO3. 

(570)  XiTKATE  OF  Potassium  (KAO3,  or  KO,AO3=101);  Sp. 

Gr.  2-070;  Comp,  in  parts  ; K^O,  46-54;  53-46. — Salt- 

petre^  or  Nitre  as  this  salt  is  frequently  termed,  is  one  of  the  most 
important  and  valuable  salts  of  potassium.  The  principal  supply 
of  nitre  is  derived  from  various  districts  in  the  East  Indies,  where 
it  occurs  sometimes  as  an  eiflorescence  upon  the  soil,  at  other  times 
disseminated  through  the  superficial  stratum  itself.  It  appears  to 
be  formed  in  the  moist  portions  of  the  soil,  at  some  little  distance 
below  the  surface,  towards  which  it  is  raised  by  capillary  action. 
The  nitre  is  obtained  by  lixi\’iating  the  soil,  and  allowing  the  solu- 


NITRE  PLANTATIONS. 


339 


tion  to  crystallize.  The  earth  which  furnishes  it  consists  princi- 
pally of  loose,  porous  carbonate  of  calcium,  mixed  with  decom- 
posing felspar,  and  it  always  contains  more  or  less  of  organic  mat- 
ters. In  temperate  climates,  both  nitrites  and  nitrates  are  almost 
always  found  in  the  shallow  well-waters  of  towns,  owing  to  the 
oxidation  of  nitrogen  contained  in  the  animal  debris  during  their 
infiltration  through  the  soil.  Notwithstanding  the  investigations 
of  J.  Davy,  of  Iliihlmann,  of  Schonbein,  and  of  others,  the  pro- 
cess of  nitrification  is  still  very  imperfectly  understood.  The 
artificial  formation  of  nitre  has,  however,  been  practised  with 
considerable  success  in  various  countries  of  Europe,  which  furnish 
annually  a large  amount  of  the  salt.  In  Sweden  this  supply  of 
nitre  is  considered  of  such  importance  that  each  landed  proprietor 
is  obliged  to  pay  a certain  tax  in  raw  nitre,  the  quantity  required 
being  proportioned  to  the  value  of  the  estate  (Berzelius). 

Where  animal  matters  are  present  in  abundance,  the  formation 
of  nitric  acid  is  chiefiy  due  to  the  gradual  oxidation  of  ammonia 
developed  in  the  process  of  putrefaction.  The  presence  of  a cer- 
tain amount  of  moisture  is  necessary,  and  the  oxidation  is  materi- 
ally favoured  by  an  excess  of  carbonate  of  potassium,  of  lime,  or 
of  some  basic  substance  which  can  combine  with  the  acid  at  the 
moment  of  its  generation.  Ozone  appears  to  have  the  power  of 
combining  directly  with  nitrogen ; it  may  possibly,  as  Schonbein 
conjectures,  be  concerned  in  the  natural  production  of  nitric  acid, 
and  indeed  it  is  not  improbable  that  nitrification  is,  in  favourable 
cases,  due  to  the  slow  combination  of  atmospheric  nitrogen  and 
oxygen.  The  process  of  nitrification  becomes  arrested  if  the 
temperature  be  allowed  to  fall  much  below  60°. 

Nitre  Plantations. — The  method  adopted  in  the  artificial  pro- 
duction of  nitre  consists  in  placing  animal  matters,  mingled  with 
ashes  and  lime  rubbish,  in  loosely  aggregated  heaps,  exposed  to 
the  air,  but  sheltered  from  rain.  These  heaps  are  watered  from 
time  to  time  with  urine  or  stable  runnings  ; at  suitable  intervals 
the  earth  is  lixiviated,  and  the  salt  crystallized.  Three  years  usu- 
ally elapse  before  the  nitre  bed  is  washed : after  this  interval  a 
cubic  foot  of  the  debris  should  yield  between  4 and  5 ounces  of 
nitre.  As  there  is  always  a considerable  quantity  of  the  nitrates 
of  calcium  and  magnesium  present,  which  will  not  crystallize, 
carbonate  of  potassium,  in  the  shape  of  wood  ashes,  is  added  so 
long  as  any  precipitate  occurs.  By  tliis  means  the  nitrate  of  cal- 
cium is  decomposed,  and  the  insoluble  carbonate  of  calcium  sepa- 
rated. The  clear  liquor  is  then  evaporated  and  crystallized.  It 
is  found  by  the  saltpetre-boiler  that  the  earth  in  which  nitre  lias 
once  been  formed  furnishes  fresh  nitre  more  readily  than  on  the 
first  occasion.  Care  is  taken  that  the  nitre  plantations.^^  as  they 
are  termed,  shall  rest  upon  an  impervious  fiooring  of  clay,  so 
that  the  liquid  which  drains  away  from  them  may  be  collected 
and  preserved. 

In  Prussia,  by  a more  methodical  treatment,  a cubic  foot  of  the 
earth  yields  about  20  ounces  of  nitre.  The  heajis  are  so  construct- 
ed as  to  form  a terrace  of  steps,  exposing  the  back  in  the  form  of 


340 


PEOPEKTIES  OF  NITRE REFINING  OF  SALTPETRE. 


an  npi’ig'lit  wall  to  tlie  prevailing  wind ; the  watering  is  thus  facili- 
tated, while  the  evaporation  proceeds  with  rapidity  upon  the 
exposed  side,  and  here,  from  capillary  action,  the  nitre  chiefly 
accumulates:  from  time  to  time  a layer  of  earth  is  removed  from 
this  wall  for  lixiviation,  and  the  washed  earth,  mixed  with  a fresh 
portion  of  animal  matter,  is  returned  systematically  to  the  othei 
side  of  the  heap.  The  washing  of  the  earth  charged  with  salt- 
petre is  conducted  in  a systematic  manner  (589),  so  as  to  avoid 
using  a larger  quantity  of  water  than  is  actually  needed  to  dis- 
solve the  saltpetre. 

Besides  tlie  natural  and  artiflcial  sources  of  nitre  just  described, 
this  salt  occurs  also  in  solution  in  the  sap  of  certain  plants,  among 
which  the  sunflower,  the  tobacco  plant,  and  common  borage  may 
be  enumerated. 

Properties. — Xitre  usually  crystallizes  in  long  six-sided  stri- 
ated prisms,  terminated  by  dihedral  summits ; but  it  is  a dimor- 
phous salt,  and  is  occasionally  obtained  by  spontaneous  evapor- 
ation of  small  drops  of  its  solution  in  microscopic  rhombohedra, 
isomorphous  with  those  of  nitrate  of  sodium : it  is  soluble  in  3| 
times  its  weight  of  cold  water,  and  in  about  a third  of  its  weight 
of  boiling  water ; it  is  insoluble  in  alcohol : its  taste  is  cooling 
and  saline.  If  paper  be  dipped  in  a solution  of  nitre  and  dried, 
it  forms  what  is  well  known  as  toiicJt-paper^  which,  when  once 
kindled,  steadily  smoulders  away  till  consumed,  and  hence  it  is 
largely  employed  in  tiring  trains  of  powder,  flreworks,  &c.  klitre 
fuses  easily  without  decomposition  at  a temperature  of  642°,  and 
when  cast  into  moulds,  solidities  to  a white,  fibrous,  translucent, 
radiated  mass,  known  as  sal  prunelle.  When  heated  to  redness, 
part  of  its  oxygen  is  expelled,  and  a deliquescent  mass  of  nitrite 
of  potassium  is  formed.  By  a still  stronger  heat  the  nitrite  is  de- 
composed, nitrogen  mixed  with  oxygen  escapes,  and  a mixture  of 
potasli  and  peroxide  of  potassium  remains. 

Owing  to  the  facility  with  which  nitre  parts  with  oxygen,  it 
is  a powerful  oxidating  agent,  and  is  in  frequent  demand  in  the 
laboratory  for  this  purpose  : when  thrown  upon  glowing  coals  it 
produces  a brisk  scintillation.  If  nitre  be  intimately  mixed  with 
any  metallic  sulphide  in  flue  powder,  such  as  sulphide  of  anti- 
mony, and  thrown,  in  small  quantities  at  a time,  into  a red-hot 
crucible,  the  sulphur  burns  with  a brisk  deflagration.,  or  rapid  com- 
bustion, at  the  expense  of  the  oxygen  of  the  nitre,  and  with  a 
portion  of  its  potassium,  forms  sulphate  of  potassium,  Avhilst  the 
metal  at  the  same  time  becomes  oxidized  to  the  maximum.  In 
the  case  of  antimony,  the  oxide  produced  possesses  acid  characters, 
and  it  also  enters  into  combination  AAuth  the  potassium.  Advan- 
tage is  frequently  taken  of  this  oxidizing  action  of  nitre  in  order 
to  convert  small  quantities  of  sulphur  in  bodies  of  organic  origin 
into  sulphuric  acid,  for  the  puiq^ose  of  estimating  the  proportion 
of  sulphur  which  they  contain.  The  quantity  of  sulphuric  acid 
thus  produced,  admits  of  easy  and  accurate  determination  in  the 
form  of  sulphate  of  barium. 

(571)  Pejming  of  Saltpetre.  — The  impurities  of  most  fre- 


REFINING  OF  SALTPETRE. 


341 


quent  occurrence  in  nitre  are  sulphates  and  chlorides  of  potassium 
and  sodium,  and  nitrates  of  calcium  and  magnesium : after  it  has 
been  fused,  unless  the  heat  has  been  cautiously  regulated,  a little 
nitrite  of  potassium  is  liable  to  be  formed  ; in  the  latter  case  a 
fragment  of  the  salt,  when  moistened  with  solution  of  sulphate 
of  copper,  becomes  of  a bright  green  colour,  hlitre  may  be  quickly 
deprived  of  chlorine  by  moistening  the  powdered  salt  with  pure 
nitric  acid  and  gently  heating  it,  until  a portion  of  it,  when  dis- 
solved in  water,  gives  no  precipitate  with  nitrate  of  silver.  I^itre, 
when  pure,  is  not  deliquescent,  and  its  solution  gives  no  precipi- 
tate with  solutions  of  chloride  of  barium,  of  nitrate  of  silver,  or 
of  carbonate  of  potassium. 

In  the  refining  of  nitre,  advantage  is  taken  of  the  circumstance 
that  whilst  the  solubility  of  nitrate  of  potassium  increases  rapid- 
ly as  the  temperature  rises,  tliat  of  the  chloride  of  sodium  is 
scarcely  affected  by  it.  It  was  formerly  the  practice  to  jmrify 
the  salt  by  three  successive  crystallizations  ; but  the  same  object 
is  now  effected  by  a single  operation,  in  the  following  manner  ; — In 
a deep  copper  boiler,  about  50  gallons,  or  500  lb.,  of  water  is  placed, 
and  twice  its  weight  of  crude  nitre  is  added  : this  salt  gradually 
becomes  dissolved,  and  fresh  nitre  is  added,  until,  when  the  water 
has  attained  the  boiling-point,  a quantity  of  nitre  has  been  added 
equal  to  three  times  the  weight  of  the  water  employed  when 
the  liquid  has  been  rendered  clear  by  a few  minutes’  ebullition,  it 
is  strained  through  bag  filters,  and  allowed  to  run  into  the  crys- 
tallizing pan. 

The  crystallization  is  effected  in  a shallow  vessel,  the  bottom 
of  which  is  formed  by  two  inclined  planes  which  meet  in  the 
middle.  In  this  vessel  the  solution  is  kept  in  continual  agitation, 
in  order  to  prevent  the  formation  of  large  crystals  : such  crystals 
would  mechanically  retain  the  mother-liquor,  from  which  they 
could  not  be  subsequently  freed  without  recrystallization.  The 
chloride  of  sodium,  being  nearly  as  soluble  in  cold  water  as  in 
hot,  remains  almost  entirely  in  the  solution,  wdiilst  the  saltpetre 
is  deposited  in  extremely  small  crystals,  technically  termed  salt- 
])etre  flour  ‘ these  are  allowed  to  drain,  and  are  then  removed  to 
tanks  provided  with  false  perforated  bottoms,  where  they  are  de- 
})rived  of  the  mother-liquor  with  which  they  are  saturated.  For 
this  purpose,  the  tanks  are  completely  hlled  with  the  crystals, 
and  upon  them  is  poured  a solution  of  saltpetre  saturated  in  the 
cold  ; this  liquid  dissolves  the  chlorides,  but  leaves  the  pure 
nitrate  of  potassium  undissolved.  In  the  course  of  a few  hours, 

* The  quantity  of  chloride  of  sodium  in  East  Indian  nitre  is  generally  small ; but 
in  the  artificial  nitre  obtained  from  the  ‘beds,’  it  often  rises  to  a large  amount:  iu 
such  a case  the  liquid  is  skimmed  from  time  to  time,  and  the  chloride  of  sodium,  a 
large  proportion  of  which  remains  undissolved,  is  removed  by  means  of  perforated 
ladles;  as  soon  as  nitre  equal  to  about  5 times  the  weight  of  the  water  lias  been 
added,  the  solution  is  diluted  with  twice  the  quantity  of  water  at  first  employetl, 
after  which,  if  the  liquid  be  strongly  coloured,  2^  lb.  of  glue,  dissolved  in  hot  water, 
are  added,  and  thoroughly  incorporated  by  briskly  stirring ; the  coagulum  which  is 
formed  rises  in  a scum  to  tho  surface,  collecting  tho  greater  part  of  the  organic  im- 
purities derived  from  the  nitre  heap ; this  is  carefully  removed,  and  the  operation  is 
afterwards  continued  as  above  described. 


342 


GUNPOWDER. 


tlie  liquid  is  drawn  off  and  tlie  tanks  are  then  filled  up  with  pure 
water ; this  becomes  charged  with  nitre  containing  traces  of  chlo- 
rides,whilst  the  undissolved  salt  is  almost  chemically  pure  : the 
solution  of  nitre  thus  obtained  serves  to  wash  a fresh  portion  of 
the  crystals  ; the  refined  saltpetre  is  then  dried,  and  is  fit  for  use. 

(572)  Gunpowder. — The  principal  consumption  of  nitre  is  in 
the  manufacture  of  gunpowder,  which  consists  of  an  intimate 
mechanical  mixture  of  nitre,  sulphur,  and  charcoal,  in  pro- 
portions approaching  to  1 atom  of  sulphur,  2 of  nitre,  and  3 of 
charcoal : — 

In  100  parts. 


Nitre 2 KNOs 

- 202  ... 

...  74-8 

Sulphur  ....  S 

- 32  ... 

...  11-9 

Charcoal ....  -63 

- 36  ... 

...  13  3 

270 

100-0 

The  proportions  used  vary  a little 

in  difierent  countries,  as  will  be 

seen  from  the  following  table  : — 

Composition  of  Gunpowder  in  parts. 


English  and 
Austrian. 

Prussian. 

Swedish. 

Chinese. 

French. 

Nitre 

75 

75-0 

75 

75-7 

75-0 

76-9 

62 

Sulphur 

10 

11-5 

9 

9-9 

12-5 

9-6 

20 

Charcoal  .... 

15 

13-5 

16 

14-4 

12-5 

13-5 

18 

Musket. 

Musket. 

Musket. 

Musket. 

Sporting. 

Blasting. 

An  excess  of  sulphur  is  carefully  avoided,  on  account  of  its  inju- 
rious action  upon  the  metal  of  the  gun.  The  great  explosive  powder 
of  gunpowder  is  due  to  the  sudden  development  of  a large  volume 
of  gaseous  bodies,  chiefiy  consisting  of  nitrogen  and  carbonic 
anhydride,  which,  at  the  ordinary  temperature  of  the  air,  would 
occupy  a space  equal  to  about  300  times  the  bulk  of  the  powder 
used ; but  from  the  intense  heat  developed  at  the  moment  of  the 
explosion,  the  dilatation  amounts  to  at  least  1500  times  the  volume 
of  the  gunpowder  employed.  Supposing  the  mixture  to  be  made 
in  the  proportion  of  1 atom  of  sulphur,  2 atoms  of  nitre,  and  3 of 
carbon,  the  reaction  is  often  approximatively  represented  thus  : — 

S,  -f-  6 e + 4 KXO3  = 6 eo,  -f  2 -f  2 Kfi. 

The  actual  results,  however,  cannot  readily  be  represented  by  any 
simple  formula,  and  the  solid  residue,  instead  of  consisting  chiefiy 
of  sulphide  of  potassium,  contains  but  a small  quantity  of  this 
substance,  whilst  sulphate  and  carbonate  of  potassium  are  found  in 
abundance ; they  become  volatilized  by  the  heat  of  the  explosion, 
and  constitute  the  white  smoke  observed  when  gunpowder  is  fired.* 

* In  burning  gunpowder  in  a copper  tube  with  the  view  of  collecting  the  gases 
over  mercury,  Chevreul  found  a small  proportion  of  nitric  oxide,  of  carbonic  oxide, 
and  of  carburetted  hydrogen,  with  a httle  sulphuretted  hydrogen,  mixed  with  the 
nitrogen  and  carbonic  acid.  Bunsen  and  Linck  obtained  results  somewhat  different, 
but  the  temperature,  and  consequently  also  the  results  of  the  combustion  procured 


GUNPOWDER PRODUCTS  OF  ITS  COMBUSTION. 


343 


Much  care  is  requisite  in  the  selection  of  the  materials  for  the 
manufacture  of  gunpowder.  The  charcoal  must  be  burned  tho- 
roughly, but  not  at  too  high  a temperature  : that  from  the  willow, 
alder,  or  dogw^ood  is  preferred  for  the  purpose,  dogwood  charcoal 
being  employed  only  in  making  rifle  powder.  The  charcoal 
always  contains  a notable  proportion  of  hydrogen  and  oxygen. 
In  the  Government  works  at  W altham  AblDey,  sulphur  is  never 
used  in  the  state  of  flowers  of  sulphur ; in  this  condition  it  is  pre- 


by  this  regulated  action,  are  different  from  those  attending  the  firing  of  ordnance. 
Karolyi,  however  {Phil  Mag.  Oct.  1863),  has  succeeded  in  analyzing  the  gases  of 
gunpowder  which  had  been  fired  in  conditions  closely  resembling  those  which  occur 
in  active  artillery  practice.  For  this  purpose  he  enclosed  a charge  of  powder  in  an 
iron  cylinder  of  such  strength  that  it  just  burst  when  the  powder  was  fired  by  means 
of  the  electric  spark.  This  charged  cylinder  was  suspended  in  a hollow  spherical 
bomb,  from  which  the  air  was  exhausted  before  firing.  After  the  explosion  had  been 
produced,  the  gases  and  the  solid  residue  of  the  powder  were  submitted  to  analysis 
The  results  obtained  were  the  following: — 


1.  Composition  of  the  Powder  used. 

Ordnance 

powder. 

Nitrate  of  potassium 73*78 

Sulphur 12*80 

r Carbon 10*88'! 

tAsh  0*31  J 

99*97 


Small-arms 

powder. 

77*15 

8*63 

ll*78'j 

0*28  J 


100*05 


2.  Products  of  Combustion  by  weight. 


Gaseous 


Solid 


r Nitrogen  

...  9*77  j 

10*06') 

Carbonic  anhydride 

...  17*39 

21*79 

j Carbonic  oxide 

. . . 2*64 

O A.K  O 

1*47 

1 Hydrogen 

. ..  0*11 

oU  Oo 

0*14  ' 

Sulph.  hydrogen 

...  0*27 

0-23 

Marsh  gas 

. . . 0*40 

0*49^ 

'Sesquicarb.  ammonium  . 

. ..  2*68^ 

2*66' 

Sulphate  potassium 

. . . 36*95 

36*17 

Carbonate  “ 

. . . 19*40 

20*78 

K Hyposulphite  “ 

. . . 2*85  1 

i-  69*25 

1*77  ^ 

Sulphide  “ 

1 

0*00 

Charcoal  

...  2*57  1 

1 

2*60 

Sulphur 

. ..  4*69  J 

1*16 

Loss 

. . . 0*17 

0*68 

100*00 

100*00 

34*18 


65*14 


3.  Products  of  Combustion  by  volume  in  100  of  Gas. 


Nitrogen 

35*33' 

Carbonic  anhydride 

42*74 

48*90 

Carbonic  oxide 

10*19 

► 100*0 

5*18 

Hydrogen  

6*90  ( 

Sulphuretted  hydrogen 

0*67 

Marsh  gas 

3*02  J 

These  gases  contained  a sufficient  amount  of  carbonic  oxide,  and  of  hydrogen  and  its 
compounds,  to  take  fire  on  the  application  of  a lighted  match.  The  formation  of  sos- 
quicarbonate  of  ammonium  and  of  carbonate  of  potassium  in  such  large  proportion 
is  remarkable.  The  results  obtained  by  the  analysis  of  sporting  powder  by  Bunsen 
and  Schischkoff  {Poggend.  Annal.  cii.  321)  do  not  materially  differ  from  those  quoted 
above,  but  are  slightly  modified  by  the  excess  of  nitre  used  in  the  preparation  of 
this  kind  of  powder. 


34A 


GUNPOWDER. 


ferred  for  fireworks ; but  distilled  sulphur,  reduced  to  a fine  meal 
by  grinding,  is  always  used  for  gunpowder.  The  flowers  of  sul- 
phur always  contain  sulphurous  acid,  which  becomes  speedily 
converted  into  sulphuric  acid  and  attracts  moisture,  biitre  of 
the  purest  quality  is  alone  employed.  These  three  materials 
hawng  been  separately  ground  and  sifted,  are  mixed  in  powder 
in  the  proper  proportions,  and  are  intimately  blended  in  a revolv- 
ing drum ; they  are  then  made  into  a stiff  paste  with  water,  and 
ground  for  some  hours  under  edge-stones  in  the  incoT])OTating 
mill  • the  slightly  coherent  mass  thus  procured  is  broken  up,  and 
spread,  in  layers  of  about  an  inch  in  thickness,  between  plates  of 
gun-metal ; it  is  then  subjected  to  the  action  of  a hydi'aulic  press 
which  exerts  a force  of  70  tons  upon  the  square  foot : a hard, 
sonorous  mass,  termed  press  cake^  is  thus  obtained : th^se  masses, 
whilst  still  damp,  are  broken  into  small  fragments,  or  granulated ^ 
by  submitting  them  to  the  action  of  toothed  rollers  in  a machine 
constructed  for  the  purpose.  The  grains  are  next  sorted  by  means 
of  sieves  into  different  sizes,  after  which  they  are  thoroughly  dried 
in  closets  heated  by  steam,  and,  finally,  are  glazed^  or  polished,  by 
placing  them  in  barrels  caused  to  revolve  about  39  times  in  a 
minute.  Mining  powder  is  often  glazed  by  adding  powdered 
graphite  in  the  polishing  barrels  ; this  operation  retards  the  rate 
of  ignition,  and  diminishes  the  hygroscopic  character  of  the 
powder.  A cubic  foot  of  good  English  cannon  powder  weighs 
about  58  lb. ; if  below  55  lb.,  it  is  considered  unfit  for  use.  The 
heavier  the  powder  the  greater  is  its  explosive  power.  Two 
ounces  of  the  best  English  powder,  when  introduced  into  a mortar 
of  8 inches  diameter,  set  at  an  angle  of  45°,  should  throw  a 68-lb. 
shot  from  260  to  280  feet,  on  level  ground. 

Good  gunpowder  burns  rapidly  in  the  open  air,  leaving  little 
residue,  not  blackening  or  kindling  paper  upon  which  it  is  fired. 
It  has  been  found  that  a powerful  concussion  of  powder  between 
two  pieces  of  iron  will  frequently  kindle  it,  and  if  the  powder  be 
placed  upon  lead,  or  even  upon  a board,  it  may  be  exploded  by 
the  blow  of  a leaden  bullet  fired  at  it.  The  temperatm’e  at  which 
it  takes  fire  is  about  480°. 

The  object  of  granulating  the  powder,  independently  of  its 
diminishing  its  tendency  to  absorb  moisture,  is  to  favour  the 
rapidity  of  inflammation,  by  leaving  interstices  through  which  the 
flame  is  enabled  to  penetrate  and  envelope  each  grain.  The 
ignition  of  the  whole  charge  does  not  take  place  simultaneously 
throughout,  nor  is  it  desirable  that  it  should  do  so,  otherwise 
sufticient  time  would  not  be  given  to  allow  the  ball  to  receive  the 
full  advantage  of  the  expansive  force  of  the  air  generated  ; too 
rapid  an  action  would  be  expended  upon  the  barrel  of  the  gun 
itself,  and  effects  would  be  produced  like  those  due  to  fulmi- 
nating mercury ; where  a prolonged  heaving  force  is  required, 
as  in  blasting  for  mining  operations,  the  action  of  the  powder  is 
still  further  retarded  by  mixing  it  with  sawdust ; the  powder 
employed  for  this  purpose  usually  contains  65  parts  of  nitre,  20 
of  sulphur,  and  15  of  charcoal.  In  the  formation  of  the  fusee, 


NITRITE  AND  CHLORATE  OF  POTASSIUM. 


345 


the  quick  and  slow  match,  and  certain  kinds  of  fireworks,  gun- 
powder is  mingled  with  combustibles  in  various  proportions. 

The  analysis  of  gunpowder  is  easily  effected  : 100  grains  of 
the  powder  for  examination  are  dried  over  snlphnric  acid  in 
vacuo  / the  loss  indicates  the  amount  of  moisture.  The  residue  is 
digested  in  water  and  washed  : the  solution,  when  evaporated  in 
a counterpoised  capsule,  and  weighed,  furnishes  the  amount  of 
nitre  and  other  salts.  Mtrate  of  barium,  when  added  to  a 
solution  of  these  salts,  acidulated  wdth  nitric  acid,  will  yield  the 
sulphuric  acid  in  the  form  of  sulphate  of  barium ; and  nitrate  of 
silver,  when  added  to  the  liquid  filtered  from  the  sulphate  of 
barium,  will  give  the  data  for  ascertaining  the  amount  of  chlorine 
from  the  precipitated  chloride  of  silver.  The  charcoal  and 
sulphur  are  contained  in  the  portion  wdiich  did  not  dissolve  in 
water ; they  may  be  separated  by  means  of  bisulpliide  of  carbon, 
or  by  the  use  of  benzol  at  a boiling  temperature,  which  dissolves 
out  the  sulphur,  and  leaves  it  in  the  crystalline  form  by  spon- 
taneous evaporation,  whilst  the  charcoal  is  left  undissolved  and 
may  be  weighed. 

A mixture  of  3 parts  of  nitre,  2 of  carbonate  of  potassium,  and 
1 part  of  sulphur,  produces  a substance  known  as  'pulvis  fulmi- 
nans^  which  when  heated  on  an  iron  shovel  until  fusion  takes 
place,  explodes  suddenly  with  a very  loud  report. 

(573)  Nitrite  of  Potassium  (KN0-2  oi*  is  a white 

anhydrous,  deliquescent  salt,  which  may  be  obtained  in  crystals. 
It  may  be  procured  by  decomposing  nitre  by  fusion  at  a red  heat, 
dissolving  the  residue  in  water,  and  allowing  the  nitre  to  crystal- 
lize out  of  the  deliquescent  nitrite,  which  may  be  obtained  by 
evaporating  the  solution  to  dryness. 

(574)  Chlorate  of  Potassium  (KCIO3  or  KO, 0103=122-5) ; 

Sp.  Gr.  1*989 : Composition  in  100  parts^  38-36,  and 

CI2O3,  61*64. — One  mode  of  preparing  this  salt  has  already  been 
explained  (382).  It  may  be  more  economically  obtained  by  con- 
verting milk  of  lime  into  a mixture  of  chlorate  and  chloride  of 
calcium  by  transmitting  chlorine  gas  in  excess ; to  a concentrated 
solution  of  the  mixed  salts,  chloride  of  potassium  is  then  added  in 
the  proportion  of  74*5  parts  of  the  cldoride  to  168  parts  of  the 
caustic  lime  originally  employed.  The  chlorate  of  calcium  and 
chloride  of  potassium  decompose  each  other,  and  chlorate  of  po- 
tassium and  chloride  of  calcium  are  formed : boiling  water  dis- 
solves both  the  chlorate  of  potassium  and  the  chloride  of  calcium. 
The  two  salts  are  easily  separated  by  crystallization,  as  the  chlo- 
rate requires  16  parts  of  cold  water  for  solution,  and  the  chloride 
is  soluble  to  almost  any  extent.  Prom  this  mixture  the  crude 
chlorate  is  deposited  in  6-sided  prisms,  which,  on  being  redis- 
solved in  water,  are  crystallized  in  anhydrous  rhomboidal  ])early 
tables  ; it  has  a cooling  taste,  somewhat  analogous  to  that  of  nitre  : 
100  parts  of  boiling  water  dissolve  61*5  of  the  salt.  AVlien  heated 
to  between  700°  and  800°  the  salt  melts,  and  at  a higher  tenqiera- 
ture  is  decomposed,  furnishing  oxygen  gas  of  great  purity,  and 
leaving  chloride  of  potassium  as  a fixed  residue  behind.  When 


346 


PEKCHLOEATE  AXD  CAEBOXATE  OF  POTASSIUM. 


heated  to  redness,  100  parts  of  the  salt  leave  60*79  parts  of  chlo- 
ride of  potassium,  and  39*21  of  oxygen  are  evolved.  The  chlorate 
is  a more  povrerfnl  oxidizing  agent  than  nitrate  of  potassium ; and 
if  combustible  substances,  such  as  sulphur  or  phosphorus,  be  rub- 
bed with  it  forcibly,  the  combination  of  the  combustible  with 
oxygen,  accompanied  by  detonation,  ensues.  Chlorate  of  potas- 
sium is  principally  consumed  in  the  manufacture  of  Incifer 
matches,  and  as  an  oxidizing  agent  in  certain  operations  of  the 
calico-printer.  When  added  to  a solution  acidulated  with  hydi*o- 
chloric  acid,  it  is  often  used  in  the  laboratory  as  an  oxidizing  agent. 

The  friction  tubes  employed  for  firing  cannon  are  charged 
with  a mixture  of  2 parts  of  chlorate  of  potassium,  2 of  sulphide 
of  antimony,  and  1 part  of  powdered  glass.  A mixture  known 
under  the  name  of  white  gunpowder^  consisting  of  chlorate  of 
potassium,  dried  ferrocyanide  of  potassium,  and  sugar,  has  some- 
times been  manufactured  for  blasting  purposes ; but  its  prepara- 
tion is  attended  with  very  great  danger,  owing  to  the  facility  with 
which  it  explodes  by  friction,  a circumstance  which  has  caused 
several  fatal  accidents. 

(575)  Peechloeate  of  Potassium  (KCIO^,  or  KO, CIO, =138*5); 
Comj).  in  jparts^  33*93 ; Cl^O,,  66*07. — This  salt  crystal- 
lizes in  anhydrous  prismatic  needles,  which  are  very  sparingly 
soluble  in  cold  water ; its  principal  properties  and  the  mode  of 
preparing  it  have  been  already  described  (383).  When  heated 
to  redness  it  gives  ofi*  46*11  per  cent,  of  oxygen,  leaving  53*89  of 
chloride  of  potassium. 

(576)  CAEBoxATEOFPoTAssnM(K2003=138,  orKO,C03=69); 

Sp.  Gr.  2*207;  m 100  K^O,  68*11 ; -BOj,  31*89. — 

This  important  salt  is  obtained  in  large  quantities  for  commercial 
purposes  by  lixiviating  wood  ashes,  and  evaporating  the  solution 
until  it  crystallizes  ; the  mother-liquor,  when  it  cools,  is  poured  ofi* 
from  the  crystallized  salts,  as  it  retains  the  more  soluble  carbon- 
ate of  potassium,  and  when  evaporated  to  dryness,  affords  the 
potashes  of  commerce,  and  these,  when  calcined,  yield  the  impure 
carbonate  known  as  pearlash.  Different  plants,  when  burned, 
furnish  varying  quantities  of  the  alkali,  which  they  extract  from 
the  soil : the  leaves  and  young  shoots,  where  the  vital  action  is 
the  most  vigorous,  are  the  parts  which  furnish  the  greatest  quan- 
tity of  alkali.  Herbaceous  plants,  therefore,  generally  furnish 
more  than  shrubs,  and  shrubs  more  than  an  equal  weight  of  tim- 
ber. It  appears  from  the  experiments  of  Yiolette  that  the  varia- 
tion in  the  quantity  of  ash  obtained  from  different  parts  of  the 
same  tree  is  extremely  great.  Thus,  taking  the  quantity  of  ash 
found  in  the  heart-wood  as  the  unit  of  comparison,  the  proportion 
in  other  parts  was  as  follows : — 


Heart-wood 1 

Root  bark 6 

Bark  of  trunk 9 


Bark  of  branches 11 

Root  fibres 15 

Leaves 25 


and  it  is  stated  by  Chevandier  {Ann.  de  Chimne^  III.  x.  129)  that 
the  quantity  of  ash  varied  as  follows  for  100  parts  of  different 


CARBONATE  OF  POTASSIUM. 


34T 


portions  of  the  wood  of  the  undermentioned  trees  after  drying  at 


Solid  stem. 

Arms. 

Small  branches. 

Beech 

0-91 

2*15 

1'29 

Oak 

2-43 

2*03 

1*68 

Birch 

0*71 

1*03 

0-60 

In  the  wine-producing  countries,  a considerable  cpiantitv  of 
carbonate  of  potassium  of  good  quality  is  furnished  by  burning 
the  refuse  yeast  after  the  fermentation  is  complete.  The  yeast, 
for  this  purpose,  is  pressed,  dried  in  the  sun,  and  burned  in  shal- 
low enclosures  : this  dry  yeast  furnishes  nearly  10  per  cent,  of 
its  weight  of  the  carbonate.  Potassium  does  not  exist  in  plants 
in  the  form  of  carbonate ; it  occurs  in  them  in  union  with  the 
radicles  of  different  organic  acids : these  organic  acids  are  de- 
stroyed by  the  action  of  the  heat  during  incineration.  Such  acids 
always  contain  more  carbon  than  is  sufficient,  when  oxidized  by 
the  air,  to  form  the  amount  of  carbonic  acid  radicle  requisite  to 
neutralize  the  potassium  ; and  the  carbonate  of  potassium  thus 
produced,  as  it  is  not  decomposed  by  a red  heat,  remains  behind. 
In  the  ashes  of  plants  various  other  saline  substances  are  likewise 
present,  but  those  which  are  soluble  consist,  in  addition  to  the 
carbonate,  principally  of  the  sulphate  and  chloride  of  potassium  ; 
these  alkaline  salts  usually  amounting  to  from  10  to  20  per  cent, 
of  the  entire  quantity  of  ash. 

A purer  carbonate  is  obtained  for  chemical  purposes  by  defla- 
grating a mixture  of  purified  cream  of  tartar  with  an  equal  quan- 
tity of  pure  nitre.  The  mass  is  thrown,  in  small  portions  at  a 
time,  into  a red-hot  crucible  : in  this  operation  the  nitre  yields 
oxygen  to  the  vegetable  acid,  converting  the  carbon  which  it  con- 
tains into  carbonic  acid,  which  enters  into  combination  with  the 
alkali  both  of  the  tartar  and  of  the  nitre,  since  the  two  acids 
undergo  mutual  decomposition  : the  carbonate  of  potassium  is 
extracted  from  the  dry  mass  by  lixiviation. 

Carbonate  of  potassium  is  a deliquescent  salt,  which  is 
with  difficulty  obtained  in  oblique  rhombic  octohedral  crystals 
(K2-0Q3,2  ITjO).  Its  reaction  upon  test-paper  is  strongly  alka- 
line ; it  has  an  acrid,  alkaline  taste.  Its  solutions  have  a peculiar 
lixivial  smell : 100  parts  of  water  at  60°  dissolve  90  of  carbonate 
of  potassium  ; and  at  the  boiling-point  take  up  205  parts,  or 
rather  more  than  twice  their  weight,  of  the  salt.  Alcohol  does 
not  dissolve  it.  Carbonate  of  potassium  fuses  by  exposure  to  a 
red  heat,  and  at  a very  high  temperature  is  partially  volatilized ; 
at  a red  heat  it  is  decomposed  by  silica,  carbonic  anhydride  being 
expelled  with  eftervescence,  whilst  the  silica,  uniting  witli  the 
alkali,  forms  with  it  a true  silicate,  the  basis  of  one  of  the 
varieties  of  glass.  Advantage  is  taken  of  this  property  in  tlie 
analysis  of  mineral  substances  which  contain  a large  quantity  of 
silica,  and  which  are  not  easily  decomposed  by  the  action  of 
acids.  For  this  purpose  the  mineral  to  be  analysed  is  reduced 
to  an  extremely  fine  powder  by  careful  levigation  ; a portion  of 
this  powder  is  accurately  weighed,  and  then  intimately  mixed 
with  about  3 times  its  weight  of  carbonate  of  potassium  (or,  still 


348 


ALKALIMETET. 


better,  with  thrice  its  weight  of  a mixture  of  5|-  parts  of  dried 
carbonate  of  sodium  and  7 parts  of  carbonate  of  potassium) ; the 
whole  is  introduced  into  a platinum  crucible  and  exposed  to  a 
bright  red  heat  for  an  hour.  The  mass  enters  into  fusion,  car- 
bonic anhydride  escapes  with  effervescence,  and  a silicate  of  potas- 
sium is  formed ; by  which  means  all  the  bases  of  the  mineral,  which 
before  were  confined  with  the  silica,  are  set  at  liberty.  Upon  now 
treating  the  mass  with  diluted  hydrochloric  acid,  the  silicate  of 
potassium  is  decomposed,  the  earths  and  metallic  oxides  are  dis- 
solved, and  the  silica  is  partially  dissolved  and  partially  separated 
in  the  hydrated  form.  In  order  to  decompose  the  hydrate  of  sil- 
ica, the  solution  is  evaporated  to  dryness,  moistened  with  hydro- 
chloric acid,  and  again  treated  with  water  ; the  whole  is  now 
placed  upon  a filter,  and  the  silica,  after  being  well  washed,  re- 
mains behind  in  a state  of  purity.  The  analysis  of  the  filtered 
liquid  is  then  finished  according  to  the  ordinary  method  adopted 
for  substances  directly  soluble  in  acids. 

Carbonate  of  potassium  is  largely  consumed  in  the  arts,  as,  for 
example,  in  the  manufacture  of  soap  and  of  glass,  and  for  prepar- 
ing caustic  potash  and  other  compounds  of  potash.  It  also  fur- 
nishes the  chemist  with  one  of  Ins  most  indispensable  reagents. 

(577)  Since  the  quantity  of  alkaline  carbonate, 

technically  known  as  alkali^  is  liable  to  great  variations  in  different 
samples  of  the  ash, — and  since  the  commercial  value  of  pearlash 
depends  upon  the  amount  of  carbonate  which  it  contains,  a rapid 
and  sufficiently  accurate  method  of  analysis  of  this  salt  becomes 
a desideratum.  In  order  to  effect  this  object,  the  process  termed 
alkalimetry  has  been  invented.  In  principle  it  depends  upon  the 
determination  of  the  number  of  divisions  of  a diluted  acid,  of 
definite  strength,  which  100  grains  of  the  different  samples  of  ash 
are  capable  of  neutralizing ; the  neutralization  being  estimated  by 
the  action  of  the  solution  upon  blue  litmus. 

The  acid  solution  which  is  to  be  employed  is  measured  from  a 
burette  or  alkalimeter^  which  is  a tube  of  the  form  shown  in  fig. 
331.  It  has  an  internal  diameter  of  about  five-eighths  of  an  inch, 
and  is  sufficiently  tall  to  contain  rather  more  than  1000  grains  of 
distilled  water.  The  space  occupied  by  1000  grains  of  water  at 
60°  is  marked  off  and  indicated  as  0,  and  the 
tube  is  then  subdivided  into  100  equal  parts, 
each  capable  of  containing  10  grains  of  water ; 
opposite  every  tenth  division  the  number  corre- 
sponding to  it  is  placed,  the  numbers  increas- 
ing from  above  downwards. 

Various  plans  have  been  proposed  for  pre- 
paring the  diluted  acid  ; the  following  is  sub- 
stantially the  same  as  that  recommended  by 
Faraday  {Chemical  Manipulation^  3rd  ed.  p. 
281).  It  has  the  advantage  of  being  readily 
applicable  to  any  alkali. 

A solution  of  sulphuric  acid  is  prepared  by 
diluting  the  ordinary  commercial  acid  with  8 times  its  hulk^  or 


ALKALmETRT. 


349 


nearly  5 times  its  weiglit  of  distilled  water  ; when  cool,  the 
liquid,  which  may  he  termed  alkalimetriG  acid^  should  have  a 
specific  gravity  of  1'1268.  In  order  to  ascertain  whether  the 
strength  of  this  alkalimetric  acid  be  accurately  adjusted,  a 
quantity  of  crystallized  bicarbonate  of  potassium  is  fused  in  a 
platinum  crucible  in  order  to  convert  it  into  the  carbonate  : the 
fused  mass  is  poured  upon  a clean  iron  plate,  and  100  grains  of  it 
are  quickly  weighed,  and  dissolved  in  about  3 ounces  of  water  in 
a small  evaporating  basin.  Diluted  acid,  sufficient  to  fill  35  divi- 
sions, is  now  to  be  introduced  into  the  alkalimeter,  which  conse- 
quently is  to  be  filled  up  to  the  mark  65  with  the  diluted  acid,  and 
water  is  to  be  added  until  it  stands  at  the  mark  0 : the  acid  and 
water  are  to  be  thoroughly  mixed  by  closing  the  tube  wdth  the 
thumb  and  finger,  then  inverting  and  agitating  the  tube  ; after 
which  the  liquid  is  added  to  the  solution  of  carbonate  of  potassium, 
which  is  to  be  gently  warmed  in  order  to  expel  the  carbonic  anhy- 
dride as  it  is  liberated.  A piece  of  blue  litmus-paper,  or  a small 
quantity  of  infusion  of  litmus,  is  placed  in  the  basin,  and  the  acid 
is  cautiously  added  until  the  litmus  is  distinctly  but  permanently 
reddened.  The  acid  liquid,  if  properly  diluted,  ought  to  contain, 
in  each  division,  sufficient  sulphuric  acid  to  neutralize  1 grain  of 
carbonate  of  potassium  ; and  the  entire  contents  of  the  alkalime- 
ter should  therefore  exactly  produce  this  effect.  If  more  than  100 
divisions  of  the  acid  be  required,  the  test  acid  is  too  weak  ; if  less 
than  100  divisions,  it  is  too  strong. 

Suppose  that  95  divisions  of  the  acid  were  sufficient,  the  alka- 
limetric acid  from  which  it  was  prepared  must  have  contained 
one-twentieth  too  much  acid  ; every  95  measures  of  this  acid, 
therefore,  must  be  diluted  with  5 measures  of  water.  If,  on  the 
other  hand,  more  acid  than  100  divisions  be  required,  say  105  be 
needed,  the  acid  contains  one-twentieth  too  much  water:  the 
quantity  of  alkalimetric  acid  used  in  the  experiment  requires  the 
addition  of  one-twentieth  more  of  acid  than  it  originally  con- 
tained ; now  the  quantity  of  alkalimetric  acid  used  was  35  divi- 
sions, and  the  one-twentieth  part  of  this  is  1*75,  but  only  one- 
fifth  of  this  is  pure  acid  (II^SO^),  so  that  0*25  parts  by  weight  of 
the  oil  of  vitriol  originally  used,  must  be  added  to  each  35  parts 
by  weight  of  alkalimetric  acid.  Tliis  correction,  though  not 
mathematically  exact,  is  perfectly  sufficient  for  all  practical  pur- 
poses. The  alkalimetric  acid,  when  duly  adjusted,  is  preserved 
in  bottles  which  are  accurately  closed. 

Kaving  thus  prepared  a test  acid  of  the  proper  strength,  100 
grains  of  the  sample  of  pearl  ash  for  trial  are  dissolved  in  3 or  4 
ounces  of  water,  filtered  if  necessary,  and  then  tested  in  the  same 
manner:  the  number  of  divisions  of  acid  consumed  will  indicate 
the  per-centage  of  carbonate  of  potassium  present  in  the  sample. 

The  same  acid  may  be  employed  to  determine  the  quantity  of 
soda  present  in  any  sample  of  soda  ash  ; but  as  a certain  weight 
of  soda  neutralizes  a proportionately  larger  amount  of  acid  than 
an  equal  weight  of  potash,  the  alkalimeter  must  be  filled  to  a 
higher  mark  with  the  acid.  For  the  determination  of  the  quan- 


350 


METHOD  OF  WILL  AND  FEESENIHS. 


tity  of  anliydroiis  potash  in  any  sample,  the  acid  must  be  poured 
into  the  burette  till  it  stands  at  the  division  49,  and  the  tube 
must  he  then  filled  np  to  0 with  water.  Each  division  will  then 
contain  acid  sufficient  to  neutralize  1 grain  of  anhydrous  potash. 

If  filled  with  acid  to  65,  and  then  filled  up  with  water,  each 
division  will  correspond  to  1 grain  of  carbonate  of  potassium. 

If  filled  to  54*6,  and  then  filled  up  with  water,  each  division 
will  indicate  1 grain  of  dry  carbonate  of  sodium  : and  if  filled  to 
23*4,  and  then  water  be  added  to  0,  the  acid  in  each  division 
will  neutralize  1 grain  of  anhydrous  soda. 

In  cases  where  greater  accuracy  is  required,  the  acid  solution, 
instead  of  being  measured  from  the  burette,  is  weighed ; and  for 
this  purpose  the  solution  is  placed  in  a light  flask  of  the  form 
shown  in  par.  (939). 

In  estimating  the  value  of  soda  ash,  which  often  contains  sul- 
phide and  hyposulphite  of  sodium,  an  error  might  be  occasioned 
by  adopting  this  method ; because  both  the  sulphide  and  the 
hyposulphite  would  be  decomposed  by  the  sulphuric  acid,  and 
would  neutralize  it^  and  thus  would  he  reckoned  as  carbonate  of 
sodium. 

The  presence  of  caustic  alkali  in  any  sample  is  easily  ascer- 
tained by  the  action  of  the  solution  upon  nitrate  of  silver  : the 
carbonates  of  the  alkaline  metals  occasion  a white  precipitate  of 
carbonate  of  silver ; hut  if  they  contain  any  caustic  alkali,  a brovTi 
precipitate  of  hydrated  oxide  of  silver  is  produced.  The  presence 
of  sulphides  in  the  ash  is  immediately  manifested  by  the  odour  of 
sulphuretted  hydrogen  which  is  evolved  on  neutralizing  the  solu- 
tion with  an  acid ; if  any  sulphide  he  present,  it  will  blacken  the 
salts  of  silver,  and  interfere  with  their  application  as  a test  for 

(578)  Alkalimetry  Process  of  Will 
and  Fresenius. — The  proportion  of  car- 
bonic anhydride  in  any  sample  of  alkali 
is  readily  ascertained  by  means  of  the 
apparatus  employed  for  the  purpose  by 
Will  and  Fresenius,  represented  in  fig. 
332  : ^ is  a light  flask,  of  about  3 ounces 
capacity,  in  which  100  grains  of  the  al- 
kali are  placed  with  about  1 ounce  of 
water : <3  is  a similar  flask,  in  which 
about  an  ounce  and  a half  by  measure 
of  oil  of  vitriol  is  placed.  A sound  cork  is  fitted  into  the  neck 
of  each  flask,  and  is  pierced  with  two  apertures  for  the  reception 
of  the  tubes,  a^  c,  and  e^  all  of  which  are  open  at  both  ends : the 
tube,  a^  is  sufficiently  long  to  dip  into  the  liquid  in  the  flask ; c is 
a bent  tube,  the  longer  limb  of  which  passes  into  tlie  acid  in  the 
flask,  d.  The  outer  extremity  of  a is  closed  during  the  experi- 
ment, by  a plug  of  wax  or  of  soft  cement.  The  apparatus  is 
charged  in  the  manner  already  described,  and  is  accurately  weighed 
after  it  has  been  connected  together.  A partial  vacuum  is  now 
made  by  applying  the  mouth  to  the  tube,  and  exhausting  a por- 


caustic  potash  or  soda. 
Tig.  332. 


CHARACTERS  OF  THE  SALTS  OF  POTASSHJM. 


351 


tion  of  the  air ; on  ceasing  to  exhanst,  the  acid  rises  in  the  tube, 
and  passes  over  into  to  supply  the  place  of  the  air  which  has 
been  withdrawn  ; effervescence  is  occasioned  by  the  escape  of  the 
carbonic  anhydride,  which  passes  off  through  the  tube,  c,  and  is 
dried  as  it  bubbles  up  through  the  oil  of  vitriol  in  the  flask,  d. 
As  soon  as  the  effervescence  has  ceased,  a fresh  portion  of  acid  is 
forced  over  from  d into  h by  again  partially  exhausting  the  air : 
and  this  process  is  repeated  until  no  further  effervescence  is  occa- 
sioned by  the  fresh  acid.  The  plug  of  wax  is  now  withdrawn 
from  the  tube  <2,  and  a current  of  air  is  forced  through  the  appa- 
ratus by  exhausting  with  the  mouth  at  and  the  carbonic  anhy- 
dride is  thus  completely  displaced.  The  plug  is  now  replaced  in 
the  tube  and  the  apparatus  is  weighed  a second  time.  The 
difference  between  this  weight  and  that  obtained  on  the  first  oc- 
casion, indicates  the  amount  of  carbonic  anhydride  which  has 
been  expelled. 

If  any  sulphide  or  sulphite  of  the  alkaline  metal  be  present, 
the  error  which  it  might  occasion  by  loss  of  sulphuretted  hydrogen, 
or  of  sulphurous  anhydride,  in  the  gaseous  state,  and  which  would 
be  reckoned  as  carbonic  anhydride,  is  prevented  by  mixing  from 
20  to  30  grains  of  neutral  chromate  of  potassium  with  the  sample 
under  trial:  the  chromic  acid  which  is  liberated  by  the  subse- 
quent action  of  the  sulphuric  acid  upon  the  chromate,  imparts 
oxygen  to  the  sulphuretted  hydrogen  or  sulphurous  acid,  and  con- 
s^erts  both  into  sulphuric  acid,  which  would  be  retained,  and  would 
in  no  way  interfere  with  the  result. 

(579)  Acid  Carbonate  or  Bicarbonate  of  Potassium  (KITOOg, 
or  KO,lTO,  2 CO^^lOO) ; Sjp.  Gr.  2*052. — By  passing  a current 
of  carbonic  acid  through  a strong  solution  of  the  carbonate  of 
potassium,  crystals  of  the  carbonate  are  deposited  in  the  form  of 
right  rhombic  prisms  ; they  are  permanent  in  the  air,  and  require 
about  4 parts  of  cold  water  for  solution.  The  solution  of  the  acid 
carbonate,  if  exposed  to  the  atmosphere,  gradually  loses  one-fourth 
of  its  carbonic  acid,  forming  a sesquicarbonate  ; and  if  boiled,  the 
same  change  occurs  much  more  quickly.  The  acid  carbonate  is 
converted  into  the  normal  carbonate  when  fused  by  means  of 
heat.  The  acid  carbonate  of  potassium  has  no  alkaline  reaction 
upon  turmeric.  It  may  be  employed  for  procuring  the  compounds 
of  potassium  in  great  purity,  since,  if  well  crystallized,  it  is 
almost  absolutely  pure,  and  may  be  obtained  in  this  state  with 
less  difficulty  than  any  other  salt  of  potassium.  It  is  consumed 
medicinally  in  considerable  quantities,  for  making  effervescing 
draughts  by  the  addition  of  citric  or  tartaric  acid  to  its  solution 
in  water. 

The  Silicates  of  Potassium  are  important  compounds  in  con- 
nexion with  the  manufacture  of  glass : they  will  be  noticed  in 
treating  this  subject  (593  et  seq.). 

(580)  Characters  of  the  Salts  of  Potassium. — The  salts  of 
potassium,  with  a colourless  acid,  are  all  colourless.  They  seldom 
contain  any  water  of  crystallization,  yet  many  of  them  are  deli- 
quescent ; the  carbonate  and  acetate  offer  striking  instances  of  this 


352 


SODIUM. 


peciiliaritv,  and  fiirnisli  in  tliis  respect  a marked  contrast  to  tlie 
coiTesponding  salts  of  sodium.  The  salts  of  potassium,  when  pime, 
if  introduced  upon  a platinnm  wire  into  the  reducing  flame  of  the 
hloiepipe^  commnnicate  to  it  a violet  tint ; the  presence,  however, 
of  a small  quantity  of  a salt  of  sodimn  masks  this  eflect,  in  conse- 
quence of  the  strong  yellow  flame  occasioned  in  similar  circum- 
stances by  the  compounds  of  sodium ; by  means  of  the  spectro- 
scope, however,  the  potassium  is  distinctly  recognizable,  though 
the  sodium  salt  may  be  in  very  large  excess.  The  light  emitted 
by  a salt  of  potassium,  in  the  flame  of  a Bunsen  burner,  consists 
of  a feeble  continuous  spectrum,  terminated  at  one  end  by  a bright 
line  in  the  red,  and  at  the  other  by  a feebler  bnght  line  in  the 
violet  (K,  flg.  S2,  page  151.  Part  I.).  Solutions  of  the  salts  of 
potassium  yield  no  precipitate  with  solutions  of  the  carbonates  of 
the  alkaline  metals,  with  ferrocyanide  of  potassium,  or  with  sul 
phide  of  ammonium.  The  presence  of  potassium  in  solution  is 
recognized,  after  the  absence  of  every  metal  but  sodium  has  been 
ascertained,  by  the  following  characters  : if  moderately  concen- 
trated, a solution  of  tartaric  acid  in  excess  causes,  upon  brisk 
stirring,  a white  crystalline  precipitate  of  acid  tartrate  of  potassium, 
which  is  readily  dissolved  upon  adding  an  alkali.  Percldorate  or 
cartjazotate  of  sodium  has  also  sometimes  been  employed  as  a test 
for  potassium,  since  both  the  perchloric  and  carbazotic  acids  form 
potassium  salts  of  sparing  solubility.  These  compounds,  however, 
are  all  soluble  to  a considerable  extent  in  cold  water,  and  unless 
tolerably  strong  solutions  are  employed,  they  do  not  immediately 
subside.  AVith  silicofluoric  acid  they  yield  a transparent  gelatin- 
ous silicofluoride,  which  fomis  a white  powder  on  drying.  The 
most  conclusive  reaction,  however,  is  produced  with  the percMo- 
ride  of  platinum  upon  mixing  a strong  solution  of  this  salt  with 
a concentrated  one  of  a salt  of  potassium,  a yellow  double  salt, 
consisting  of  (2  KCl.PtClJ  is  separated  in  crystals ; it  is  quite 
insoluble  in  alcohol  and  ether,  but  is  slightly  taken  up  by  cold 
water.  It  is  therefore  best  for  analytical  purposes  to  acidulate  the 
solution  suspected  to  contain  potassium  with  a little  hydrochloric 
acid,  and  having  added  a slight  excess  of  the  solution  of  perchlo- 
ride  of  platinum,  to  evaporate  to  dryness  over  the  water-bath,  and 
to  wash  the  residue  with  alcohol  so  long  as  an;\i:hing  is  dissolved. 
This  salt  when  heated  to  redness  is  decomposed,  the  platinum  loses 
its  chlorine,  and  the  chloride  of  potassium  may  be  dissolved  out  of 
the  grey  residue  with  cold  water,  whilst  metallic  platinum  is  left 
behind  : 100  parts  of  the  chloride  of  platinum  and  potassium  are 
equivalent  to  15 ’OS  of  potassium,  or  to  19-26  of  potash. 

§ II.  Sodium:  Xa=23.  Sp.  Gr.  0*972;  Fusing-pt.  207°-7. 

(5S1)  Sodium  maybe  obtained  trom  its  carbonate  by  a process 
analogous  to  that  used  in  procuring  potassium.  Deville  recom- 
mends the  employment  of  the  following  mixture  in  the  extraction 
of  sodium:  dried  carbonate  of  sodium,  TIT  parts;  powdered  char- 
coal, 1T5  parts  ; flnely  powdered  chalk,  lOS.  These  materials  are 


OXIDES  OF  SODIUM. 


353 


mixed  intimately  and  kneaded  into  a stiff  paste  with  oil,  and 
calcined  in  a covered  iron  pot ; the  mass  is  then  introduced  into 
an  iron  retort  and  distilled,  with  the  precautions  described  when 
speaking  of  potassium ; it  ought  to  yield  nearly  one-third  of  its 
weight  of  sodium : the  object  of  adding  the  chalk  is  to  prevent  the 
charcoal  from  separating  from  the  carbonate  of  sodium  when  this 
salt  fuses.  As  a reducing  agent  sodium  is  but  little  inferior  to 
potassium  in  energy,  and  since  its  combining  number  is  lower,  and 
the  metal  is  much  less  expensive,  it  may  generally  be  substituted 
for  potassium  with  advantage  in  such  operations. 

Sodium  has  a bluish- white  colour;  in  appearance  and  pro- 
perties it  much  resembles  potassium,  but  is  somewhat  more  vola- 
tile ; it  fuses  at  a temperature  of  20T°'7.  It  burns  with  a bright 
yellow  flame.  When  dropped  into  cold  water,  it  decomposes  a 
portion  of  it,  extricating  hydrogen,  but  the  gas  does  not  take  fire 
unless  the  water  be  heated  previously. 

The  great  storehouse  of  sodium  is  common  salt,  which  is  met 
with  in  nature  in  extensive  deposits ; it  is  also  contained  in  vast 
quantities  in  the  water  of  the  ocean ; the  immense  quantities  of 
soda  consumed  in  the  arts  are  almost  exclusively  obtained  from 
chloride  of  sodium,  by  a process  presently  to  be  described,  though 
sodium  occurs  in  several  minerals,  such  as  albite  or  sodium-fel- 
spar and  cryolite,  the  double  fluoride  of  sodium  and  aluminum. 
Borax  or  the  acid  borate  of  sodium,  and  trona  or  the  sesqui- 
carbonate,  as  well  as  the  nitrate,  are  also  native  compounds  of 
sodium. 

The  metal  forms  two  well-known  oxides,  one  of  which  con- 
tains twice  as  much  oxygen  as  the  other  : — 

Sodium.  Oxygen. 

Soda NaaO  = 62  74-79  + 25-81  = 100 

^ sodium = 18  58-97  + 41-03  = 100 

A blue  suboxide  appears  also  to  exist. 

(582)  Oxide  of  Sodium,  or  Soda  (IIa20=62,  or  IIaO  = 31), 
forms  the  basis  of  the  important  series  of  salts  of  sodium.  It  can 
be  procured  in  an  anhydrous  state  by  burning  the  metal  in  dry  air 
or  oxygen  gas  : it  is  of  a yellowish-white  colour,  attracts  moisture 
as  greedily  as  the  corresponding  oxide  of  potassium,  and  this 
Avatei*  cannot  again  be  expelled  from  it  by  heat.  In  appearance 
and  properties  the  hydrate  closely  resembles  that  of  potash  ; it 
may  be  formed  from  the  carbonate  by  a similar  method ; its  action 
upon  acids,  liowever,  is  less  energetic.  According  to  Filhol  the 
solid  hydrate  (i^allO)  has  a sp.  gr.  of  2T3.  The  table  on  the 
following  sliows  the  proY)ortion  of  anhydrous  soda  wliich 

is  contained  in  solutions  of  hydrate  of  soda  of  different  densi- 
ties. Hydrate  of  soda  is  extensively  used  in  tlic  manufacture  of 
hard  soaps. 

Caustic  soda  is  now  manufactured  on  a large  scale  in  the 
alkali  works,  which  supply  it  in  the  form  of  a solid  hydrate  con- 
taining 60  per  cent,  of  anhydrous  soda  ; for  this  purpose  ad  van- 
23 


354 


CHLOEEDE  OF  SODIUM. 


Strength  of  Solutions  of  Soda  {Dalton). 


. _ NaOinlOO 

parts. 

g XaO  in  100 

parts. 

1-56 41-2 

1*50  36-8 

1*47 34-0 

1-44 31'0 

1-40 29-0 

1*36  26-0 

1-32  23-0 

1-29 19-0 

1-23 16-0 

1-18 13-0 

112 9'0 

1-06 4-7 

tage  is  taken,  as  proposed  by  Mr.  Gossage,  of  the  caustic  soda 
present  in  the  solutions  of  crude  soda.* 

Tlie  sulphides  of  sodium  correspond  in  number  with  those  of 
potassium,  which  they  closely  resemble.  They  may  be  prepared 
by  analogous  methods. 

(583)  Chloride  of  Sodihm  (NaCl  = 58*5) ; Sp.  Gr.  2-078  ; 
Comp,  in  100  parts,  17a,  39-32 ; Cl,  60-68. — This  important  and 
well-known  compound,  formerly  called  muriate  of  soda,  consti- 
tutes common  culinary  table-salt.  It  is  found  native  in  the  solid 
form,  and  it  exists  in  solution  in  sea-water  in  a proportion  of  about 
2-7  per  cent.,  which  amounts  to  nearly  four  ounces  per  gallon,  or 
to  a bushel  in  from  300  to  350  gallons. 

The  extraction  of  the  chloride  from  sea-water  was  formerly 
practised  to  some  extent  upon  the  southern  coast  of  our  own 
island : in  Great  Britain  the  manufacture  is  now  unimportant, 
though  in  the  southern  countries  of  Europe  the  preparation  of 
bay-salt  is  still  a branch  of  industry  of  some  magnitude.  In  con- 
ducting this  process  the  sea  water  is  allowed  to  run  into  shallow 
pools,  in  which  the  water  evaporates  and  the  liquor  becomes  con- 
centrated by  the  heat  of  the  sun  : crusts  of  the  salt  are  formed,  and 
are  raked  off  from  time  to  time  : the  rough  crystals  thus  obtained 
furnish  the  hay-salt  of  commerce.  The  concentrated  sea-water, 
or  hittern,  is  employed  as  a source  of  bromine.  Balard,  who  has 

* In  order  to  effect  this  the  crude  solution  obtained  from  the  black-ash  vats  is 
evaporated  down  till  it  acquires  a sp.  gr.  of  1‘5  or  1'6,  during  which  operation  almost 
all  the  carbonate,  sulphate,  and  chloride  of  sodium  crystallize  out.  The  solution, 
(technically  known  as  red  liquor)  is  of  a red  colour,  o-wing  to  the  presence  of  a peculiar 
soluble  compound  of  sulphide  of  sodium  and  sulphide  of  iron,  and  is  likewise  con- 
taminated with  ferrocyanide,  and  occasionally  with  sulphocyanide  of  sodium.  By 
forcing  air  under  pressure  for  several  hours  through  the  hot  liquid,  the  iron  is  preci- 
pitated as  sesquioxide,  and  the  sulphur  compounds  are  converted  into  sulphates.  The 
completion  of  the  oxidation  is  effected  by  the  addition  of  nitrate  of  sodium.  The 
entire  process  of  oxidation  may  indeed  be  more  rapidly  effected  by  means  of  the 
nitrate.  After  its  addition  the  evaporation  is  carried  further,  until  the  mass  by 
degrees  becomes  heated  nearly  to  redness.  When  the  temperature  rises  to  310^, 
large  quantities  of  ammonia  are  evolved,  and  subsequently,  as  the  heat  becomes  much 
greater,  nitrogen  escapes  abundantly  (Pauli).  The  ammonia  is  produced  partly  by 
the  decomposition  of  the  cyanogen  compounds,  but  also  in  part  from  the  removal  of 
oxygen  from  water  by  the  sulphides,  whilst  the  hydrogen  reduces  the  nitric  acid  to 
the  form  of  ammonia.  The  fused  soda  is  poured  into  sheet-iron  vessels,  in  which  it 
solidities,  and  is  preserved  for  the  market.  {HofmariTCs  Jury  Report,  Int.  Exhib.  1862, 

p.  28.) 


CHLOEIDE  OF  SODIUM. 


355 


devoted  much  attention  to  the  study  of  these  mother-liquors,  has 
devised  a method  of  extracting  from  them  not  only  sulphate  of 
sodium,  hut  also  an  important  quantity  of  salts  of  potassium,  in 
the  form  of  a double  sulphate  of  potassium  and  magnesium,  as 
well  as  of  a double  chloride  of  potassium  and  magnesium.  The 
process  requires  a careful  attention  to  the  temperature  at  which 
the  crystallizations  are  effected.  At  temperatures  below  27°  the 
chloride  of  sodium  still  present  in  the  brine  decomposes  the  sul- 
phate of  magnesium,  chloride  of  magnesium  and  sulphate  of 
sodium  being  formed;  whilst  at  temperatures  above  100°  F.,  a 
sparingly  soluble,  double  sulphate  of  sodium  and  magnesium  is 
formed.* 

Immense  beds  of  common  salt  are  met  with  in  Cheshire,  at 
Wielitzka  in  Poland,  and  at  Cardona  in  Spain.  It  has  also  re- 
cently been  found  in  abundance  in  the  north  of  Ireland,  near 
Belfast,  and  on  the  southern  borders  of  the  Durham  coal-field. 
Hear  Horthwich,  the  principal  deposit  of  rock-salt  in  England, 
the  mineral  occurs  in  two  beds,  situated  one  above  another,  sepa- 
rated by  about  30  feet  of  clay  and  marl  intersected  with  small 
veins  of  salt : the  two  beds  together  are  not  less  than  60  feet  in 
thickness,  300  yards  broad,  and  a mile  and  a half  long.  These 
beds  occur  in  magnesian  limestone.  The  celebrated  and  beauti- 
ful mine  of  Wielitzka  contains  sufficient  salt  to  supply  the  entire 
world  for  ages.  It  is  calculated  that  the  mass  of  rock  salt  here 
is  500  miles  in  length,  20  miles  broad,  and  not  less  than  1200  feet 
in  thickness.  This  salt  deposit  occurs  in  the  chalk  formation. f 
Chloride  of  sodium  is  sometimes  found  crystallized,  and  is  then 
termed  sal  gem^  or  rock  salt.  Where  coal  is  cheap,  the  solubility 
of  the  chloride  is  frequently  taken  advantage  of  in  diminishing 
the  labour  of  raising  the  salt  to  the  surface,  water  being  let  down 
into  the  bed  of  salt  and  allowed  to  remain  till  it  has  become  sat- 
urated : it  is  then  pumped  out  and  the  brine  is  boiled  down  and 
crystallized.  Some  brine  springs  contain  too  small  a propor- 
tion of  salt  to  render  it  profitable  to  effect  the  evaporation  by  heat ; 
the  water  in  these  cases  is  therefore  concentrated  by  graduation^ 
as  at  Salzburg : this  process  consists  in  exposing  the  brine,  dif- 

* The  following  is  the  modification  of  Balard’s  plan,  adopted  by  M.  Merle : Sea 
water  is  concentrated  in  the  salt-pans  by  spontaneous  evaporation  till  it  acquires  a 
density  of  1-24,  by  which  time  it  has  deposited  about  ^ths  of  the  quantity  of  common 
salt  which  it  contains.  The  mother-liquor  is  then  diluted  with  one-tenth  of  its  bulk 
of  water,  and  cooled  down  artificially  by  the  use  of  Carre’s  refrigerator,  {nole^  Part  I. 
p.  261),  till  the  temperature  falls  to  0°  F.  As  the  liquor  passes  through  the  refrige- 
rator, sulphate  of  sodium  is  deposited  in  nearly  a pure  state,  and  is  dried  in  a centri- 
fugal hydro-extractor.  The  mother-liquor — retaining  chlorides  of  magnesium,  sodium, 
and  potassium — is  boiled  down  to  a sp.  gr.  of  and  deposits  nearly  all  the  re- 

maining chloride  of  sodium.  The  hot  liquor  is  run  into  shallow  coolers,  where  it 
deposits  the  whole  of  the  potash  in  the  form  of  the  double  chloride  of  magnesium  and 
potassium.  On  treating  tliis  with  half  its  weight  of  water,  the  salt  is  decomposed, 
the  deliquescent  chloride  of  magnesium  is  dissolved,  together  with  one-fourth  of  the 
chloride  of  potassium,  and  the  solution  is  returned  to  be  recrystallizcd  with  the  fresh 
mother-liquor — while  the  undissolved  ctiloride  of  potassium  is  ready  for  sale  after  it 
has  been  dried. 

f Some  specimens  of  the  salt  from  this  mine  decrepitate  when  thrown  into  water, 
owing  to  the  escape  of  condensed  gas  (^Hs;  Rose),  which  is  liberated  during  the  so- 
lution of  the  crystals. 


356 


CHLORIDE  OF  SODIOI. 


fused  over  a large  surface,  to  the  air,  by  pumping  it  up  to  a height, 
and  then  allowing  it  to  trickle  slowly  over  large  stacks  of  fagots, 
piled  in  suitable  buildings  screened  from  rain,  but  freely  exposed 
to  the  prevaihng  wind  : after  this  process  has  been  repeated  eight 
or  ten  times,  the  solution  acquires  a density  of  about  I’ldO,  and 
is  suthciently  concentrated  to  allow  the  evaporation  to  be  finished 
as  usual  by  the  direct  application  of  heat.  In  the  first  basin  an 
insoluble  double  sulphate  of  calcium  and  sodium  is  deposited, 
partly  in  the  form  of  mud,  or  scJdot  as  the  Germans  term  it,  partly 
in  the  form  of  a hard  scale,  which  adheres  to  the  bottom  of  the 
pan  : when  the  liquor  reaches  a density  of  1’236  it  is  decanted  into 
another  pan,  and  evaporated ; the  crusts  of  salt  are  removed  as 
they  are  formed. 

The  appearance  of  the  salt  varies  according  to  the  rate  at 
which  the  evaporation  is  conducted ; when  the  brine  is  boiled 
down  rapidly,  it  furnishes  the  mealy,  fine-grained  salt  used  upon 
our  tables  ; if  evaporated  more  slowly,  the  hard,  crystallized  salt, 
preferred  for  fishery  purposes  is  obtained.  The  salt  of  commerce 
always  contains  a certain  proportion  of  chloride  of  magnesium, 
vdiich  gives  it  a slightly  deliquescent  character,  and  adds  to  the 
pungency  of  its  flavour.  It  is  stated,  that  when  the  proportion 
of  cliloride  of  magnesium  in  the  brine  is  considerable,  the  crystals 
of  chloride  of  sodium  form  a scum  over  the  surface  which  much 
retards  the  evaporation.  This  inconvenience  maybe  remedied  by 
the  addition  of  a quantity  of  sulphate  of  sodium,  which  decomposes 
the  chloride  of  magnesium  and  converts  it  into  sulphate. 

Properties. — Chloride  of  sodium  has  an  agreeable,  sahne  taste. 
It  crystallizes  in  colourless  transparent  cubes,  which  are  anhy- 
drous, soluble  in  about  3 parts  of  cold  water,  and  scarcely  more 
soluble  at  a temperatm-e  of  212^ ; the  saturated  solution  has  a 
sp.  gr.  of  1’205.  AVater  at  32°  dissolves  35‘5  per  cent,  of  the  salt, 
and  41-2  per  cent,  at  229°’5,  the  boiling-point  of  the  solution. 
AVhen  heated  suddenly,  the  crystals  decrepitate  with  violence  ; at 
a bright  red  heat  they  fuse,  and  by  a stronger  heat  are  converted 
into  vapour.  Chloride  of  sodium  is  insoluble  in  pure  alcohol,  but 
is  taken  up  in  considerable  quantity  by  dilute  spirit.  By  exposing 
its  aqueous  solution  to  a temperature  of  about  14°,  it  crystallizes 
in  hexagonal  tables,  whicii  contain  2 : as  the  temperature 

rises,  the  water  is  separated,  the  crystals  fall  to  pieces,  and  become 
converted  into  a heap  of  minute  cubes. 

Chloride  of  sodium  is  consumed  in  large  quantities  in  the 
manufacture  of  the  salts  of  sodium,  it  is  extensively  employed  in 
glazing  stoneware,  and  is  an  article  of  daily  domestic  use,  being 
indeed  an  essential  constituent  of  the  food  both  of  man  and  of 
animals,  who  languish  if  it  be  supplied  in  insufficient  quantity. 
The  process  of  salting  meat  is  resorted  to  on  account  of  the  pow- 
erfully antiseptic  qualities  of  the  chloride  of  sodium.  In  this 
operation  a large  quantity  of  the  nutritive  juice  of  the  meat  is 
extracted,  and  this  liquid  when  saturated  whh  the  salt  forms  the 
Im/iie.  Meat  thus  prepared  is  much  less  digestible  and  nutritious 
than  fresh  meat. 


EROMroE  AND  IODIDE  OF  SODHTM SULPHATE  OF  SODILTkI. 


357 


Chloride  of  sodium,  when  fused  with  rather  more  than  one- 
third  of  its  weight  of  sodium  in  a current  of  dry  hydrogen,  fur- 
nislies  a blue  compound,  supposed  to  be  a subchloride,  h^a^Cl 
(Bunsen). 

(584)  Bromide  of  Sodium  (^7aBr=:103)  is  analogous  to  bromide 
of  potassium  ; it  is  soluble  both  in  water  and  in  alcohol,  and  crys- 
tallizes at  temperatures  above  86°  in  anhydrous  cubes.  At  lower 
temperatures  it  forms  hexagonal  tables  with  2 H2O. 

(585)  Iodide  of  Sodium  (Nal=150  ; /§:>.  (xr.  3 ’45)  crystallizes 

at  temperatures  above  100°  F.  in  cubes,  which  are  anhydrous ; 
but  if  crystallized  at  ordinary  temperatures  it  yields  large  trans- 
parent, striated,  oblique  rhombic  prisms,  with  2 H^O.  Iodide  of 
sodium  occurs  native  in  sea-water  in  minute  proportion,  but  small 
as  this  proportion  is,  it  furnishes  the  commercial  supply  of  iodine  ; 
many  marine  plants  appropriate  it  to  their  nutrition,  and  when 
these  plants  are  burned,  the  iodide  remains  in  the  residue : the 
ash  thus  obtained  goes  by  tlie  name  of  A ton  of  good  Irish 

kelp  from  drift-weed  furnishes  about  8 lb.  of  iodine. 

(586)  Sulphate  of  Sodium  (Fra2Si04,  10  1120=142-1-180,  or 

F’a0,S03,  10  HO  = Tl-f90).  Sjp.  Gr.  anhydrous^  2'597 ; cryst. 
1*469  : Composition  in  100  parts  oi  dry  salt,  43*67 ; SO3 

56*33  ; of  crystallized  salt,  ]Sra20,  19*24;  SO3,  24*84;  H2O,  55*91. 
— This  salt  has  long  been  known  under  the  name  of  Glauheds 
salt.  It  crystallizes  usually  in  long  four-sided  prisms,  terminated 
by  dihedral  summits.  It  is  remarkably  efflorescent,  and  loses  the 
whole  of  its  10  atoms  of  water  by  mere  exposure,  at  common 
temperatures,  to  the  atmosphere.  It  has  a saline,  bitter  taste,  and 
is  occasionally  used  medicinally  as  a purgative. 

The  solubility  of  sulphate  of  sodium  in  water  offers  some  re- 
markable anomalies  (55),  which  have  been  the  subject  of  many 
inquiries,  the  most  complete  of  which  are  those  of  Loweh*  It 
has  already  been  mentioned  (74)  tliat  a boiling  saturated  solution 
of  this  salt,  if  closed  hermetically,  may  be  kept  for  months  with- 
out crystallizing,  but  the  moment  that  air  is  admitted,  the  whole 
becomes  semi-solid,  from  the  sudden  formation  of  crystals  through 
the  mass.  It  is  most  probable  that  the  salt  exists  in  the  super- 
saturated solution  in  the  form  of  the  anhydrous  salt,  and  that 
crystallization  occurs  when  any  circumstance  occasions  the  for- 
mation of  the  less  soluble  10-atom  hydrate.  The  crystallization 
of  such  a solution  may,  for  example,  be  instantly  determined  by 
dropping  in  a fragment  of  the  sulphate,  or  by  contact  with  a rod 
of  glass  or  of  metal.  If,  however,  the  glass  rod  or  the  metallic 
wire  be  boiled  with  water,  and  allowed  to  cool  under  water  or  in 
a closed  vessel,  it  may  be  introduced  into  the  supersaturated  solu- 
tion without  causing  the  crystallization  of  the  salt. 

Cr^^stallized  sulphate  of  sodium  is  soluble  in  hydrochloric  acid, 
with  great  depression  of  temperature.  A convenient  freezing 

* Three  forms  of  sulphate  of  sodium  may  be  obtained  in  crystals, — viz.  1.  the 
anhydrous  sulphate;  2.  the  ordinary  crystallized  sulphate  with  10  ir..>f>;  and  3.  tbe 
hydrate  with  7 HjO,  which  crystallizes  in  rhombic  prisms.  Each  of  these  varieties 
has  a specific  solubility.  The  10-atom  hydrate  is  the  least  soluble,  and  the  7-atom 


358 


SULPHATE  OF  SODIUM. 


mixture  is  obtained  by  pouring  5 parts  of  the  commercial  acid 
upon  8 of  the  crystallized  sulphate. 

Sulphate  of  sodium,  to  which  the  name  of  Thenar dite  has 
been  given,  has  been  met  with  nearly  pure  not  far  from  Madrid, 
deposited  at  the  bottom  of  some  saline  lakes,  in  anhydrous  octo- 
hedra.  It  has  likewise  been  found,  not  far  from  the  same  place, 
combined  with  sulphate  of  calcium,  as  Glauberite^  in  anhydrous 
crystals  (Xa2-Ga  2 

hydrate  the  most  so  of  the  three  forms.  The  following  table  (Lowel,  Ann.  de  Chimie, 
III.  xlLx.  50)  exhibits  the  varying  solubility  of  each  form  of  the  sulphate  of  sodium, 
as  the  temperature  rises : — 

100  Parts  of  Water  when  saturated  contain,  of 


Temp.  F°. 

Anhydrous  salt. 

jsalt  with  10  H.2-0. 

Salt  -with  7 

_ . JL 

H2O. 

Anhydr.: 

■with 

= 10  Anhydr. 

with 

= 10  H2O. 

Anhydr. 

with 
= 7H20 

■with 

= 10H20. 

32 

5-02 

12-16 

19-62 

44-84 

59-23 

53-0 

9-00 

23-04 

30-49 

78  90 

112  73 

55'9 

13-20 

35-96 

37-43 

105-79 

161-57 

64-4 

53-25 

371-97 

16-80 

48-41 

41-63 

124-59 

200-00 

77*1 

52-76 

361-51 

19-40 

58-35 

44-73 

140-01 

234-40 

83-8 

51-53 

337-16 

28-00 

98-48 

52-94 

188-46 

365-28 

87-3 

51-31 

333-06 

30-00 

109-81 

54-97 

202-61 

411-45 

89-3 

50-37 

316-19 

40-00 

184-09 

90-9 

49-71 

305-06 

50-76 

323-13 

93-0 

49-53 

302-07 

55  00 

412-22 

104-3 

48-78 

290-00 

113-1 

47-81 

275-34 

122-7 

46-82 

261-36 

139-6 

45-42 

242-89 

159-3 

44-35 

229-87 

184-0 

42-96 

213-98 

217-7 

42-65 

210-67 

From  this  table  it  appears  that  the  solubility  of  the  anhydrous  salt  decreases 
from  64° "4  to  the  boiling-point  (217°’7)  of  the  solution.  Below  64°  the  molecular 
constitution  of  the  salt  is  changed,  a saturated  solution  depositing,  in  vessels  from 
which  air  is  excluded,  crystals  of  the  7-atom  hydrate.  100  parts  of  water  at  64°'4 
retain  as  mnch  as  53'25  of  the  anhydrous  salt,  whilst  at  the  boiling-point  only  42'65 
parts  are  held  in  solution.  Hence  if  a solution  saturated  at  64°  be  simply  heated  to 
boiling,  without  allowing  any  loss  of  hquid  by  evaporation,  it  will  deposit  in  hard, 
gritty,  anhydrous  crystals  more  than  one-fifth  of  the  salt  which  it  previously  held  in 
solution. 

In  the  case  of  the  least  soluble  form  of  the  sulphate,  the  10-atom  hydrate,  the 
solubihty  increases  until  the  temperature  reaches  93",  at  which  point  the  salt  begins 
to  liquefy  in  its  water  of  crystallization : its  molecular  constitution  then  undergoes  a 
change,  and  it  becomes  gradually  converted  into  the  anhydrous  variety,  which  at  that 
particular  temperature  has  a lower  solubility  than  the  hydrated  salt,  and  consequently 
is  partially  separated  in  crystalline  grains. 

The  hydrate  with  7 is  more  soluble  than  either  of  the  foregoing  forms ; but 
under  ordinary  circumstances  it  cannot  exist  in  contact  with  the  atmosphere,  and  is 
only  deposited  from  supersaturated  solutions  in  closed  vessels,  or  in  flasks  which 
have  been  aUovved  to  cool  covered  with  small  capsules,  so  as  to  prevent  the  entrance 
of  particles  of  dust  or  of  foreign  matter.  Crystals  of  the  7-atom  hydrate  may  also 
be  obtained  by  pouring  a boding  solution  of  the  sulphate  into  a capsule  and  allow- 
ing it  to  cool  under  a bell-glass,  over  a vessel  of  chloride  of  calcium.  In  whatever 
mode  the  crystals  of  the  7-atom  hydrate  have  been  produced,  they  undergo  change 
from  very  shght  causes,  and  become  white  and  opaque  with  evolution  of  heat,  either 


SULPHATE  OF  SODIUM. 


359 


Crystallized  sulpliate  of  sodium  also  frequently  occurs  in 
needles  as  an  efflorescence  upon  plaster,  and  upon  brickwork  in 
damp  situations. 

Preparation. — Sulpliate  of  sodium  is  made  from  oil  of  vitriol 
and  common  salt  in  enormous  quantities,  under  the  name  of  salt- 
cake^  as  a preliminary  step  in  the  manufacture  of  carbonate  of 
sodium.  The  operation  is  carried  on  in  a reverberatory  furnace, 
connected  with  an  apparatus  for  condensing  the  hydrochloric  acid, 
which,  till  within  the  last  few  years,  was  allowed  to  escape  into 
the  atmosphere,  to  the  serious  injury  of  vegetation  in  the  surround- 
ing district.  One  of  the  best  forms  of  furnace  is  shown  in  section 
in  fig.  333 : the  course  of  the  flues,  however,  is  not  exactly  such 

Fig.  333. 


as  is  there  represented  : A,  the  smaller  of  the  two  compartments 
which  compose  the  furnace,  is  of  cast  iron ; into  this  (the  decom- 
poser') from  5 to  6 cwt.  of  common  salt  are  introduced,  and  an 
equal  weight  of  sulphuric  acid,  of  specific  gravity  1*6,  is  gradually 
mixed  with  it,  a gentle  heat  being  applied  to  the  outside ; enor- 
mous volumes  of  hydrochloric  acid  gas  are  disengaged,  and  pass 
off  by  the  flue,  rZ,  to  the  condensing  towers,  e and  f ; these  towers 
are  filled  with  fragments  of  broken  coke  or  stone,  over  which  a 
continuous  stream  of  water  is  caused  to  trickle  slowly  from  A,  A. 

when  exposed  to  the  air,  or  when  the  solution  is  allowed  to  crystallize  around  them, 
or  when  touched  with  a glass  rod.  The  solubility  of  the  T-atom  hydrate  rises  with 
the  temperature,  as  is  shown  in  the  table ; but  this  form  of  the  salt  cannot  exist  at 
temperatures  above  84° ; for  when  heated  to  this  point  its  crystals  begin  to  liquefy 
in  their  water  of  crystallization;  and,  in  consequence  of  a molecular  change,  crystals 
of  the  anhydrous  variety  are  deposited. 

From  the  foregoing  details  it  will  be  easy  to  perceive  why  it  is  that  a hot  solution 
of  the  sulphate  deposits  crystals  so  slowly : — When  a solution  of  sulphate  of  sodium, 
saturated  at  its  boiling-point,  is  poured  into  an  open  capsule,  a film  of  crystals  of 
the  anhydrous  sulphate  is  formed  at  first  upon  its  surface,  owing  to  the  rapid  evapo- 
ration of  a portion  of  the  solvent.  No  crystals,  however,  are  deposited  in  the  body 
of  the  liquid  until  the  temperature  has  fallen  to  about  91°.  The  film  of  crystals  first 
formed  is  gradually  redissolved,  and  crystals  of  the  10-atom  hydrate  are  formed  as 
the  temperature  continues  to  fall.  If  the  solution  be  evaporated  at  temperatures 
above  93°,  acute  rhombic  octohedra  of  the  anhydrous  salt  are  produced : but  if  a 
boiling  saturated  solution  be  allowed  to  cool  in  closed  vessels,  no  crystals  are  depos- 
ited until  the  temperature  falls  to  64°,  when  oblique  rhombic  prisms  of  the  7-atom 
hydrate  are  formed. 


360  SULPHATE  OF  POTASSIUM  AXD  SODIUM SULPHITE  OF  SODIUM. 

A steady  current  of  air  is  drawn  throiigli  tlie  furnace  and  con- 
densing towers,  by  connecting  the  first  tower  with  the  second,  as 
represented  at  y,  and  the  second  tower  with  the  main  chimney,  k, 
of  the  works.  In  the  first  bed  of  the  furnace,  about  half  the 
hydrochloric  acid  is  exjielled  from  the  salt : the  pasty  mass  thus 
produced  is  then  pushed  through  a door  for  the  purpose  into  the 
roaster^  or  second  division,  b,  of  the  furnace.  In  this  state  it 
consists  of  a mixture  of  acid  sulphate  of  sodium  and  nndecomposed 
salt.  The  reaction  in  the  first  bed  of  the  furnace  may  be  repre- 
sented as  follows : — 

2 XaCl  + H,Se,=:NaCl+XaHSe,-f  HCl. 

In  the  second  stage  of  the  operation  a higher  temperature 
is  required;  the  acid  sulphate  of  sodium  then  reacts  upon  the 
unchanged  chloride,  and  the  conversion  into  normal  sulphate  of 
sodiimi  is  complete;  thus  ]SraCl-|-XaIIS04=IICl+Xa2S04.  The 
hydrochloric  acid  gas,  as  it  is  liberated  from  b,  passes  ofi*  through 
the  fine,  c7,  and  is  carried  on  to  the  condensing  towers.  Heat  is 
applied  to  the  outside  of  the  roaster,  b ; the  smoke  and  products 
of  combustion  circulate  in  separate  flues  around  the  chamber,  in 
the  direction  indicated  by  the  arrows,  but  never  come  into  con- 
tact with  the  salt-cake  in  b. 

Sulphate  of  Potassium  and  Sodium  (Isalv32  SO^,  Penny ; Sp. 
Gr.  2'668). — This  double  salt  is  anhydrous;  it  may  be  formed  by 
dissolving  the  two-  salts  in  water  and  evaporating.  Gladstone 
has  shown  that  the  emplo^nnent  of  a large  excess  of  sulphate 
of  sodium  does  not  alter  the  composition  of  the  salt,  the  sulphate 
of  sodium  in  excess  crystallizing  in  its  usual  form. 

It  is  obtained  upon  a large  scale  from  kelp  liquors  during  the 
manufacture  of  iodine,  and  is  known  under  the  name  Si  plate  sul- 
phate^ from  the  manner  in  which  it  is  deposited  in  hard  crystal- 
line layers  or  plates,  upon  the  sides  of  the  crystallizing  vats. 
During  the  act  of  crystallizing  it  emits  Hvid  scintillations  of 
phosphorescent  light : this  phosphorescence  is  most  striking  when 
the  temperature  is  near  100°  F.  A very  brilliant  elfect  is  pro- 
duced by  dashing  a pailful  of  the  warm  mother-liquor  upon  a crop 
of  crystals  in  a vat  from  which  the  mother-liquor  has  been  di’ained 
ofi*  a few  hours  previously. 

An  Acid  Sulphate  of  Sodium^  often  called  hisulphate  of  soda ^ 
(XallSO,  or  XaO,IIO,2  120;  Sp.  Gr.  2-71:2)  corresponding 

to  the  acid  sulphate  of  potassium,  may  be  formed.  It  is  more 
easily  deprived  of  basic  hydrogen  by  heat  than  the  acid  sulphate 
of  potassium;  2 HaHSO^  yielding  Xa2S0^,S03  + IIjO.  Tho 
anhydro-salt,  by  a stronger  heat  loses  its  sulphuric  anhydride, 
and  may  hence  be  employed  as  a convenient  source  of  this  anhy- 
dride (116). 

(587)  Sulphite  of  Sodium  (XaSOg,  7 H^O  = 126  -f  126  or 
Ha0,S02,  7 Aq=63-f-63  ; Sp.  Gr.  1*736)  is  now  prepared  largely 
under  the  name  of  antichlore.^  for  the  purpose  of  removing  the 
last  traces  of  chlorine  from  the  bleached  pulp  obtained  from  rags 
in  the  manufacture  of  paper.  It  is  procured  by  passing  sulphu- 


NITRATE  AND  CARBONATE  OF  SODIUM. 


361 


rolls  anhydride,  obtained  by  the  combustion  of  sulphur  in  air, 
over  moistened  crystals  of  carbonate  of  sodium,  so  long  as  the  acid 
gas  is  absorbed,  the  mass  is  dissolved  in  water  and  crystallized. 
Sulphite  of  sodium  forms  efflorescent,  oblique  prisms,  which  fuse 
at  113°  ; they  are  soluble  in  about  4 parts  of  cold  water : the  solu- 
tion has  a slightly  alkaline  reaction  and  a sulphurous  taste. 

An  Acid  Suljpliite  of  Sodiutn  (iN’aHSB-a)  may  be  obtained  in 
crystals. 

(588)  Nitrate  of  Sodium,  or  Cubic  Nitre^  (NaNOg  or  NaO, 
N05=85  ; Sp.  Gr.  2-26),  occurs  abundantly  2 or  3 feet  below  the 
surface  of  the  soil  near  Iquique,  in  the  district  of  Atacama,  in 
Peru.  It  is  a somewhat  deliquescent  salt,  and  is  soluble  in  about 
twice  its  weight  of  cold  water : it  crystallizes  in  obtuse  rhombo- 
hedra,  and  has  a cooling,  saline  taste.  When  heated,  it  fuses  at 
591°,  and  at  a higher  temperature  it  undergoes  decomposition. 
It  is  employed  in  the  manufacture  of  nitric  and  sulphuric  acids, 
but  from  its  deliquescence  cannot  be  substituted  for  nitrate  of 
potassium  in  gunpowder.  It  is  frequently  used  as  a manure,  as 
in  top-dressing  barley. 

(589)  Carbonate  of  Sodtoi  (Na2'00-3,1O  H2O=106  180,  or 

Na0,C02,  10  Aq=53-|-90) ; Sp.  Gr.^  anhydrous^  2-509,  cryst. 
1-454;  Comp,  in  parts  of  dry  salt,  Na20,  58-49 ; 41-51 ; 

cryst.  H^O,  62-93  ; Na^O,  21-68  ; 15-39. — The  preparation 

of  this  salt  constitutes  one  of  the  most  important  branches  of  che- 
mical manufacture  in  this  country,  immense  quantities  of  it  being 
consumed  in  the  production  of  glass,  in  the  fabrication  of  soap, 
and  in  the  preparation  of  the  various  compounds  of  sodium,  be- 
sides a considerable  consumption  as  a detergent  by  the  calico- 
printer,  as  well  as  in  the  laundry  for  softening  hard  waters  by 
precipitating  the  salts  of  calcium  and  magnesium.  Compounds 
of  sodium,  from  their  lower  price,  are  now  substituted  in  a great 
number  of  cases  in  which  those  of  potassium  were  formerly  em- 
ployed, but  tliere  are  a few  in  which  their  substitution  is  not 
practicable : nitrate  of  potassium  is  still  required  in  the  manufac- 
ture of  gunpowder ; in  the  finest  varieties  of  glass,  potash  is  used 
on  account  of  the  green  tint  occasioned  by  soda ; and  chlorate, 
chromates,  and  tartrate  of  potassium,  as  well  as  the  cyanogen 
compounds  of  potassium,  still  are  preferred  to  the  corresponding 
salts  of  sodium. 

The  greater  portion  of  the  carbonate  of  sodium  formerly  em- 
]doyed  was  obtained  from  barilla^  which  is  the  asli  furnished  by 
burning  marine  plants.  The  Salsola  soda  was  extensively  culti- 
vated for  this  purpose  on  tlie  southern  coast  of  Si)ain,  and  on 
being  burnt,  it  yields  a semi-vitrihed  mass,  which  contains  trom 
25  t(j  30  ])er  cent,  of  carbonate  of  sodium.  The  Salicornia  was 
cultivated  for  a similar  purpose  on  the  southern  coast  of  France ; 
but  these  sources  of*  supply  have  almost  entirely  given  way  to  a 
])rocess  by  which  the  carbonate  may  be  manufactured  from 
sea-salt. 

Manufacture. — In  the  ]:)rocess  of  manufacture  a rough  sul- 
phate of  sodium  is  first  formed,  in  the  manner  already  described 


362 


MAmiFACTUEE  OF  BLACK  ASH. 


(586).  The  sulphate  of  sodium  is  then  mingled  with  chalk  and 
powdered  coal  in  the  proportion  of  about  3 parts  of  sulphate  of 
sodium,  3 of  chalk,  and  or  2 of  coal ; this  mixture  is  thrown, 
in  quantities  of  about  2^  cwt.  at  a time,  into  a hot  reverberatory 
furnace,  and  frequently  stirred,  until  the  mass  is  thoroughly 
melted. 

The  furnace,  fig.  334,  is  constructed  with  two  doors,  n,  e,  and 
a double  floor,  b,  c ; one  charge  is  introduced  at  tlie  further  door. 


Fig.  334. 


E,  whilst  another,  nearer  the  fire,  is  fusing  at  b ; towards  the  con- 
clusion of  the  operation  the  mass  melts,  and  effervesces  violently 
from  the  escape  of  carbonic  oxide  gas,  which  biums  with  a greenish 
or  yellow  flame  ; the  mass  is  stirred  briskly  for  a few  minutes,  and 
when  completely  and  tranquilly  fused,  is  raked  out  into  a square 
trough  or  mould ; when  cold,  this  loaf  is  turned  out  and  forms 
hall  soda^  or  hlach  ash,  containing  from  20  to  27  per  cent,  of  pure 
soda,  mixed  with  sulphide  of  calcium,  quicklime,  and  unburned 
coal.  In  order  to  extract  the  salts  of  sodium  from  it,  the  black 
ash  is  broken  up  into  coarse  fragments,  and  digested  with  warm 
water  for  six  hours,  in  vats  provided  with  false  bottoms  : this 
washing  is  systematically  carried  on  till  the  soluble  portions  are 
extracted,  the  last  washings  being  employed  to  act  upon  fresh 
portions  of  ball  soda. 

One  of  the  forms  of  apparatus  for  the  lixiviation  of  ball  soda 
is  shown  in  fig.  335.  The  principle  on  which  it  is  constructed  is 
simple,  but  it  admits  of  extensive  application  ; for  in  many  cases 
much  of  the  economy  of  a manufacturing  process  depends  upon 
the  systematic  washing  of  the  product  in  such  a manner  as  to 
extract  the  largest  amount  of  soluble  matter  by  means  of  the 
smallest  quantity  of  water,  in  order  to  reduce  to  a minimum  the 
time  and  quantity  of  fuel  required  to  effect  the  subsequent  evapo- 
rations. In  the  case  before  us  this  is  effected  by  placing  the 
material  for  lixiviation — the  black  ash,  in  perforated  sheet-ii’on 


CARBONATE  OF  SODIUM LIXIYIATION. 


363 


vessels,  h,  h,  which  can  be  raised  or  lowered  into  outer  lixiviating 
vessels,  also  made  of  iron,  by  means  of  the  cords  and  pulleys,  i,  k. 
When  a charo-e  is  received  from  the  furnace  it  is  introduced  into 


FlO.  335. 


^ 


the  lowest  vessel,  o,  where  it  is  submitted  to  the  dissolving  action 
of  a liquid  already  highly  charged  with  alkali  by  digestion  upon 
the  black  ash  contained  in  the  tanks  above  it : after  a certain  time 
this  charge  is  raised  by  the  rope  from  q into  the  tank,  f,  where  it 
is  submitted  to  a weaker  liquid,  and  so  on,  successively.  The 
alkali  at  each  stage  becomes  more  completely  exhausted,  and  the 
residue  is  successively  submitted  to  the  action  of  weaker  ley,  till 
at  length,  in  a,  it  is  acted  upon  by  water  only,  supplied  from  the 
cistern  l.  Wlien  fresh  water  is  admitted  from  m,  to  the  top  of 
the  vessel,  a,  as  it  is  specifically  lighter  than  the  saline  solution, 
it  lies  upon  its  surface,  and  gradually  displaces  the  solution  from 
A,  through  the  bent  tube,  whilst  the  w^ater  takes  its  place ; the 
liquid  from  A acts  in  a similar  manner  upon  that  contained  in  b ; 
and  this  displacement  proceeds  simultaneously  through  each  suc- 
cessive tier  of  the  arrangement,  until  the  concentrated  ley  flows 
off  from  G,  and  is  transferred  to  the  evaporating  pans.* 

Almost  the  whole  of  the  sulphur  originally  present  in  the  salt- 
cake  is  retained  in  the  insoluble  residue  in  the  form  of  sulphide 
of  calcium,  together  with  the  excess  of  lime  and  coal  employed. 
It  accumulates  at  the  soda  works  till  it  forms  a mountain  of  soda 

* A still  more  convenient  arrangement  in  which  all  the  tanks  are  upon  the  same 
level,  is  now  in  common  use  in  the  alkali  works  of  this  country.  The  charge  after  it 
has  once  been  introduced  into  the  tank  is  not  removed  again  until  completely  ex- 
hausted. By  a suitable  arrangement  of  pipes  each  tank  can  be  made  in  succession 
the  recipient  of  the  fresh  water,  or  of  leys  of  gradually  increasing  strength  derived 
from  the  neighbouring  tanks  ; advantage  being  taken  of  the  fact,  that  as  the  solution 
becomes  more  highly  charged  with  the  soluble  material,  the  height  of  the  column,  or 
the  water-level,  in  each  successive  vat  stands  progressively  lower,  until  the  liquid 
flows  off  saturated ; and  thus  a continuous  flow  of  liquid  through  the  system  is 
maintained.  {Chemical  Technology,  Richardson  & Watts,  2nd  ed.  vol.  1.  part  iii.  p.  267.) 


364 


MAXTrACTTKE  OF  SODA  ASH. 


icaste^  to  the  annoyance  both  of  the  neighhonrhood  and  of  the 
manufacturer. 

The  water  for  lixiviation  must  not  be  employed  at  a tempe- 
rature exceeding  110°,  otherwise  the  sulphide  of  calcium  is  decom- 
posed into  a mixture  of  sulph-hydrate,  which  is  soluble,  and  hydi-ate 
of  lime  ; 2 OaS-f2  becoming  OaS,Il2S-f  OaO-,H20,  and  this 
sulph-hydi’ate  immediately  reacts  upon  the  carbonate  of  sodium, 
furnishing  sulphide  of  sodium  and  carbonate  of  calcium,  whilst 
the  hydrosulphuric  acid  converts  the  caustic  soda  into  sulphide : 
eaS,H,S  -f  Xa,-e03  -f-  2 XaHO^ 2 Xa^S  -h  eaee3  4-  2 H.O.  The 
black  solution  thus  obtained  is  allowed  to  settle,  and  is  then 
pmnped  up  into  large  shallow  iron  pans,  where  it  is  evaporated 
by  the  waste  heat  from  the  black-ash  furnaces.  A large  portion 
of  the  salt  crystallizes  during  the  ebullition,  and  is  removed  by 
means  of  perforated  ladles,  ^n  order  to  convert  the  caustic  soda 
which  the  solution  contains  into  carbonate,  it  is  evaporated  to 
dryness,  and  after  being  mixed  with  about  a seventh  of  its  weight 
of  sawdust,  is  roasted  in  a reverberatory  furnace  ; most  of  the  sul- 
phur escaj^es  during  this  operation  in  the  form  of  sulphurous 
anhydride,  the  residue  yields  the  soda  ash,  or  alkali  of  commerce, 
which  contains  about  56  per  cent,  of  pure  caustic  alkali,  Aa^O. 
If  required  in  crystals,  the  crude  carbonate  thus  obtained  is  re- 
dissolved, the  liquid  allowed  to  settle,  and,  while  hot,  is  run  into 
deep  pans,  capable  of  containing  150  gallons  of  liquid,  and  about 
a ton  of  crystallized  carbonate.  The  liquid  cools  in  the  course  of 
five  or  six  days,  and  crystals  of  large  size  are  formed ; the  mother- 
liquor,  which  is  drained  off  by  withdrawing  a plug  in  the  bottom, 
is  then  further  evaporated  down,  and  yields  an  ash  of  inferior  quality. 

The  preparation  of  carbonate  of  sodimn,  therefore,  comprises 
three  principal  operations  : — 

1st,  The  production  of  salt-cahe,  or  crude  suljDhate  of  sodium, 
from  common  salt,  by  the  action  of  sulphuric  acid. 

2nd.  The  making  of  Uach  ash,  or  inpure  carbonate  of  sodium, 
mixed  with  sulphide  of  calcium,  by  deoxidation  of  the  salt-cake 
after  mixtime  with  chalk,  by  means  of  carbon. 

3rd.  The  preparation  of  soda  ash,  or  the  separation  of  the 
carbonate  of  sodium  from  the  black  ash  by  lixi^uating  the  latter 
in  warm  water,  and  evaporating  the  solution  to  dryness. 

Of  these  operations  the  most  remarkable  is  the  preparation  of 
the  black  ash,  by  fusion  of  the  sulphate  with  chalk  and  coal. 
The  chemical  changes  which  occur  consist,  first  in  the  deoxidation 
of  the  salt-cake,  and  its  conversion  into  sulphide  of  sodium  with 
evolution  of  carbonic  oxide;  and,  secondly,  in  the  formation  of 
carbonate  of  sodium  and  sulphide  of  calcium  by  interchange 
of  the  constituents  of  the  sulpliide  of  sodium  and  carbonate  of 
calcium.*  These  reactions  occur  simultaneously,  and  may  be 
represented  in  the  following  equation  : — 

Ka,se,  -f-  2 03  + eaee3  = OaS  4- 1 ee  -p 

* Monosulphide  of  calcium  is.  as  Mr.  Grossage  has  pointed  out.  nearly  insoluble  in 
cold  water.  Oxysulphide  of  calcium,  supposed  by  Dumas  to  be  formed,  and  to  furnish 
the  condition  required  for  rendering  the  sulphur  insoluble,  appears  not  to  exist. 


PKOPEKTIES  OF  CARBONATE  OF  SODIUM. 


365 


An  excess  both  of  coal  and  of  chalk  is  always  employed  in 
practice,  as  a good  deal  of  coal  burns  off  unavoidably,  and  an 
excess  of  chalk  is  needed  to  prevent  the  formation  of  a poly- 
sulphide of  calcium.  This  chalk  becomes  quicklime  in  the 
furnace,  and  when  the  ball  is  lixiviated,  the  hydrate  of  lime  at 
first  produced  is  converted  into  carbonate,  while  hydrate  of  soda 
is  formed  in  equivalent  quantity  (Gossage).  Many  attempts  have 
been  made  to  recover  the  sulphur  from  the  soda  waste,  but  hitherto 
without  commercial  success. 

Various  processes  have,  from  time  to  time,  been  proposed,  to 
supersede  the  one  just  described,  which  was  invented  by  Leblanc ; 
and  of  late  years  works  on  a considerable  scale  have  been  estab- 
lished, in  wliich,  upon  a plan  patented  by  Mr.  Longmaid,  by 
roasting  iron  or  copper  pyrites  directly  with  chloride  of  sodium,  a 
sulphate  of  sodium  has  been  obtained  without  the  preliminary 
manufacture  of  oil  of  vitriol,  whilst  chlorine  ^is  evolved.  The 
reaction  with  iron  pyrites  is,  4 FeS^  + 16  V aCl  19  0^= 2 Fe^Og  -f 
8 J^agSO^  + S Clg.  A portion  of  the  sulphur,  however,  always 
burns  off  in  the  form  of  sulphurous  anhydride.  By  the  employ- 
ment of  poor  ores  of  copper  and  tin,  it  has  been  found  possible  to 
extract  these  metals  with  advantage  from  materials  which  would 
not  otherwise  have  paid  for  working. 

Properties. — Carbonate  of  sodium  has  a nauseous  alkaline 
taste  ; it  is  an  efflorescent  salt,  usually  crystallizing  in  large  trans- 
parent rhomboidal  prisms,  which  are  soluble  in  any  proportion 
in  hot  water,  and  even  melt  in  their  water  of  crystallization  ; 
they  are  also  very  soluble  in  cold  water.  The  salt  readily  parts 
with  its  water,  and  melts  at  a red  heat.  If  crystallized  at  a tem- 
perature of  —4°,  an  unstable  hydrate  with  15  may  be 

obtained  (Jacquelain).  Mitscherlich  has  also  obtained  carbonate 
of  sodium  crystallized  with  6 H^O.  If  crystallized  above  93°, 
the  salt  is  deposited  in  forms  derived  from  the  square-based 
octohedron,  which  contain  5 IlgO ; whilst,  if  crystallized  between 
158°  and  176°,  four-sided  prisms  are  produced,  which  contain 
only  HgO  (Berzelius).  Solutions  of  carbonate  of  sodium  may, 
according  to  Ldwel  {Ann.  de  Gliirnie^  III.  xxxiii.  382),  be  ob- 
tained in  the  condition  of  supersaturation,  by  adopting  precau- 
tions similar  to  those  mentioned  when  speaking  of  the  sulphate. 
The  carbonate  exhibits  a maximum  solubility  at  100°  F. ; the 
decrease  of  solubility  above  this  point  arises  from  the  formation 
of  the  hydrate  (VagOOg,  14,0),  and  this  is  deposited  when  a 
solution  saturated  at  219°  is  concentrated  by  boiling.'^' 

(590)  Acid  Carhonate  of  Sodium.,  or  Blcarhonate  of  Soda 


* This  hydrate  is  more  soluble  in  cold  than  in  hot  water,  and  beoomer  redissolvod 
in  the  mother-liquor  if  allowed  to  cool.  The  supersaturated  solution  contains  a hy- 
drate uith  7 H-.f).  Lowel  describes  two  modifications  of  this  '7-atom  hydrate,  which 
diifer  in  solubility  and  in  crystalline  form  : one  variety,  a,  is  deposited  in  rhombohe- 
dral  crystals,  if  a solution  saturated  at  the  boiling-point  be  corked  whilst  boiling,  and 
allowed  to  cool  down  to  between  50°  and  G0°,  but  it  is  redissolved  on  raising  the  tem- 
perature to  70° ; and  on  cooling  down  to  between  40°  and  50°,  the  modification  b is 
deposited  in  square  tables.  If  cooled  below  40°  the  solution  gradually  deposits  tho 
10-atoin  hydrate,  and  the  condition  of  supersaturation  ceases.  The  following  table 


1 


366  SESQUICAEBOXATE  OF  SODITir,  TROXA. 

or  XaO.HO,  2 002=84 ; Sp.  Gr.  2*192)  is  obtained 
by  saturating  a strong  solution  of  the  neutral  carbonate  with  car- 
bonic acid ; the  solid  crystallized  carbonate  also  absorbs  carbonic 
anhydride  with  considerable  evolution  of  heat ; and  as  the  bicar- 
bonate is  less  soluble  than  the  carbonate,  this  process  is  employed 
for  procuring  pure  carbonate  from  the  commercial  crystals ; for  on 
washing  the  powdered  bicarbonate  with  cold  water  till  the  wash- 
ings are  free  from  sulphates  and  chlorides,  a pm*e  bicarbonate  is 
obtained.  This  salt  is  thus  manufactured  upon  a large  scale  by 
moistening  the  crushed  crystals  of  carbonate  of  sodium  with  water, 
and  exposing  them,  upon  cloths,  to  the  depth  of  2 or  3 inches,  in 
stone  or  wooden  boxes,  to  a current  of  gaseous  carbonic  anhy- 
di’ide : the  water  of  crystallization  is  separated  dmdng  the  pro- 
cess, and  the  temperature  rises  considerably.  The  sesquicarbon- 
ate  is  first  formed,  and  as  the  operation  proceeds  it  is  converted 
into  the  bicarbonate.  The  bicarbonate  crystallizes  in  rectangular 
four-sided  prisms,  which  require  10  parts  of  water  for  solution  at 
ordinary  temperatures.  If  its  solution  be  heated,  it  loses  one-half 
of  the  additional  equivalent  of  carbonic  acid,  and  is  converted 
into  sesquicarbonate.  At  a red  heat  the  salt  is  converted  into  the 
normal  carbonate. 

A native  Sesquicarbonate  of  Sodium  (2  Xa2‘0O-3,H2-0O3.  3 H2O 
=2714-51,  or  2 XaO,HO,  3 CO2 . 3 Aq=13T-f  27),  which,  how- 
ever, always  contains  sulphate  and  chloride  of  sodium,  has  been 
long  knovm  in  commerce  as  trona  or  natron : it  is  chiefiy  obtained 
as  a saline  etfiorescence  on  the  borders  of  some  lakes,  of  which 
those  of  Eg^q)t  are  the  best  known.  Many  other  countries,  however, 
such  as  those  in  the  neighbourhood  of  the  Black  and  the  Caspian 
Seas,  as  well  as  some  parts  of  Thibet  and  of  Siberia,  also  furnish  this 
salt.  It  crystallizes  in  rhombic  prisms,  terminated  by  four-sided 
j^ryamids ; it  is  less  soluble  than  the  carbonate,  but  more  so  than 
the  bicarbonate,  and  has  a feebly  alkaline  reaction. 

The  carbonates  of  sodium  and  potassium,  when  melted  to- 
gether in  the  proportion  of  1 atom  of  each,  readily  combine  and 
form  a salt  which  fuses  at  a lower  temperature  than  either  of  its 

gives  a comparative  view  of  the  quantities  of  the  10-atom  hydrate,  and  the  two  vari- 
ties  of  the  7-atom  hydrate  contained  in  100  parts  of  the  saturated  solutions  at  differ- 
ent temperatures : — 

100  parts  of  Water,  when  saturated,  contain,  of 


\ 

Temp. 

"F. 

Xaa^Os, 

Anhydr, 

salt. 

10  H2O  I 

Xa^eOs,  7 H2O  (&).  1 

Xa2-e03,  7 H2O  (a). 

Crystd. 

salt. 

Anhydr. 

salt. 

Crystd. 

with 

7 HsO  &. 

Crystd. 
with 
10  H2O 

Anhydr.  Crystd. 
bait.  vnth 

7 H2O.  a. 

Crystd. 

with 

IOH2O 

32 

6-97 

21-33 

20-39 

58-93 

84-28 

31-93 

112-94 

188-37 

50 

12-06 

40-94 

26-33 

83-94 

128-57 

37  85 

150-77 

286-13 

59 

16-20 

63-20 

29-58 

100-00 

160-51 

41-55 

179-90 

381-29 

68 

21-71 

92-82 

38-55 

122-25 

210-58 

45-79 

220-20 

556-71 

77 

28-50 

149-13 

38-07 

152-36 

290-91 

86 

37-24 

273-64 

43-45 

196-93 

447-93 

100-4 

51-67 

1142-17 

219-2 

45-47 

539-63 

PHOSPHATES  OF  SODHJM. 


367 


components.  On  account  of  its  ready  fusibility,  this  mixture  is 
preferred  to  carbonate  of  potassium  or  carbonate  of  sodium  alone, 
as  a means  of  decomposing  siliceous  minerals  in  analytical  opera- 
tions (576).  If  carbonate  of  sodium  be  dissolved  in  a solution  of 
carbonate  of  potassium  in  excess,  the  solution,  on  evaporation, 
yields  transparent  crystals  which,  according  to  Margueritte,  con- 
sist of  2 IIa2003,K2003 . 18  : this  salt  is  decomposed  if  it 

be  attempted  to  recrystallize  its  aqueous  solution,  carbonate  of 
sodium  being  deposited. 

(591)  Phosphates  of  Sodium. — Phosphoric  acid  forms  with 
sodium  several  crystallizable  salts  : some  account  has  already  been 
given  of  these  compounds  (118,  119,  150). 

Normal  Trihasic  Phosphate  of  Sodium,  or  Suhphosphate  of 
Soda  (lla3PO^ . 12  H^O,  or  3 lla0,P03 . 21  Aq  = 161  + 216) ; Sp. 
Gr.  cryst.  1*622. — This  salt  is  prepared  from  the  rhombic  phos- 
phate by  adding  caustic  soda  to  its  solution  till  it  feels  soapy  to 
the  fingers.  It  crystallizes  readily  in  small  prisms,  which  efflo- 
resce in  the  air,  and  gradually  absorb  carbonic  acid.  A remark- 
able double  salt  of  this  phosphate  with  fiuoride  of  sodium 
(llaF,lla3PO-4  . 12  H2O)  was  obtained  by  Briegleb,  by  fusing  the 
rhomliic  phosphate  of  sodium  with  fiuoride  of  calcium  and  car- 
bonate of  sodium : and  also  by  digesting  powdered  cryolite  with 
a mixture  of  phosphate  of  sodium  and  caustic  soda. 

Rhombic  Phosphate  of  Sodium  (HaJIPO^  . 12  H^O,  or 
2 lsra0,H0,P03 . 21  Aq  = 112  + 216)  ; Sp.  Gr.  cryst.  1*586; 
Kopp. — This  salt  is  the  one  from  which  most  of  the  phosphates 
are  formed : it  is  the  one  which  has  been  longest  known,  and  is 
that  commonly  called  phosphate  of  soda.  It  is  best  procured  by 
neutralizing  with  carbonate  of  sodium  the  acid  phosphate  of 
calcium,  prepared  as  directed  for  obtaining  phosphorus  (113) ; by 
this  means  carbonate  of  calcium  is  precipitated,  and  allowed  to 
subside  ; the  clear  liquid  is  then  decanted  from  the  precipitate, 
evaporated  if  necessary,  and  set  aside  to  crystallize.  Phosphate 
of  sodium  forms  large,  transparent,  efflorescent  rhombic  prisms : 
they  have  a cooling  saline  taste,  and  are  soluble  in  1 parts  of 
cold  water ; at  99°  they  fuse  in  their  water  of  crystallization,  and 
are  therefore  soluble  in  boiling  water  to  an  unlimited  extent ; the 
solution  has  a faintly  alkaline  reaction.  It  corrodes  flint-glass 
bottles,  and  occasions  the  separation  of  white  siliceous  flakes  from 
their  surface.  Clark  found  that  when  the  solution  of  this  salt  is 
evaporated  at  temperatures  above  90°,  the  salt  crystallizes  with  7 
atoms  of  water,  and  is  not  efflorescent ; in  both  forms  it  is  isomor- 
plious  with  the  corresponding  arseniate  of  sodium.  If  heated  to 
300°,  it  loses  all  its  water  of  crystallization  ; but  if  redissolved  in 
water,  it  may  be  obtained  from  its  solution  with  all  its  character- 
istic properties.  If  a solution  of  this  phosphate  l)e  mixed  with 
free  phosphoric  acid,  until  it  ceases  to  precipitate  chloride  of 
barium,  another  phosphate  is  produced,  formerly  known  as  the 
Inphosphate  of  soda  (Nall^PO,  . II^O,  or  2 II(),NaO,PO„  2 A(] 
= 120  -I-  18) ; it  crystallizes  with  difficulty  in  right  rhombic 
prisms,  and  has  a strongly  acid  reaction. 


368 


PHOSPHATES  AND  BIBOKATE  OF  SODHJM. 


All  these  are  tribasic  phosphates  ; they  precipitate  nitrate  of 
silver  of  a yellow  colour. 

Pyroj)ho82)hate  of  Sodium  (ISTa^P^O,,  10  = 266  + 180, 

or  2 h[aO,PO„  10  Aq  = 133  + 90)  Sjy.  Gr.  cryst.  1-836. — If  the 
rhombic  phosphate  be  ignited  it  loses  all  its  water,  and  on  then 
treating  it  with  water,  anew  dibasic  salt  is  dissolved,  whicli  crys- 
tallizes in  prisms.  Its  solution  has  an  alkaline  reaction,  and 
yields  a dense  white  precipitate  with  nitrate  of  silver,  which  is 
not  changed  by  exposure  to  light. 

Metaphosphate  of  Sodium  (HaPOg,  or  102). — 

If  microcosmic  salt,  or  if  the  acid  tribasic  phosphate,  or  the  acid 
pyrophosphate  of  sodium  be  heated  to  redness,  all  the  volatile 
bases  are  expelled,  the  residue  fuses  to  a clear  glass,  and  on  re- 
dissolving, the  metaphosphate  or  monobasic  phosphate  of  sodium 
is  obtained.  It  forms  a deliquescent  and  very  soluble  salt,  which 
has  a feebly  acid  reaction  upon  litmus.  It  cannot  be  obtained  in 
crystals.  The  solution  of  this  salt  causes,  with  nitrate  of  silver, 
a white  gelatinous  precipitate,  soluble  in  excess  of  the  meta- 
phosphate; with  nitrate  of  barium  or  of  calcium  a similar  gela- 
tinous precipitate  is  formed.  This  salt  is  susceptible  of  various 
modifications  by  the  application  of  different  temperatures  (150). 

(592)  Borax,  or  Aero  Borate  of  Sodium  (Ha^O  2 B^Og  10 
H2O  = 202  + 180,  or  HaO,  2 BO3 . 10  Aq  = 101  -f  90) ; Sp.  Gr. 
fused^  2-367,  cryst.  1*740  ; Composition  in  parts  of  dried  salt, 
IvTa^O,  30*7 ; B^Og,  69-3  ; of  crystallized  salt,  Na^O,  16-23  ; B^Og, 
36*65  ; IlgO,  47*12. — This  well-known  salt  is  produced  in  con- 
siderable quantities  in  various  parts  of  the  world,  particularly  in 
Thibet,  whence  for  many  years  the  principal  part  of  the  borax 
consumed  was  supplied.  The  crude  borax,  or  tincal,  is  obtained 
by  the  spontaneous  evaporation  of  the  waters  of  the  lakes  whence 
it  is  derived,  and  occurs  crystallized  in  fiattened  six-sided  prisms, 
terminated  by  trihedral  summits.  These  crystals  are,  however, 
very  impure,  being  covered  with  a greasy  coating,  said  to  be  de- 
rived from  the  skins  in  which  they  are  imported.  In  order  to  re- 
move this  grease,  the  crystals  are  powdered,  thrown  upon  a filter, 
and  washed  with  a weak  solution  of  caustic  soda,  which  forms  a 
soap  with  the  grease,  and  dissolves  it ; the  remaining  salt  is  dis- 
solved in  water.  Carbonate  of  sodium  equal  to  one-eighth  of  the 
weight  of  the  borax  is  added  to  the  solution  ; a copious  precipitate 
of  earthy  impurities  ensues,  the  liquid  is  cleared  by  filtration, 
and  allowed  to  cool  very  slowly  : the  borax  is  deposited  in  rectan- 
gular or  in  six-sided  prisms,  containing  10  H^O,  one  atom  of  which 
is  probably  basic. 

A large  quantity  of  borax  is  now  manufactured  from  the 
boracic  acid  obtained  from  the  lagoons  of  Tuscany,  by  saturating 
it  with  carbonate  of  sodium,  and  allowing  the  salt  to  crystallize. 
In  the  course  of  this  operation  the  crude  boracic  acid  is  mixed 
with  about  half  its  weight  of  soda  ash,  and  is  thrown,  in  quan- 
tities of  about  3 cwt.  at  a time,  upon  the  fioor  of  a reverberatory 
furnace  ; the  mixture  soon  frits  and  effervesces,  and  must  be  well 
stirred  during  the  process  : a quantity  of  carbonic  anhychide,  of 


SILICATES  OF  SQDIUM. 


369 


ammonia,  and  of  organic  matter  which  always  accompanies  the 
boracic  acid,  is  got  rid  of  in  this  operation.  The  fritted  mass  is 
then  lixiviated  in  deep  iron  ‘boilers.  Here  the  solution  is  allowed 
to  remain  at  rest,  in  order  to  allow  the  impurities — which  con- 
sist chiefly  of  alumina,  carbonate  of  calcium,  and  some  silica — to 
subside : and  the  liquid,  when  brought  to  the  sp.  gr.  1T66,  is 
ckawn  off  into  wooden  tanks,  lined  with  lead,  where  the  solution 
cools  very  slowly.  The  large  crystals  in  which  borax  is  demanded 
for  the  market  can  be  procured  only  by  operating  on  very  large 
masses  of  the  salt,  and  allowing  it  to  crystallize  from  a solution 
containing  carbonate  of  sodium  in  excess.  Borax  may  also  be  ob- 
tained in  octohedral  crystals  (HaH  2 ; sp.  gr.  1’815), 

if  the  salt  be  allowed  to  crystallize  at  a temperature  between  1Y4° 
and  133^,  from  a solution  of  sp.  gr.  1-256,  to  which  about  one- 
third  more  of  carbonate  of  sodium  is  added  than  is  required  to 
form  the  salt. 

Borax  has  a feebly  alkaline  taste  and  reaction.  The  prismatic 
crystals  are  soluble  in  about  half  their  weight  of  boiling  water,  and 
in  12  parts  of  cold  water  ; they  are  slightly  efflorescent.  When 
heated,  borax  bubbles  up,  loses  its  water,  and  melts  below  redness 
into  a transparent  glass  : • this  glass  dissolves  many  metallic  oxides, 
which  often  impart  intense  and  characteristic  colours  to  the  bead. 
Borax  is  hence  much  used  as  a test  before  the  blowpipe  for  recog- 
nizing the  presence  of  certain  metallic  oxides.  For  this  purpose 
a small  crystal  of  borax  is  fused  upon  the  end  of  a bent  platinum 
wire,  and  a minute  quantity  of  the  substance  to  be  tested  is 
melted  with  the  salt  in  the  flame  of  the  blowpipe : the  colour  of 
the  glass  varies  according  as  the  bead  is  heated  in  the  oxidizing 
or  in  the  reducing  flame  (494).  The  power  which  this  salt  pos- 
sesses of  dissolving  the  metallic  oxide,  renders  it  advantageous,  in 
the  process  of  soldering  oxidizable  metals,  to  sprinkle  the  metallic 
surfaces  with  powdered  borax ; on  the  application  of  heat  the 
l)orax  melts  as  well  as  the  solder,  and  the  film  of  oxide  which 
would  otherwise  prevent  the  adhesion  is  removed  from  the  pieces 
of  metal  at  the  moment  that  the  alloy  is  presented  to  unite  them. 
Borax  is  used  in  the  arts  as  a flux,  and  by  the  refiner  in  the  melt- 
ing of  gold  and  silver.  In  making  enamels,  it  is  frequently 
added  for  the  purpose  of  rendering  the  compound  more  fusible, 
and  it  is  largely  employed  in  fixing  colours  on  procelain. 

Other  borates  of  sodium  may  be  formed,  but  ordinary  borax 
is  the  only  salt  of  any  practical  importance ; the  quadriborate, 
2 (NaBO,,  3 IIBO^)?!  crystallizes  with  great  difliculty  : a 
neutral  borate  may  be  obtained  by  fusing  1 atom  of  ordinary 
borax  with  1 of  carbonate  of  sodium ; it  crystallizes  in  oblique 
prisms  (NaBO„4  11,0). 

(593)  Silicates  of  Sodium. — When  finely  divided  silica  is 
p-adually  added  to  fused  carbonate  of  sodiunq’carbonic  anhydride 
is  evolved  with  effervescence,  and  a mixture  of  various  silicates  of 
sodium  is  formed.  Fritsche  obtained  a silicate  of  the  form  (Na,SiO„ 
9 H,0),  by  dissolving  in  a strong  solution  of  hydrate  of  soda  a 
quantity  of  silica  equal  in  weight  to  the  anhydrous  soda  present 
24 


370 


SILICATES  OF  SODIUM. 


in  the  liquid : it  crystallizes  sometimes  with  6,  sometimes  with 
9,  atoms  of  water.  When  a concentrated  solution  of  carbonate 
of  sodium  is  boiled  with  finely  divided  silica,  a large  proportion  of 
silica  is  dissolved : but  the  clear  liquid,  as  it  cools,  deposits  a gela- 
tinous precipitate,  which,  according  to  Forchhammer,  contains 
Na^O,  36  SiO^.  Other  silicates  have  been  obtained,  to  which  the 
formulge  (2  Xa^O,  5 SiO^)  3Si02)  and  (Xa^O,-!  SiO^)  have 

been  assigned.  It  is  difficult,  however,  to  prove  the  existence  of 
these  compounds  with  the  exception  of  the  one  last  named. 
The  silicate  (Xa^SiOg)  has  the  property  of  being  dissolved  by  an 
excess  of  fused  carbonate  of  sodium,  and  the  glass,  which  is 
clear  and  transparent  while  hot,  becomes  opaque  on  cooling; 
but  the  same  silicate,  if  heated  sufficiently  with  an  excess  of  silica 
melts,  and  forms  a homogeneous  mixture,  which  yields  a trans- 
parent glass  on  cooling,  the  fusibility  decreasing  as  the  propor- 
tion of  silica  increases,  until,  when  the  quantity  of  silica  amounts 
to  9 atoms,  the  heat  of  a forge  is  required  for  its  fusion.  These 
silicates  are  all  more  or  less  soluble  in  boiling  water. 

A peculiar  silicate,  usually  represented  by  the  formula 
Xa20,4SiO-2,  which  has  received  the  name  of  soluble  glass^  is 
prepared  by  melting  together  8 parts  of  carbonate  of  sodium 
(or  10  of  carbonate  of  potassium),  with  15  of  pure  quartz  sand 
and  1 part  charcoal  (Fuchs)  ; the  charcoal  by  its  tendency  to 
form  carbonic  oxide,  at  the  expense  of  the  oxygen  of  the  car- 
bonate, facilitates  the  decomposition  o'f  this  salt : a black  glass 
is  thus  obtained,  which  is  not  soluble  in  cold  water,  but  is 
almost  completely  dissolved  by  5 or  6 times  its  weight  of  boiling 
water.  Soluble  glass  is  employed  in  fixing  fresco  colours,  by  the 
process  known  as  stereochromy.  The  ground  employed  in  this 
process  for  the  reception  of  the  colour  consists  of  a mixture  of 
lime  and  fine  sand,  cemented  by  a solution  of  soluble  glass.  The 
colours,  ground  up  with  water,  are  then  applied  and  a varnish  of 
soluble  glass  is  brushed  over  the  whole. 

Allusion  has  already  been  made  to  the  application  of  a solution 
of  soluble  glass  as  a cement  in  the  preparation  of  an  artificial 
siliceous  stone  (469).  Many  metallic  oxides — such  as  lime,  mag- 
nesia, and  oxide  of  zinc,  and  their  salts — are  acted  upon  by  the 
solution  of  silicate  of  sodium,  carbonate  of  calcium  and  other 
salts  being  converted  by  it  into  masses  of  great  hardness  and  dura- 
bility ; double  decomposition  of  the  silicate  and  earthy  salt  occur- 
ring to  a greater  or  less  extent.  Upon  this  principle,  Mr.  Eansome 
has  applied  a solution  of  silicate  of  potassium  to  the  prevention 
of  the  decay  of  magnesian  and  other  limestones  which  are  ex- 
posed to  the  weather : a solution  of  the  silicate  is  brushed  over 
the  surface  of  the  stonework,  which  becomes  gradually  converted 
superficially  into  silicate  of  calcium. 

A solution  of  silicate  of  sodium  as  nearly  neutral  as  possible  is 
now  very  generally  used  as  a substitute  for  cow-dung  in  preparing 
mordanted  calico  for  dyeing.  This  constitutes  one  of  the  most 
important  applications  of  the  salt.  This  solution  maybe  obtained 
of  a sp.  gr.  of  1*53.  It  may  be  prepared  either  by  fusing  silica 


GLASS. 


371 


with  carbonate  of  sodium  in  the  proper  proportions,  or  by  digest- 
ing calcined  flints  under  pressure  in  a concentrated  solution  of 
caustic  soda,  as  practised  by  Messrs.  Ransome  (469), 

When  heat  is  applied  to  the  silicates  of  the  alkalies,  they  do 
not  at  once  become  liquid,  but  pass  through  an  intermediate  vis- 
cous stage  : they  impart  this  viscidity,  and  the  transparency  which 
they  preserve  on  cooling,  to  many  other  silicates  if  they  are  fused 
with  them,  and  they  destroy  the  tendency  to  crystallize  on  solidi- 
fying which  the  silicates  of  the  earths  and  of  the  heavy  metallic 
oxides  possess.  This  property  is  of  the  highest  importance  to 
mankind,  for  upon  it  depend  the  most  valuable  pro]3erties  of  glass 
— ductility,  wdiich  enables  it  to  be  moulded  whilst  in  this  inter- 
mediate state,  and  transparency,  which  renders  it  applicable  to  a 
multitude  of  important  uses.  The  silicates  of  the  alkalies  are 
unable  alone  to  resist  the  action  of  water  and  other  solvents  suffi- 
ciently to  fit  them  for  many  of  the  applications  of  glass ; but  when 
combined  with  silicates  of  the  earths  and  certain  metallic  oxides, 
mixtures  may  be  obtained  after  fusion  which  are  no  longer  soluble 
in  water  or  in  acids. 


Glass. 

(594)  The  composition  of  glass  differs  considerably  with  the 
nature  of  the  purposes  to  which  it  is  destined,  but  it  consists 
mainly  of  mixtures,  in  varying  proportions,  of  silicates  of  potas- 
sium, sodium,  calcium,  barium,  magnesium,  aluminum,  and  lead, 
coloured  by  the  addition  of  small  quantities  of  different  metallic 
oxides,  particularly  those  of  iron,  manganese,  cobalt,  uranium,  and 

The  degree  of  fusibility  of  these  different  silicates  varies  con- 
siderably. The  silicates  of  calcium  and  magnesium  fuse  with 
great  difficulty  when  heated  jper  se : the  most  fusible  compound 
contains  2 atoms  of  basyl  to  3 of  silica,  the  quantity  of  oxygen 
in  the  base,  being  to  that  in  the  silica  as  1 is  to  3.  The  silicates 
of  iron,  2 FeO,  3 Si02,  and  of  manganese,  are  readily  fused,  and 
crystallize  on  cooling.  The  silicate  of  lead,  2 PbO,3  SiO^? 
still  more  fusible,  and  on  cooling  forms  a yellow  transparent  glass. 
On  the  other  hand,  silicate  of  aluminum,  Al20-3,2  SiO^,  is  nearly 
infusible  in  the  furnace.  All  these  silicates,  however,  when  mixed 
with  each  other,  or  with  the  silicates  of  the  alkalies,  melt  at  con- 
siderably lower  temperatures,  the  fusing-point  being  generally 
much  below  that  of  the  mean  of  the  different  silicates  emjfloyed. 
The  silicates  of  calcium  and  aluminum  are  nearly  infusible  when 
separate,  but  they  melt  readily  after  they  have  been  mixed 
together. 

Many  of  the  properties  of  glass  are  familiar  to  every  one.  It 
is  a transparent  brittle  solid,  more  or  less  fusible,  and  just  before 
fusion  possessed  of  remarkable  ductility,  a property  which  enables 
the  workman  to  fashion  it  into  the  numberless  forms  which  luxury 
or  convenience  dictates.  The  different  varieties  of  glass  are  not 
to  be  regarded  as  definite  compounds,  but  as  mixtures  of  various 


VARIETIES  OF  GLASS. 


sn 

silicates  in  different  proportions,  with  an  excess  of  silica.  It  is 
generally  found,  however,  in  the  best  kinds  of  glass,  that  the  mix- 
tures are  very  nearly  in  such  proportions  that  but  little  silica 
remains  in  the  uncombined  form.  The  proportion  of  silica  to  the 
bases  is  most  conveniently  expressed  by  ascertaining  the  propor- 
tion which  the  oxygen  of  the  bases  bears  to  that  of  the  silica. 
The  subjoined  table  gives  the  result  of  some  analyses  of  the  more 
important  kinds  of  glass : — 


Composition  of  different  Varieties  of  Glass  in  parts. 


Dumas.  Richardson. 

Dumas. 

Berthier. 

Rowney. 

Bottle. 

Window. 

Plate. 

A ^ 

/ * V 

Glass  tube. 

French 

French. 

soft. 

English. 

French. 

Venetian. 

Bohemian. 

Silica 

53-55 

69-65 

66-37 

73-85 

68-6 

73-13 

Potash 

5-48 

5-50 

6-9 

11-49 

Soda 

15-22 

14-23 

12-05 

8-1 

3-07 

Lime 

29-22 

13-31 

11-86 

5-60 

11-0 

10-43 

Magnesia 

2-1 

0-26 

Alumina 

6-01 

1-82 

8-16 

3-50 

1-2 

0-30 

Oxide  of  iron 

5-74 

0-2 

0-13 

Oxide  of  manganese . . . 

... 

0-1 

0-46 

Ratio  of  the  oxygen  1 

in  the  bases  to  that  v 

1 : 2 

1 : 4 

2 : 7 

1 : 6 

1 : 5 

1 : 6 

in  the  silica  ) 

Dumas. 

Faraday. 

Dumas. 

Bohemian 

goblet. 

German 

crown. 

English 

flint. 

Guinand’s 

optical 

Strass. 

Enamel. 

Silica. 

69-4 

62-8 

51-93 

42-5 

38-1 

31-6 

Potash 

11-8 

22-1 

13-77 

11-7 

7-9 

8-3 

Lime 

9-2 

12-5 

0-5 

Alumina 

9-6 

2-6 

0-47 

1-8 

1-0 

Oxide  of  lead 

33-28 

43-5 

53-0 

50-3 

Oxide  of  tin 

9-8 

Oxides  of  iron  and  ) 
manganese  ) 

... 

0-27 

AS2O3  ) ; 
B2O3  ) ? 

Ratio  of  the  oxygen  1 
in  the  bases  to  that  >- 
in  the  silica  ) 

1 : 4 

1 : 5 

1 : 6 

1 : 4 

1 : 4 

3 : 7 

(595)  Glass  in  which  Silicates  of  Potassium  a/nd  Calcium 
predorwmate. — The  sihcates  of  potassium  and  calcium  are  the 
principal  components  of  the  celebrated  Bohemian  glass,  including 
the  variety  which  is  employed  in  the  preparation  of  the  hard  glass 
of  difficult  fusibility,  so  much  prized  in  the  laboratory  in  the  tubes 


BOHEMIAl^  GLASS — ^PLATE  GLASS. 


373 


used  for  tlie  combustion  of  organic  compounds : tlie  composition 
of  this  glass  may  be  represented  approximatively  by  the  formula 
(K^O,  3 SiOa  . -GaO,  3 SiO-2)?  of  the  potassium  having  its 

place  supplied  by  sodium,  and  part  of  the  calcium  by  magnesium, 
aluminum,  and  traces  of  iron  and  manganese.  The  more  fusible 
glass  which  is  employed  in  the  manufacture  of  the  beautiful  orna- 
mental objects  for  which  Bohemia  has  long  been  distinguished, 
contains  silicate  of  aluminum,  with  silicates  of  potassium  and  cal- 
cium, in  a proportion  which  approaches  [K^O,  2 SiO^  . 2 (OaO, 
2 SiOj)  • ^12^3?  ^ SiOj.  The  crown  glass  employed  for  optical 
purposes  has  nearly  the  formula  (K^^,  2 SiO^  . -GaO,  2 SiG2 ; 
Dumas,  Ann.  de  Chimie,  II.  xliv.  151).  In  the  last  two  cases 
the  proportion  of  oxygen  in  the  bases  to  that  in  the  silica  is  very 
nearly  as  1 : 4. 

In  the  finer  kinds  of  glass,  potash  is  always  employed  in  pre- 
ference to  soda,  because  the  glass  made  from  soda,  however  care- 
fully the  materials  are  selected,  has  a bluish-green  tinge,  which  is 
not  observed  when  potash  is  used.  The  potash  glass,  however,  is 
rather  less  brilliant  than  that  which  contains  soda. 

(596)  Glass  consisting  of  Silicates  of  Sodium  and  Calcium. — 
French  plate  glass  and  ordinary  window  glass  are  the  most  im- 
portant varieties  of  this  description.  Plate  glass  is  very  fusible, 
although  the  oxygen  of  the  bases  wdiich  it  contains  amounts  only 
to  about  one-sixth  of  that  of  the  silica.  Soda  produces  a more 
liquid  and  fusible  compound  than  potash.  The  addition  of  lime 
to  glass  diminishes  its  fusibility  whilst  it  increases  its  lustre  and 
hardness  without  afiecting  the  colour.  Care  must  be  taken  not 
to  employ  an  excess  of  lime,  for  it  is  liable  to  render  the  glass  milky 
on  cooling,  althougli  it  may  be  perfectly  transparent  wliilst  hot. 

Great  care  is  required  in  the  selection  of  the  materials  em- 
ployed in  the  manufacture  of  the  finer  kinds  of  glass.  The  ingre- 
dients used  in  the  plate  glass  of  St.  Gobain  consist  of  300  parts 
of  white  quartzose  sand,  100  of  dry  carbonate  of  sodium,  43  of 
lime,  slaked  by  exposure  to  the  air,  and  300  of  fragments  of  broken 
glass  from  previous  meltings.  The  fuel  employed  in  the  furnace 
is  wood. 

These  materials  are  intimately  mixed,  and  then  melted  in  a 
large,  deep,  conical  crucible,  in  which,  after  they  have  been  com- 
j)letcly  fused,  they  are  allowed  to  stand  at  a high  temperature  for 
several  hours,  in  order  that  the  impurities  may  subside.  Quanti- 
ties of  this  mixture  sufficient  for  casting  a single  sheet  are  then 
removed,  by  means  of  co])per  ladles,  into  a smaller  square  crucible, 
termed  the  cuvette  A When  the  glass  is  thoroughly  melted  the 
cuvette  is  removed  from  the  furnace  by  a crane,  and  the  glass  is 
cast  by  pouring  it  upon  a solid  table  oi*  cast  iron  ; along  the  edge 
of  this  table  are  ledges  of  metal,  to  regulate  the  thickness  of  the 
sheet  of  glass  ; the  molten  mass  is  immediately  s])rea(l  and  formed 
into  a plate  by  means  of  a heavy,  hollow  metallic  roller.  These 

* In  the  Thames  Plate-glass  Works,  the  glass  is  melted  in  the  same  pot  as  that 
from  which  it  is  poured  in  casting.  The  pots  are  cylindrical,  and  the  fuel  employed 
is  coal. 


374 


PLATE  GLASS — WIXDOW  GLASS. 


sheets  are  next  annealed  by  being  placed  in  a heated  oven,  and 
allowed  to  cool  very  slowly  down  to  the  temperature  of  ihe  air — 
an  operation  which  requires  from  a week  to  a fortnight  for  its 
completion.  They  are  then  levelled  by  cementing  one  plate  with 
plaster  of  Paris  upon  a slab,  and  causing  a second  plate  to  move, 
by  machinery,  over  the  surface  of  the  first,  the  grinding  material 
being  fine  sand  and  water  : a level  surface  having  been  thus  ob- 
tained, it  is  smoothed  by  emery  of  gradually  increasing  fineness, 
and  the  final  polish  is  given  by  friction  with  finely  levigated  col- 
cothar  or  peroxide  of  iron. 

Window  glass  is  made  of  a mixture  of  100  parts  of  sand,  with 
from  35  to  40  of  chalk,  30  to  35  of  soda  ash,  and  from  50  to  150 
of  broken  glass  or  cullet.  An  equivalent  amount  of  the  cheaper 
sulphate  of  sodium  may  be  substituted  in  this  mixture  for  the 
carbonate,  for  at  a very  elevated  temperature  the  silica  expels 
the  elements  of  sulphuric  anhydride ; this  decomposition  may  be 
facilitated  by  mixing  the  sulphate  with  about  a tenth  of  its  weight 
of  charcoal ; the  sulphate  is  thus  reduced  to  a lower  state  of  oxi- 
dation, and  the  sulphur  escapes  in  the  form  of  sulphm’ous  anhy- 
dride at  a lower  temperature  than  that  required  to  expel  the  acid 
from  the  sulphate. 

When  carbonate  of  sodium  is  used,  the  materials  are  first 
subjected  to  a heat  insufficient  completely  to  fuse  the  mass,  and 
are  fritted  together,  or  heated  until  they  agglomerate ; moistime 
is  thus  completely  expelled,  and  a part  of  the  gaseous  carbonic 
anhydride  is  got  rid  of:  the  frothing  up  of  the  mixture  in  the 
subsequent  fusion,  due  to  the  expulsion  of  the  gas,  is  also  dimi- 
nished, and  the  loss  of  alkali  by  volatilization  is  considerably  les- 
sened. The  fritted  mass  is  then  transferred  to  other  pots,  and 
the  temperature  of  the  furnace  is  raised  until  complete  fusion  is 
effected.  The  mixture,  after  it  has  been  thoroughly  melted,  is 
allowed  to  stand,  in  order  that  the  bubbles  of  air  may  escape,  and 
that  the  mass  may  become  uniform  in  composition : the  excess  of 
sulphate  or  of  chloride  of  sodium  which  may  have  escaped  decom- 
position rises  to  the  surface  and  is  skimmed  off,  forming  wliat  the 
manufacturer  terms  glass-gall  or  sandiver.  The  glass  is  then 
allowed  to  cool  until  it  assumes  the  pasty,  tenacious  condition 
required  for  the  manipulations  of  the  glass-blower. 

(597)  Silicates  of  Aluminum^  Calcium^  Iron^  Magnesium^ 
and  Sodium  or  Potassium. — The  inferior  descriptions  of  glass 
which  are  used  for  making  wine-bottles,  carboys,  and  other  articles 
in  which  a dark  colour  is  unimportant,  consist  of  a mixture  of 
these  silicates.  The  materials  employed  are  of  a coarser  kind  than 
those  used  in  the  preceding  varieties  of  glass.  A ferruginous  or 
ochry  sand,  mixed  with  soap-maker’s  waste,  are  common  ingre- 
dients. Mr.  Pellatt  gives  the  following  as  a composition  employed 
in  making  bottle  glass : — Sand,  100  measures  ; soap-maker’s  waste, 
80 ; gas-lime,  80 ; common  clay,  5 ; and  rock  salt,  3 measures.  The 
ordinary  English  bottles  are  of  an  olive-green  colour,  produced  by 
the  presence  of  ferrous  oxide : while  some  of  the  German  bottles 
are  of  a pale  brown,  resulting  from  a mixture  of  the  oxides  of  iron 


DEVITRIFICATION  OF  GLASS — FLINT  GLASS. 


375 


and  manganese.  Sometimes  sulphate  of  barium  is  added,  with 
the  view  of  rendering  the  glass  more  fusible.  Bottle  glass  con- 
tains a smaller  proportion  of  silica  than  any  of  the  preceding 
varieties.  One  specimen,  analysed  by  Dumas,  presented  a com- 
position which  would  be  approximatively  represented  by  the  for- 
mula 6 [(0aK)0,Si02]  . (AlPe)203,  3 SiO^ ; whilst  in  a second 
specimen  the  composition  would  be  more  nearly  represented  by 
6 [(0aK)0,Si02]  . 2 (AlFe)203,  3 SiO^.  The  oxygen  of  the  bases, 
in  the  first  instance,  is  in  the  proportion  to  that  of  the  silica  as 
1 to  2,  and  in  the  second  case  nearly  as  2 to  3. 

(598)  Devitrification : Reaumur'’ s Porcelain. — Bottle  glass  is 
particularly  liable  to  become  devitrified  by  slow  cooling,  and  to 
be  converted  into  what  is  termed  Reaumur'’s  Porcelain.  In 
order  to  produce  this  effect,  the  glass  may  be  imbedded  in  sand, 
or,  still  better,  in  a mixture  of  gypsum  and  sand,  and  heated  up 
to  a point  sufficient  to  soften  it,  but  just  short  of  that  required  for 
its  fusion.  If  it  be  now  allowed  to  cool  very  slowly,  it  will  be 
found  to  have  entirely  altered  its  aspect  and  properties ; having 
become  opaque  and  milk-white,  and  much  resembling  porcelain 
in  appearance.  It  is  now  somewhat  less  fusible  and  less  liable  to 
crack  on  the  application  of  sudden  changes  of  temperature,  and  is 
much  harder  than  the  glass  from  which  it  was  procimed.  It  is  a 
bad  conductor  of  heat,  but  conducts  electricity  to  a considerable 
extent,  being  comparable  in  this  respect  to  marble  (Pelouze).  This 
alteration  appears  to  be  due  to  the  partial  separation  of  certain 
silicates,  particularly  of  the  silicates  of  calcium  and  aluminum, 
and  their  assumption  of  a more  or  less  definite  crystalline  form. 
This  crystallization  is  sometimes  very  beautifully  and  perfectly 
exhibited  in  the  residues  at  the  bottom  of  the  glass-pots,  which 
are  allowed  to  cool  down  with  great  slowness  and  regularity. 
Xodules  of  opaque  radiated  crystals  are  there  often  found  sur- 
rounded by  a transparent  glass.  A mass  of  these  opaque  crystals, 
analysed  by  Dumas,  presented  a composition  which  corresponded 
with  the  formula,  18  [(■0al7a)0-,2  Si02]  . 2 (AI2O3)  9 Si02 ; whilst 
the  transparent  glass  from  which  they  had  separated  contained  3*5 
per  cent,  less  of  silica,  1*4  less  alumina,  and  a proportionately 
larger  quantity  of  soda. 

The  devitrification  of  glass  has  been  made  the  subject  of  ex- 
periment by  Belouze  {Chem.  Gaz.^  1855).  He  finds  that 

the  same  sheet  of  glass  may  be  devitrified,  and  again  rendered 
transparent  by  fusion,  many  times  in  succession.  Glass  of  any 
descrij)tion  may  be  devitrified,  but  the  finer  kinds  of  potash-glass 
exhibit  tliis  phenomenon  with  difiiculty.  The  throwing  in  of  a 
small  quantity  of  sand,  or  even  of  powdered  glass,  into  a pot 
after  it  has  cooled  down  to  the  viscid  condition,  greatly  [)romotes 
the  devitrification  of  the  mass.  The  soluble  sodium-glass  of 
Fuchs  (bra20,  4 Si02)  especially  liable  to  devitrification  from 
crystallization. 

(599)  S'dicates  of  Potassium  and  Lead. — The  ordinary  white 
glass  in  use  in  this  country,  commonly  known  as  Hint  glass  (the 
cristal  of  French  writers),  consists  almost  entirely  of  these  sili- 


376 


OPTICAL  GLASS. 


cates.  Potash  is  used  instead  of  soda  in  the  preparation  of  hint 
glass,  in  order  to  avoid  the  bluish  tint  which  is  produced  by  soda 
in  combination  with  oxide  of  lead.  The  oxide  of  lead  imparts  a 
greater  degree  of  fusibility  and  density,  as  well  as  a high  refrac- 
tive and  dispersive  power ; in  consequence  of  which  such  glass, 
from  its  superior  brilliancy,  is  better  fitted  for  the  manulactiu’e  of 
ornamental  articles,  and  fr-om  its  greater  softness  is  more  easily  cut 
and  polished.  Lead  glass  has,  however  the  inconvenience  of 
being  readily  scratched,  and  it  is  liable  to  tarnish  and  change 
colour,  especially  if  the  proportion  of  alkali  be  large.  The  alkahes 
corrode  it  slowly,  and  it  becomes  gradually  blackened  when  left 
in  contact  with  solutions  of  the  sulphides.  According  to  Fara- 
day's experiments,  English  flint  glass  contains  one-third  or  more 
of  its  weight  of  oxide  of  lead  : it  may  be  represented  very  nearly 
by  the  formula  (K^O,  3 SiOj  . PbO,  d SiO^).  But  in  a specimen 
from  Newcastle,  examined  by  Berthier,  the  proportion  of  silicate 
of  lead  was  larger : this  glass  corresponded  nearly  to  [2(E20,  3 
SiO^)  . 3 ( PbO,  3 SiOj)].  The  composition  of  flint  glass,  however, 
is  liable  to  considerable  variation,  even  in  difierent  parts  of  the 
same  pot,  the  lower  portions  haOng  generally  a greater  density 
than  those  in  the  upper  part  of  the  pot.  This  arises  from  the 
density  of  the  oxide  of  lead  being  much  greater  than  that  of  the 
other  materials,  so  that  it  is  extremely  difficult  to  preserve  a 
uniform  mixture.  Faraday  found,  for  example,  that  glass  taken 
from  the  top  of  pots  not  more  than  six  inches  deep,  might  have  a 
density  of  3'2S,  while  that  from  the  bottom  might  have  a density 
of  3*85  : in  one  instance  the  glass  at  the  top  had  a density  of  3 ’81, 
that  at  the  bottom  of  4*75 ; and  though  these  are  extreme  dif- 
ferences, there  is  no  doubt  that  considerable  variations  occur  in 
every  pot  of  glass  made  in  the  usual  way.  This  variation  in  the 
density  of  the  glass  occasions  great  inconvenience  in  its  applica- 
tion to  the  constmction  of  optical  instruments,  owing  to  the  dif- 
ference of  its  refracting  power  in  difierent  portions  of  the  same 
mass ; and  many  endeavours  have  been  made  to  overcome  these 
defects.  A lead  glass  of  still  higher  refracting  power  was  made 
by  Guinand,  in  which  the  proportion  of  lead  was  very  large,  the 
foiTuula  being  very  nearly  [2  2 SiO^) . 3 (PbO,  2 Si^J],  the 

proportion  of  oxygen  in  the  bases  being  to  that  in  the  silica  as  1 
to  4 : its  specific  graOty  was  3'61.  Faraday  {Phil.  Trans. ^ 1830, 
p.  42)  proposed,  for  a similar  purpose,  a compound  of  silicate  and 
borate  of  lead,  the  density  of  which  is  5*44  : this  glass  has  a pale 
lemon-yellow  tint,  and  consists  of  [3  (Pb0,Si02)  . 3 PbO,  2 B^Oj]. 
Of  late  years  a borosilicate  of  zinc  has  been  introduced  by  Maez 
and  Clemandot  into  the  glass  used  for  optical  purposes,  with  con- 
siderable success. 

Much  of  the  success  in  the  preparation  of  glass  for  optical 
pui*poses  depends  upon  the  selection  of  pure  materials,  and  also 
on  their  complete  incorporation.  The  plan  which  succeeds  best 
in  attaining  the  latter  object  was  introduced  by  Guinand.  After 
the  fusion  is  complete,  the  melted  glass  is  thoroughly  stirred  with 
a paddle  of  crucible  clay ; the  crucible  and  its  contents  are  then 


COLOrRED  GLASSES. 


377 


allowed  to  cool  down  slowly  in  the  furnace  ; when  cold,  the  pot  is 
broken,  and  the  mass  of  glass  cut  horizontally  into  slices,  by  which 
means  pieces  of  uniform  density  may  generally  be  obtained.  A 
good  optical  glass  may  be  made  from  a mixture  of  100  parts  of 
pm’e  sand,  100  of  minium,  and  30  of  refined  pearlash. 

The  oxide  of  lead  which  is  employed  in  the  manufacture  of 
flint  glass  is  not  ordinary  litharge  (897),  but  minium,  or  red  lead 
(898),  which  is  a higher  oxide  of  lead,  and  is  prepared  with  care 
from  pure  lead.  The  proportions  of  the  materials  usually  em- 
ployed in  the  manufacture  of  flint  glass  are,  300  of  fine  white 
sand,  such  as  that  from  Lynn  on  the  coast  of  h7orfolk,  or  from 
Fontainebleau,  200  of  minium,  and  100  of  refined  pearlash,  with 
about  30  parts  of  nitre.  In  all  cases  the  selection  of  materials 
for  the  melting-pot  is  of  high  importance.  These  pots  are  best 
made  of  an  infusible  clay,  such  as  that  from  Stourbridge,  which 
contains  but  little  lime  and  iron  : 5 parts  of  clay  and  1 part  of 
ground  burnt  pots  are  trodden  into  a mass  by  the  workman,  and 
allowed  to  stand  for  three  or  four  months  : the  mixture  is  then 
carefully  Avrought  into  pots  about  four  inches  thick,  great  care 
being  taken  to  exclude  air-bubbles.  The  pots  are  allowed  to  dry 
for  several  months  in  a warm  room,  after  which  they  are  removed 
to  an  annealing  oven,  where  they  are  raised  very  gradually  to  the 
temperature  of  the  furnace.  Flint  glass  is  always  made  in  pots 
Avhich  are  arched  over  at  top,  and  have  an  opening  at  the  upper 
part  of  one  side  for  the  introduction  of  the  charge  and  the  withdraAv- 
al  of  the  glass  : they  are  set  in  the  furnace  in  such  a manner  as  to 
prevent  the  access  of  smoke  and  combustible  gases  to  the  interior, 
Avhich  Avould  endanger  the  reduction  of  the  oxide  of  lead  to  the 
metallic  state.  Plate  glass,  crown  glass,  and  the  other  varieties 
of  glass,  are  made  in  open  crucibles.  The  alumina,  which  is  con- 
tained even  in  the  finest  glass,  is  chiefly  derived  from  the  action 
of  the  vitrified  materials  upon  the  clay  of  the  pots. 

(600)  Coloured  Glasses. — For  the  purpose  of  producing  imita- 
tions of  precious  gems,  a lead  glass  of  still  higher  refracting  power, 
termed  jpaste.^  or  strass.^  is  employed,  the  proportion  of  oxide  of 
lead  exceeding  53  per  cent.  ; the  composition  of  this  substance  is 
very  nearly  represented  by  the  formula  [KjO,  2 SiO^  . 3 (PbO,  2 
],  the  proportion  of  oxygen  in  the  bases  being  one-fourth  of 
tliat  present  in  the  silica.  A little  borax  is  often  added  to  this 
glass  to  increase  its  fusibility.  Glass  of  this  description,  when 
properly  cut,  is  employed  to  imitate  the  diamond.  Tlie  yelloAV 
colour  of  topaz  is  given  to  the  strass  by  the  addition  of  about  1 
per  cent,  of  peroxide  of  iron,  or  by  a mixture  of  4 per  cent,  of  ox- 
ide of  antimony  with  a minute  proportion  (OT  per  cent.)  of  pur- 
ple of  Cassius.  The  brilliant  blue  of  sapphire  is  imitated  by  means 
of  a small  quantity  of  oxide  of  cobalt. 

It  is,  indeed,  a property  of  glass  to  dissolve  small  quantities  of 
many  of  the  metallic  oxides  Avithout  losing  its  transparency  ; but 
the^  glass  becomes  coloured  Avith  more  or  less  intensity,  and  Avith 
different  hues,  according  to  the  nature  of  the  metallic  oxide  em- 
ployed. Protoxide  of  iron  appears  to  pass  into  the  condition  of 


378 


COLOUEED  AXD  PAIXTED  GLASS EXAMEL. 


magnetic  oxide,  which  even  in  small  quantities,  communicates 
colours  which  vary  from  a pale  green  to  a deep  bottle-green,  ac- 
cording to  the  proportion  in  which  it  is  present : sesquioxide  of 
iron,  on  the  contrary,  has  hut  feeble  colouring  power,  unless  pre- 
sent in  considerable  quantity,  when  it  produces  a yellow  colour ; 
protoxide  of  manganese  is  nearly  colomdess,  hut  the  sesquioxide 
communicates  a violet  tint  to  the  glass.  Advantage  is  taken  of 
the  knowledge  of  these  facts  in  preparing  colourless  glass  : prot- 
oxide of  iron,  in  minute  quantity,  is  a ti’equent  impurity  in  the 
materials  used,  and  it  produces  the  green  tinge  often  observed  in 
ordinary  glass  : a minute  quantity  of  black  oxide  of  mans^anese 
corrects  this ; it  imparts  oxygen  to  the  magnetic  oxide  ol  iron, 
which  thus  becomes  converted  into  the  colourless  peroxide,  whilst 
the  manganese  itself  being  reduced  to  the  state  of  protoxide  exerts 
no  injurious  colouring  effect.  A little  nitre  or  arsenious  anhydride 
is  sometimes  added  to  glass  instead  of  oxide  of  manganese,  with  a 
similar  effect  in  converting  the  iron  into  sesquioxide.  The  man- 
ganese is,  however,  the  more  effectual  agent ; this  may  arise,  as 
Liebig  suggests,  fi-om  the  circumstance  that  the  colours  produced 
by  the  iron  and  manganese  are  each  complementary  to  the  other. 
Oxide  of  chromium  imparts  an  emerald-green  tinge  to  glass  ; ox- 
ide of  cobalt  a deep  blue.  A mixtm’e  of  the  oxides  of  cobalt  and 
manganese  gives  a black  glass  ; black  oxide  of  copper  (OuO)  pro- 
duces a green  ; suboxide  of  copper  (OujO)  an  intense  ruby  red  ; 
whilst  the  sparkling  appearance  of  avanturine  is  due  to  the  disse- 
mination of  tetrahedral  crystals  of  reduced  metalhc  copper  through 
the  mass.  Oxide  of  uranium  communicates  to  the  glass  a peculiar 
opalescent  yellow ; different  shades  of  yellow  are  also  produced 
by  oxides  of  silver  and  antimony,  and  by  finely  divided  charcoal ; 
and  a compound  of  gold  with  oxide  of  tin  gives  a magnificent 
ruby  glass. 

Sometimes  glass  is  flashed^  or  superficially  coated  with  the 
coloured  portion.  A mass  of  colomdess  glass  is  in  this  case  taken 
by  the  workman  upon  the  end  of  his  blowing  tube,  and  then 
dipped  into  a pot  of  the  coloured  glass  ; on  blowing  out  the  lump 
of  glass,  a vessel  is  obtained  the  exterior  layer  of  which  is  colom-ed, 
whilst  the  inner  layer  consists  of  colomdess  glass. 

Painting  on  glass  is  effected  by  means  of  a very  fusible  glass, 
which  when  melted  gives  the  required  tint ; this  glass  is  reduced 
to  a very  fine  powder,  and  worked  up  with  tm-pentine  into  a pig- 
ment : it  is  then  applied  with  a pencil  to  the  surface  of  a sheet  of 
ordinary  glass.  The  painted  glass  is  afterwards  subjected  to  a 
heat  which  is  sufficient  to  melt  the  coloured  glass,  but  is  not  in- 
tense enough  to  soften  the  glass  to  which  it  is  applied. 

Enamd  is  the  term  given  to  an  easily  fusible  glass,  through 
which  is  disseminated  an  opaque  white  substance  which  is  infusi- 
ble at  the  temperature  employed,  such  for  example  as  the  binoxide 
of  tin ; a metallic  ash  is  prepared  by  calcining  at  a low  red  heat 
a mLxture  of  1 part  of  tin  with  from  1 to  6 parts  of  lead,  in  a flat 
cast-iron  vessel ; the  ash  so  obtained  is  mixed  with  sand  and  alkali, 
the  proportions  of  which  may  vary  considerably.  In  one  recipe 


ENAMELS SOLUBILITY  OF  GLASS. 


379 


for  the  preparation  of  enamel  given  hj  Knapp,  the  ashes  of  4 
parts  of  tin  and  10  of  lead  are  directed  to  be  ground  np  with  10 
parts  of  powdered  quartz  and  2 of  pure  soda  ash.  Other  opaque 
bodies  may  be  substituted  for  the  oxide  of  tin  in  the  preparation 
of  enamel : in  this  manner  bone  ash,  oxide  of  antimony,  and  even 
arsenions  anhydride,  are  sometimes  employed  to  produce  the  opa- 
city required.  The  enamel  may  be  tinged  of  any  desired  colour 
by  the  suitable  addition  of  metallic  oxides.  The  enamel  is  applied 
with  a brush  to  the  surface  to  which  it  is  to  be  attached,  and  is 
then  fused  by  exposure  to  heat. 

A modification  of  glass  resembling  enamel  has  been  used  to 
glaze  cast-iron  pots,  as  a substitute  for  tinning.  It  consists  of 
powdered  flints  ground  with  calcined  borax,  fine  clay,  and  a little 
felspar.  This  mixture  is  made  into  a paste  with  water,  and 
brushed  over  the  pots,  after  they  have  been  scoured  with  diluted 
sulphuric  acid  and  well  rinsed  in  water ; while  they  are  still  moist, 
they  are  dusted  over  with  a glaze  composed  of  felspar,  carbonate 
of  sodium,  borax,  and  a little  oxide  of  tin.  Having  been  thus 
prepared,  the  pots  are  next  carefully  dried,  and  finally  the  glaze 
is  fused  ors^  fired  under  a muffle  at  a bright  red  heat.  Oxide  of 
lead,  though  it  increases  the  fusibility  of  the  glaze,  should  be 
carefully  avoided,  for  it  does  not  resist  the  action  of  acids  in  culi- 
nary operations. 

(601)  Properties  of  Glass. — ^Well  made  glass  is  unacted  upon 
by  any  acid  or  mixture  of  acids  except  the  hydrofluoric,  which 
destroys  it  by  combining  with  its  silica.  But  it  is  not  absolutely 
insoluble,  though  it  is  generally  considered  to  be  capable  of  with- 
standing the  action  of  water.  If  glass  be  powdered  and  moistened 
w'itli  water,  the  liquid  will  dissolve  a small  quantity  of  alkali, 
sufficient  to  turn  turmeric-paper  brown.  Most  varieties  of  pow- 
dered glass  when  exposed  for  some  time  to  the  air,  were  found  by 
Pelouze  to  absorb  carbonic  acid  in  quantity  sufficient  to  effervesce 
when  treated  with  an  acid,  particularly  if  they  had  been  kept 
moistened  with  water.  If  left  long  in  water,  or  buried  in  moist 
earth,  many  kinds  of  glass  become  disintegrated  slowly,  and  scale 
off  in  flakes  which  exhibit  the  brilliant  colours  of  Kewton’s  rings 
(116).  This  is  particularly  the  case  with  the  coarse  glass  used 
for  wine  bottles.  Faraday  found  that  some  inferior  kinds  of 
bottle  glass  w^ere  destroyed  rapidly  by  the  action  of  diluted  sul- 
phuric acid. 

At  a higli  temperature  water  acts  upon  glass  very  rapidly ; 
pieces  of  plate  and  window  glass  were  suspended  by  Turner  in  the 
steam  of  a high  pressure  boiler,  and  in  the  course  of  four  months, 
specimens  of  plate  glass  one-fifth  of  an  inch  thick  were  completely 
decomposed;  and  Faraday  found  that  flint  glass,  under  similar 
circumstances,  was  still  more  rapidly  acted  upon. 

If  glass  be  suddenly  cooled  after  fusion,  it  becomes  extremely 
brittle.  When  drops  of  melted  glass  are  allowed  to  fall  into  water, 
they  solidify  in  pear-shaped  masses,  which  may  be  subjected  with- 
out breaking  to  considerable  pressure,  if  gradually  applied;  but 
if  the  tail  of  one  of  these  drops,  known  as  Puperfs  drops^  be 


380 


CHAEACTERS  OF  THE  SALTS  OF  SODITM. 


suddenly  nipped  off,  the  glass  flies  to  pieces  with  a kind  of  explo- 
sion, and  is  shattered  to  powder.  This  effect  appears  to  he  due  to 
the  unequal  tension  to  which  the  particles  composing  the  drop 
are  subjected,  owing  to  the  sudden  cooling  of  the  outer  surface  of 
the  glass,  while  the  interior  is  still  dilated  : as  the  mass  cools,  the 
particles  within,  by  adhesion  to  the  external  solid  portion,  are 
still  kept  in  their  dilated  state ; hut  a very  slight  distm’hance  of 
their  relative  position  sufiices  to  overcome  their  equilibrium,  and 
when  once  the  mass  gives  way  at  any  one  point,  the  cohesion  of 
the  whole  is  suddenly  destroyed. 

Similar  changes  occur  if  glass  articles  are  allowed  to  cool 
rapidly  by  exposing  them  whilst  red  hot  to  the  external  air.  Glass 
objects  of  various  descriptions,  if  their  surface  be  but  scratched,  or 
if  they  be  brought  suddenly  from  a cold  room  into  a warm  one, 
will  often  crack  and  fall  to  pieces.  In  order  to  prevent  this  mis- 
hap, it  is  necessary  to  subject  the  different  articles,  after  they  have 
received  their  destined  shape  at  the  hands  of  the  workman,  to  the 
operation  of  annealing,  which  is  a very  slow  and  gradual  process 
of  cooling,  by  which  the  parts  are  enabled  to  assume  their  natural 
l^osition  with  regard  to  each  other.  Even  then,  since  glass  dilates 
considerably  on  the  application  of  heat,  and  is  likewise  a bad  con- 
ductor, a sudden  and  incautious  elevation  of  temperature,  such  as 
that  occasioned  by  pouring  boiling  water  into  a cold  glass,  often 
determines  its  fracturei  Care  is  required  dining  the  process  of 
annealing,  especially  with  the  coarser  kinds  of  glass,  not  to  raise 
the  temperature  too  high ; as  otherwise  devitriflcation  to  a greater 
or  less  extent  would  be  liable  to  ensue. 

(602)  Characters  of  the  Salts  of  Sodioi. — ^e  have  no 
good  direct  tests  for  the  salts  of  this  metal,  as  it  forms  scarcely 
any  insoluble  compounds.  Its  most  insoluble  salt  is  what  Fremy 
has  termed  the  bimetantimoniate  of  sodium  (853),  which  is  de- 
posited in  transparent  octohedra  when  a solution  of  freshly  pre- 
pared himetanthnoniate  of  jyotassium  is  added  to  a neutral  solution 
containing  sodium,  provided  that  the  liquid  has  been  previously 
freed  from  all  bases  except  the  alkalies : 1 part  of  sodium  in 
10,000  of  water  will  produce  a precipitate  with  this  test  after 
twenty-four  hours.  In  analysis,  a salt  of  sodium  is  concluded  to 
be  present  when  the  absence  of  every  other  metal  has  been  proved, 
and  yet  a saline  residue  remains,  which  with  perchloride  of  pla- 
tinum gives  yellow  striated  prismatic  crystals  (2  XaCl,PtCh,6  H^O) 
by  spontaneous  evaporation.  Andrews  {Chem.  Gaz.  x.  378)  has 
pointed  out  a property  of  this  salt  which  admits  of  its  identiflca- 
tion  in  extremely  minute  quantities ; a drop  of  the  solution  sus- 
pected to  contain  sodium  is  mixed  with  a minute  quantity  of  a 
solution  of  perchloride  of  platinum,  and  allowed  to  evaporate  in 
a warm  place ; if  before  it  is  quite  dry  it  be  placed  in  the  field  of 
the  microscope,  and  examined  by  means  of  polarized  light,  minute 
crystals  of  the  double  chloride  of  sodium  and  platinum  will  be 
distinguished  from  the  other  salts  with  which  they  are  accom- 
panied, by  their  power  of  transmitting  the  polarized  light,  tinged 
with  various  colours,  according  to  the  thickness  of  the  crystals. 


LITHIIJM LITHIA. 


381 


Before  the  Uoiopipe  the  salts  of  sodium  are  known  by  the  intense 
yellow  which  they  communicate  to  the  outer  flame,  if  a fragment 
be  introduced  at  the  point  of  the  blue  cone  upon  a loop  of  pla- 
tinum wire ; and  this  flame,  if  examined  by  the  spectroscope,  is 
seen  to  consist  of  a pure  yellow  light  exactly  coincident  in  position 
with  Fraunhofer’s  double  line  d in  the  solar  spectrum.  Fig.  82, 

Part  1.  p.  151. 

The  salts  of  sodium  are  in  general  more  soluble  than  those  of 
potassium  ; the  sulphates  of  the  two  metals  afford  a striking  in- 
stance of  this  difference : the  sodium  salts  also  often  effloresce 
when  exposed  to  the  air,  whilst  those  of  potassium,  on  the  other 
hand,  frequently  deliquesce,  a fact  well  exemplifled  by  the  car- 
bonates of  the  two  metals. 


§ III.  Lithium:  L=:7.  Sj).  Gr.  0*5936;  Fusing-pt.  356°. 

(603)  Lithium,  the  metallic  base  of  the  third  of  the  alkalies, 
is  of  comparatively  recent  discovery,  and  derives  its  name  from 
W&og  (a  stone),  as  it  was  at  first  found  only  in  the  mineral  king- 
dom. It  was  supposed  to  be  a very  rare  substance,  but  Bunsen 
and  Kirchhoff*  have  shown,  by  means  of  the  method  of  spectrum 
analysis,  that  though  sparingly  it  is  widely  distributed  ; they  found 
it  in  many  micas  and  felspars,  in  the  ash  of  tobacco  of  many  kinds, 
and  in  several  mineral  springs.  The  minerals  of  most  frequent 
occurrence  wFich  contain  lithium  are  the  three  which  follow  ; they 
yield  this  alkali  in  proportion  varying  from  3 to  6 per  cent,  of 
their  weight : — 

Lepidolite,  or  lithia  mica. . . 2 [(LK)  FJ,  4 (AlaOg,  3 SiOa)  ? 

Triphane,  or  spodumene. . . 3 [(LNa)2O,Si02],  4 (■A:l203,  3 SiOg) 

Petalite 3 [(LN’a)20,  2 Si02],  4 (AlgOg,  6 SiOg). 

Metallic  lithium  is  easily  reduced  from  its  chloride  by  means 
of  an  electric  current  obtained  from  four  or  six  pairs  of  the  nitric 
acid  battery.  The  metal  is  of  a white  colour,  and  is  fusible  at 
356°.  It  is  harder  than  potassium,  but  softer  than  lead,  and  ad- 
mits of  being  welded  by  pressure  at  ordinary  temperatures ; it  can 
be  squeezed  into  wire,  which,  however,  is  inferior  in  tenacity  to 
lead  wire  of  the  same  dimensions.  Lithium  appears  to  be  the 
lightest  solid  body  known ; it  floats  in  naphtha,  and  has  a density 
of  only  0*5936.  At  high  temperatures  it  is  volatile,  and  may  be 
distilled  at  a full  red  heat  in  a current  of  hydrogen.  It  cannot, 
however,  be  obtained  by  processes  similar  to  those  employed  for 
potassium  and  sodium.  A fragment  of  lithium  burns  upon  a plate 
of  mica  with  a very  brilliant  white  light,  emitting  a heat  suffi- 
ciently intense  to  melt  a hole  in  the  mica ; when  thrown  upon 
water  it  swims  and  becomes  oxidized,  like  sodium.  If  thrown 
into  sulphuric  or  into  nitric  acid  it  usually  takes  fire. 

(601)  Lithia  (L^O— 30)  was  discovered  by  Arfwedson,  in  1818. 
It  may  be  extracted  by  carefully  levigating  the  minerals  that  con- 
tain it,  and  igniting  the  flue  powder  with  twice  its  weight  of 
quicklime.  The  mass  is  treated  with  hydrochloric  acid,  then  with 


382 


SALTS  OF  LITHITJIVI. 


sulphuric  acid,  and  the  sulphate  of  lithium  is  dissolved  out  from 
the  sulphate  of  calcium ; the  last  traces  of  calcium  are  removed 
from  tlie  solution  of  sulphate  of  lithium  by  oxalate  of  ammonium. 
This  solution  may  then  he  deprived  of  sulphuric  acid,  and  con- 
verted into  caustic  lithia  by  the  addition  of  baryta  water;  the 
solution  on  evaporation  yields  hydrate  of  lithia. 

Troost  {^Ann.  de  Chimie^  III.  li.  103)  considers  it  to  be  more 
advantageous  to  melt  10  parts  of  powdered  lepidolite  with  10  of 
carbonate  of  barium,  5 of  sulphate  of  barium,  and  3 of  sulphate 
of  potassium.  The  fused  mass  separates  into  two  portions,  a 
heavy  transparent  glass  and  a supernatant  white  slag ; this  white 
mass  consists  of  a mixture  of  the  sulphates  of  barium,  potassium, 
and  lithium,  and  contains  nearly  all  the  lithium.  The  sulphates 
of  the  alkaline  metals  are  separated  from  that  of  barium  by  wash- 
ing, and  a portion  of  the  sulphate  of  potassium  is  removed  by 
crystallization.  The  remaining  sulphates  of  potassium  and  lithium 
may  be  converted  into  chlorides  by  the  addition  of  chloride  of 
barium,  and  the  two  chlorides  separated  by  evaporating  to  dry- 
ness and  digesting  them  in  a mixture  of  equal  parts  of  alcohol 
and  ether,  which  dissolves  the  chloride  of  lithium  only. 

Hydrate  of  lithia  (LIIO)  fuses  easily  below  redness,  and  cor- 
rodes platinum  vessels  powerfully : silver  capsules  should  there- 
fore always  be  used  in  preparing  it.  This  action  upon  platinum 
is  one  of  the  best  indications  of  the  presence  of  lithium.  It 
appears  to  be  due  to  the  formation  of  an  unstable  jperoxide  of 
lithium^  which  imparts  its  oxygen  rapidly  to  the  platinum. 

(605)  Chloride  of  Lithium  (LC1,.2  H^O  = 42-5  -f  36)  is  fusible 
at  a dull  red  heat : it  crystallizes  at  temperatures  above  60°  in 
anhydrous  octohedra ; but  below  50°  in  square  prisms  with  2 II2O : 
it  is  one  of  the  most  deliquescent  salts  known.  If  its  aqueous 
solution  be  evaporated  at  a high  temperature,  it  loses  a ]>ortion  of 
its  chlorine,  whilst  lithia  is  formed.  Chloride  of  lithium  is  very 
soluble  in  alcohol,  and  in  a mixture  of  equal  parts  of  alcohol  and 
ether ; as  this  mixture  does  not  dissolve  the  chlorides  of  sodium 
and  potassium,  it  may  be  used  to  separate  chloride  of  lithium 
from  these  salts. 

Sulphate  of  Lithium  (L^SO,,  = 110  -f  18;  Sp.  Gr.  2-02) 

crystallizes  in  flat  tables,  which  are  very  soluble  in  water.  There 
appears  to  be  no  acid  sulphate  of  lithium,  though  a double 
sulphate  of  potassium  and  lithium  may  be  formed,  consisting  of 

LKSe,. 

l^hosphate  of  Lithium  (LgPO^  = 116 ) is  one  of  the  most 
characteristic  salts  of  this  alkali : it  is  insoluble  in  water  contain- 
ing phosphates  of  the  alkalies,  and  in  alkaline  solutions,  but  very 
soluble  in  acids  even  when  very  dilute.  In  order  to  prepare  it, 
caustic  soda  is  added  to  the  solution  of  a pure  salt  of  lithium 
till  it  has  an  alkaline  reaction ; phosphate  of  sodium  is  added ; 
the  liquid  is  then  boiled,  and  left  for  at  least  12  hours.  A heavy 
granular  crystalline  deposit  of  phosphate  of  lithium  gradually 
occurs.  This  salt  fuses  with  carbonate  of  sodium  to  a glass  which 
is  transparent  while  hot,  but  becomes  opaque  on  cooling.  The 


SALTS  OF  LITHIUM EUBIDIUM. 


383 


salt  supposed  by  Berzelius  to  be  a double  phosphate  of  sodium 
and  lithium,  appears  to  have  been  a mixture  and  not  a definite 
compound. 

Carbonate  of  Lithium  (L2OO3  = 74,  or  L0,C02  ==  37)  is  only 
sparingly  soluble  in  water,  but  is  rather  more  soluble  in  a solution 
of  carbonic  acid  : it  has  an  alkaline  reaction  upon  turmeric.  At 
a dull  red  heat  it  melts  into  a white  enamel,  and  by  prolonged 
ignition  loses  a large  portion  of  its  carbonic  acid. 

Characters  of  the  Salts  of  Lithium. — Generally  speaking 
the  salts  of  lithium  are  remarkably  fusible ; many  of  them  are 
very  deliquescent.  They  have  a burning  saline  taste,  and  are 
distinguished  by  yielding  a white  precipitate  of  carbonate  of 
lithium  in  cold  concentrated  solutions  with  carbonate  of  potassium^ 
but  the  precipitate  disappears  on  adding  water  and  applying  heat ; 
this  reaction  is  less  delicate  when  salts  of  ammonium  are  present. 
On  the  addition  of  phosphate  of  sodium  to  solutions  which  are 
neutral  or  alkaline,  the  phosphate  of  lithium  is  formed;  it  is 
soluble  in  the  acids  and  in  solutions  of  salts  of  ammonium.  Before 
the  blowpipe  the  salts  of  lithium  communicate  a purplish  red 
colour  to  the  flame,  which  is  masked  by  the  presence  of  salts  of 
sodium  in  very  small  proportion.  By  means  of  the  spectroscope 
the  occurrence  of  very  minute  traces  of  lithium  may  be  discovered 
by  a brilliant  crimson  band,  which  has  a refrangibility  between 
that  of  the  lines  b and  c of  the  solar  spectrum.  At  very  high 
temperatures  a faint  band  in  the  orange  may  sometimes  be  seen. 
In  these  two  lines  the  whole  light  of  the  lithium  spectrum  is  con- 
tained when  formed  by  the  gas-flame  of  Bunsen’s  gas-burner  (flg. 
82).  When  hthium  salts  are  heated  on  platinum  foil  they  corrode 
it  rapidly. 

§ TV.  Kubidium  : Eb  = 85*36.  Sp.  Gr.  1*52 ; Fusing-pt.  101*3. 

(606)  Eubidium  derives  its  name  from  rubidus  (dark  red), 
because  the  spectra  of  its  salts,  when  volatilized  in  the  colourless 
flame  of  a Bunsen  gas-burner,  exhibit  a remarkable  parir  of  red 
lines,  less  refrangible  than  Fraunhofer’s  line  a (Part  1,  Fig.  82, 
p.  151).  Eubidium  was  discovered  in  1860  by  Bunsen  and 
Kirclihofl*  during  their  investigations  on  the  spectra  of  artificial 
flames  (Liebig’s  Annal.  cxix.  107,  and  cxxii.  347).  It  is  usually 
present  in  small  quantity  in  lepidolite,  and  traces  of  it  occur  in 
many  of  the  mineral  springs  of  Germany.  It  has  also  been  found 
by  Grandeau  {Ann.  de  Chimie^  III.  Ixvii.  155)  in  minute  quantity 
in  beet-root,  in  tobacco,  and  in  the  ashes  of  a great  variety  of 
])lants,  being,  though  sparingly,  yet  very  widely  distributed.  The 
separation  of  rubidium  from  other  metals  is  founded  upon  the 
sparing  solubility  of  the  chloride  of  rubidium  and  platinum,  by  a 
method  which  will  be  described  when  speaking  of  the  extractimi 
of  coesium.  Metallic  rubidium  was  extracted  by  Bunsen  from  the 
charred  acid  tartrate,  1100  grains  of  which  Avhen  distilled  fur- 
nished about  80  grains  of  a brilliant  silver- white  metallic  mass. 
It  tarnishes  rapidly  on  exposure  to  the  air,  becoming  coated  with 


384 


SALTS  OF  ETJBIDIOr. 


a blue  suboxide ; in  a few  moments  it  takes  fire  spontaneously. 
At  14°  F.  it  is  soft,  like  wax;  at  101°'3  it  melts;  and  at  a beat 
below  redness  it  furnishes  a blue  vapour  with  a shade  of  green. 
Kubidium  is  decidedly  more  electropositive  than  potassium  : when 
thrown  upon  water  it  takes  fire  and  burns  with  a fiame  in  appear- 
ance exactly  resembling  that  of  potassium. 

(607)  liubidia,  or  protoxide  of  riibidittm  is  a 

powerful  alkaline  base  which  may  be  obtained  from  the  carbonate 
or  sulphate  in  the  form  of  hydi'ate  (IlbHO^  102*3)  by  processef^ 
resembling  those  adopted  for  hydrate  of  potash.  It  is  very  de- 
liquescent, is  soluble  in  alcohol,  and  absorbs  carbonic  acid  with 
avidity. 

Cldoride  of  rubidium  (RbCl= 120*9)  crystallizes  with  diffi- 
culty in  cubes ; it  is  easily  fusible,  and  is  more  soluble  than  chloride 
of  potassium,  but  is  permanent  :n  the  air.  With  chloride  of 
platinum  it  forms  a sparingly  soluble  double  chloride  (2RbCl, 
PtCl^)  which  requires  185  times  its  weight  of  boiling  water  for 
its  solution.  If  fused  chloride  of  rubidium  is  submitted  to  elec- 
trolysis, the  reduced  metal  is  dissolved  by  the  chloride  and  forms 
a smalt-blue  subchloride. 

Sulphate  of  rubidium  (Eb^SO^^  266*7)  crystallizes  in  hard 
brilliant  anhydrous  prisms,  isomorphous  with  those  of  sulphate  of 
potassium,  but  it  is  much  more  soluble  than  this  salt.  A true 
rubidium  alum  may  be  obtained  in  octohedral  crystals  by  allow- 
ing a mixture  of  the  sulphate  with  sulphate  of  aluminum  to  evap- 
orate spontaneously.  An  acid  sulphate  of  rubidium  (EbHSO^)  is 
also  known. 

Nitrate  of  rubidium  (EblSTOg^  147*3)  is  a very  soluble  salt 
requiring  2*3  parts  of  water  at  51°  for  its  solution.  It  crystallizes 
in  diliexagonal  prisms,  terminated  by  dihexagonal  pyramids. 

Carbonate  of  rubidium  (Eb2'0O3= 230*7)  is  a deliquescent  salt 
which  may  be  obtained  with  difficulty  in  crystals  with  H^O.  It 
absorbs  carbonic  acid  with  avidity  and  fiumishes  an  acid  carbonate 
(EbH-GOg)  which  crystallizes  in  brilliant  prisms  that  are  perma- 
nent in  the  air  and  insoluble  in  alcohol.  When  heated  they  are 
converted  into  the  normal  carbonate,  which  by  fiu’ther  elevation 
of  temperature  fuses  easily. 

Ch*aracteus  of  the  Salts  of  Eubldhtm. — The  salts  of  rubi- 
dium are  distinguished  from  those  of  potassium  with  difficulty. 
The  chloride  of  rubidium  and  platinum  is  the  most  characteristic : 
by  its  sparing  solubility  in  boiling  water,  it  may  be  separated  from 
the  potassium  salt,  which  is  soluble  in  one-eighth  of  the  quantity 
of  water  required  for  solution  of  an  equal  weight  of  the  rubidium 
salt.  The  most  certain  test  is  the  appearance  of  the  fiame  in  the 
spectroscope,  which  exhibits  two  characteristic  lines  in  the  red, 
less  refrangible  than  that  of  potassium,  and  two  lines  in  the  blue, 
intermediate  between  those  of  coesium  and  potassium. 

§ Y.  C(ESioi:  Csi=133. 

(608)  This  metal  derives  its  name  from  coesius^  sky  blue,  in 


CCESIUM. 


385 


allusion  to  the  two  brilliant  blue  bands  which  it  produces  in  the 
spectrum  of  a gas  flame  in  which  its  compounds  are  undergoing 
volatilization.  It  was  discovered  by  Bunsen  and  Kirchhofi*  at  the 
same  time  as  rubidium  (Pogg.  Annal.  cxiii.  337),  which  indeed  it 
usually  accompanies  in  very  small  quantity.  Coesium  was  origi- 
nally discovered  amongst  the  saline  constituents  of  the  Durkheim 
spring,  the  water  of  which  contains  about  one  five-millionth  of 
its  weight  of  a salt  of  coesium,  or  about  1 grain  in  140  gallons. 
Ordinary  lepidolite  contains  only  traces ; but  a variety  of  this 
mineral  from  Hebron,  in  the  State  of  Maine,  JST.A.,  was  found, 
by  Johnson  and  Allen,  to  yield  0*24  per  cent,  of  the  metal.  Still 
more  recently,  Pisani  has  found  coesinm  to  the  extent  of  32  per 
cent,  in  a rare  mineral  named  pollux,  analogous  to  analcime,  ob- 
tained from  the  island  of  Elba  {Comptes  Pendus,  21  April,  1864). 

Bdttger,  in  examining  the  salt  obtained  by  evaporating  down 
the  mother-liqnor  of  the  Kauheim  spring,  discovered  in  it  coesium, 
rubidium,  and  thallium.  He,  indeed,  recommends  it  as  the 
cheapest  source  of  the  two  new  alkaline  metals  ; they  exist  in  the 
spring  in  the  form  of  chlorides. 

In  order  to  obtain  the  compounds  of  coesium,  advantage  is 
taken  of  the  insolubility  of  its  double  chloride  with  platinum, 
which  is  little  more  than  half  as  soluble  in  boiling  water  as  the 
corresponding  salt  of  rnbidium.  The  mixture  which  contains  the 
rubidium  and  coesium  is  freed  from  compounds  of  the  earths  and 
other  metals  by  the  ordinary  methods,  and  the  residue,  which 
contains  salts  of  the  alkalies  only,  is  mixed  with  a solution  of  per- 
chloride  of  platinum,  which  if  added  in  excess  precipitates  nearly 
the  whole  of  the  rubidium  and  coesium,  together  with  a large  pro- 
portion of  potassium.  By  continued  boilings  of  the  precipitate 
with  small  quantities  of  water,  repeated  eighteen  or  twenty  times 
in  succession,  so  long  as  the  washings  have  a yellow  colour,  the 
potassium  salt  is  removed.  The  platinum  salt  is  reduced  by 
heating  it  in  a current  of  hydrogen.  The  mixed  chlorides  of 
rubidium  and  coesium  are  dissolved  out  by  water,  and  converted 
into  sulphates  by  heating  them  with  an  excess  of  sulphuric  acid, 
which  is  expelled  by  ignition.  On  adding  pure  baryta  water  to 
the  solution  of  the  sulphates,  the  alkalies  are  obtained  in  the 
caustic  state,  and  may  then  easily  be  converted  into  carbonates, 
either  by  carbonic  acid  or  carbonate  of  ammonium.  Once  more 
the  solution  of  the  mixed  carbonates  is  evaporated  to  complete 
dryness,  and  treated  with  boiling  absolute  alcohol,  which  dissolves 
out  the  carbonate  of  coesium,  and  leaves  the  carbonate  of  rubi- 
dium.* On  evaporation  of  the  alcoholic  solution  a tolerably  pure 
carbonate  of  coesium  is  obtained. 

* The  best  plan  of  separating  coesium  from  rubidium,  according  to  Allen  and  John- 
son, consists  in  taking  advantage  of  the  inferior  solubility  of  the  acid  tartrate  of  rubi- 
dium. The  mixed  carbonates  are  to  bo  neutralized  with  tartaric  acid,  and  then  a 
quantity  of  the  acid  is  added  equal  to  that  required  for  converting  the  rubidium  into 
the  acid  tartrate,  leaving  the  coesium  in  the  solution  as  normal  tartrate,  which  is  deli- 
quescent. The  solution  is  concentrated  by  evaporation  until  it  is  nearly  saturated  at 
the  boiling-point.  The  rubidium  salt  crystallizes  out  on  cooling,  and  may  bo  pnrillcd 
by  recrystallization.  This  acid  tartrate  (RbH04H406)  requires  parts  of  boiling 
25 


386 


AMMONIUM. 


An  amalgam  of  coesium  may  be  procured  by  submitting  a 
solution  of  the  chloride  to  electrolysis,  employing  a globule  of 
mercury  for  the  negative  electrode.  This  amalgam  is  even  more 
electropositive  than  that  of  rubidium,  so  that  coesium  is  the  most 
electropositive  element  as  yet  discovered. 

(609)  Cmsia  (Cs^O). — Coesium  appears  to  form  two  oxides; 
a blue  suboxide,  and  a powerfully  basic  oxide  corresponding  to 
potash  and  soda,  termed  cmsia.  The  hydrate  of  cmsia  (CsHO=150) 
is  very  deliquescent,  and  powerfully  caustic  : it  is  readily  soluble 
in  alcohol.  When  heated,  it  fuses  readily,  and  attacks  platinum. 

Chloride  of  cmsium  (CsCl=168'5)  crystallizes  in  cubes,  and  is 
deliquescent ; it  melts  at  a low  red  heat.  100  parts  of  cliloride 
of  coesium  contain  21*07  parts  of  chlorine,  while  an  equal  weight 
of  chloride  of  rubidium  contains  29*7,  and  of  chloride  of  potassium 
4:7*5  of  chlorine. 

The  chloride  of  platinum  and  cmsium  (2  CsCl,  PtCl4=676) 
crystallizes  in  yellow  transparent  octohedra  ; 100  parts  of  boiling 
water  dissolve  0*377  of  the  salt  (Bunsen). 

Sulphate  of  cmsium  (Cs^SO^)  is  anhydrous,  permanent  in  the 
air,  but  very  soluble  in  water.  It  forms  double  salts  with  sul- 
phate of  magnesium,  and  other  sulphates  of  that  class  of  the  form 
(Cs^SO^,  WgSO-4  . 6 It  also  yields  a crystallizable  alum. 

An  acid  sulphate  (CsHSO^)  may  be  obtained  in  short  rhombic 
prisms. 

Nitrate  of  cmsium  (CsI703=195)  is  anhydrous  and  isomorphous 
with  nitrates  of  rubidium  and  potassium.  It  is  permanent  in  the 
air,  has  a cooling  taste,  and  is  soluble  in  ten  times  its  w^eight  of 
cold  water. 

Carbonate  of  cmsium  (Cs2C03=326)  is  deliquescent : it  requires 
five  times  its  weight  of  boiling  alcohol  for  solution.  An  acid  car- 
bonate (CsII-0O-3=194)  may  be  obtained  in  brilliant  prismatic 
crystals,  which  are  permanent  in  the  air. 

The  salts  of  coesium  are  not  easily  distinguished  from  those  of 
potassium  and  rubidium,  except  by  the  characteristic  lines  in  the 
spectrum  of  their  fiame  (Part  I.  p.  151). 

§YI.  A:mmonium  : —1"^  (hypothetical). 

(610)  Action  of  Oxyacid  Anhydrides  on  Ammonia.— ’WIiqtv  dry 
gaseous  ammonia  (II3II)  is  presented  to  the  oxans^  or  anhydrides 
of  the  oxy acids,  such  as  sulphuric  (SO3),  sulphurous  (SO,),  or 
carbonic  (-602)  anhydride,  the  gas  enters  into  combination  Avith 
the  anhydride,  and  a peculiar  compound  is  formed,  in  which  it  is 
maintained  by  Laurent  and  G erhardt  that  one-half  of  the  ammonia 
only  exists  in  the  form  of  an  ordinary  ammoniacal  salt,  tlie  other 
half  having  entered  into  combination  with  the  elements  of  the 
anhydride,  to  form  a compound  termed  an  amidated  acid ; the 
product  obtained  difters,  therefore,  in  many  important  particulars 

and  94  parts  of  water  at  7 1®  for  its  solution.  The  acid  coesium  salt  is  soluble  in  its  own 
weight  of  boiling  water,  and  in  10  parts  of  water  at  77°,  and  the  normal  salt  is  deli- 
quescent.— Bunsen,  Fogg.  Annal.  cxix.  i. 


A^mONIDES. 


38T 


from  the  compound  '^diich  would  be  obtained  by  neutralizing 
with  ammonia  a solution  of  the  same  acid  in  water.  In  the 
latter  case,  one  of  the  ordinary  ‘ salts  of  ammonia,’  as  they  are 
usually  termed,  is  produced : in  the  former  case  an  ammoniacal 
salt  of  new  amidated  acid  would  be  the  result ; but  the  prepara- 
tion of  these  amidated  compounds  is  difficult,  and  their  true  nature 
is  not  as  yet  thoroughly  ascertained.* 

The  general  properties  of  these  bodies  may  be  illustrated  by 
examining  the  several  combinations  formed  between  the  sulphuric 
and  sulphurous-anhydrides  and  dry  ammoniacal  gas. 

(611)  Sulphuric  Ammonide^  Sulp)hat-ammon  (11311)2803. — At 
least  three  distinct  compounds  may  be  obtained  by  the  action  of 
dry  ammonia  on  sulphuric  anhydilde.  When  a current  of  dry 
ammoniacal  gas  is  transmitted  over  sulphuric  anhydride,  placed  in 
a flask,  and  maintained  at  a low  temperature,  taking  care  to  leave 
the  anhydride  somewhat  in  excess,  a hard  gummy  mass  is  pro- 
duced, which  when  exposed  to  the  air  absorbs  moisture  and 
gradually  deliquesces.  The  liquid  thus  obtained  is  saturated 
with  carbonate  of  barium,  in  order  to  remove  the  excess  of  acid, 
and  is  then  evaporated  ; it  yields  large  transparent  crystals  derived 
from  an  octoheffion  with  a square  base.  This  compound  is  the 
parasulphut-ammon  of  Rose,  and  consists,  according  to  this  che- 
mist, of  (11311)2803.  It  is  freely  soluble  in  water,  but  insoluble  in 
alcohol.  Its  solution  has  a bitter  taste,  and  gives  no  jjrecipitate 
with  salts  of  barium,  and  none  with  perchloride  of  platinum.  By 
long  boiling  with  w^ater,  or  with  a solution  of  tartaric  acid,  it  is 
slowly  changed  into  ordinary  sulphate  of  ammonium ; but  if 
heated  with  a free  alkali,  sulphate  of  the  alkaline  metal  is  speedily 
produced,  and  ammonia  is  expelled. 

If  ammoniacal  gas  in  excess  be  made  to  act  upon  sulphuric 
anhydride,  another  compound,  isomeric  with  the  former,  termed 
sulphat-ammon  by  Rose,  is  obtained.  It  does  not  crystallize, 
and  is  quickly  transformed  when  in  solution  into  sulphate  of 
ammonium. 

A third  compound,  which  may  be  procured  in  beautiful  trans- 
parent crystals,  is  prepared  by  transmitting  the  vapour  of  sul- 
phuric anhydride  into  ammoniacal  gas  in  excess ; the  solid  com- 
pound thus  obtained  is  fused  in  a current  of  dry  ammonia,  and 
dissolved  in  water.  The  crystals  obtained  on  evaporation,  accord- 
ing to  Jacquelain,  consist  of  (11311)3  2 8O3.  Although  the  solution 

* These  compounds  of  ammonia  with  the  anhydrides  are  often  incorrectly  spoken 
of  as  amides.  The  amides  of  monobasic  acids  are,  properly  speaking,  salts  of  ammo- 
nium which  have  been  deprived  of  1 atom  of  water.  Benzoate  of  ammonium 
(n4N67H602),  for  example,  when  deprived  of  II.2O,  furnishes  a white  fusible  volatile 
solid  known  as  hanzamide  The  amides  of  the  dibasic  acids  are  salts 

of  ammonium  which  have  been  deprived  of  2 atoms  of  water.  Sulpharnide  would  bo 
(H2N)2S02,  and  would  contain  an  atom  of  water  less  than  sulphuric  ammonide.  The 
amraonides^  or  ammons,  as  these  compounds  of  ammonia  with  the  anhydrides  of  dibasic 
acids  have  been  termed,  contain  only  1 atom  of  water  less  than  the  ordinary  salts  of 
ammonium.  Sulphate  of  ammonium,  for  instance,  may  be  represented  as  (1I4N)2K04, 
while  sulphuric  ammonide  contains  The  different  varieties  of  compounds 

obtained  from  the  salts  of  ammonia  by  dehydration  will  be  considered  amongst  the 
products  of  organic  chemistry. 


388 


THEORY  OF  AMMOXIUM. 


of  this  compound  has  an  acid  reaction,  it  gives  no  precipitate  with 
salts  of  barium. 

(612)  BulpTiit- Ammon  (H3K)2S02. — If  diy  gaseous  sulphurous 
anhydride  be  mixed  with  an  excess  of  perfectly  diy  ammoni- 
acal  gas,  1 volume  of  the  anhydride  and  2 of  ammonia  combine 
and  form  a yellow  amorphous,  volatile,  deliquescent  compound, 
which  when  dissolved  in  water  undergoes  gradual  decomposition 
(Rose). 

If  the  sulphurous  anhydi’ide  be  in  excess,  a different  com- 
pound is  fonned  (HgXSO^),  corresponding  in  composition  to  acid- 
sulphite  of  ammonium  from  which  1 atom  of  water  has  been 
abstracted:  Il3XS02-l-Il20=H^XIIS03.  It  is  a reddish-yellow, 
crystalline,  volatile  substance,  freely  soluble  in  water : when  in 
solution,  it  is  speedily  decomposed  into  sulphate  and  trithionate  of 
ammonium  ; d -f  2 (H^lSi  )2S04  Ko 

such  decomposition  occurs  when  the  ordinary  acid  sulphite  of 
ammonium  is  dissolved  in  water. 

Phosphoric  and  carbonic  anhydrides  also  form  ammonides, 
which  are  analogous  to  those  which  have  just  been  described. 

(613)  Action  of  Anhydrous  Hydracids  mi  Ammonia. — Dry 
ammoniacal  gas  likewise  unites  with  facility  with  the  anhydrous 
hydracids,  but  the  compounds  which  are  produced  do  not  corre- 
spond in  properties  to  the  ammonides,  but,  on  the  contrary,  form 
ordinary  salts  of  ammonium.  For  example,  dry  hydrochloric  acid 
and  dry  ammoniacal  gases  unite  with  avidity,  and  a white  solid 
compound  is  produced,  Avhich  is  ordinary  sal  ammoniac ; when 
dissolved  in  water  it  gives  with  solution  of  nitrate  of  silver  the 
usual  curdy  precipitate  indicative  of  chlorine,  and  with  perchloride 
of  platinum  the  usual  yellow  double  salt  characteristic  of  salts  of 
ammonium  is  deposited. 

(614)  Theory  of  Ammonium. — The  differences  between  the 
characters  of  the  compounds  which  dry  ammonia  forms  with  the 
oxyacid  anhydrides,  and  those  which  it  produces  with  the  anhy- 
drous hydracids  were  ex]^)lained  by  Berzelius  with  the  aid  of  a 
hjq^othesis  originally  suggested  by  Ampere,  wliich  has  been  termed 
the  ammonium  theory,  by  the  adoption  of  which  the  salts  of 
ammonia  admit  of  being  considered  as  possessing  a constitution 
analogous  to  that  of  the  metallic  salts. 

According  to  this  view,  the  compounds  which  are  frequently 
spoken  of  as  salts  of  ammonia  with  the  oxyacids  do  not  contain 
ammonia  at  all,  but  a compound  in  which  the  elements  of  an  atom 
of  water  have  been  added  to  those  of  ammonia  [H3R  -f  II3O]  : in 
consequence  of  the  assimilation  of  this  atom  of  water,  the  sub- 
stance which  is  formed  may  be  regarded  as  (H,X)IIO,  hydrated 
oxide  of  ammonium,  analogous  to  hydrate  of  potash  (KHO),  and 
the  basis  of  the  salts  which  it  yields  would  be  the  compound  body 
ammonium  (H^X),  which  takes  the  place  of  a metal.  Anhydrous 
ammonia,  when  it  unites  with  the  oxyacid  anhydiddes,  must 
therefore  produce  bodies  very  different  from  those  obtained  by  the 
combination  of  hydrated  ammonia  with  the  compounds  formed  by 
the  action  of  the  same  anhydiddes  upon  water,  as  may  be  seen,  for 


AMALGAM  OF  AMMONIUM. 


389 


instance,  by  comparing  tlie  formula  of  tlie  compound  with  sulphuric 
anhydride,  and  with  sulphuric  acid  when  water  is  present : — 

Sulphuric  ammonide.  Sulphate  of  ammonium. 

It  is  likewise  easy  to  see  why,  by  the  combination  of  anhydrous 
ammonia  with  a hydracid  equally  free  from  water,  a true  salt  of 
ammonium  should  be  formed : for  instance,  hydrochloric  acid  and 
ammonia  by  their  union  yield  chloride  of  ammonium,  a salt  which 
obviously  presents  the  closest  analogy  with  the  metallic  chlorides  ; 

ii3N+HCi=.(H,]sr)CL  ; 

With  the  oxy acids,  then,  ammonia  forms  two  classes  of  com- 
pounds ; the  more  important  class  constitutes  the  normal  salts 
of  the  alkali  in  which  the  elements  of  water  are  necessarily  pres- 
ent ; the  other  class  consists  of  the  ammonides  already  described. 

The  theory  of  ammonium  is  supposed  to  derive  considerable 
support  from  the  following  remarkable  experiment : — If  an  amal- 
gam of  potassium  or  of  sodium  be  moistened  with  a concentrated 
solution  of  sal  ammoniac  (Il^lSrCl),  the  amalgam  immediately  be- 
gins to  increase  in  bulk,  and  ultimately  swells  up  till  it  acquires  8 
or  10  times  its  original  volume,  and  it  at  the  same  time  assumes  a 
pasty  consistence,  but  still  preserves  its  metallic  lustre.  This  sub- 
stance, if  exposed  to  a temperature  of  0°  F.,  crystallizes  in  cubes. 
It  begins  to  undergo  spontaneous  decomposition  immediately  after 
its  production,  and  the  same  effect  occurs  still  more  rapidly  if  it 
be  placed  in  water  : hydrogen  gas  is  given  off*  in  minute  bubbles, 
and  ammonia  is  found  in  the  solution.  It  is  generally  supposed 
that  this  remarkable  amalgam  consists  of  a combination  of  II^N 
(or  ammonium)  with  mercury.  On  attempting  to  expel  the  mer- 
cury by  heat,  however,  the  compound  is  decomposed,  metallic 
mercury  is  sublimed,  and  a mixture  of  hydrogen  and  annnoniacal 
gas  evolved : all  other  attempts  to  isolate  the  ammonium  have 
been  equally  unsuccessful.  The  proportion  of  ammonium  present 
in  the  amalgam,  notwithstanding  the  great  change  in  bulk  and  in 
properties  experienced  by  the  mercury,  is  extremely  minute, 
amounting,  according  to  Gay-Lussac  and  Tla^nard,  to  little  more 
than  one  two-thousandth  of  the  weight  of  the  mercury. 

(615)  Solution  of  Ammonia. — The  preparation  of  ammoniacal 
^as  and  of  its  aqueous  solution  have  been  already  described  (369). 
The  solution  in  water  has  an  intensely  alkaline  reaction,  and  may 
be  regarded  as  a solution  of  hydrated  oxide  of  ammonium  (II4N 
liO) ; but  when  heated,  pure  ammoniacal  gas  (Hgll)  alone  is  ex- 
pelled, and  by  passing  the  gas  through  a tube  tilled  with  quick- 
lime, to  absorb  the  water  wliich  it  carries  over  with  it  in  suspen- 
sion, ammonia  maybe  obtained  in  a state  of  purity.  The  solu- 
tion in  water,  when  neutralized  by  acids  and  evaporated,  yields  the 
ordinary  salts  of  ammonium. 

The  compounds  of  ammonium  are  continually  receiving  fresh 
applications.  The  sulphate  and  the  chloride  are  extensively  used 
in  the  preparation  of  ammonia-alum,  as  a substitute  for  the  cor- 


390 


SULPHIDES  OF  AMMONIUM. 


responding  compounds  of  potassium ; for  agricultural  purposes 
the  sulphate  is  largely  used,  as  a manure  for  cereal  crops.  Caustic 
ammonia  is  employed  by  the  dyer  as  a solvent  for  cochineal ; it 
is  essential  in  the  preparation  of  orchil  and  the  lichen  colours. 
A remarkable  application  of  ammonia  has  also  lately  been  made 
in  Carre’s  refrigerating  machines  {note^  Part  I.,  p.  261),  which  are 
already  extensively  used  in  chemical  operations  on  a large  scale. 

(616)  Sulphides  of  Amaionium. — Ammonium  forms  several 
sulphides  which  are  freely  soluble  in  water.  The  ^rotosul^hide 
[(1141^)28],  if  it  exist  at  all,  cannot  be  procured  in  a solid  form : 
it  may  be  prepared  in  solution  by  dividing  a quantity  of  solution 
of  ammonia  into  two  equal  portions,  through  one  of  which  sul- 
j^huretted  hydrogen  is  transmitted  so  long  as  it  is  absorbed ; tlie 
saturated  liquid  is  then  added  to  the  second  portion  of  tlie  solution. 
It  is,  however,  possible,  though  not  probable,  that  the  two  solu- 
tions and  Il4hI,HO  may  remain  uncombined,  instead  of 

uniting  to  form  (H4N)2SH-H20.  This  liquid  dissolves  many  of 
the  sulphides  of  the  metals  which  furnish  acids  with  oxygen,  and 
forms  double  sulphides  with  them  (535,551).  Many  of  these 
donble  sulphides  may  be  obtained  in  crystals ; this,  for  example, 
is  the  case  with  those  which  contain  the  pentasulphide  of  anti- 
mony and  of  arsenic,  and  the  tersulphide  of  molybdenum. 

Bisulphide  of  ammonium  (H^I^)2S2,  or  (II4NS2)  may  be  ob- 
tained in  large  yellow,  transparent,  very  deliquescent  crystals, 
by  passing  sulphur  vapour  and  dry  ammonia  through  a red-hot 
porcelain  tube.  In  the  hydrated  form  it  has  been  long  known  as 
Boyle’s  fuming  liquor^  and  is  prepared  by  calcining  3 parts  of 
slaked  lime  with  2 of  sulphur,  and  distilling  three  parts  of  this 
mixture  with  2 of  sal  ammoniac  and  1 part  of  sulphur  : a yellow, 
oily,  foetid  liquor  passes  over  which  fumes  in  the  air,  and  on  cool- 
ing, deposits  deliquescent  yellow  lamellar  crystals  ; acids  disen- 
gage hydrosulphuric  acid  from  it,  and  cause  a deposit  of  sulphur. 
Its  aqueous  solution  dissolves  a large  quantity  of  sulphur,  forming 
2.  pentasulphide^  (114^)286,  which  crystallizes  from  its  solution  in 
long  orange-yellow  oblique  rhombic  prisms.  Fritsche  has  also  ob- 
tained a crystallized  compound  containing  (1141^)28,. 

Sulphide  of  ammonium  and  hydrogen^  or  sidphhydrate  of 
ammonium  (11411118=:  51)  is  the  liquid  commonly  used  as  a re- 
agent under  the  name  of  hydrosulphate  of  ammonia  : it  is  formed 
by  transmitting  sulphuretted  hydrogen  through  a solution  of  am- 
monia to  saturation.  This  liquid,  when  newly  prepared,  is  col- 
ourless, but  it  absorbs  oxygen  rapidly  from  the  air,  and  becomes 
yellow  from  formation  of  bisulphide  of  ammonium,  whilst  a hy- 
])Osulphite  of  ammonium  is  produced  in  the  liquid;  8 Il4NII8-f 
5 O2  = 2 [(114^)2^2]  + 2 [(114^)28211204]  4-  2 H2O.  A solution 
of  sulphhydrate  of  ammonium  dissolves  the  sulphides  of  the  elec- 
tro-negative metals  as  readily  as  the  protosulphide  of  ammonium 
does,  but  sulphuretted  hydrogen  is  liberated : for  example,  6 II, 
NII8  -h  As28,= 2 [(Il4N)3As8J  + 3 II28.  Sulphhydrate  of  ammo- 
nium may  be  obtained  in  the  anhydrous  form,  by  mixing  dry  sul- 
phuretted hydrogen  with  dry  ammoniacal  gas  ; 2 volumes  of  ammo- 


CHLOELDE  OF  AMMONIUM. 


391 


nia  combine  with  2 of  sulphuretted  hydrogen,  and  condense  in 
yellowish,  transparent,  brilliant  plates,  which  are  very  volatile,  and 
sublime  without  decomposition ; they  are  very  soluble  in  water. 

(617)  Chloeide  of  Ammonium  ; Sp,  Gr.  of 

1 1 ^ 

Solid,  1-578  ; of  Vapour,  0*89  ; Mol.  Yol.  of  Vapour, . 

Composition  in  parts,  HCl,  68*22  ; 31*78. — Muriate  of 

Ammonia,  or  Sal  Ammoniac  as  it  is  commonly  termed,  is  the 
most  important  of  the  salts  of  ammonium.  It  may  be  formed  di- 
rectly by  the  union  of  hydrochloric  acid  and  ammoniacal  gases  : 
it  was  formerly  imported  from  Egypt  in  considerable  quantity  as 
a product  of  the  distillation  of  dried  camel’s  dung,  but  in  this 
country  it  is  now  furnished  almost  entirely  from  ammoniacal 
liquor,  a waste  product  from  the  coal-gas  t\^orks.  Coal  contains 
a portion  of  nitrogen,  which,  during  the  process  of  distillation,  is 
partially  converted  into  ammonia ; this  combines  with  carbonic 
acid  and  with  sulphuretted  hydrogen  : these  compounds  are  con- 
densed with  the  gas  liquor  from  which  the  ammonia  is  subse- 
quently extracted.  The  best  process  for  preparing  sal  ammoniac 
consists  in  neutralizing  the  gas  liquor  with  hydrochloric  acid. 
For  this  purpose  the  liquid  is  pumped  up  from  a tank  into  the 
decomposer, — a large  wooden  vat  closely  fitted  with  a cover,  con- 
nected with  flues  for  carrying  off  the  gaseous  products  ; the  acid 
in  suitable  quantity  is  placed  in  jars,  from  which  it  is  slowly 
drawn  off  by  siphons,  and  is  thus  allowed  to  mix  gradually  with 
the  liquor  ; abundance  of  gas  is  disengaged,  and  is  made  to  pass 
through  a fire,  where  the  sulphuretted  hydrogen  is  burned : much 
of  the  tarry  matter  (derived  from  the  coal)  which  was  held  in 
solution,  is  deposited  during  this  operation,  and  the  liquid  froths 
up  considerably,  any  loss  which  might  be  thus  occasioned  being 
prevented  by  the  use  of  a waste-pipe,  by  which  the  overfiow  is 
carried  back  into  the  tank  below.  When  the  liquor  has  thus  been 
neutralized,  it  is  run  into  a covered  evaporating  pan,  where  the 
remaining  portions  of  sulphuretted  hydrogen  are  expelled ; after 
further  concentration  it  is  drawn  off  into  shallow  wooden  vessels, 
lined  witli  lead,  to  crystallize  : the  crystals  thus  procured  are 
drained,  and  the  mother-liquor  is  again  concentrated.  The  rough 
crystals  are  next  heated  in  a cast-iron  pan,  to  a point  approaching 
that  at  which  sublimation  commences  ; a good  deal  of  tarry  mat- 
ter, wliich  the  salt  still  retains,  is  expelled  during  this  roasting. 
The  salt  is  then  sublimed  in  a strong  cylindrical  iron  pot,  fur- 
nished witli  a leaden  or  iron  cover  lined  with  fire-clay  ; the  fire 
underneath  is  gradually  raised,  and  the  salt  sublimes  and  is  depo- 
sited in  large  dome-shaped  cakes  on  the  inner  surface  of  the  cover. 

The  liquors  which  are  condensed  during  the  distillation  of 
bones  in  closed  iron  cylinders,  in  the  process  of  preparing  animal 

* T?ie  vapour-volume  of  this  and  of  several  of  the  salts  of  ammonium,  including 
the  hydrobromate  and  hydrocyanate,  is  anomalous,  bding  double  that  of  most  com- 
pounds. Many  chemists  consider  that  in  the  act  of  evaporation  the  acid  aud  base 
are  dissociated  (Part  I.  p.  87)  in  these  salts. 


392 


SULPHATE  OF  AMMONIUM. 


charcoal,  are  highly  charged  with  an  impure  carbonate  of  aminO' 
ninm,  contaminated  with  volatile  oily  and  tarry  products  derived 
from  the  action  of  heat  upon  animal  matter : these  liquors  furnish 
a source  of  ammoniacal  salts  of  some  importance : formerly  this 
liquid,  after  being  subjected  to  a partial  purification,  was  com- 
monly known  as  spirit  of  Imrt^ s-liorn^  because  a similar  liquor 
was  originally  obtained  by  the  distillation  of  horn  shavings. 

Sublimed  chloride  of  ammonium  forms  semi-transparent, 
tough,  fibrous  masses.  It  is  very  soluble  in  water,  100  parts  of 
which  at  60°  dissolves  36  parts,  and  at  the  boiling-point,  88*9  parts 
of  the  salt : a great  reduction  of  temperature  occurs  whilst  it  is 
undergoing  solution,  and  it  is  hence  employed  as  a common  ingre- 
dient in  freezing  mixtures ; it  crystallizes  usually  in  an  arborescent 
form,  but  sometimes  in  cubes  and  octohedra.  Sal  ammoniac  has 
a sharp,  acrid  taste ; it  is  slightly  soluble  in  alcohol.  When  heated, 
it  sublimes  much  below  redness,  before  undergoing  fusion.  It  has 
a strong  tendency  to  form  double  salts  with  the  chlorides  more 
electro-negative  than  itself.  The  compounds  of  many  metals 
which  form  volatile  chlorides,  such  as  the  arseniates  and  arsenites, 
the  antimoniates  and  the  stannates,  when  heated  with  chloride 
of  ammonium,  lose  the  arsenic,  antimony,  and  tin  in  the  form  of 
chlorides  of  these  metals  ; and  tlie  salts  of  lead,  iron,  zinc,  and 
aluminum,  are  decomposed  and  completely  volatilized  when  ignited 
with  a large  excess  of  chloride  of  ammonium.  Rose  observed 
that  all  the  basic  protoxides  of  the  form  such  as  protoxides 

of  iron,  cobalt,  and  manganese, — and  oxides  of  the  form  such 

as  suboxide  of  copper,  also  decompose  chloride  of  ammonium, 
when  heated  with  its  solution,  the  ammonia  being  displaced  by  the 
metallic  oxide,  and  a fixed  metallic  chloride  being  formed,  whilst 
not  one  of  the  sesquioxides  has  this  power. 

(618)  Sulphate  of  Ammonium  [(Il4R)2SO,=132,  or  H.RO, 
80.3=66  ; Sp.  Gr.  1-695]  is  prepared  in  large  quantity  by  subject- 
ing gas  liquor  to  distillation,  and  condensing  the  volatilized  am- 
monia in  sulphuric  acid.  Tlie  salt  crystallizes  out  from  the 
strongly  acid  liquor,  wdiich  is  employed  to  condense  fresh  am- 
monia in  subsequent  operations.  On  a small  scale  it  may  be  ob- 
tained in  a pure  form  by  adding  sesquicarbonate  of  ammonium 
to  dilute  sulphuric  acid  so  long  as  any  effervescence  ensues.  It 
crystallizes  in  flattened  prisms,  which  are  isomorphous  with 
those  of  sulphate  of  potassium  : it  is  soluble  in  twice  its  weight  of 
cold  water,  and  has  a sharp,  disagreeable  taste ; when  heated  it 
decrepitates,  at  284°  it  melts,  and  between  500°  and  600°  it  under- 
goes partial  decomposition,  sulphite  of  ammonium  being  among 
the  products.  It  forms  a great  number  of  double  salts  isomor- 
phous with  the  corresponding  salts  of  potassium.  Sulphate  of 
ammonium  has  lately  been  applied  to  muslins  and  other  fabrics 
for  the  purpose  of  preventing  them  from  burning  with  flame  in 
case  they  should  accidentally  take  fire.  The  finished  goods  are 
dipped  into  a solution  containing  10  per  cent,  of  the  salt,  and 
dried  in  a.  npntrifno-al  machine,  or  hydro-extractor. 


formed  which  has  the  formula 


NITRATE  AND  CARBONATE  OF  AMMONIUM. 


393 


[(II^]^)3H  2 §0-4],  and  a double  sulphate  of  sodium  and  ammo- 
nium (H4NI^aS04,  2 H^O)  may  be  readily  formed  by  mixing  solu- 
tions of  the  two  salts,  and  evaporating  the  liquid  till  it  begins  to 
crystallize. 

(619)  JMitrate  of  AikiMONiiTM  (H4KN'03,  or  Ii4NO,brO3=80) ; 
Sp.  Gr.  1*635. — This  is  a salt  of  some  importance  to  the  chemist, 
as  it  furnishes  him  with  a ready  source  of  pure  nitrous  oxide.  It 
is  procured  by  neutralizing  nitric  acid  with  a solution  of  sesqui- 
carbonate  of  ammonium : on  evaporation,  the  salt  crystallizes  in 
long  striated  anhydrous  prisms  ; by  rapid  evaporation  it  is  obtained 
either  in  a fibrous  or  in  an  amorphous  mass.  It  has  a bitter 
acrid  taste,  is  somewhat  deliquescent,  and  during  the  act  of  solu- 
tion causes  a great  depression  of  temperature,  hence  it  is  often 
used  in  frigorific  mixtures : when  heated  to  226°  it  melts,  and  at 
480°  it  undergoes  complete  decomposition,  being  converted  into 
nitrous  oxide  and  water,  in  the  manner  already  described  (364) ; 
H4ll]^03  = 1130-1-2  H3O.  If  thrown  on  a red-hot  plate  it  melts, 
hisses,  and  is  dispersed  with  a faint  bluish  fiame. 

(620)  Carbonates  of  Ammonium. — Heutral  carbonate  of  am- 
monium is  not  known  in  the  solid  form.  When  carbonic  anhy- 
dride and  dry  ammonia  are  mixed,  no  matter  in  what  proportions,  2 
volumes  of  ammonia  and  1 of  carbonic  anhydride  unite,  and  are  con- 
densed into  a white  solid,  carbamate  of  ammonium  being  formed : 
according  to  Gerhardt,  2 11311-1-003= 114^112X003.  This  com- 
pound is  rapidly  converted  by  water  into  neutral  carbonate  of  am- 
monium : 114X113X003  4-  II3O  = (Il4X)3003.  There  are,  how- 
ever, several  compounds  of  ammonium  with  carbonic  acid.  The 
most  important  of  these  is  the  sesquicarhonate^  the  common  car- 
bonate or  smelling-salts  of  the  shops  (2[Il4X)3003]003=  236,  or 
2 H,X0,3  CO3  = 118)  ; Composition  in  100  parts^  28*81; 
OO3,  55*93  ; IT^O,  15*26.  It  is  usually  obtained  as  a"  semi-trans- 
parent fibrous  mass,  by  mixing  chalk  with  half  its  weight  of  sul- 
phate, or  of  chloride  of  ammonium,  collecting  in  leaden  vessels 
the  crude  product  which  comes  over  on  applying  heat,  and  resub- 
liming the  mixture  at  a temperature  of  about  150°  F.*;  the  salt  is 
received  in  leaden  hoods,  in  the  interior  of  which  it  is  deposited. 
During  this  process  a large  quantity  of  free  ammonia  escapes, 
because  the  neutral  carbonate  of  ammonium  cannot  exist  at  that 
temperature.  The  decomposition  of  the  chloride  of  ammonium 
may  be  represented  thus  : — 

6 1I4NC1  + 3 eaeoa  = 3 eacu  + 2[(H4N)2ee3]  €02  + 2 H3N  + n20. 

The  sesquicarbonate  of  ammonium  has  a strong,  pungent  smell, 
like  that  of  pure  ammonia,  arising  from  the  continual  volatiliza- 
tion of  carbonic  amrnonide  at  ordinary  temperatures  : 

2 [(n4X)3OO3]-0O3  becoming  2 (II4XIIOO3)  4-  (Tl3X)2003. 

Owing  to  this  loss  of  ammonia  the  salt  st)eedily  becomes  coated 
with  a white  spongy  crust  of  bicarbonate.  If  the  powdered  salt 
be  placed  upon  a filter,  and  washed  with  successive  small  quanti- 
ties of  cold  water,  the  neutral  carbonate  may  be  gradually  dissolv- 


394 


PHOSPHATES  OF  AMMONIUM AMMONIATED  SALTS. 


ed  away,  and  bicarbonate  of  ammonium,  wbicli  is  a more  spar- 
ingly soluble  salt,  will  be  left  upon  the  filter.  The  sesquicarbo- 
nate  has  an  acrid  taste  and  a strongly  alkaline  reaction.  In  its 
ordinary  form  the  sublimed  salt  has  a composition  which  is  excep- 
tional, since  in  order  to  convert  it  into  a normal  sesquicarbonate 
it  would  require  an  additional  atom  of  water,  which  is  never 
found  in  the  commercial  salt ; but  its  aqueous  solution,  if  satu- 
rated and  exposed  to  a temperature  of  32°,  deposits  large,  trans- 
23arent  octohedra  with  a rhombic  base,  of  the  true  hydrated  ses- 
quicarbonate 3 OOg,  2 HgO].  According  to  the  re- 

searches of  Rose  there  are  several  compounds  resulting  from  the 
combination  of  the  carbonate  with  different  proportions  of  bi- 
carbonate of  ammonium. 

The  Acid  Carbonate  or  Bicarbonate  of  Ammonium  (II^bTHOOg 
=79 ; /§>.  Gr.  1*586)  is  isomorphous  with  the  corresponding 
potassium  salt : it  is  soluble  in  8 parts  of  cold  water,  and  if  the 
solution  be  heated,  carbonic  acid  escapes ; when  exposed  to  the 
air  the  dry  salt  becomes  slowly  volatilized.  It  may  be  obtained 
in  large  transparent  prismatic  crystals,  derived  from  a rhombic 
octohedron  [4  (IT4OTI-0O3)Il2O],  by  pouring  boiling  water  upon 
the  sesquicarbonate,  corking  the  flask,  and  allowing  it  to  cool.  It 
is  sometimes  formed  spontaneously  during  the  decomposition  of 
guano,  and  is  then  deposited  in  large  regularly  formed  crystals. 

Carbonate  of  ammonium  combines  with  many  metallic  carbo- 
nates, forming  double  salts. 

(621)  Phosphates  of  Ai^imonium,  corresponding  to  those  of 
sodium,  may  be  formed ; but  the  only  one  of  any  importance  is 
the  tribasic  phosphate  of  sodium  ammonium  and  hydrogen,  known 
as  microcosmic  salt  (IIaH4NII,PO-4 . 4 H^O,  or  ]SraO,H4lsrO,IIO, 
PO-  . 8 110=137  + 72).  It  is  prepared  by  mixing  a hot  solution 
of  6 parts  of  phosphate  of  sodium  with  a solution  of  1 part  of  chlo- 
ride of  ammonium  in  the  smallest  possible  quantity  of  water; 
common  salt  remains  in  solution,  and  the  phosphate  crystallizes 
in  large  transparent  prisms,  which  are  efflorescent  in  a dry  air. 
It  may  be  purified  by  a second  crystallization  from  a small 
quantity  of  hot  water  to  which  a little  free  ammonia  has  been 
added,  to  compensate  for  the  loss  of  ammonia  which  the  salt 
sustains  when  heated  in  solution.  By  ignition,  all  the  ammonia 
and  water  are  expelled,  metaphosphate  of  sodium  remains,  and 
fuses  into  a colourless  glass  at  a red  heat.  This  salt  is  sometimes 
employed  as  a flux  for  experiments  wfith  the  blowpipe,  as  the  glass 
dissolves  many  metallic  oxides,  and  forms  transparent  beads,  from 
the  colour  of  which  the  presence  of  certain  metals  can  in  many 
cases  be  ascertained. 

(622)  Ammoniated  Salts. — Anhydrous  ammonia  enters  into 
combination  with  many  anhydrous  metallic  salts  in  a manner 
somewhat  analogous  to  that  of  water  of  crystallization.  In  other 
cases,  salts  which  usually  retain  water  of  crystallization  lose  it 
either  partially  or  entirely  when  they  combine  with  ammonia, 
but  the  number  of  atoms  of  ammonia  is  not  influenced  by  the 
proportion  of  water  with  which  the  salt  generally  unites.  Chloride 


ACTION  OF  AISTMONIA  UPON  SALTS  IN  SOLUTION. 


395 


of  silver,  of  tin,  of  copper,  and  of  calcium,  sulphate  of  copper,  and 
of  zinc,  nitrate  of  silver,  and  of  copper,  form  compounds  of  this 
kind  with  ammonia.  The  composition  of  some  of  these  salts  is 
exliibited  in  the  subjoined  table : — 


At.  Wt. 

Sp.gr. 

Ammoniated  chloride  of  silver 

. AgCl,2  H3N 

177-5 

1. 

U 

“ copper  . . . 

. -611010,6  H3N 

236-4 

2. 

iL 

“ copper  . . . 

. 6uCl2,4  H3N,H2e  .... 

220-4 

1-671 

3. 

U 

“ copper  . . . 

. 6uCl2,2H3N 

168-4 

2-194 

U 

“ calcium. . . 

. 6aCl2,8  H3N  

247 

U 

sulphate  of  silver  .... 

. Ag2Se4,4H3N 

380 

2-918 

(t 

“ copper  . . . 

. -euS04,4  H3N,H20  . . . 

245-4 

1-790 

U 

nitrate  of  silver 

. AgN03,3H3N 

221 

U 

“ copper  . . . 

. 6u  2 Ne3,4  H3N 

255-0 

1-874 

These  compounds  when  exposed  to  the  air  lose  a portion  of 
the  ammonia : if  heat  be  applied,  the  ammonia  is  often  entirely 
expelled,  as  in  the  case  of  ammoniated  chloride  of  silver,  the  com- 
pound originally  employed  by  Faraday  for  obtaining  ammoniacal 
gas  in  the  liquid  form  : the  chloride  of  silver  is  left  unaltered  when 
the  ammonia  is  driven  off.  In  other  instances  the  elements  of 
ammonia  react  upon  the  salt  and  decompose  it.  For  example, 
ammoniated  chloride  of  copper,  -GuCh  6 Hgll,  when  heated,  first 
loses  4 atoms  of  ammonia,  and  then  the  residue  (GuCh  2 HgN) 
undergoes  the  following  decomposition ; 6 (GuCh  2 ITglST)  = 
6 GuCl  + 6 H4IICI  + 4 Hgll+hlg.  The  corresponding  compound 
of  nickel  is  reduced  to  the  metallic  state  when  heated. 

In  solution  ammonia  also  combines  with  many  metallic  salts, 
forming  analogous  compounds : by  exposure  to  air  the  ammonia 
escapes.  Salts  of  zinc  form  a colourless  solution  with  excess  of 
ammonia ; those  of  cobalt  give  a brown,  which  passes  into  red ; 
whilst  the  salts  of  nickel  and  of  copper  give  a violet-blue  so- 
lution. 

(623)  Action  of  Ammonia  upon  Salts  in  Solution. — From 
what  has  been  already  stated,  it  is  evident  that  ammonia  acts 
upon  metallic  salts  not  merely  as  a powerful  base,  as  in  cases 
where  caustic  potash  or  soda  are  made  to  decompose  them.  The 
results  produced  by  the  addition  of  ammonia  to  a solution  of  a 
metallic  salt  may  be  stated  as  follows : — 

1. — If  the  ammonia  be  insufficient  in  quantity  to  neutralize 
the  whole  of  the  acid  contained  in  the  metallic  salt,  a sparingly 
soluble  basic  salt  of  the  metal  may  be  precipitated : in  this  way 
basic  sulpliate  of  copper,  basic  nitrate  of  lead,  or  basic  sulphate  of 
aluminum,  may  be  formed;  for  instance,  4 GuSG^  + G IlglST-f- 
7 11^0=3  [(n,N)gSej+(Guse„3  Gue,4  iigO). 

— If  tlie  ammonia  be  present  in  excess,  it  may,  by  reacting 
upon  the  acid  of  the  salt,  produce  with  it  a soluble  salt  of  am- 
monium, whilst  a precipitate  of  the  metallic  oxide  in  a hydrated 
form  is  occasioned:  as  when  alumina,  oxide  of  chromium,  or  per- 
oxide of  iron,  is  thrown  down  from  its  salts : — for  example, 

2 (Fe,  3 Se,)  + 12  IlglST  + 9 11^0= 6 [(II,N)gSe,]  + 2 Fe^Og,  3 11^0. 

3. — Sometimes  the  ammonia,  if  in  excess,  combines  with  the 


396 


kane’s  amide  theoet  of  ammonia. 

precipitated  oxide,  as  it  does  witli  peroxide  of  uranium,  when 
mixed  wdtli  a solution  of  uranic  nitrate  : — 

djeNe3+2  ii3]sr+H3e.=H,mo3+H,]srdJ03 

4.  — In  other  cases  a double  salt  of  ammonium  and  the  metal 
may  be  precipitated,  as  when  ammonia  is  mixed  with  a solution 
containing  phosphoric  acid  and  magnesium,  in  which  case  a 
double  phosphate  of  magnesium  and  ammonium  is  formed  and 
deposited  in  crystals:  figSO^H-  (H4]Sr)3P04= (11411)2804 + 114^1 
MgFO,. 

Reactions  corresponding  to  the  four  modes  of  action  just  indi- 
cated frequently  occur,  when  a solution  of  a caustic  alkali,  such  as 
potash  or  soda,  is  mixed  with  a metallic  salt  in  solution. 

5.  — A soluble  compound  may  be  formed,  into  the  composition 
of  which  both  the  metallic  oxide  and  the  ammonia  enter,  and 
unite  with  the  acid  so  as  to  form  a species  of  double  basic  salt. 
Hydrate  of  magnesia,  hydrated  oxide  of  copper,  of  zinc,  of  cobalt, 
or  of  nickel,  when  free  from  acid,  is  very  sparingly  dissolved  by  a 
solution  of  pure  caustic  ammonia,  but  a mixture  of  chloride  of 
ammonium,  or  even  of  carbonate  of  ammonium,  with  caustic 
ammonia,  dissolves  them  without  difficulty.  The  compounds 
thus  dissolved  are  definite  in  composition,  and  similar  in  nature 
to  those  enumerated  in  the  table  given  in  the  preceding  page  as 
the  result  of  the  action  of  ammoniacal  gas  upon  the  dry  salts  of 
the  metals.  The  solutions  of  these  salts  in  ammonia  frequently 
absorb  oxygen  rapidly  if  exposed  to  the  air  : salts  of  iron,  manga- 
nese, and  cobalt  furnish  examples  of  this  kind. 

6.  — But  it  occasionally  happens  that  the  elements  of  ammonia 
enter  into  the  composition  of  the  salt  in  a more  intimate  manner. 
When  a solution  of  corrosive  sublimate  (HgCh)  is  mixed  with  a 
solution  of  potash,  a yellow  precipitate  of  oxide  of  mercury  is 
formed,  and  chloride  of  potassium  remains  in  solution  ; HgCh  -f 
2 KHO=HgO-f  2 KC1  + H20- ; but  the  case  is  otherwise  if  am- 
monia be  added ; a white  precipitate  is  then  formed,  the  compo- 
sition of  which  is  unchanged  by  the  addition  of  an  excess  of 
ammonia.  Kane  {Phil.  Mag.^  June,  1836,  p.  495)  showed  that 
this  body  has  a composition  which  may  be  represented  by  the  for- 
mula of  HgCl2HgH4K2.  Its  formation  may  be  explained  by  the 
following  equation : — 

2 HgCl2  + 4 Il3K=(HgCl2,HgH4K2)  + 2 H4KCI. 

From  this  result,  conjoined  with  others  obtained  from  an 
examination  of  other  ammoniacal  derivatives  from  copper,  palla- 
dium, and  other  metals,  Kane  was  led  to  believe  that  ammonia  is 
not  a direct  compound  of  hydrogen  with  nitrogen,  but  rather  a 
combination  of  an  atom  of  amidogen  with  one  of  hydrogen  ; so 
that  he  represents  ammonia  as  IIAd  (Ad  standing  for  amidogen, 
H^K)  ; the  atom  of  hydrogen  being  liable  to  displacement  by  an 
equivalent  either  of  mercury  or  of  certain  other  metals.  One 
atom  of  such  an  amide  of  mercury  (IlgAd,  or  HgAd^)  is,  according 
to  Kane,  contained  in  white  precipitate,  in  combination  with  1 
atom  of  chloride  of  mercury. 


CHAEACTERS  OF  THE  COMPOUNDS  OF  AAEMONIUM. 


397 


Later  experiments,  however,  especially  those  of  Hofmann,  on 
the  formation  of  bases  by  substitution  from  ammonia,  have  not 
strengthened  the  theory  proposed  by  Kane  ; they  have  shown  that 
not  only  does  1 atom  of  hydrogen  admit  of  being  displaced  by 
some  equivalent  substance,  but  that  each  of  the  3 atoms  of  hydro- 
gen in  ammonia  admits  of  being  thus  displaced  ; nay  more,  that 
bodies  may  be  obtained  wliicli  are  derived  from  ammonium,  in 
which  all  the  4 atoms  of  hydrogen  in  this  compound  have  been 
displaced  by  other  equivalent  bodies.  These  investigations  point 
rather  to  the  view  that  white  precipitate  is  a body  corresponding 
in  composition  to  chloride  of  ammonium  (114^,01)  but  in  which  2 
atoms  of  hydrogen  are  displaced  by  1 atom  of  the  dyad  metal 
mercury  (Hg'^Il2K,Cl).  We  shall  recur  to  these  investigations 
when  considering  the  properties  of  the  organic  bases. 

7. — Within  the  last  few  years  several  remarkable  bases  which 
are  derived  from  ammonia  have  been  formed,  but  into  the  compo- 
sition of  which  certain  metals  enter.  Although  these  compounds 
contain  the  elements  of  ammonia,  and  of  the  oxides  of  the  metals, 
yet  they  do  not,  by  means  of  the  ordinary  tests,  give  any  indica- 
tions either  of  ammonia  or  of  the  metals  which  enter  into  their 
composition. 

In  this  manner  several  series  of  compounds  have  been  pro- 
cured, some  of  which  contain  platinum,  others  contain  cobalt,  and 
others  palladium  ; in  most  instances  they  form  cry stalliz able  and 
well  characterized  salts. 

Amongst  the  compounds  thus  formed,  four  of  those  obtained 
from  platinum  may  be  selected  by  way  of  illustration.  The  first 
of  these  contains  a base  for  which  Gerhardt  has  proposed  the  name 
oi platosamine^  PtH6K20 ; the  second,  he  has  termed  diplatosa- 
mine^  PtHj2N40  . ; the  third,  platinamine^  PtldgK^O^ ; and 

the  fourth,  diplatinamine^  PtHi^K^O^*  The  base  last  mentioned 
has  not  as  yet  been  obtained  in  a separate  form. 

Each  of  these  bases  forms  with  hydrochloric  acid  a crystalliz- 
able  salt,  the  composition  of  which  is  represented  by  the  empiri- 
cal formula  given  in  the  second  column  of  the  following  table, 
whilst  the  third  column  shows  the  relation  of  the  compound  to 
the  chloride  of  platinum  from  which  it  is  obtained ; the  first  two 
compounds  being  derived  from  platinous  chloride,  the  last  two 
from  platinic  chloride : — 


Chloride  of  platosamine  PtH6K2Cl2  or 

diplatosamine  PtH.^K^Clj  “ 

“ platinamine  PtH^K^Cl^  “ 

‘‘  diplatinamine  Ptllj^N^Cl^  ‘‘ 


PtCl„  2 lEK 
PtCl„  4 II3K 
PtCl„  2 II3K 
PtCl„  4 113^. 


(624)  Characters  of  the  Compounds  of  Ammonium. — The 
salts  of  ammonium  are  colourless ; they  are  all  decomposed  by 
heat,  unless  the  acid  itself  be  capable  of  volatilization,  in  which 
case  they  may  generally  be  sublimed  without  change.  They  are 
distinguished  from  the  salts  of  all  the  metals,  with  the  exception 
of  those  of  the  alkaline  group,  by  the  absence  of  any  precipitate 


398 


ESTIMATION  OF  AMMONIA. 


when  their  solutions  are  mixed  with  a solution  of  carbonate  of 
potassium  or  of  sodium. 

The  salts  of  ammonium  may  be  recognised  by  heating  them 
in  the  solid  form  with  quicklime  or  with  caustic  potash^  when 
pungent  fumes  of  ammonia  are  extricated : if  their  solutions  be 
boiled  with  hydrate  either  of  potash  or  lime  a similar  extrication 
of  ammonia  ensues,  and  if  the  quantity  of  ammonia  be  too  small 
to  be  detected  by  the  smell,  a rod  dipped  into  hydrochloric  acid 
diluted  with  an  equal  bulk  of  water,  produces  white  fumes  when 
brought  into  the  vapour’;  these  fumes  are  due  to  the  production 
of  sal  ammoniac,  which  is  formed  by  the  union  of  the  gaseous 
ammonia  with  the  vapour  of  the  hj^drochloric  acid,  and  is  preci- 
pitated in  the  solid  form.  A characteristic  test  of  free  ammonia 
is  the  formation  of  the  black  iodide  of  nitrogen  in  a solution  of 
iodine  in  iodide  of  potassium ; but  if  the  proportion  of  ammonia 
be  very  minute,  the  only  perceptible  change  is  the  disappearance 
of  the  brown  colour  of  the  solution. 

Another  very  characteristic  and  extremely  delicate  test  of 
ammonia  and  of  its  salts  is  the  following  : — Prepare  a solution  of 
corrosive  sublimate  to  which  iodide  of  potassium  is  added  until 
the  precipitate  of  iodide  of  mercury  is  nearly  redissolved ; then 
pour  into  the  clear  liquid  a solution  of  caustic  potash,  and  allow 
it  to  become  perfectly  clear  by  standing,  then  decant  the  liquid. 
If  this  solution  be  added  in  excess  to  a liquid  containing  a trace 
of  ammonia,  or  of  its  salts,  it  assumes  a brown  tinge,  or  furnishes 
a brown  precipitate,  according  as  the  proportion  of  ammonia  is  less 
or  more,  iodide  of  hydrarg-ammonium,  or  ammonium  in  which  4 
atoms  of  hydi'ogen  are  displaced  by  2 of  mercury  (Hg/'H,  I,  H^O) 
being  formed  (Hessler).  The  reaction  does  not  occur  in  the  pres- 
ence of  sulphides  or  cyanides  of  the  metals  of  the  alkalies. 

The  Pliosjyhomolyhdate  of  Sodium  is  also  a very  delicate  test 
for  the  presence  of  a salt  of  ammonium  in  solution.  The  mode 
of  preparing  and  applying  it  is  described  under  the  head  of 
molybdic  acid  (829).  Another  still  more  delicate  test  of  the  pres- 
ence of  free  ammonia  is  afforded  by  the  use  of  a liquid  consisting 
of  a mixture  of  equal  parts  of  a saturated  solution  of  arsenious 
acid  and  of  a solution  of  nitrate  of  silver  containing  10  grains  to 
the  ounce ; traces  of  ammonia  cause  the  formation  of  the  yellow 
arsenite  of  silver  (Dr.  A.  Taylor).  This,  however,  though  a sen- 
sitive, is  not  a characteristic  test,  since  a trace  of  any  free  alkali 
or  alkaline  earth  produces  a similar  result. 

(625)  Estimation  of  Ammonia. — The  most  accurate  method 
of  determining  the  quantity  of  ammonia  in  any  substance,  if  the 
absence  of  potassium  has  been  ascertained,  consists  in  precipitat- 
ing it  by  i\\Q  perchloride  of  platinum.,  obser^dng  all  the  precau- 
tions mentioned  when  speaking  of  the  use  of  this  test  for  potas- 
sium; a yellow  insoluble  double  salt  falls,  consisting  of  (211,^01, 
PtClJ  : it  contains,  in  100  parts,  T'65  of  ammonia.  This  salt  is 
easily  distinguished  from  the  corresponding  compound  of  potas- 
sium by  heating  it  to  redness,  in  which  case  metallic  j^latinum 
alone  remains ; whereas  the  potassium  salt,  though  decomposed 


ESTIMATION  OF  AIVCMONIA. 


399 


by  this  treatment,  leaves  the  platinum  mixed  with  chloride  of 
potassium,  which  may  be  dissolved  out  of  the  residue. 

(626)  The  following  method  of  determining  the  amount  of 
ammonia  in  guano  or  in  crude  ammoniacal  salts  will  often  be 
found  useful.  One  hundred  grains  of  the  matter  for  trial  are 
placed  in  a small  retort,  fig.  336,  and  two  ounces  of  water  are 
added : by  means  of  a bent  funnel  half  an  ounce  of  a solution  of 
potash,  of  specific  gravity  1-25,  is  also  introduced;  about  an 
ounce  and  a half  of  liquid  is  gradually  distilled  into  the  fiask, 
which  contains  a measure  of  1000  water-grains  of  sulphuric  acid 
(one  burette  full,  fig.  331)  diluted  to  the  strength  required  for  the 
determination  of  soda  for  alkalimetrical  purposes  (577).  If  the 
mixture  froths  up  inconveniently  when  boiled,  milk  of  lime  may 
be  substituted  for  the  solution  of  potash.  As  soon  as  about  an 
ounce  and  a half  of 
liquid  has  been  distilled, 
the  contents  of  the  re- 
tort are  allowed  to  cool  a 
little,  and  another  ounce 
of  water  is  introduced 
into  the  retort  by  the 
funnel;  a second  distil- 
lation is  then  proceeded 
with,  until  the  quantity 
of  water  just  added  has 
passed  over ; an  ounce 
more  of  water  is  added 
to  the  contents  of  the 
retort,  and  the  distilla- 
tion is  renewed  a third 
time  until  this  addition- 
al quantity  of  water  has 
passed  over : the  liquid  in  the  flask  is  then  mixed  with  a few 
drops  of  infusion  of  litmus.  This  is  now  to  be  neutralized  in  the 
usual  way,  by  means  of  a standard  solution  of  caustic  soda ; the 
soda  solution  being  of  such  a strength  that  one  measure  of  it 
exactly  neutralizes  an  equal  measure  of  the  acid  liquid  originally 
introduced  into  the  flask.  Suppose  that  this  liquid  from  the  flask 
now  requires  67  measures  of  soda  solution  instead  of  100 ; 33 
measures  of  the  acid  will  have  been  neutralized  by  the  ammonia ; 
a quantity  of  ammonia  will  therefore  have  passed  over  equivalent 
to  33  grains  of  anhydrous  soda.  The  corresponding  quantity  of 
ammonia  may  be  calculated  from  the  equivalent  numbers  of  the 
two  alkalies : — 

Eq.  Na^e.  Eq.  II3N 

Thus,  31  : 17  ::  33  : 18-09. 

100  grains  of  the  material  operated  on  in  this  case  would 
therefore  have  contained  18*09  grains,  or  the  sample  would  contain 
18*09  per  cent,  of  ammonia. 


400 


COMPOUNDS  OF  BAEIUM  WITH  OXYGEN. 


CHAPTEK  XIII. 

GROUP  II. METALS  OF  THE  ALKALINE  EARTHS. 


Metal. 

Symbol. 

Atomic 

weight. 

Atomic 

vol. 

Specific 

gravity. 

1 

Electric 
conductivity. 
68-62  F“. 

Barium 

fia 

137-0 

Strontium 

Sr 

87-5 

34-56 

2-54 

6-71 

Calcium 

ea 

40-0 

25-28 

1-578 

22-14 

These  metals  furnish  but  a single  basic  oxide ; this  is  soluble 
in  water,  combining  with  it  with  great  avidity.  The  hydrate 
absorbs  carbonic  acid  rapidly,  forming  a white  carbonate,  insoluble 
in  water.  The  hydrates  also  absorb  chlorine,  forming  bleaching 
compounds.  Each  metal  forms  several  sulphides.  The  proto- 
sulphide is  less  soluble  than  the  others,  and  is  colourless,  whilst 
all  the  others  are  yellow.  The  sulphates,  phosphates,  and  oxalates 
are  insoluble  or  nearly  so  (see  also  p.  290). 

§ I.  Barium  : Ba'^  = ISY’O,  or  Ba  = 68*5. 

(62Y)  Barium  occurs  abundantly  under  the  form  of  sulphate, 
and  is  not  unfrequently  found  as  carbonate  of  barium.  Davy 
first  procured  it  in  the  metallic  state  by  making  mercury  the 
negative  electrode  of  a voltaic  battery  in  a strong  solution  of 
hydrate  of  baryta ; the  barium  was  thus  obtained  as  an  amalgam, 
from  which  the  mercury  was  expelled  by  heating  it  strongly  in  a 
green  glass  tube  filled  with  hydrogen ; but  it  does  not  appear  to 
have  been  thus  isolated  in  a state  of  purity.  When  procured  by 
the  voltaic  decomposition  of  its  fused  anhydrous  chloride,  it  is  of 
a pale  yellow  colour ; but  it  is  not  easily  obtained  in  distinct  beads. 
Barium  decomposes  water  rapidly  at  ordinary  temperatures.  In 
the  air  it  is  quickly  tarnished  by  absorbing  oxygen.  It  decom- 
poses glass  at  a red  heat. 

(628)  Compounds  of  Baril^i  with  Oxygen. — Barium  forms 
two  oxides,  a protoxide,  BaO,  and  a peroxide,  BaO^ : the  first  is 
the  only  one  which  forms  salts. 

Baryta  (BaO  = 153'0,  or  BaO  = 76'5);  Sp.  Gr.  5’456. — 
Anhydrous  baryta  may  be  obtained  by  exposing  nitrate  of  barium 
to  a red  heat  in  a capacious  porcelain  crucible ; the  salt  decrepi- 
tates, melts,  and  then  boils  up  and  gives  off  a large  quantity  of 
oxygen  mixed  with  nitrogen,  leaving  the  baryta  as  a grey  porous 
mass,  which  absorbs  moisture  and  carbonic  acid  if  exposed  to  the 
air.  If  mixed  with  one-eighth  of  its  weight  of  water  it  slakes, 
forming  a hydrate,  with  extrication  of  great  heat.  Baryta  may 
be  fused  before  the  oxyhydrogen  blowpipe. 

The  sulphide  of  barium  may  be  employed  for  procuring  pure 
hydrate  of  haryta^  by  boiling  its  solution  with  oxide  of  copper : 
hyposulpiiite  of  barium  and  subsulphide  of  copper,  both  of  which 


PEROXIDE  OF  BARIIJlVr. 


401 


are  insoluble,  are  produced,  and  hydrate  of  baryta  is  dissolved ; 
6 fiaS  + 6 H,e  + 8 OuO  = 5 (BaOH.O)  + fiaS ,11,0,  + 4 Ou,S  : 
the  hot  liquid  is  filtered,  and  crystals  of  tlie  hydrate  (Ba0H,0, 
8 H2^)  are  deposited  as  the  solution  cools.  Crystals  of  hydrate 
of  baryta  ma}^  also  be  obtained  by  adding  to  a boiling  solution  of 
caustic  soda,  of  sp.  gr.  1-12,  an  equivalent  quantity  of  nitrate  of 
barium  in  small  quantities  at  a time.  The  hot  solution  is  filtered 
into  a vessel  covered  from  the  air,  and  the  hydrate  is  deposited  as 
the  liquid  cools.  The  crystals  are  soluble  in  3 times  their  weight 
of  boiling  water,  and  in  20  of  cold  water ; the  liquid  has  a strongly 
alkaline  reaction.  When  exposed  to  the  air,  both  the  crystals  and 
the  solution  absorb  carbonic  acid ; by  heat  8 H,0-  are  expelled 
from  the  crystals,  and  a monohydrate  is  left,  of  sp.  gr.  4-495 ; 
it  fuses  at  a heat  above  redness,  and  retains  its  water  at  all 
temperatures.  Hydrate  of  baryta  is  sparingly  soluable  in  alco- 
hol. 

Peroxide  of  Barium  (BaO,  ==  169)  is  formed  by  passing 
oxygen  over  anhydrous  baryta  at  a low  red  heat ; or  by  mixing 
pure  baryta  with  an  equal  weight  of  chlorate  of  potassium  and 
heating  to  low  redness  ; in  the  latter  case  ignition  commences  at 
one  point,  and  spreads  through  the  mass  like  tinder ; 3 BaO  + 
KC103=KC1  + 3 BaO, ; the  chloride  of  potassium  may  be  dissolved 
out  by  water,  and  a bulky  white  hydrated  peroxide  of  barium 
(BaO„  6 H,0),  insoluble  in  water,  remains.  Brodie,  however, 
finds  that  it  is  impossible  to  convert  much  more  than  half  the 
baryta  into  peroxide  by  either  of  these  methods.  In  order  to 
obtain  the  pure  peroxide,  he  recommends  {Phil.  Trans.  1863, 
p.  409)  that  the  crude  material  be  completely  converted  into 
hydrate  by  pulverizing  finely  in  a mortar,  and  rubbing  it  with 
water.  It  is  then  to  be  mixed  gradually  with  a very  dilute  solu- 
tion of  hydrochloric  acid,  taking  care  that  the  acid  is  always  in 
excess.  The  solution  is  to  be  filtered,  and  rendered  slightly  alka- 
line by  the  addition  of  baryta  water,  which  separates  alumina  and 
peroxide  of  iron.  The  alkaline  solution  is  to  be  filtered  as  rapidly 
as  possible  through  linen  filters,  and  an  excess  of  baryta  water 
added  to  the  clear  filtrate ; the  peroxide  is  precipitated  in  bril- 
liant plates,  which  are  insoluble  in  water,  and  may  be  washed  by 
decantation  ; if  pressed  between  blotting-paper  it  may  be  rendered 
anhydrous  by  desiccation  in  vacuo  over  sulphuric  acid.  It  is  then 
quite  stable,  and  appears  as  a fine  white  powder  resembling 
magnesia. 

By  strong  ignition  the  peroxide  of  barium  again  parts  with 
its  oxygen.  Boussingault  {Ann.  de  Chimie.^  III.  xxxv.  5)  even 
proposed  to  make  use  of  caustic  baryta  as  a means  of  preparing 
oxygen  on  a large  scale  by  alternately  passing  atmos})heric  air 
over  the  baryta  raised  to  a dull  red  heat,  and  then  ex})elling  the 
absorbed  oxygen  by  intense  ignition  : the  presence  of  a small 
quantity  of  aqueous  vapour  greatly  assists  the  exi)ulsion  of  the 
oxygen,  but  the  y)rocess  cannot  be  worked  with  facility.  The 
anhydrous  peroxide  combines  with  water  when  moistened  without 
evolving  any  sensible  amount  of  heat,  and  crumbles  down  to  a 
26 


402 


SULPHIDES  AND  CIILOEIDE  OF  BAEIUM. 


white  powder ; it  is  used  for  procuring  the  peroxide  of  liydrogen. 
Peroxide  of  barium  becomes  white  hot  when  heated  over  a spirit- 
lamp  in  a rapid  current  of  carbonic  or  of  sulphurous  anhydride ; 
small  white  flames  burst  out  from  its  surface,  whilst  carbonate  or 
sulphate  of  barium  is  formed. 

(629)  Sulphides  of  Barium. — Of  these  the  most  important  is 
\l\Q  protosul2?hide  (BaS  = 169).  The  preparation  of  this  substance 
from  the  native  sulphate  of  barium  presents  some  interest  to  the 
chemist,  for  it  enables  him  to  obtain  with  ease  the  soluble  salts  of 
barium  from  its  insoluble  sulphate.  In  order  to  prepare  the  sul- 
phide, either  the  native  or  the  artiflcial  sulphate  is  reduced  to  a 
very  fine  powder,  and  intimately  mixed  with  an  equal  weight  of 
starch  or  flour  or  with  one-tenth  of  its  weight  of  powdered  char- 
coal ; this  is  made  up  into  a paste  with  oil,  and  introduced  into  a 
crucible  lined  with  charcoal : the  cover  is  luted  on,  and  the 
crucible  with  its  contents  are  exposed  for  an  hour  to  an  intense 
heat.  By  this  treatment  the  sulphate  of  barium  is  deoxidized, 
carbonic  oxide  escaping,  whilst  sulphide  of  barium  remains: 
fiaSO,  -f  4 O = fiaS  + 4 OO.  When  the  mass  thus  obtained  is 
treated  with  successive  small  quantities  of  boiling  water,  the 
sulphide  is  decomposed  ; the  first  portions  of  the  solution  have  a 
yellow  colour,  owing  to  the  formation  of  hydrosulphate  of  the  sul- 
phide of  barium,  which  absorbs  oxygen  and  becomes  partially 
converted  into  bisulphide  of  barium,  whilst  the  later  w^ashings 
contain  gradually  increasing  quantities  of  hydrate  of  baryta ; 
2 BaS  + 2 II,e  = BaS,H;S  + Bae,H,e,  'and  2 (fiaS,H,S) 
-f  O2  r=  2 BaS2  + 2 ; but  if  the  mass  be  treated  with  a suf- 

ficient quantity  of  boiling  water,  it  becomes  entirely  dissolved, 
and  the  sulphide  is  deposited  as  the  solution  cools  in  colourless 
transparent  crystals,  wdth  6 H2O.  When  treated  wfith  hydro- 
chloric or  any  other  acid,  the  sulphide  of  barium  is  decomposed, 
and  the  corresponding  barium  salt  is  formed,  whilst  sulphuretted 
hydrogen  escapes  ; thus  BaS  + 2 HCl  = BaCl2  + H2S. 

(630)  Chloride  of  Barium  (BaCl2,  2 H2O  = 208  -f  36,  or 
BaCl,  2 HO  = 104  + 18);  Sp.  Gr.,  anhydrous^  3*750,  cryst. 
2*664;  Comp,  in  100  parts ^ Ba  65*86;  Cl,  34*14. — This  salt  is 
obtained  by  dissolving  the  sulphide  or  the  carbonate  of  barium  in 
hydrochloric  acid.  On  the  large  scale  it  may  be  procured  by 
fusing  together  one  part  of  crude  chloride  of  calcium  (the  residue 
of  the  preparation  of  carbonate  of  ammonium),  wfith  2 parts  of 
powdered  native  sulphate  of  barium  ; chloride  of  barium  and  sul- 
phate of  calcium  are  formed ; the  chloride  is  washed  out  rapidly 
with  hot  water,  and  purified  by  crystallization.  Chloride  of  barium 
crystallizes  in  flat  four-sided  tables,  containing  2 H2O,  which  may 
be  expelled  by  heat : water  dissolves  nearly  half  its  weight  at  60°, 
and  three-fourths  at  212° : the  presence  of  hydrochloric  or  of 
nitric  acid  greatly  diminishes  its  solubility.  A solution  of  this 
salt  is  the  usual  test  for  ascertaining  the  presence  of  sulphuric 
acid  in  solutions,  which  it  indicates  by  the  formation  of  a white 
precipitate  insoluble  in  nitric  acid.  If  anhydrous  baryta  be  intro- 
duced into  a jar  of  hydrochloric  acid  gas  it  becomes  incandescent, 


TOTEATE  AND  CAEBONATE  OF  BAEIIIM. 


403 


chloride  of  barium  is  formed,  and  water  becomes  condensed  on 
the  sides  of  the  vessel. 

(631)  SiLicoFLiroEiDE  OF  Baeium  (BaF2,SiF4  = 279)  is  pro- 
cured by  adding  silicolluoric  acid  to  a salt  of  barium  ; it  is  quickly 
deposited  in  microscopic  crystals,  which  are  insoluble  in  an  excess 
of  the  acid.  The  salt  is  anhydrous.  It  is  decomposed  by  ignition, 
which  converts  it  into  fluoride  of  barium.  The  silicofluoride  of 
strontium  is  soluble,  and  hence  silicofluoric  acid  may  be  employed 
to  distinguish  salts  of  barium  from  those  of  strontium. 

(632)  Sulphate  of  BAEnjM  (fiaSO^  = 233,  or  Ba0,S03  = 

116*5) ; Sp.  Gr.  4*59  : Composition  in  X^^parts^  BaO,  65*66  ; SO3 
34*34. — This  is  the  principal  native  mineral  of  baryta.  It  occurs 
in  the  mountain  limestone  in  large  veins,  and  is  found  accom- 
panying the  ores  of  lead  and  other  metals.  It  is  met  with  both 
massive  and  crystallized  in  modiflcations  of  the  right  rhombic 
prism.  The  name  ‘ baryta  ’ is  derived  from  heavy,  in  allu- 

sion to  the  high  speciflc  gravity  of  this  compound,  which  is  about 
4*6.  It  is  insoluble  in  water,  and  in  all  the  acids  except  boiling 
concentrated  sulphuric  acid : as  the  solution  in  this  acid  cools, 
crystals  of  the  sulphate  are  deposited.  De  Senarmont  found  that 
when  the  recently  precipitated  sulphate  is  heated  to  472°,  for  60 
hours  in  a sealed  tube,  with  diluted  hydrochloric  acid,  or  with  a 
solution  of  the  acid  carbonate  of  sodium,  microscopic  crystals  of 
the  same  form  as  those  of  the  native  sulphate  of  barium  are  de- 
posited upon  the  sides  of  the  tube.  At  a briglit  red  heat  the 
sulphate  fuses  into  a white  enamel : and  by  boiling  the  powdered 
sulphate  of  barium  with  the  carbonate  either  of  potassium  or  of 
sodium,  or,  more  rapidly  by  fusing  it  with  either  of  these  salts, 
the  artiflcial  sulphate  is  partially  converted  into  the  carbonate. 
It  may  be  easily  formed  by  precipitating  a salt  of  barium  with 
any  soluble  sulphate,  when  it  falls  as  a heavy  white  powder.  If 
nitric  acid  or  any  nitrate  be  present  in  the  solution,  the  precipi- 
tate carries  down  with  it  a portion  of  the  nitrate,  and  this  can 
only  be  removed  by  long  washing  with  boiling  water.  Sulphate 
of  barium  is  used  as  2^, permanent  tohitehj  artists  in  water  colours. 
It  is  also  employed  for  adulterating  white  lead ; when  ground 
with  oil,  however,  it  becomes  partially  transparent,  and  impairs 
the  opacitv  of  the  lead  pigment. 

(633)  JliTEATE  OF  Baeium  (Ba  2 NO3  =261,  or  Ba0,]^06=: 
130*5;  Sp.  Gr.  3*284:  Composition  in  100  parts,  BaO,  58*62; 
N3OJ,  41*38)  crystallizes  in  anhydrous  octohedra,  when  a solution 
of  the  carbonate  of  barium  in  nitric  acid  is  evaporated.  It  is 
insoluble  in  alcohol,  and  requires  eiglit  or  ten  times  its  weiglit  of 
cold  water,  and  3 of  boiling  water,  for  solution.  Nitric  acid  pre- 
cipitates it  in  crystals  from  its  solution,  unless  very  dilute:  when 
heated,  it  first  decrepitates  strongly,  and  afterwards  fuses ; on 
ignition,  the  whole  of  the  acid  is  expelled,  with  an  appearance  of 
ebullition  owing  to  the  escape  of  oxygen  and  nitrogen,  whilst 
pure  baryta  remains. 

(634f  Caebonate  of  Baeium  (BaOO,  = 197,  or  BaO,C()3  = 
98*5) ; Sp.  Gr.  4*4 : Composition  in  100  parts ^ BaO,  77*69  ; OO,, 


404 


CHARACTERS  OF  THE  SALTS  OF  BARIUM:. 


22*31. — This  compound  forms  the  mineral  called  witherite : it 
occurs,  both  massive  and  crystallized,  usually  in  six-sided  prisms 
terminated  by  six-sided  pyramids.  It  is  abundant  in  the  lead- 
veins  in  the  north  of  England,  and  is  also  found  in  Styria  and  in 
Siberia.  It  is  easily  prepared  artificially  by  precipitating  a salt 
of  barium  by  the  carbonate  of  one  of  the  alkali-metals ; it  then 
forms  a white  powder,  which  is  very  sparingly  soluble  in  pure 
water,  and  is  insoluble  in  water  charged  with  saline  matter : an 
aqueous  solution  of  carbonic  acid  dissolves  it  rather  freely.  If 
suspended  in  a solution  of  sulphate  of  potassium,  or  of  sulphate 
of  sodium,  in  the  cold,  and  frequently  agitated,  freshly  precipitated 
carbonate  of  barium  is  converted  into  sulphate ; but  if  sulphate 
of  barium  be  boiled  with  a carbonate  of  one  of  the  alkali-metals, 
carbonate  of  barium  and  sulphate  of  the  alkaline  metal  are  pro- 
duced. Ignition  of  tlie  carbonate  does  not  expel  the  carbonic 
acid,  but  if  it  be  mixed  with  charcoal  and  intensely  ignited,  it  is 
partially  decomposed ; pure  baryta  is  obtained,  and  may  be  dis- 
solved out  with  water.  If  mixed  with  an  equal  weight  of  car- 
bonate of  calcium,  carbonate  of  barium  is  decomposed  without 
mucli  difficulty  when  ignited  in  a current  of  steam : the  hydi*ate 
of  baryta  may  be  dissolved  out  of  the  mixture  by  water. 

Carbonate  of  barium  is  now  manufactured  to  some  extent  as 
a substitute  for  a portion  of  the  alkali  and  oxide  of  lead  in  the 
making  of  plate  and  flint  glass  : the  silicate  of  barium  fuses  and 
becomes  incorporated  with  the  other  silicates.  This  carbonate 
is  prepared  from  the  sulphate,  which  is  reduced  to  the  form  of 
sulphide  by  ignition  with  carbonaceous  matter : the  sulphide  is 
then  dissolved  in  water,  and  decomposed  by  a current  of  car- 
bonic acid : the  carbonate  is  thus  precipitated  as  a fine  white 
powder. 

(635)  Characters  of  the  Salts  of  Baritm. — The  salts  of 
barium  with  colourless  acids  are  colourless.  The  carbonate  and 
all  the  soluble  salts  act  as  powerful  poisons,  and  have  an  acrid, 
disagreeable  taste.  The  best  antidote  when  they  have  been  taken 
internally  is  the  sulphate  of  sodium  or  of  magnesium. 

Salts  of  barium  when  in  solution  are  easily  recognised  by 
giving  with  suljphuric  acid  a white  precipitate  of  sulphate  of 
barium,  which  is  insoluble  in  the  acids.  Barium  is,  for  the  pur- 
poses of  analysis,  usually  estimated  in  the  form  of  sulphate : 100 
parts  correspond  to  65*66  of  BaO  and  34*34  of  SO3.  The  pres- 
ence of  citrate  either  of  sodium  or  ammonium  prevents  the  pre- 
cipitation of  sulphate  of  barium  in  neutral  and  alkaline  solutions ; 
but  these  salts  do  not  redissolve  the  sulphate  of  barium  after  it 
has  once  been  deposited.  On  acidulating  with  hydrochloric  acid 
the  solution  containing  the  citrates,  the  sulphate  of  barium  is  pre- 
cipated  in  the  usual  manner  (Spiller). 

With  carbonate  of  potassium  or  of  sodium  a white  precipitate 
of  carbonate  of  barium  is  produced  in  solutions  which  contain 
barium.  Ilydrosulphate  of  ammonium  gives  no  precipitate  in 
such  solutions.  Phosphate  of  sodium  gives  a white  precipitate 
which  is  soluble  in  diluted  nitric  or  hydrochloric  acid.  Salts  of 


CHLORIDE  AND  SULPHATE  OF  STRONTIUM. 


405 


barium,  when  mingled  with  alcohol,  tinge  its  flame  of  a yellow- 
ish-green colour.  In  the  spectroscope  the  spectrum  of  the  barium 
salts  is  distinguished  by  a remarkable  series  of  bright  bands  in 
the  green,  with  fainter  bands  in  the  red.  (Part  I.,  fig.  82,  Ba^ 
page  151.)  Barium  salts  are  distinguished  from  those  of  stron- 
tium by  forming  an  insoluble  silicofiuoride  of  barium  when  mixed 
with  silicojluorio  acid ; and  by  yielding  no  immediate  precipi- 
tate wdth  oxalic  acid^  but  the  mixture  on  standing  deposits  tufts 
of  acicular  crystals  of  acid  oxalate  of  barium.  A solution  of 
hyposidphite  of  sodium  occasions  a crystalline  precipitate  of  the 
sparingly  soluble  hyposulphite  of  barium. 

§ II.  Strontium:  Sr"=:87*5,  or  Sr=43'8.  Gr.  2*54. 

(636)  Strontium  is  an  element  much  less  abundantly  diffused 
than  barium,  which  it  closely  resembles  in  properties.  It  is 
found  both  as  carbonate  and  as  sulphate,  and  is  procured  in  the 
metallic  state  in  the  same  way  as  barium,  to  which  it  bears  a 
relation  similar  to  that  existing  between  potassium  and  sodium. 
Strontium  is  a malleable  metal  of  a pale  yellow  colour.  When 
heated  in  the  air,  it  burns  with  a crimson  flame,  emitting  sparks. 
AV ater  is  decomposed  by  it  with  evolution  of  hydrogen : diluted 
nitric  acid  dissolves  it,  but  the  concentrated  acid  is  almost  with- 
out action  even  when  boiled  upon  it. 

(637)  Strontia  (SrO=103'5,  or  SrO=51‘8:  Sp.  Gr.  4-611) 
may  be  obtained  from  its  nitrate  by  ignition.  AYhen  mixed  with 
water  it  slakes,  and  forms  a crystalline  hydrate  (81-0,1120 . 8 PI2O ; 
Bloxam) : these  crystals  require  50  times  their  weight  of  cold 
and  2*4  of  boiling  water  for  solution ; 8 1120-  are  expelled  by 
heat,  the  remaining  atom  being  fixed  at  all  temperatures ; at  a 
full  red  heat  the  latter  hydrate  fuses,  furnishing  a mass  of  sp.  gr. 
3*625 : both  the  hydrate  and  its  solution  absorb  carbonic  acid 
rapidly  from  the  air.  Ho  peroxide  of  strontium  can  be  formed. 

(638)  Chloride  of  Strontium  (SrCl2 . 6 1120=158-5 -f  108, 
or  SrCl,  6 HO=79-3-f  54 ; Sp.  Gr.  anhydrous^  2*96,  cryst.  1*603) 
crystallizes  in  slightly  deliquescent  needles,  which  require  less 
than  tlieir  w-eight  of  cold  water  for  solution ; alcohol  dissolves  it, 
and  the  solution  burns  wdth  a crimson  flame.  Chloride  of  stron- 
tium is  rendered  anhydrous  by  a moderate  heat ; if  heated 
strongly  it  fuses. 

Sihcofluoride  of  strontium  (SrF2,SiF,= 229*5)  is  prepared  by 
adding  hydrofiuosilicic  acid  to  a salt  of  strontium : it  is  tolerably 
soluble  in  water,  thus  furnishing  a character  which  distinguishes 
the  compounds  of  strontium  from  those  of  barium. 

(639)  Sulphate  of  Strontium  (Si*S04  = I83*5,  or  SrO,S03 
= 91*8;  Sp.  Gr.  3*9):  Composition  in  100  pyarts^  SrO,  56*52; 
SOj,  43*48.  — This  substance  is  found  crystallized  in  rhombic 
prisms  isomorphous  with  those  of  sulphate  of  barium;  it  is,  how- 
ever, easily  distinguished  from  it  by  its  lower  density.  Many 
specimens  of  this  mineral  have  a delicate  blue  tint,  whence  it 
derives  its  mineralo<>rical  name  of  celestine : it  often  contains 

O 


406 


NTTEATE  CARBONATE  OF  STRONTIUM. 


crystals  of  native  snlpliur.  Sulphate  of  strontium  is  very  spar- 
ingly soluble  in  water,  but  is  taken  up  by  boiling  sulphuric  acid, 
and  is  soluble  to  some  extent  in  a solution  of  chloride  of  sodium. 
It  may  be  formed  by  mixing  a solution  of  any  sulphate  with  a 
solution  of  a salt  of  strontium. 

(640)  XiTRATE  OF  Strontium  (Sr  2 = 211*5,  or  Sr0,1105 

= 105*8  ; Sp.  Gr.  anhydr.  2*857,  cryst.  2*113)  crystallizes  from  hot 
concentrated  solutions  in  anhydrous  octohedra,  which  are  soluble 
in  5 parts  of  cold  water  and  half  their  weight  of  boiling  water ; 
by  crystallizing  it  at  a low  temperature  it  may  be  obtained  in 
efflorescent  crystals  with  5 H^O.  If  strongly  heated,  it  decrepi- 
tates, and  then  is  decomposed  with  loss  of  oxygen  and  nitrogen, 
leaving  pure  strontia.  It  is  used  by  the  makers  of  tire-works  to 
give  a splendid  crimson  colour  to  their  frames,  and  is  prepared  for 
them  by  reducing  the  native  sulphate  to  sulphide  by  heating  it 
with  charcoal,  dissolving  the  sulphide  in  water,  and  decomposing 
it  with  diluted  nitric  acid.  It  crystallizes  best  from  an  acid  solu- 
tion. A mixture  of  40  parts  of  nitrate  of  strontium  with  from 
5 to  10  of  chlorate  of  potassium,  13  of  sulphur,  and  4 of  sulphide 
of  antimony,  defragrates  with  a magnifrcent  red  colour  ; the  mix- 
tm’e  is  dangerous  both  to  prepare  and  to  preserve,  having  more 
than  once  been  the  occasion  of  frightful  accidents  to  the  manu- 
facturers from  its  becoming  ignited  spontaneously,  hlitrate  of 
strontium  is  insoluble  in  alcohol. 

(641)  Carbonate  of  Strontium  (Sr-G0-3  = 147*5,  orSrO,C02= 
73*8) ; Sp.  Gr.  3*65  : Composition  in  100  parts.^  SrO,  70*2 ; 

29*8.  — This  compound  forms  the  strontianite  of  mineralogists  ; it 
occurs  both  massive  and  crystallized,  near  Strontian  in  Argyle- 
shire,  and  hence  the  name  ‘ strontia’  given  to  the  earth  which  it 
contains.  Mere  ignition  is  insufficient  to  decompose  this  salt.  It 
is  scarcely  soluble  in  water,  but  is  dissolved  by  a solution  of  car- 
bonic acid.  The  process  of  preparing  it  consists  in  precipitat- 
ing a salt  of  strontium  by  the  carbonate  of  one  of  the  alkaline 
metals. 

(642)  CmARACTERS  OF  THE  Salts  OF  Strontium. — The  salts  of 
strontium  with  colourless  acids  are  all  colourless  : they  have  a 
bitter  acrid  taste,  but  are  not  poisonous.  They  are  distinguished 
hefore  the  lloicpipe  by  the  red  colour  which  they  communicate  to 
the  frame.  By  the  spectroscope  they  are  seen  to  furnish  several 
bright  bands  in  the  red  and  orange  part  of  the  spectrum,  and  a 
brilliant  band  in  the  blue.  (Fig.  82,  /Sr,  Part  I.  p.  151.)  The 
frame  of  strontium  to  the  eye  seems  to  have  the  same  colour  as  that 
of  lithium,  but  the  spectra  of  the  two  cannot  be  confounded.  Pe- 
agents  produce  upon  strontium  salts  the  same  effects  as  upon  salts 
of  barium,  excepting  that  neither  silicofluoric  acid  nor  the  hypo- 
sulphite of  sodium  yields  any  precipitate  in  the  solutions  of  the 
salts  of  strontium.  Oxalic  acid  gives  an  immediate  turbidity  in 
them.  The  compounds  of  strontium  are  distinguished  from  those 
of  calcium  by  the  gradual  formation  of  a white  precipitate  on  agi- 
tation after  the  addition  of  a solution  of  sidphate  of  calcium. 
The  sulphate  of  strontium  is  used  for  determining  the  amount  of 


CALCIUM LIME.  407 

strontia  in  analysis ; 100  parts  of  it  correspond  to  50*52  of 
strontia. 


§ III.  Calcium:  Oa^'^lO,  or  Ca=20.  Sj>.  Gr.  1*57. 

(643)  Calcium  forms  one  of  the  most  abundant  and  important 
constituents  of  the  crust  of  the  globe.  It  is  the  metallic  basis  of 
lime,  and  derives  its  name  from  calx^  lime.  Calcium  occurs  in 
nature  in  combination  with  fluorine,  forming  the  different  vari- 
-eties  of  fluor-spar  ; it  is  still  more  abundant  in  the  various  forms 
of  carbonate  of  calcium ; and  it  is  also  met  with  in  large  quanti- 
ties as  gypsum,  w’hich  is  a hydrated  sulphate  of  calcium. 

Calcium  was  obtained  by  Matthiessen  {Q.  J.  Cliem.  8og.  viii.  27) 
by  the  electrolytic  decomposition  of  a mixture  consisting  of  2 
equivalents  of  chloride  of  calcium  and  1 equivalent  of  chloride 
of  strontium.  The  mass  may  be  fused  in  a Hessian  crucible,  in 
the  centre  of  which  is  placed  a porous  tube  filled  with  the  same 
mixture,  and  into  this  an  iron  wire  passed  through  the  stem  of  a 
tobacco-pipe  is  inserted  : this  wire  is  connected  with  the  platinode 
of  the  battery,  the  zincode  of  which  consists  of  a plate  of  sheet- 
iron  bent  into  a cylindrical  form,  and  immersed  in  the  melted 
mass  exterior  to  the  porous  tube : the  calcium  is  reduced,  and 
preserved  from  oxidation  by  so  regulating  the  heat  that  a film  of 
solidified  salt  shall  form  upon  the  surface  of  the  mixture  in  the 
porous  cell.  Lies  Bodart  obtains  it  still  more  easily  by  fusing 
iodide  of  calcium  with  an  equivalent  quantity  of  sodium. 

Calcium  is  a light,  yellowish  metal,  of  the  colour  of  gold  al- 
loyed with  silver;  in  hardness  it  is  intermediate  between  lead  and 
gold ; it  is  very  malleable,  and  can  readily  be  hammered  into 
leaves  thinner  than  writing  paper.  It  melts  at  a red  heat.  At 
ordinary  temperatures  it  tarnishes  within  a day  or  two,  even  in 
dry  air,  and  in  the  presence  of  moisture  it  is  slowly  oxidized. 
When  heated  to  redness  on  platinum  foil,  it  burns  with  a brilliant 
scintillating  white  light.  It  readily  amalgamates  with  mercury  : 
when  heated  in  chlorine,  or  in  the  vapour  of  bromine,  iodine,  or 
sulphur,  combustion  occurs,  accompanied  by  an  extremely  vivid 
light.  Water  is  rapidly  decomposed  by  calcium,  hydrate  of  lime 
being  formed  and  hydrogen  evolved.  Concentrated  nitric  acid 
does  not  attack  the  metal  until  heated  to  the  boiling-point,  though 
it  is  rapidly  dissolved  by  the  diluted  acid.  Matthiessen  found 
that  the  chloride  of  calcium  is  not  decomposed  by  heating  it  with 
potassium  or  sodium ; and  he  concludes  that  the  pro})erties  for- 
merly assigned  to  calcium  were  really  due  to  a mixture  of  potas- 
sium with  aluminum  and  silicon. 

((>44)  Limp;  (OaO  = 50,  or  CaO  = 28) ; A/;.  Gp.  3*18:  Com- 
position in  100  parts,  Oa  71*43  ; O 28*57. — Calcium  forms  only 
one  oxide — viz.,  lime,  which  has  been  known  from  time  immemo- 
rial. It  is  obtained  in  a state  of  purity  by  heating  pure  carbonate 
of  calcium  (054)  to  full  redness;  this  carbonate  occurs  very  nearly 
pure  either  in  black  or  in  Carrara  marble,  which  if  burnt  for  an 
hour  or  two  in  an  open  fire — or,  better  still,  in  a crucible  with  a 


408 


SLAKED  LDLE. 


hole  at  the  bottom — yields  lime  very  nearly  free  from  foreign 
matters.  For  commercial  purposes,  common  limestone,  which  is 
an  impure  carbonate  of  calcinm,  is  burned  in  a kiln,  the  cavity  of 
which  is  usually  egg-shaped.  Over  the  fire-grate  an  arch  is  formed 
with  lumps  of  limestone,  and  the  kiln  is  filled  up  with  smaller 
fragments,  the  fire  is  then  kindled  below,  and  kept  up  continu- 
ously for  three  days  and  nights ; the  kiln  is  then  allowed  to  cool, 
the  lime  is  removed,  and  a fresh  charge  introduced.  A better 
method  is  that  known  as  the  continuous  process.  The  kiln  in 
this  case  is  in  the  form  of  an  inverted  truncated  cone : it  is 
charged  with  alternate  layers  of  coal  and  limestone,  and  the  fire 
is  kindled.  The  lime,  as  it  is  burned,  gradually  sinks  down,  and 
is  removed  by  openings  at  the  base  of  the  furnace,  and  a fresh 
supply  of  coal  and  limestone  is  supplied  at  the  top  of  the  kiln. 
The  limestone  should  not  be  too  dry ; that  which  has  been  quar- 
ried recently  answers  best.  In  damp  weather,  too,  the  operation 
succeeds  better  than  in  a dry  state  of  the  atmosphere ; indeed,  the 
process  is  facilitated  by  injecting  steam  into  the  kiln,  although  in 
practice  the  advantage  which  is  gained  does  not  compensate  for 
the  increased  expense  and  trouble.  In  the  presence  of  aqueous 
vapour  an  interchange  between  the  steam  and  the  carbonic 
anhydi-ide  of  the  limestone  appears  to  be  effected,  and  hydrate  of 
lime  is  fomied ; but  the  hydrate  which  is  produced  is  quickly 
destroyed  again. 

Pure  lime,  or  is  a white  caustic  powder  which 

resists  even  the  heat  of  the  oxyhydrogen  fiame,  and  emits  an 
intense  white  light  when  thus  ignited,  as  is  commonly  seen  in  its 
application  to  the  Drummond  light.  The  extreme  infnsibility  of 
lime  has  led  Deville  to  employ  it  as  a material  for  lining  crucibles 
which  are  to  be  exposed  to  very  intense  heat. 

Hydrate  o f Lime.  Slaked  Lime  (DaO.H^O  = 74,  or  CaO,IIO 
= 37);  Sp.  Gr.  2*078:  Composition  in  iS)t)  parts ^ -GaO,  75*68; 
H^O,  24*32. — AVhen  water  is  poured  upon  lime,  it  swells  up  and 
enters  into  combination  with  the  water ; if  the  proportion  of 
water  be  not  too  great,  a light  di’y  powder  is  formed,  attended 
with  a powerful  extrication  of  heat : so  great  is  the  heat  thus 
developed  that  fires  have  several  times  been  traced  to  this  source. 
The  hydrate  which  is  formed  is  a definite  compound  of  1 atom  of 
water  with  1 of  lime.  Lime,  when  exposed  to  the  air,  slowly 
attracts  both  water  and  carbonic  anhydride ; as  a result  of  this 
action  it  falls  to  powder,  and  becomes  what  is  termed  air  slaked  / 
in  this  case  a compound  is  gradually  formed,  which  is  by  some 
chemists  regarded  as  a combination  of  an  atom  of  carbonate  with 
one  of  hydrate  of  lime  (GaO,0O2 . Ga0,H20). 

Lime  is  soluble  in  about  700  parts  of  cold  water ; this  solu- 
tion is  knovm  as  lime-water ; the  earth,  however,  is  less  soluble 
in  hot  than  in  cold  water,  so  that  if  lime-water  saturated  in  the 
cold  be  raised  to  the  boiling-point,  half  the  lime  is  deposited. 
Lime  is  much  more  soluble  in  syrup  than  it  is  in  water,  the  solu- 
tion in  this  case  also  becomes  turbid  when  heated,  but  clears  again 
as  it  cools.  Lime-water  is  mucli  employed  as  a test  for  the  pre- 


MORTARS  AND  CEMENTS. 


409 


sence  of  carbonic  acid,  which  instantly  renders  it  turbid : it  has  a 
distinctly  alkaline  reaction,  and  an  acrid  taste : by  evaporating  it 
in  vacuo^  Gay-Lussac  obtained  from  it  the  protohydrate  of  lime 
crystallized  in  liexahedral  plates.  Hydrate  of  lime  is  decomposed 
by  a red  heat,  and  pure  lime  remains. 

Milk  of  Lime  is  merely  hydrate  of  lime  diffused  through 
water  : in  slaking  lime  for  its  preparation,  and,  indeed,  generally 
where  small  quantities  of  the  hydrate  are  required  in  a tine  state 
of  subdivision,  it  is  best  to  use  boiling  water  in  quantity  nearly 
equal  to  twice  the  weight  of  the  lime ; the  powder  may  afterwards 
be  readily  diffused  through  cold  water. 

(645)  Mortars  and  Cement. — The  great  consumption  of  lime 
in  the  arts  is  for  the  purpose  of  making  mortars  and  cements. 
Pure  lime,  when  made  into  a paste  with  water,  forms  a somewhat 
plastic  mass,  which  sets  into  a solid  as  it  dries,  but  it  gradually 
cracks  and  falls  to  pieces.  It  does  not  possess  sufficient  cohesion 
to  be  used  alone  as  a mortar ; to  remedy  this  defect  and  to  pre- 
vent the  shrinkage  of  the  mass,  the  addition  of  sand  is  found  to 
be  necessary.  Ordinary  mortar  is  prepared  by  mixing  1 part  of 
lime  into  a thin  paste  with  water,  and  adding  3 or  4 parts  of  sharp 
sand,  of  tolerable  fineness  : the  materials  are  then  thoroughly 
incorporated,  and  passed  through  a sieve  to  separate  lumps  of 
imperfectly  burned  lime : a suitable  quantity  of  water  is  after- 
wards worked  into  it,  and  it  is  then  applied  in  a thin  layer  to  the 
surfaces  of  the  stones  and  bricks  which  are  to  be  united.  The 
bricks  or  stones  are  moistened  with  water  before  applying  the 
mortar,  in  order  that  they  may  not  absorb  the  water  from  the 
mortar  too  rapidly.  The  completeness  of  the  subsequent  harden- 
ing of  the  mortar  depends  mainly  upon  the  thorough  intermixture 
of  the  lime  and  sand. 

The  theory  of  the  hardening  of  mortar  is  obscure.  The  mor- 
tar gradually  becomes  dry  upon  its  surface,  and  at  the  same  time 
it  absorbs  carbonic  anhydride  from  the  air ; but  this  change  is 
never  complete,  for  the  central  portions,  after  a lapse  of  many 
ages,  are  still  found  to  contain  free  lime  in  abundance ; mortar 
taken  by  Dr.  Malcohnson  from  the  Great  Pyramid,  was  still 
found  to  contain  a large  proportion  of  hydrate  of  lime.  A gra- 
dual combination  also  takes  place  between  tlie  lime  and  the  silica 
of  the  sand : each  grain  of  sand  thus  becomes  superficially  con- 
verted into  a hydrated  silicate  of  calcium,  forming  a compound 
wliicli  by  degrees  acquires  considerable  hardness,  and  contributes 
greatly  to  the  solidification  of  the  mortar.  All  old  mortar,  when 
treated  with  an  acid,  yields  a small  proportion  of  gelatinous  silica. 
A mixture  of  carbonate  of  calcium  with  the  lime  apj)ears  to  set 
harder  than  pure  lime  only  ; so  that  for  many  ])urposes  lime  which 
has  been  slaked  by  exposure  to  the  air,  and  contains  a conside- 
rable proportion  of  carbonate,  is  preferred  to  that  slaked  rapidly 
by  water. 

Limestones  vary  greatly  in  composition ; being  rocks  of  sedi- 
mentary origin,  they  are  not  ])ure  chemical  compounds,  but  con- 
sist of  a mixture  of  various  bodies,  in  which  carbonate  of  calcium 


410 


HYDRAULIC  MORTARS. 


is  tlie  prevailing  ingredient.  The  different  varieties  of  limestone 
are  distinguished  according  to  the  nature  of  the  most  important  of 
these  admixtures.  Thus  a limestone  is  described  as  magnesian, 
argillaceous,  ferruginous,  sandy,  or  bituminous,  according  as  it  is 
cliaracterized  by  the  presence  of  carbonate  of  magnesium,  clay, 
oxide  of  iron,  sand,  or  bituminous  matter.  These  different  lime- 
stones, when  burned,  yield  lime  of  very  different  characters, 
which  are  particularly  manifested  by  the  action  of  water  upon 
them.  The  purer  the  lime,  the  more  quickly  does  it  combine 
with  water  when  mixed  with  it.  Such  pure  limes  are  technically 
termed  rich  or  fat  limes  ; when  the  amount  of  impurities  present 
does  not  exceed  10  per  cent,  tiiey  slake  rapidly,  during  which 
operation  they  swell  up  and  greatly  increase  in  bulk ; they 
become  extremely  hot,  and  yield  a soft,  fine,  dense  paste ; while 
those  which  contain  much  magnesia,  silica,  or  alumina,  slake 
slowly,  emit  but  little  heat,  and  are  technically  termed 

In  slaking  for  mortar,  a fine  smooth  paste  is  required : in  order 
to  secure  this  condition,  the  slaking  should  be  effected  quickly, 
with  about  3 parts  of  water  to  1 part  of  lime ; the  mass,  if  com- 
posed of  a fat  lime,  then  swells  to  between  3 and  4 times  its  for- 
mer bulk : if  too  little  water  be  used,  a crystalline  granular 
hydrate  is  formed. 

The  temperature  required  for  burning  lime  varies  with  the 
composition  of  the  limestone.  TThen  a siliceous  limestone  is 
burnt,  the  silica  combines  with  the  lime  if  the  temperature  be 
too  high  and  be  too  suddenly  raised,  and  a coating  of  silicate  forms 
on  the  surface  of  the  mass,  wTich  becomes  partially  vitrified. 
Such  lime  slakes  very  imperfectly,  and  is  said  to  be  dead  hurnt. 
If  ordinary  quicklime  be  mixed  with  a small  quantity  of  sulphate 
of  calcium,  or  if  it  be  re-burnt  at  a dull  red  heat  in  an  atmosphere 
containing  a small  proportion  of  sulphurous  anhydifide,  it  acquires 
the  property  of  setting  slowly  like  stucco  when  mixed  with  cold 
water,  but  if  boihng  water  be  used  it  slakes  like  common  lime. 
Lime  so  prepared  is  known  as  Scotfs  dement. 

(646)  Hydraulic  Mortars. — Ordinary  mortar,  when  placed  in 
water,  becomes  gradually  softened  and  disintegrated,  whilst  the 
lime  is  dissolved  away.  It  cannot  therefore  be  used  for  sub- 
aqueous constructions.  Some  poor  limes,  however,  which  con- 
tain from  15  to  35  per  cent,  of  finely  divided  silica  or  clay,  furnish 
a mortar  which  possesses  the  valuable  property  of  hardening  under 
water,  forming  what  are  termed  hydraulic  limes.  These  limes 
may  be  artificially  imitated  by  mixing  with  the  lime  a due  pro- 
portion of  clay  not  too  strongly  burnt.  At  Puzzuoli,  near  Xaples, 
a porous  volcanic  material,  which  has  received  the  name  oipuzzuo- 
lana^  is  found.  This  substance,  when  powdered  and  mixed  with 
ordinary  lime,  confers  upon  it  the  property  of  yielding  an  excel- 
lent hydraulic  mortar,  which  was  employed  by  the  Romans  in 
many  of  their  buildings,  in  which  it  is  still  in  perfect  preservation, 
having  resisted  the  ravages  of  time  more  perfectly  than  the  bricks 
which  it  was  used  to  cement.  It  is  found  that  a puzzuolana 
which  is  easily  attacked  by  sulphuric  acid  is  more  effective  than 


HrDEAULIC  MOKTAES. 


411 


one  which  resists  the  action  of  the  acid.  The  comparative  value 
of  a puzzuolana  may  also  be  roughly  and  rapidly  estimated  by 
taking  a given  measure  of  lime-water,  and  agitating  it  with  suc- 
cessive small  quantities  of  finely  powdered  puzzuolana  until  the 
alkaline  reaction  disappears ; the  puzzuolana  combines  with  the 
lime  and  abstracts  it  from  the  w^ater.  The  smaller  the  quantity 
of  the  powder  required,  the  more  active  are  its  hydraulic  powers. 
Puzzuolana  consists  chiefiy  of  silicates  of  aluminum,  calcium, 
and  sodium. 

Many  other  substances,  when  added  to  lime,  confer  upon  it 
hydraulic  properties  to  a greater  or  less  extent.  Gelatinous  silica 
shows  it  slightly,  and  a mixture  of  hydrate  of  silica  with  freshly 
precipitated  alumina  or  magnesia  shows  it  in  a remarkable  degree. 
Sand,  oxide  of  iron,  and  oxide  of  manganese,  are  destitute  of  this 
property.  From  a knowledge  of  these  facts  it  is  easy  to  convert 
ordinary  lime  into  one  possessed  of  hydraulic  properties.  Clay  is 
a silicate  of  alumina ; when  it  is  heated  with  lime,  decomposition 
occurs,  the  alumina  is  set  free,  and  silicate  of  lime  is  formed. 
Tlie  materials  are  in  this  way  reduced  to  a condition  suitable  for 
use  as  a hydraulic  cement ; but  great  care  is  required  in  regulat- 
ing the  temperature.  If  it  be  allowed  to  rise  too  high,  partial 
vitrification  occurs,  which  impairs  the  tendency  of  the  cement  to 
combine  with  water ; wdiile,  on  the  other  hand,  if  the  heat  be 
insufficient,  the  alumina  is  not  liberated  from  its  combination  with 
the  silica.  The  immediate  cause  of  the  solidification  of  these 
hydraulic  limes  appears  to  be  the  formation  of  a hydrated  com- 
pound of  lime  with  the  silica  and  alumina,  which  is  very  hard, 
and  insoluble  in  water. 

The  manufacture  of  artificial  hydraulic  lime  was  first  estab- 
lished upon  sound  principles  by  Yicat.  He  proceeds  thus  in  its 
preparation  : — Four  parts  of  chalk  are  ground  and  levigated  in 
water  with  1 part  of  clay,  so  as  to  obtain  a very  intimate  mixture 
of  the  materials,  wdiich  are  allowed  to  subside,  moulded  into 
blocks,  dried,  and  calcined  at  a carefully  regulated  temperature. 
Portland  cement  is  a hydraulic  mortar  similar  to  the  above.  It 
is  made  from  clay  obtained  from  the  valley  of  the  Medway,  and 
from  chalk  found  in  the  same  neighbourhood : it  derives  its  name 
from  the  circumstance  that  in  colour,  when  dry,  it  resembles 
Portland  stone.  It  is  prepared  by  thoroughly  grinding  the  clay 
and  chalk  with  water,  allowing  them  to  subside,  then  drying  and 
burning  the  mixture  until  it  undergoes  slight  vitrification  ; the 
mass  is  again  ground,  and  when  mixed  with  a proper  ])roportion  of 
water  it  forms  a cement  which  possesses  great  hardness  and 
tenacity ; it  expands  as  it  solidifies.  If  in  preparing  this  cement 
the  lime  be  first  burned  and  then  mixed  with  clay  and  reburned, 
it  does  not  require  more  than  a full  red  heat  to  produce  a good 
cement. 

Hydraulic  limes  do  not  slake  with  any  considerable  emission 
of  heat  when  moistened ; they  absorb  the  water  without  increas- 
ing much  in  bulk,  and  form  a paste  of  small  i)lasticity.  In  order 
that  hydraulic  lime  may  harden  properly,  it  must  not  be  sub- 


412 


APPLICATIONS  OF  LIME. 


merged  till  it  begins  to  set ; it  should  then  be  kept  moist  until  it 
is  quite  hard,  otherwise  it  will  always  remain  porous. 

The  rapidity  with  which  these  different  kinds  of  hydi’aulic 
limes  set,  varies  considerably  with  their  composition.  If  the  clay 
do  not  exceed  10  or  12  per  cent,  of  the  weight  of  the  original 
limestone,  the  mortar  requires  several  weeks  to  harden.  If  the 
clay  amount  to  from  15  to  25  per  cent.,  it  sets  in  two  or  three 
days,  and  if  trom  25  to  35  per  cent,  of  clay  be  present,  the  solidifi- 
cation occurs  in  a few  hours.  The  substance  to  which  the  term 
Roman  cement  is  now  applied  is  a lime  of  tliis  latter  description. 
Eoman  cement  is  extensively  prepared  from  nodules  of  septaria 
which  occur  in  the  valley  of  the  Thames.  It  sets  in  a few  hours 
after  the  mixture  with  water  has  been  eflected,  and  it  soon  rivals 
stone  in  hardness.  According  to  eyer,  the  composition  of  the  no- 
dules employed  in  the  preparation  of  the  cement  is  the  following : — 


f Carbonate  of  calcium 66-99 

Matter  soluble  in  acid  J “ magnesium 1'67 

'16-0  j “ iron 6-95 

[Alumina 0*39 

fSmca 16-89 

Insoluble  in  add  (Clay)  Alumina 4-32 

23-305  -(Oxide  of  iron 1-72 

I Lime 0-005 

[Magnesia 0-37 


The  cement  obtained  from  the  neighboimhood  of  Boulogne  is 
almost  identical  in  composition  with  the  foregoing ; and  similar 
materials  have  been  obtained  in  other  countries,  particularly  in 
the  beds  of  the  Jurassic  formation. 

Concrete  is  a mixture  of  hydraulic  mortar  with  small  pebbles 
coarsely  broken. 

(647)  Other  Uses  of  Lime. — Lime  is  also  largely  employed  as 
a manure,  and  it  is  particularly  valuable  upon  very  rich  vegetable 
soils  such  as  those  formed  over  peat  bogs  : its  eftects  in  these  cases 
are  partially  due  to  the  decomposition  of  the  organic  matter, 
which  it  rendem  soluble  and  capable  of  assimilation,  while  the 
lime  itself  is  converted  into  carbonate.  It  has  been  found  that 
limestone  containing  much  carbonate  of  magnesium  yields  a lime 
unsuited  to  agricultural  purposes ; this  has  been  attributed  to  tlie 
fact  that  magnesia  absorbs  carbonic  acid  much  more  slowly 
than  lime,  and  remains  caustic  for  a longer  period,  in  which 
state  it  appears  to  be  injurious  to  the  tender  shoots  of  young  plants. 

The  strong  attraction  existing  between  lime  and  carbo^nic  acid 
renders  it  a valuable  material  for  separating  this  acid  from  the  car- 
bonates of  potassium  and  sodium,  when  these  alkalies  are  required 
in  a caustic  form.  The  attraction  of  lime  for  water  furnishes 
a means  of  removing  this  liquid  from  many  substances,  whicli 
retain  it  with  considerable  force,  such  as  alcohol ; the  finely 
powdered  lime  is  mixed  with  the  alcohol,  and  the  mixture  after 
being  allowed  to  stand  for  a few  days,  with  occasional  agita- 
tion, is  subjected  to  distillation  : the  anhydrous  alcohol  passes 
over,  leaving  the  water  combined  with  the  lime.  Slaked  lime 
is  employed  as  a direct  chemical  agent  in  the  pm’ification 


PHOSPHIDE  OF  CAXCIHM. 


413 


of  coal-gas,  and  as  a means  of  loosening  the  epidermis,  and 
facilitating  the  removal  of  the  hair  from  hides,  as  a preliminarj 
to  the  process  of  tanning. 

Peroxide  of  hydrogen  forms  an  insoluble  compound  with  lime, 
which  is  precipitated  in  crystalline  scales  when  the  peroxide  is 
poured  into  lime-water  : it  is  very  unstable,  and  undergoes  spon- 
taneous decomposition  at  the  temperature  of  the  air.  This  sub- 
stance has  been  described  as  Mnoxide  of  calcium. 

(648)  Sulphides  of  Calcium. — Calcium  forms  several  com- 
pounds with  sulphur,  some  of  which  are  soluble. 

The  protosidphide  of  Calcium  (■0aS=T2)  is  procured  by  de- 
composing a mixture  of  sulphate  of  calcium  and  charcoal  by  heat, 
as  directed  for  sulphide  of  barium.  It  is  insoluble  in  cold  water, 
but  when  treated  with  boiling  water  in  small  proportion  is  con- 
verted into  hydrate  of  lime,  and  a soluble  bisulphide  of  calcium. 
Protosulphide  of  calcium  is  phosphorescent  when  newly  prepared. 
This  property  was  first  observed  by  Canton,  in  an  impure  sulphide 
of  calcium,  which  he  obtained  by  calcining  oyster-shells  in  an 
open  fire  for  half  an  hour,  then  selecting  the  whitest  and  largest 
portions,  and  packing  them  with  one-third  of  their  weight  of 
fiowers  of  sulphur  in  a crucible  with  a luted  cover ; this  w^as 
heated  strongly  for  an  hour : when  cold,  the  crucible  was  broken, 
and  the  whitest  pieces  were  placed  in  well-closed  bottles. 

By  boiling  slaked  lime  with  excess  of  sulphur,  ^ jpentasuljpliide 
of  calcium  is  obtained,  and  hyposulphite  of  calcium  is  formed  at 
the  same  time  : 3 OaO-|-12  8 + 1120=2  0aS5  + 0aS2n204. 

(649)  Phosphide  of  Calcium  (OaP?=Yl). — This  compound 
presents  some  interest,  from  its  afibrding  the  most  convenient 
source  of  some  of  the  phosphides  of  hydrogen  (455).  It  is  pre- 
pared by  distilling  phosphorus  over  lime  heated  to  low  redness : 
a mixture  of  phosphide  and  pyrophosphate  of  calcium  is  the  result, 
7 P + 7 ■0aO=Oa2P2O-, + 5 OaP  (P.  Thenard).  The  most  con- 
venient method  of  conducting  the  operation 
is  shown  in  fig.  337.  In  the  lower  part  of 
a narrow  deep  crucible,  a,  a hole  is  drilled  for 
the  reception  of  the  neck  of  a fiask,  b,  which 
is  luted  into  the  aperture ; a quantity  of  dry 
phosphorus  is  placed  in  the  fiask,  and  the  cru- 
cible is  filled  with  quicklime,  broken  into  frag- 
ments of  about  the  size  of  a hazel-nut ; a lid 
is  then  luted  upon  the  top  of  the  crucible. 

Time  having  been  given  for  the  luting  to 
become  dry,  the  upper  part  of  the  crucible  is 
raised  to  a red  heat  as  quickly  as  possible,  by 
surrounding  it  with  ignited  charcoal,  the  lower 
part  of  the  furnace  having  been  filled  with  cold  charcoal,  to  pre- 
vent the  heat  from  reaching  the  phosjfiiorus  too  rapidly ; the 

Kiorus  becomes  gradually  volatilized  as  the  heat  reaches  it. 

heat  be  too  high,  the  phosphorus  distils  over  without  com- 
bining with  the  calcium. 

Phosphide  of  calcium  when  procured  in  this  manner  forms  an 


Fig.  337. 


SILICTDE  A2sT)  CHLOEIDE  OF  CALCTOI. 


anhydi'ous  mass  of  a dull  red  colour,  hard  enough  to  stiuke  fire 
with  steel : it  experiences  no  change  in  diy  air  or  in  oxygen  at 
the  ordinary  temperature.  At  a high  temperature  it  becomes 
partially  decomposed  by  oxygen,  clilorine,  or  hydrochloric  acid ; in 
a moist  atmosphere  it  slakes,  emits  phosphm'etted  hydi'ogen,  and 
crumbles  to  a brown  powder.  This  powder,  when  tlmown  into 
water,  or  heated  to  212°,  evolves  phosphuretted  hydrogen,  which 
is  not  self-lighting,  and  is  mixed  with  free  hydrogen. 

Phosphide  of  calcium,  in  its  unslaked  form,  is  decomposed 
when  thrown  into  water  ; phosphm’etted  hydrogen  gas  is  evolved, 
and  takes  fire  with  the  phenomenon  already  described  (151)  : 
diluted  acids  produce  its  decomposition  still  more  rapidly. 

(610  6?)  Silicideof  Calcium  (Sfi-Pa).- — ^o\Ac:^{Liehig's  A nnaJ. 
cxxvii.  257),  in  order  to  prepare  this  singular  compound,  directs 
300  grains  of  graphitoid  silicon  to  be  finely  powdered  and  in- 
timately mixed  with  3000  grains  of  chloride  of  calcium  in  a hot 
mortar,  and  to  be  rapidly  shaken  up  in  a wide-mouthed  bottle 
with  350  grains  of  sodium  cut  into  small  pieces:  meantime 
a Hessian  crucible  is  to  be  brought  to  a full  red  heat  in  a good 
wind-fiimace ; a little  fused  common  salt  is  to  be  thrown  into  the 
crucible,  and  upon  this  a mass  of  sodimn  of  350  grains  ; then 
the  mixtiu’e  of  silicon  and  sodium  and  chloride  of  calcium,  and 
the  whole  is  covered  with  a layer  of  pulverized  fused  chloride  of 
sodium  : after  this  the  cover  is  put  on ; the  fire  is  then  gradually 
raised,  and  maintained  for  half  an  hour  at  a temperatm-e  suflicient 
to  melt  cast  iron.  On  Tweaking  the  crucible  after  it  has  cooled, 
the  silicide  of  calcium  ought  to  be  found  in  the  fonn  of  a well- 
fused  button,  which  must  be  preseiwed  in  well-closed  vessels. 

Silicide  of  calcium  has  a leaden-grey  metallic  lustre  and  a 
scaly  crystalhne  structure,  with  an  indistinct  indication  of  hexa- 
gonal plates,  ^hen  ex|30sed  to  the  air  it  slowly  crumbles  down 
into  a mass  of  graphite-like  plates.  If  thi’own  into  water  a simi- 
lar change  occurs,  attended  with  a very  gradual  but  prolonged 
disengagement  of  hydrogen.  This  disintegration  is  due  to  the 
hydration  and  oxidation  of  part  of  the  calcium  and  silicon,  the 
new  products  remaining  mixed  with  some  unaltered  silicide. 
Fuming  nitric  acid  does  not  attack  the  silicide  of  calcium.  Hy- 
drochloric acid,  as  well  as  dilute  &ulphm*ic  and  acetic  acids,  con- 
verts it  into  the  yellow  substance  already  described  (171),  whilst 
hydrogen  escapes. 

Silicide  of  calcium  has,  in  the  hands  of  '^dhler,  proved  a 
source  fi’om  which  he  has  been  enabled  to  procure  various  com- 
pounds of  sihcon,  hydrogen,  and  oxygen,  presenting  some  analogy 
with  the  compounds  of  carbon  with  the  same  elements,  and  wiU 
no  doubt  give  rise  to  further  researclies  of  importance. 

(650)  Chlokide  of  CALcirii  (HaCl,,  6 11,0=111  -f-  lOS.  or 
CaCl,  6 Aq=55’5 -f  51) ; Sp.  Gr.  fused ^ 2'1S5,  cryst.  1’6$0; 
Composition  in  100  parts.  Oa,  36’03  ; Cl,  63’97. — This  salt  is  ob- 
tained as  a secondary  product  in  the  manufacture  of  carbonate 
from  chloride  of  ammonium,  but  it  may  be  prepared  by  dissolving 
chalk  in  hydi’ochloric  acid,  evaporating  to  dryness,  and  fusing  the 


FLUOKIDE  OF  CALCIUM,  OE  FLIJOE-SPAE. 


415 


residue  at  a red  heat.  Under  these  circumstances,  a small  portion 
of  the  chlorine  is  displaced  by  the  oxygen  of  the  air,  so  that  the 
mass  has  an  alkaline  reaction,  owing  to  the  presence  of  lime.  By 
evaporation  of  its  solution  it  may  he  obtained  in  striated  prismatic 
six-sided  crystals  with  6 H^O,  which  fuse  at  84°.  In  this  form  it 
produces  great  depression  of  temperature  when  dissolved  in  water, 
and  if  mixed  with  snow  it  furnishes  a powerful  freezing  mixture. 
If  the  hydrated  salt  be  exposed  to  a prolonged  heat  of  300°  it 
forms  a porous  mass  which  still  retains  2 II^O ; in  this  state  it  is 
well  adapted  for  the  desiccation  of  gases.  Chloride  of  calcium 
is  extremely  deliquescent ; a saturated  solution  of  the  salt  boils  at 
355°,  and  is  sometimes  employed  where  a steady  temperature,  not 
exceeding  this  point,  is  required.  It  is  soluble  in  alcohol,  and 
may  be  obtained  from  its  alcoholic  solution  crystallized  in  rectan- 
gular plates  (-GaClj,  4 O^HgO)  containing  4 atoms  of  alcohol. 
Chloride  of  calcium  absorbs  ammonia  rapidly,  and  forms  a com- 
pound with  8 atoms  of  the  gas.  A solution  of  the  chloride,  if 
boiled  wnth  quicklime  and  hltered  while  hot,  deposits  long,  flat, 
thin  crystals  of  a hydrated  oxychloride,  consisting  of  (■0aCl2  3 
OaO  . 15  H^O),  which  is  decomposed  both  by  water  and  by  alcohol. 

(651)  Fltjoeide  of  Calcium  (OaF2=T8,  orCaF=39);  /Sp.  Gr. 
3'14 ; Composition  in  parts ^ Oa,  51-28 ; F,  48-72. — This  is  an 

abundant  mineral,  well  known  flicor-spar^  which  occurs  either 
massive,  or  crystallized  in  forms  allied  to  the  cube.  It  is  found 
accompanying  the  lead  veins  in  Cumberland,  Derbyshire,  and 
Cornwall,  and  is  met  with  in  a variety  of  other  localities,  of  vari- 
ous colours,  most  frequently  blue,  green,  or  white.  Fluor-spar  is 
the  principal  source  from  which  the  compounds  of  fluorine  are 
obtained.  Fluoride  of  calcium,  in  minute  quantit}",  is  found  in 
sea  water  (Dr.  G.  Wilson),  and  in  many  springs : it  is  a never- 
failing  companion  of  phosphate  of  calcium  in  the  bones  and  teeth 
of  animals,  and  indeed  is  always  found  to  accompany  phosphate 
of  calcium  in  the  mineral  kingdom  also,  in  small  but  variable 
quantities.  Most  varieties  of  fluor-spar,  when  gently  heated,  be- 
come phosphorescent,  emitting  a pale  green  or  violet  light ; if 
heated  more  strongly,  the  crystals  decrepitate,  and  each  fragment 
becomes  enveloped  for  a few  seconds  in  a beautiful  halo  of  light. 
It  loses  this  property  after  having  been  once  heated ; a phospho- 
rescent fluor,  dissolved  in  hydrochloric  acid  and  precipitated  l)y 
ammonia,  retains  its  power  of  emitting  light  when  heated,  but  if 
it  had  been  previously  heated  sufficiently  to  destroy  the  phospho- 
rescence, this  property  is  not  restored  by  solution  and  repre- 
cipitation. 

Powdered  fluoride  of  calcium  absorbs  sulphuric  acid  if  mixed 
with  it  at  a, low  temperature,  and  forms  a transparent,  viscoTis 
mass,  from  which  fumes  of  hydrofluoric  acid  are  evolved  by  heat- 
ing it  to  100°  F.  Fluor-spar  undergoes  no  change  when  heated 
with  sulphuric  anhydride,  but  with  boracic  anhydride  it  yields 
borate  of  calcium  and  fluoride  of  boron  ; 3 OaF^q-  4 I >,03=3  (Ga 
2 BO,)  -f  2 BFg.  Hydrochloric  acid  dissolves  it  in  small  quantity. 
If  heated  in  a current  of  chlorine,  a gas  which  corrodes  glass  is 


416 


SULPHATE  OF  CALCIUM,  OR  PLASTER  OF  PARIS. 


expelled.  It  is  not  known  whether  this  is  fluorine  or  chloride  of 
fluorine.  When  fluor-spar  is  fused  with  the  hydrated  alkalies  it 
undergoes  no  change : with  the  carbonates  of  the  alkali-metals, 
fluoride  of  the  alkaline  metal  and  carbonate  of  calcium  are  formed. 
If  heated  with  sulphate  of  calcium,  it  fuses  and  forms  a glass 
which  is  transparent  when  hot,  but  enamel-white  when  cold.  In 
proper  proportions  it  often  forms  a valuable  flux  in  smelting  the 
ores  of  various  metals,  and  hence  the  ndimefliiar  is  derived,  though 
it  requires  rather  an  elevated  temperature  to  fuse  it  when  heated 
without  any  admixture. 

(652)  Sulphate  of  Calctum  (-GaSO^  = 136),  or  Sulphate  of 
Lime  (Ca0,S03  = 68):  Sj?.  Gr.  2’95  ; Composition  in  100  parts^ 
GaO,  41-18  ; SO3,  58-82  ; crystallized  as  gypsum  (GaSO„  2 li^O  = 
172) ; Sp.  Gr.  2-30 ; v:ater  in  100  parts,  20-93. — This  compound 
occurs  free  from  water  in  the  mineral  anhydrite^  crystallized  in 
rectangular  prisms,  which  are  found  in  the  salt  rocks  of  the  Tyrol, 
and  in  Tapper  Austria ; but  it  is  much  more  abundant  as  a hydrate 
with  2 TI^O : it  is  then  met  with  either  in  transparent  flattened 
prisms,  known  as  selenite^  or  still  more  frequently  in  a flbrous, 
granular,  compact,  or  earthy  form,  constituting  the  different 
varieties  of  gypsum  and  alabaster.  Sulphate  of  calcium  is  a very 
common  impurity  in  spring  water.  Such  waters  are  termed 
selenitic  ; they  deposit  upon  the  interior  of  boilers  in  which  they 
are  used,  a strongly  adherent  fur  or  crust,  the  composition  of 
which  is  2 (GaSG^) . II.^O ; the  sulphate  being  rather  less  soluble 
in  water  at  212°  than  at  ordinary  temperatures. 

Sulphate  of  calcium  is  produced  whenever  a strong  solution  of 
a salt  of  calcium  is  precipitated  by  any  sulphate,  in  which  case  it 
falls  as  a white  voluminous  sparingly  soluble  hydrate,  which 
requires  about  400  parts  of  water  for  its  solution.  It  is  insoluble 
in  alcohol,  but  is  dissolved  to  some  extent  by  diluted  nitric  and 
hydrochloric  acids.  Wlien  heated  it  loses  its  w^ater,  and  if  the 
temperature  be  raised  to  bright  redness,  the  anhydrous  mass  fuses, 
and  may  be  obtained  in  crystals  the  same  in  form  as  those  of 
anhydrite. 

Gypsum  constitutes  a manure  of  considerable  utility  when 
judiciously  employed ; but  the  most  remarkable  property  of  sul- 
phate of  calcium,  and  that  for  which  it  is  chiefly  valued,  is  the 
power  which  the  hycffated  variety  possesses,  after  it  has  been 
deprived  of  water  by  a heat  not  exceeding  500°,  of  again  combining 
with  water,  and  binding  or  setting  into  a hard  mass.  If  the  dry 
powder  be  made  into  a thin  paste  with  water,  the  mixture  becomes 
solid  in  a few  minutes,  expands  perceptibly  at  the  moment  of 
solidiflcation,  and  ex|)eriences  a considerable  rise  of  temperature, 
which  in  large  masses  may  amount  to  40°  or  50°  : a .combination 
of  2 atoms  of  water  with  1 atom  of  sulphate  of  calcium  occurs, 
and  eventually  it  becomes  as  hard  as  the  original  gypsum,  each 
atom  of  the  salt  recombining  with  the  two  atoms  of  water  it  had 
lost.  Gypsum  which  has  been  dried  at  a temperature  of  from 
400°  to  500°  F.  is  converted  into  a white  friable  mass,  which  when 
ground  to  a fine  powder  is  known  in  the  arts  under  the  name  of 


CAEBONATE  OF  CALCIEM. 


417 


'plaster  of  Paris^  from  the  circumstance  of  the  mineral  being 
extensively  found  in  the  environs  of  the  French  metropolis.  It  is, 
liowever,  particularly  worthy  of  observation,  that  if  the  sulphate 
be  heated  to  redness,  it  becomes  very  much  denser,  assumes  a 
crystalline  structure,  and  loses  the  power  of  setting  or  solidifying 
when  mixed  with  water. 

Plaster  of  Paris  is  manufactured  in  large  quantities  for  archi- 
tectural purposes  : it  is  also  extensively  used  in  modelling,  and  in 
taking  accurate  copies  of  objects  of  every  description.  Suppose, 
for  instance,  it  were  desired  to  copy  a medal : a raised  rim  of 
pasteboard  is  attached  to  the  medal,  whicli  is  anointed  with  a little 
oil,  to  prevent  the  plaster  from  adhering  to  its  surface.  The  dried 
plaster  is  then  mixed  with  water  till  it  is  of  the  consistence  of 
thin  cream,  and  is  immediately  applied  carefully  with  a hair 
pencil  to  every  part  of  the  surface,  so  as  to  exclude  air ; after 
which  a thicker  cream  is  poured  into  the  mould : in  a few  minutes 
the  mass  becomes  solid,  and  the  cast  may  be  removed  from  the 
medal. 

The  addition  of  1 or  2 per  cent,  of  many  salts — particularly  of 
alum,  of  sulphate  of  potassium,  or  of  borax — confers  upon  gypsum 
some  properties  of  considerable  practical  importance.  Gypsum 
which  has  been  thus  treated  will  endure  a dull  red  heat  without 
losing  its  power  of  setting  when  mixed  with  water.  It  becomes 
much  denser  than  ordinary  plaster,  and,  when  mixed  with  water, 
sets  in  the  course  of  a few  hours,  and  forms  a hard  material  which 
takes  a high  polish.  Keene’s,  Martin’s,  and  Keating’s  cement 
are  the  respective  names  under  which  plaster  so  treated  is  known. 
Stucco  consists  of  coloured  plaster,  mixed  with  a solution  of  size. 
The  different  colours  exhibited  by  stucco  are  obtained  by  the 
admixture  of  oxides  of  iron  and  other  metals.  By  friction  its 
surface  is  susceptible  of  a high  polish. 

Polyhallite  is  the  mineralogical  name  for  the  sulphate  of 
potassium,  magnesium,  and  calcium  (K20a2Mg  4 2 Il20), 

which  is  sometimes  found  native,  and  has  been  formed  occasion- 
ally during  the  manufacture  of  tartaric  acid.  It  is  decomposed 
by  water. 

Sulphate  of  calcium  also  forms  a double  salt  with  sulphate  of 
sodium,  which  occurs  native  under  the  name  of  glauberite  (Ka^Oa 
2 SO^) ; it  is  anhydrous,  and  nearly  insolnble  in  water. 

(053)  Nitrate  of  Calcium  (Oa  2 NO3  . 4 II^O  = 164  -f  72, 
or  (Ca0,N05 . 4 Aq  = 82  + 36) : Sp.  Gr.  anhydrous^  2*24,  cryst. 
1'780)  is  a deliquescent  salt,  which  crystallizes  in  long  prisms  : 
when  anhydrous  it  emits  light  if  gently  heated.  It  is  soluble  in 
alcohol. 

(654)  Carbonate  of  Lime,  or  Carbonate  of  Calcium  (OaOOg 
= 100,  or  CaO,CO2=50):  Sp.  Gr.  of  Iceland  spar.,  2-72;  of 
Aragonite.,  2*97 ; Gompyosition  in  100 parts,  OaO,  56,  OO^,  44. — 
This  substance  is  one  of  the  most  abundant  com])onents  of  rocks 
and  minerals.  In  the  amorphous  condition,  it  forms  the  different 
varieties  of  limestone,  oolite,  chalk,  and  calcareous  marl ; it  is 
the  principal  constituent  of  corals,  of  the  shells  of  fishes,  and  of 
27 


418 


CALCAEEOrS  WATERS. 


the  eggshells  of  birds ; it  also  enters  in  greater  or  less  quantity 
into  the  hones  of  animals.  In  minute  granular  crystals  it  forms 
the  different  kinds  of  marble,  and  it  is  found  in  a greater  variety 
of  regular  crystalline  forms  than  any  other  known  compound. 
Its  primary  form  is  a rhombohedron,  as  is  seen  in  Iceland  spar, 
but  it  also  occurs  in  the  incompatible  form  of  aragonite,  in  six- 
sided  prisms,  and  is  consequently  dimorphous.  Aragonite  is  iso- 
morphous  with  carbonate  of  strontium,  and  its  crystals  not  unfre- 
quently  contain  small  quantities  of  this  mineral,  the  occurrence 
of  which  it  is  supposed  may  assist  in  determining  the  assumption 
of  the  prismatic  form  by  the  carbonate  of  calcium.  When  arago- 
nite is  heated  it  falls  to  powder,  and  the  grains  are  stated  to 
assume  the  form  of  minute  rhombs.  Carbonate  of  calcium  is 
produced  whenever  a salt  of  calcium  is  precipitated  by  the  addi- 
tion of  an  alkaline  carbonate,  and  if  the  solutions  be  mixed  at  the 
boiling-point,  the  carbonate  falls  in  microscopic  crystals,  having 
the  form  of  aragonite. 

It  is  sometimes  necessary  to  obtain  a perfectly  pure  carbonate 
of  calcium ; for  this  purpose  a solution  of  nitrate  of  calcium  may 
be  mixed  with  an  excess  of  lime-water,  which  precipitates  mag- 
nesia, alumina,  oxide  of  iron,  and  other  metallic  oxides ; the  fil- 
tered solution  is  decomposed  by  the  addition  of  a mixture  of  am- 
monia and  sesquicarbonate  of  ammonium;  the  precipitate  is 
washed  thoroughly,  then  dried,  and  heated  to  low  redness. 

Carbonate  of  calcium  is  decomposed  by  a red  heat,  if  the  gas 
can  freely  escape ; but  in  closed  vessels  it  fuses  without  under- 
going decomposition,  and  on  cooling  becomes  converted  into  a 
granular  crystalline  mass,  like  marble. 

A combination  of  the  carbonates  of  calcium  and  sodium,  inso- 
luble in  water,  was  found  at  Merida,  in  South  America,  and  called 
Gay-LnssiU  (Oa^N’a^  2 OO3 . 5 H^O).  Barytocalcite  (^afia  2 CO3) 
is  a native  double  carbonate  of  calcium  and  barium,  which  crystal- 
lizes in  oblique  prisms. 

(655)  Calcareous  Wate7''s. — Carbonate  of  calcium  is  soluble  in 
pure  water  to  the  extent  of  rather  more  than  2 grains  in  1 gallon, 
but  it  is  freely  taken  up  by  water  charged  with  carbonic  acid,  and 
is  deposited  again  in  anhydrous  crystals  as  the  gas  escapes.  In 
this  way  enormous  masses  of  crystallized  carbonate  of  calcium 
are  formed.  In  the  limestone  hills  of  Derbyshire,  and  in  various 
other  localities,  caverns  occur  in  which  this  phenomenon  is  per- 
petually exhibited;  water  charged  with  carbonic  acid  and  car- 
bonate of  calcium  makes  its  way  through  the  roof  of  the  cavern, 
where,  as  the  carbonic  acid  gradually  escapes,  the  carbonate  of 
calcium  is  deposited  in  dependent  masses,  like  icicles,  termed 
stalactites',  whilst  the  water  falling  on  the  floor  of  the  cavern 
before  it  has  parted  with  all  its  excess  of  carbonic  acid  and  dis- 
solved limestone,  deposits  a fresh  portion  of  the  crystalline  matter ; 
and  thus  a new  growth,  or  stalagmite^  gradually  rises  up  to  meet 
the  stalactite  which  depends  from  the  roof : in  this  way  a natural 
pillar  of  crystallized  carbonate  of  calcium  is  formed. 

It  is  in  a similar  manner  that  the  calcareous  deposits  from 


Clark’s  soap-test. 


419 


the  lakes  of  volcanic  districts  are  produced.  These  deposits, 
when  porous,  have  received  the  name  of  tufa  / when  more  com- 
pact, they  are  termed  travertine.  Travertine  is  formed  abun- 
dantly in  many  of  the  Italian  lakes  ; it  was  highly  valued  for 
architectural  purposes  by  the  Homans,  as  it  is  a material  easily 
wrought,  and  possesses  great  durability  and  beauty. 

Many  spring  waters  contain  carbonate  of  calcium  held  in 
solution  by  carbonic  acid : when  the  water  is  boiled  this  acid  is 
expelled,  and  the  carbonate  is  deposited,  forming  a lining  more 
or  less  coherent  upon  the  sides  of  the  vessel.  In  steam  boilers 
this  becomes  a serious  evil : it  is  effectually  prevented  by  the 
addition  of  a small  cpiantity  of  soda-ash  or  of  sal  ammoniac  to  the 
water ; in  the  latter  case  carbonate  of  ammonium  is  formed,  and 
volatilized,  while  the  chloride  of  calcium  remains  dissolved. 

Dr.  T.  Clark  has  introduced  a plan  for  softening  such  calcare- 
ous waters,  by  removing  the  carbonic  acid  from  them,  and  caus- 
ing the  precipitation  of  the  carbonate  of  calcium  by  thus  depriv- 
ing it  of  its  solvent.  This  method  consists  essentially  in  the 
addition  of  milk  of  lime  to  such  waters,  until  the  water  gives  a 
very  faint  brown  tinge  on  testing  it  with  a solution  of  nitrate  of 
silver : this  reaction  indicates  that  a slight  excess  of  lime  has 
been  added,  which  occasions  a precipitate  of  brown  hydrated 
oxide  of  silver.  In  this  operation  the  lime  combines  with  the 
excess  of  carbonic  acid  in  the  water : the  carbonate  of  calcium 
thus  formed,  being  insoluble,  is  precipitated  along  with  a portion 
of  carbonate  of  calcium  previously  held  in  solution  by  the  car- 
bonic acid.  After  the  lapse  of  twenty-four  hours  the  water  be- 
comes perfectly  bright  and  clear.  If  colouring  or  organic  matters 
be  present  in  the  water,  a considerable  portion  of  both  goes  down 
with  the  chalk.  In  applying  this  process  upon  a large  scale,  it  is 
found  advantageous  to  add  a slight  excess  of  lime  in  the  first  in- 
stance, and  afterwards  to  destroy  this  excess  by  a fresh  addition 
of  unlimed  water.  The  carbonate  is  then  separated  in  granular 
crystals,  which  speedily  subside.  These  crystals  are  formed  much 
more  slowly  if  the  lime  be  not  first  in  slight  excess."^ 

* Dr.  Clark  has  introduced  a method  of  testing  the  hardness  of  water  by  the 
application  of  the  Soap-test^  which  has  been  extensively  used.  The  operation  may  be 
conducted  in  the  following  manner: — 

A solution  of  soap  in  proof  spirit  (containing  about  120  grains  of  curd  soap  to  the 
gallon)  is  first  prepared.  In  order  to  graduate  this  solution,  16  grains  of  Iceland 
spar,  or  Carrara  marble,  are  dissolved  in  a flask  in  pure  hydrochloric  acid,  evaporated 
to  dryness  in  the  fiask,  redissolved  in  water,  and  a second  time  evaporated  to  dry- 
ness. On  again  dissolving  it  in  water,  a perfectly  neutral  solution  of  chloride  of 
calcium  is  obtained ; this  solution  is  then  diluted  with  distilled  water  until  it  mea- 
sures 1 gallon.  It  will  now  represent  a water  of  16°  of  hardness;  that  is  to  say,  it 
will  correspond  in  hardness  to  a water  containing  16  grains  of  carbonate  of  calcium 
per  gallon,  each  degree  of  hardness  upon  Clark’s  scale  representing  an  amount  of  any 
salt  of  calcium  corresponding  to  1 grain  of  chalk  per  gallon  in  the  water.  1000 
water-grain  measures  of  this  solution  are  next  transferred  by  a pipette,  graduated  to 
deliver  exactly  this  quantity,  into  a bottle  which  will  hold  5 ounces,  and  accurately 
fitted  with  a glass  stopper.  The  soap  solution  is  then  added  to  the  water  from  a 
burette,  each  division  of  which  corresponds  to  1 0 water-grains.  After  eacli  addition 
of  the  soap-test,  the  stopper  is  replaced  in  the  bottle,  and  the  bottle  is  briskly  shaken 
for  a minute,  after  which  it  is  laid  upon  its  side ; fresh  portions  of  the  soap  being 
added  in  small  quantities  until  a fine  lather  in  uniform  small  bubbles  remains  un- 


420 


BUILDING  MATERIALS. 


(656)  Bulldog  Materials. — Carbonate  of  calcium  forms  tbe 
basis  of  some  of  the  materials  most  biglily  prized  for  building 
purposes,  besides  furnishing  the  costly  varieties  of  marble  used 
for  interiors.  The  oolites,  such  as  those  from  the  Isle  of  Portland, 
and  the  neighbourhood  of  Bath,  resist  the  weather  admirably ; 
they  admit  of  being  readily  fitted  and  cut,  and  yet  possess  con- 
siderable hardness.  Many  shelly  limestones  are  also  well  adapted 
for  these  purposes.  Where  elaborate  carving  is  required,  a well- 
crystallized  magnesian  limestone  (or  double  carbonate  of  calcium 
and  magnesium),  such  as  that  employed  in  the  new  Houses  of 
Parliament,  is  preferred ; it  is  very  close  and  compact,  suificiently 
soft  to  be  easily  sculptured,  but  retains  a sharp  outline.  Many 
fine-grained,  porous,  calcareous  and  magnesian  stones  have  the 
inconvenience  of  splitting  into  fiakes  after  a few  years’  exposure  ; 
this  generally  occurs  from  the  absorption  of  water,  and  its  expan* 
sion  when  the  moisture  thus  absorbed  becomes  frozen  during 
winter.  A simple  and  ingenious  mode  of  ascertaining  whether  a 
building  stone  is  liable  to  this  defect  was  invented  by  Brard  : — It 
consists  in  taking  a smoothly  cut  block  of  the  stone,  one  or  two 
inches  in  the  side,  and  placing  it  in  a cold  saturated  solution  of 


broken  over  the  surface  for  three  minutes.  The  number  of  measures  of  the  soap-test 
employed  is  noted,  and  the  strength  of  the  solution  is  increased  or  diminished  by  the 
addition  of  soap  or  of  spirit,  as  may  be  necessary,  until  exactly  32  measures  are 
required  for  1000  water-grains  of  the  standard  solution  of  16°  of  hardness.  After 
the  solution  has  been  made  up  to  this  strength,  the  experiment  is  repeated,  in  order 
to  ascertain  that  the  adjustment  is  correct. 

In  applying  the  test,  1000  measured  grains  of  the  water  to  be  examined  are  intro- 
duced into  the  stoppered  bottle,  and  the  operation  is  proceeded  with  as  above 
directed,  reading  off  the  number  of  test-measures  required,  in  order  to  produce  a 
permanent  lather.  The  degree  of  hardness  of  the  water  is  then  obtained  by  simple 
inspection  of  the  subjoined  table.  The  results  are,  however,  apt  to  be  inaccurate,  if 
large  quantities  of  magnesian  salts  are  present.  (D.  Campbell.  Phil.  Mag.  1850, 
xxxvii.  171.)  Sometimes  the  water  exceeds  16°  in  hardness;  in  that  case  it  should 
be  diluted  with  an  equal  measure,  or,  if  necessary,  with  twice,  or  even  with  thrice  its 
bulk  of  distilled  water.  1000  grain-measures  of  the  diluted  water  are  then  to  be 
tested  as  usual,  and  the  number  of  divisions  of  the  soap-test  employed  is  to  be  read 
off,  and  the  degree  of  hardness  corresponding  to  it  is  noted  from  the  table.  This 
degree  must  be  finally  multiplied  by  2,  by  3,  or  by  4,  according  to  the  extent  to 
which  the  water  had  been  previously  diluted. 


Clark's  Table  of  Hardness  of  Water. 
Degree  of  hardness.  Measures  of  soap-test. 


Diff.  for  the  next 
1°  of  hardness. 


0 (Distilled  water)  1‘4 

1 3-2 

2 5-4 

3 7-6 

4 9-6 

5 11-6 

6 13-6 

7 15-6 

8 17-5 

9 19-4 

10  21-3 

11  23-1 

12  24-9 

13  26-7 

14  28-5 

15  30-3 

16  32-0 


1-8 
2-2 
2-2 
2 0 
2-0 
2-0 
2-0 
1-9 
1-9 
1-9 
1-8 
1-8 
1-8 
1*8 
1-8 
1-7 


PHOSPHATES  OF  CALCIUM. 


421 


sulphate  of  sodium.  The  temperature  of  the  solution  is  gradually 
raised  to  the  boiling-point,  it  is  allowed  to  boil  for  half  an  hour, 
and  then  the  stone  is  left  to  cool  in  the  liquid.  When  cold,  it  is 
suspended  over  a dish,  and  once  a day  for  a week  or  a fortnight 
plunged  for  a few  moments  into  a cold  saturated  solution  of  the 
sulphate  of  sodium,  and  is  then  again  freely  suspended  in  the  air. 
The  sulphate  of  sodium  crystallizes  in  the  pores  of  the  stone,  and 
splits  off  fragments  of  it.  A similar  experiment  is  made  upon  an 
equal  sized  mass  of  stone  which  is  known  to  be  free  from  this 
defect.  By  the  comparative  weight  of  these  fragments  in  the 
two  cases  the  tendency  of  the  stone  to  the  defect  in  question  may 
be  estimated. 

A stone  which  is  placed  in  a building  conformably  to  its  posi- 
tion in  the  quarry,  so  that  its  seams  shall  lie  horizontally,  is  much 
less  liable  to  injury  from  the  weather  than  where  this  point  is 
neglected. 

In  the  selection  of  a building-stone,  regard  must  be  had  not 
merely  to  its  durability,  but  also  to  the  locality  in  which  it  is  to 
be  placed.  A stone  which,  like  a magnesian  limestone,  may  en- 
dure unchanged  for  ages  in  the  open  country  air,  may  yet  in  the 
atmosphere  of  a large  city  become  rapidly  disintegrated,  owing 
to  the  action  of  the  sulphuric  acid  produced  by  the  immense  quan- 
tities of  coal  which  are  burned.  Decay  from  this  cause  is  strik- 
ingly shown  in  the  stone  used  in  some  parts  of  the  new  Houses 
of  Parliament,  and  still  more  so  in  the  new  buildings  in  Lincoln’s 
Inn. 

A valuable  report  upon  the  composition  and  quality  of  vari- 
ous kinds  of  building  stones  was  made  to  the  British  Government 
in  1839,  upon  the  occasion  of  the  rebuilding  of  the  Houses  of 
Parliament. 

The  other  varieties  of  building  stones  are  mostly  siliceous. 
To  this  class  belong  all  the  sandstones,  which  consist  chiefly  of 
grains  of  silica  united  by  a cement  more  or  less  ferruginous.  The 
durability  of  the  stone  depends  mainly  upon  the  character  of  this 
uniting  material.  Many  igneous  rocks,  such  as  porphyry,  basalt, 
and  more  especially  granite,  are  also  used  for  building  purposes  ; 
but  from  their  hardness,  they  are  seldom  wrought,  except  when, 
as  in  quays,  bridges,  or  causeways,  the  constant  wear  is  unusually 
great,  and  where  softer  though  less  expensive  materials  would  soon 
be  destroyed. 

(057)  Phosphates  of  Calctievi. — The  most  remarkable  of  the 
phosphates  of  calcium  is  that  known  as  the  bone  jiliosjpliate 
2 PO„  or  3 CaG,PO, ; Comp,  in  100  parts,  OaO,  54-2  ; P2^5, 
45'8),  so  named  from  its  forming  the  principal  earthy  constituent 
of  the  animal  skeleton.  It  is  easily  procured  by  adding  chloride 
of  calcium,  drop  by  drop,  to  a solution  of  phos[)hate  of  sodium  in 
excess,  when  it  falls  as  a gelatinous  preci])itate  witli  2 1 1^0.  It 
may  also  be  obtained  from  calcined  bones  by  digesting  tliem  in 
nitric  acid,  and  precipitating  the  filtered  solution  l)y  caustic 
ammonia.  This  phosphate  is  insoluble  in  water,  but  is  readily 
dissolved  by  acetic,  and  the  stronger  acids.  It  occurs  native  as  a 


422 


CHAKACTEES  OF  THE  SALTS  OF  CALCIUM. 


white  amol’phoHS  mineral,  known  under  the  name  of  phosphoAte . 
In  the  Xoilolk  crag  considerable  deposits  of  brown  rounded 
pebbles  occur,  known  under  the  name  of  coprolites^  from  the 
erroneous  supposition  that  they  were  the  fossibzed  dung  (xcrrpo^) 
of  extinct  animals : they  contain  a large  proportion  of  phosphate 
of  calcium  mixed  with  carbonate  and  fluoride  of  calcimn.  Li 
the  green-sand  formation  near  Farnham.  and  in  other  localities, 
nodules  chiefly  composed  of  phosphate  of  calcium  are  also  foimd 
abundantly. 

A trihasic  phosphate  of  calcium  occurs  naturally  crystallized 
in  hexacronal  prisms,  which,  when  colomless.  are  called  apatite  j 
when  ot‘  a green  colour  it  is  tenued  moroxite  : in  these  minerals 
three  atoms  of  the  phosphate  are  associated  with  one  atom  of 
chloride  and  fluoride  of  calcium : 3 (-0a3  2 PO^),  -Ga  (CIF).  If 
hone-ash  he  fused  with  about  4 times  its  weight  of  chloride  of 
sodium,  and  allowed  to  cool  very  slowly,  delicate  crystals  having 
the  foiTu  of  apatite  are  found  lining  the  cavities  contained  in 
the  mass  (Forchhammer).  ^Wken  rhombic  phosphate  of  sodium 
in  solution  is  added  drop  by  drop  to  an  excess  of  chloride  of  cal- 
cium, a semi-ciwstalline  precipitate  falls,  which,  according  to  Ber- 
zelius. consists  of  (2  Ga'  HPO,.  3 H„0). 

Several  other  phosphates  of  calcium  may  he  formed,  cori'e- 
sponding  in  composition  to  the  various  phosphates  of  sodium. 
The  soluble  acid  phosphate,  or  superphosphate  of  lime  (Ga"II^ 
2 PO^,  or  CaO,  2 IIO.PO.).  is  prepared  by  treating  hone-earth 
with  two-thirds  of  its  weight  of  oil  of  vitriol,  as  in  the  prelimin- 
ary stage  of  the  extraction  of  phosphorus.  It  is  largely  manu- 
factured as  a manure  for  turnips. 

(65S)  A double  horate  of  calcium  and  sodium,  or  horo-^iatro- 
calcite,  [2  ( AaGa"  3 BO^)  3 B^Oj . IS  H„0],  is  found  at  Iquique,  in 
PeiTi,  in  the  form  of  rounded  nodules,  composed  of  tine  silky 
needles.  It  is  hut  sparingly  soluble  in  hot  water,  to  which  it 
communicates  an  alkaline  reaction ; but  it  is  easily  dissolved  by 
diluted  acids.  This  mineral  has  recently  been  imported  into  this 
country  to  some  extent  for  the  preparation  of  borax,  which  is 
easily  obtained  from  it  by  dissolving  the  compound  in  hot  diluted 
hydrochloric  acid,  and  precipitating  the  calcium  as  carbonate  by 
the  addition  of  carbonate  of  sodium  ; the  clear,  supernatant  liquid 
on  evaporation  yields  crystals  of  borax,  whilst  chloride  of  sodium 
remains  in  solution. 

(659)  Characters  of  the  Salts  of  Calcium. — The  salts  of 
calcium  are  colomless.  They  give  no  precipitate  with  ammonia^ 
but  yield  a white  precipitate  of  carbonate  of  calcium,  with  the 
carhonates  of  the  alkali-metals.  Solution  of  sulphate  of  calcium 
produces  no  precipitate ; the  calcium  salts  are  thus  distinguished 
from  those  of  barium  and  strontium : they  yield  no  precipitate 
with  hydrosulphate  of  am iram  i um . Oxalate  of  arrimon  i um , even 
in  very  dilute  neutral  or  alkaline  solutions  of  salts  of  calcium, 
throws  down  a white  oxalate  of  calcium,  which  is  soluble  in  nitric 
and  hydrochloric  acids,  but  not  in  acetic  acid.  Salts  of  calcium 
give  a greenish-yellow  tinge  to  flame,  and  when  examined  by  the 


METALS  OF  THE  EARTHS. 


423 


spectroscope  may  be  recognised  by  a bright  line  in  the  orange, 
and  a broad  rather  less  Inminons  band  in  the  green ; fainter  lines 
are  also  visible  in  the  red ; and  occasionally  a bright  blue  band  is 
seen. 

Estimation  of  Calcium. — In  the  determination  of  calcium  for 
analytical  purposes  the  oxalate  is  the  precipitate  usually  employed ; 
but  before  Aveighing  it  is  heated  to  dull  redness,  so  as  to  convert 
the  oxalate  into  carbonate  of  calcium  : 100  parts  of  the  carbonate 
represent  56  of  lime.  If  no  other  base  be  present,  calcium  may 
also  be  estimated  in  the  form  of  sulphate.  If  the  calcium  be  not 
already  in  the  state  of  sulphate,  the  salt  is  heated  with  an  excess 
of  sulphuric  acid,  and  ignited ; when  cold,  it  is  weighed : 100 
grains  of  sulphate  of  calcium  represent  41-18  of  lime. 

Magnesium  will  be  described  in  the  group  containing  zinc  and 
cadmium  (683  et  seq.). 


CHAPTEE  XIY. 

GROUP  m. METALS  OF  THE  EARTHS. 

§ I.  Aluminum  : EV"  = 2Y-5,  or  A1  = 13-7.  Sp.  Gr.  from 
2-5  to  2-67.  8p.  Heat^  0*2143.  Electric  Conductivity  at  67°-2, 
33*76.  Atomic  Yol.  solid^  10*56. 

(660)  The  pure  earths  are  white,  insipid,  insoluble  compounds, 
the  oxides  of  metals  which  possess  a high  attraction  for  oxygen. 
A single  oxide  only  of  each  metal  of  this  class  is  known,  except 
in  the  case  of  cerium.  (See  p.  290.) 

Of  these  metals  the  most  abundant  and  important  is  aluminum, 
which  derives  its  name  from  alum,  into  the  composition  of  which 
it  enters.  Indeed,  alumina  (the  oxide  of  aluminum)  constitutes 
about  10  per  cent,  of  this  salt. 

Preparation.  — 1.  Aluminum  was  originally  procured  by 
Wohler,  by  decomposing  chloride  of  aluminum  in  a porcelain  or 
platinum  tube  by  means  of  potassium.  He  obtained  it  first  as  a 
steel-grey  powder,  and  subsequently  in  malleable  globules.  In 
tlie  pulverulent  form  it  is  gradually  oxidized  by  boiling  water, 
and  more  rapidly  by  alkaline  solutions.  When  heated  in  this 
form  in  oxygen  gas,  it  takes  fire  and  burns  with  a vivid  light, 
emitting  so  intense  a heat  as  to  fuse  the  alumina,  which  forms  a 
yellowish  mass,  in  colour  and  hardness  resembling  native  crystal- 
lized alumina  as  it  exists  in  corundum. 

2. — Bunsen  obtains  aluminum  by  the  electrolytic  decomposition 
of  the  double  chloride  of  sodium  and  aluminum  (2  NaCl,AhCh). 
This  salt  melts  at  about  356°,  and  readily  furnishes  aluminum  by 
a process  similar  to  that  adopted  in  the  case  of  magnesium  (683) : 
but  as  the  aluminum  is  heavier  than  the  fused  salt,  it  is  more 
easily  collected  than  magnesium. 


424 


aloiin-oj:. 


3.  — Alnminiim  may  be  prepared  in  tlie  laboratory,  by  tbe 
method  of  Deville  (Ann.  de  Chiraie.,  III.  xliii,  5). — Into  a wide 
tube  of  hard  glass  of  an  inch  or  an  inch  and  a half  in  diameter, 
abont  half  a pound  of  dry  chloride  of  aluminum  is  introduced,  and 
kept  in  its  jdace  by  pings  of  asbestos  ; a ciuTent  of  dry  hydrogen, 
perfectly  free  from  air,  is  transmitted,  and  the  chloride  of  alnmi- 
nnm  is  yery  gently  heated ; in  this  way  traces  of  hydrochloric 
acid  and  chlorides  of  snlphnr  and  silicon  are  expelled.  Three  or 
fonr  small  porcelain  trays,  each  containing  40  or  50  grains  of  so- 
dium, freed  from  adhering  naphtha  by  pressure  between  folds  of 
blotting-paper,  are  then  introduced  into  the  tube  ; the  current 
of  hydrogen  is  still  maintained,  and  heat  is  applied  to  the  part 
of  the  tube  which  contains  the  sodium.  This  end  of  the  tube 
must  be  slightly  eleyated,  in  order  to  preyent  the  melted  chloride 
of  aluminum  from  running  down  upon  the  sodium  ; in  which  case 
the  heat  emitted  is  so  intense  as  to  crack  the  tube.  TThen  the 
sodinm  is  melted,  the  chloride  of  aluminum  is  gradually  distilled 
oyer  by  the  application  of  a regulated  heat,  and  is  reduced  with 
w^ud  incandescence.  The  aluminum  is  condensed  in  the  porce- 
lain trays,  in  which  also  a double  chloride  of  aluminum  and  sodium 
collects  around  the  reduced  aluminum.  These  trays  and  their 
contents  when  cold  are  withdrawn  from  the  glass  tube,  and  placed 
in  a porcelain  tube  through  which  a current  of  hydi-ogen  is  trans- 
mitted, whilst  the  tube  is  raised  to  a bright  red  heat ; the  alumi- 
num fuses  into  globules  in  the  porcelain  trays  ; and  by  fusing  it 
once  more  in  a porcelain  crucible  under  a layer  of  the  double 
chloride  of  aluminum  and  sodium,  a button  of  pui*e  aluminum  is 
obtained. 

Messrs.  Bell  of  Newcastle  haye  carried  out  the  process  of  De- 
^ulle  as  a manufacturing  operation.  They  prepare  an  aluminate 
of  sodium  from  Bauxite,'  an  aluminous  ore  of  iron  (663),  and  pre- 
cipitate the  alumina  as  hydrate,  by  means  of  hydrochloric  acid. 
The  precipitated  hydrate  of  alumina  is  then  mixed  with  common 
salt  and  charcoal,  made  into  balls  the  size  of  an  orange,  and  dried. 
These  balls  are  placed  in  yertical  earthen  retorts  heated  to  red- 
ness, and  through  them  dried  chlorine  is  transmitted.  A double 
chloride  of  aluminum  and  sodium  (2  XaCl,Al2Cl5)  distils  oyer. 
This  double  salt  is  heated  with  sodium  in  a reyerberatory  fimnace, 
and  the  aluminum  collects  at  the  bottom  in  a melted  fonn,  while 
the  chlorine  is  remoyed  by  combination  with  the  sodium. 

4.  — Bose  obtains  aluminum  from  cryolite  (3  AaF.AlFj)  by 
fusing  it  with  sodium.  For  this  purpose  Mohler  recommends 
7 parts  of  chloride  of  sodium  to  be  melted  with  9 of  chloride  of 
potassium,  and  the  mass  thus  furnished  to  be  finely  powdered 
and  intimately  mixed  with  its  own  weight  of  cryolite  in  fine 
powder.  This  powder  is  to  be  introduced  with  a fifth  or  a sixth 
of  its  weight  of  sodium  (arranged  in  alternate  layers  of  the  powder 
and  the  metal),  into  a dry  earthen  crucible,  which  is  to  be  heated 
rapidly  in  a wind  furnace.  An  intense  reaction  occurs,  and  a 
portion  of  the  sodium  bimis  off.  The  mixture  is  then  heated  for 
about  a cpiarter  of  an  hour  until  it  is  in  liquid  fusion,  and  is  then 


ALTBriNA. 


425 


allowed  to  cool.  The  aluminum  generally  collects  at  the  bottom 
into  a well-formed  button,  which  is  frequently  crystalline  on  its 
surface.  In  some  experiments  the  quantity  of  reduced  metal 
amounted  to  one-third  of  the  proportion  present  in  the  mineral 
employed. 

(661)  Propeidies. — As  prepared  byDeville’s  process,  aluminum 
is  a white  malleable  metal,  nearly  resembling  zinc  in  colour  and 
liardness  : it  may  be  rolled  into  very  thin  foil,  and  admits  of 
being  drawn  into  tine  wire  ; after  it  has  been  rolled,  it  becomes 
much  harder  and  more  elastic.  It  conducts  electricity  with  about 
one-third  the  power  of  silver.  Aluminum  is  remarkably  sonorous, 
and  emits  a clear  musical  sound  when  struck  with  a hard  body. 
Fused  aluminum  crystallizes  readily  as  it  cools,  apparently  in  re- 
gular octohedra ; its  point  of  fusion  is  below  that  of  silver..  It 
may  be  heated  intensely  in  a current  of  air  in  a muffle  without 
undergoing  more  than  a superficial  oxidation,  and  it  is  but  slowly 
oxidized  when  heated  to  full  redness  in  an  atmosphere  of  steam. 
When  heated  in  the  form  of  foil  with  a splinter  of  wood  in  a 
current  of  oxygen,  it  burns  with  a brilliant  bluish-white  light. 

nitric  acid,  whether  concentrated  or  diluted,  is  without  action 
upon  aluminum  at  the  ordinary  temperature,  and  dissolves  it  very 
slowly  even  when  boiled  upon  the  metal.  Hydrochloric  acid,  on 
the  contrary,  both  when  concentrated  and  when  diluted,  attacks 
it  rapidly,  forming  chloride  of  aluminum,  whilst  hydrogen  is  dis- 
engaged. Solutions  of  the  alkalies,  especially  when  aided  by 
heat,  also  attack  aluminum  with  energy,  producing  alumina, 
which  is  dissolved  by  the  alkaline  solution,  whilst  hydrogen  gas 
is  liberated.  From  its  lightness  and  inalterability  in  the  air, 
aluminum  has  been  applied  to  the  preparation  of  small  weights : 
but  some  difficulty  is  experienced  in  working  the  metal  for 
want  of  a suitable  solder.  It  is  chiefly  used  for  ornamental 
articles. 

Aluminum  readily  forms  alloys  with  copper,  silver,  and  iron, 
but  it  may  be  melted  with  lead,  without  any  combination  between 
the  two  metals  taking  place.  Its  alloys  with  copper  are  very 
hard,  and  susceptible  of  a high  polish  ; they  vary  in  colour  from 
white  to  golden  yellow,  according  to  the  proportion  of  the  two 
metals : one  of  these,  a beautiful  alloy  of  a golden  yellow  colour, 
containing  about  10  per  cent,  aluminum,  is  manufactured  by 
Messrs.  Bell  under  the  name  of  alitminum  hronze.  Copper  of  high 
purity  is  needed.  Aluminum  also  combines  readily  with  carbon 
and  silicon,  forming  greyish,  granular,  brittle,  and  crystalline 
compounds,  which  present  a considerable  analogy  to  cast  iron. 
It  does  not  combine  with  mercury. 

Finely  divided  aluminum  burns  brilliantly  in  the  vapour  of 
sulphur,  and  forms  a black  sulphide  (Al^Sg),  of  semi-metallic  ap- 
pearance, which  is  rapidly  decomposed  by  water,  with  formation 
of  hydrate  of  alumina  and  sulphuretted  hydrogen. 

(662)  Alumina  (Al^Og  = 103,  or  Al/)3  = 51-5);  Sp.  Gr.  of 
Tu})]p  3*95  ; Composition  in  \i)i)  parts 53*39;  O,  46*61. — This 
is  the  only  known  oxide  of  aluminum  : from  its  isomorphism  with 


426 


ALTJMIN’A. 


the  sesqiiioxide  of  iron,  and  its  general  resemblance  to  it  in  pro- 
perties, it  is  regarded  as  a sesqnioxide.  It  forms  one  of  the 
materials  that  enter  most  largely  into  the  composition  of  the 
superficial  strata  of  the  earth.  It  is  the  basis  of  all  the  varieties 
of  clay,  and  is  present  in  greater  or  less  quantity  in  almost  every 
soil.  Alumina  occurs  nearly  pure,  and  crystallized  in  six-sided 
prisms,  in  comndum^  in  which  mineral  it  has  a specific  gravity  of 
3*95,  and  is  hard  enough  to  cut  glass.  The  sapphire  and  the 
rvhy  are  also  composed  of  this  earth,  tinged  with  a small  quantity 
of  oxide  of  chromium.  They  are  only  inferior  to  the  diamond  in 
hardness.  Emery ^ which  from  its  hardness  is  so  largely  used  in 
grinding  and  polishing,  after  it  has  been  powdered  and  levigated, 
is  another  form  of  alumina,  coloured  with  oxides  of  iron  and 
martganese. 

In  order  to  obtain  alumina,  it  is  sufficient  to  ignite  pure  am- 
monia alum  2 SO^,  12  H^O)  intensely  for  some  time  ; 

the  water,  ammonia,  and  sulphuric  acid  are  expelled,  and  anhy- 
drous alumina  is  left,  in  the  proportion  of  11*34  parts  of  alumina 
for  100  of  the  crystallized  salt.  It  is,  however,  nearly  impossible 
to  drive  off  the  last  portions  of  sulphuric  acid,  as  the  salt  swells 
up  enormously,  and  forms  a white,  porous,  infusible  mass,  which 
is  an  extremely  bad  conductor  of  heat.  Alumina  may  also  be 
procured  from  alum  quite  free  from  iron  ; the  salt  should  be  dis- 
solved in  water  and  precipitated  by  carbonate  of  potassium  in 
slight  excess  : the  liquid  should  be  warmed,  and  the  precipitate 
well  washed ; but  since  traces  of  potash  always  adhere  to  it  ob- 
stinately, it  must  be  redissolved  in  hydrochloric  acid,  and  then 
thrown  down  by  ammonia  or  carbonate  of  ammonium  ; in  which 
case  it  falls  as  a wdiite,  semitransparent,  bulky,  gelatinous  hydrate, 
which  must  be  again  thoroughly  washed.  In  this  form  alumina 
is  completely  soluble  in  a solution  of  potash,  and  is  readily  taken 
up  by  acids.  On  drying  it  contracts  very  much,  and  forms  a 
yellowish  translucent  mass,  like  gum,  retaining  3 H^O.  Diaspore 
is  a natural  hydrate  (Al^Og,  H^O),  which  decrepitates  strongly 
when  heated,  and  falls  to  powder.  Alumina  may  also  be  obtained 
from  aluminate  of  sodium  (663)  by  adding  hydrochloric  acid  in 
quantity  just  sufficient  to  form  ehloride  of  sodium. 

The  hydrate  of  alumina  when  ignited  loses  its  water,  and  at 
a certain  temperature  presents  an  appearance  of  sudden  incan- 
descence ; it  contracts  greatly  at  the  moment  that  this  effect  is 
produced,  and  is  afterwards  nearly  insoluble  in  acids.  Hydrate 
of  alumina  is  strongly  hygroscopic,  and  adheres  to  the  tongue 
when  applied  to  it. 

Alumina  fuses  before  the  oxyhydrogen  blowpipe,  and  yields  a 
colourless,  transparent  mass,  resembling  corundimi.  Gaudin 
states  that  artificial  crystals,  having  the  form  and  hardness  of  the 
ruby,  may  be  obtained  by  calcining  equal  parts  of  sulphate  of 
potassium  and  alum,  and  introducing  the  mixture  in  fine  powder 
into  a crucible  lined  with  lampblaok.  The  cover  is  then  to  be 
luted  on,  and  the  crucible  exposed  to  the  highest  heat  of  a forge 
for  a quarter  of  an  hour.  In  this  operation  the  sulphuric  acid  of 


ALUMINA ^ALUMINATE  OF  SODIUM. 


427 


the  sulphate  of  aluminum  is  expelled,  the  sulphate  of  potassium 
is  reduced  to  sulphide  of  potassium,  and  this  compound  dissolves 
a portion  of  the  liberated  alumina,  depositing  in  it  minute  pris- 
matic colourless  crystals,  during  the  slow  cooling  of  the  mass. 
These  crystals  may  be  cleansed  from  adliering  impurities  by  diges- 
tion in  dilute  aqua  regia.  Similar  crystals  have  also  been  ob- 
tained by  Deville,  who  has  succeeded  in  obtaining  the  hue  both 
of  the  ruby  and  the  sapphire.  Alumina  forms  salts  with  the  more 
powerful  acids,  but  these  salts  are  readily  decomposed : they  all 
have  an  acid  reaction ; and  indeed  alumina  possesses  properties 
which  approach  somewhat  to  those  of  an  acid,  for  it  has  a strong 
tendency  to  unite  with  basic  oxides.  The  s^inelle  ruby^  for  ex- 
ample, is  a native  aluminate  of  magnesium  (^^0Al203),  and 
gahnite  is  an  aluminate  of  zinc  (ZnOAl^Og).  Fremy  has  also 
obtained  a white  granular  compound  of  alumina  with  potash, 
to  which  he  assigns  a composition  corresponding  with  the  formula 
(K2OAI2O3).  When  the  solution  of  alumina  in  potash  is  exposed 
to  the  air  it  absorbs  carbonic  acid,  and  a terhydrate  of  alumina  is 
deposited  in  regular  crystals. 

Alumina  when  combined  with  silica  forms  clay,  which  is  the 
basis  of  porcelain  and  of  earthenware.  To  the  dyer  and  the 
calico-printer  the  compounds  of  alumina  are  of  high  value : the 
hydrate  of  alumina  has  the  property  of  combining  intimately  with 
certain  kinds  of  organic  matter,  and  when  salts  of  aluminum  are 
mingled  with  coloured  vegetable  or  animal  solutions,  and  preci- 
pitated by  the  addition  of  an  alkali,  the  alumina  carries  down  the 
greater  portion  of  the  colouring  matter,  forming  a species  of  pig- 
ments termed  lakes.  By  soaking  the  cloth  with  a preparation  of 
aluminum,  the  earth  attaches  itself  to  the  fibre ; and  if  cloth  thus 
prepared  be  plunged  into  a bath  of  the  colouring  matter,  it  be- 
comes permanently  dyed.  Most  colouring  matters  would  be  re- 
moved by  washing,  were  it  not  for  the  intervention  of  some  mor- 
dant^ or  substance  which  thus  adheres  to  the  fibre  as  well  as  to  the 
colouring  matter.  Binoxide  of  tin  and  the  sesquioxides  of  iron 
and  chromium  resemble  alumina  in  this  respect,  and  are  largely 
used  as  mordants  in  dyeing  calicoes  and  woollens. 

Mr.  Crum  {Q.  J.  (Jliem.  Soc.  vi.  216)  has  described  a remark- 
able modification  of  hydrate  of  alumina,  which  in  the  presence  of 
a very  small  proportion  of  acetic  acid,  is  largely  soluble  in  water, 
and  is  coagulated  and  rendered  insoluble  by  a minute  trace  of 
sulphuric  acid.  It  appears  to  be  probable  from  the  experiments 
of  Bean  de  St.  Gilles  {Chem.  Gaz.  1855,  p.  165)  that  sesquioxide 
of  iron  admits  of  a similar  modification : these  compounds  will  be 
further  alluded  to  when  the  salts  of  acetic  acid  are  described. 

(663)  Aluminate  of  Sodium  — This  compound  now 

forms  an  article  of  commerce.  It  is  obtained  by  heating  Bauxite, 
a hydrated  aluminous  peroxide  of  iron,  which  contains  from  60  to 
75  per  cent,  of  alumina,  and  only  from  1 to  3 j)er  cent,  of  silica. 
It  is  mixed  in  fine  powder  with  carbonate  of  sodium  or  soda  ash, 
and  heated  to  bright  redness,  until  no  efiervescence  occurs  on 
the  addition  of  an  acid.  On  lixiviation,  the  aluminate  is  dissolved 


428 


CHLORIDE  OF  ALLlLDsTM. 


out  and  separated  by  filtration  into  a vessel,  from  wliicb,  to  accel- 
erate the  operation,  the  air  is  exhausted.  The  filtrate  when  eva- 
porated to  dryness,  gives  a whitish,  infusible,  but  freely  soluble 
compound,  wliich  fm*nishes  a valuable  material  in  the  preparation 
of  lakes  for  pigments,  as  well  as  for  the  pui’poses  of  a mordant  to 
the  calico-printer,  which  will  probably  to  a large  extent  supersede 
the  use  of  the  difierent  forms  of  alum.  The  silica  remains  behmd 
in  the  form  of  an  insoluble  aluminosilicate  of  sodium. 

If  a solution  of  aluminate  of  sodium  is  exposed  to  the  action 
of  a current  of  carbonic  acid,  carbonate  of  sodium  is  produced, 
and  hydrate  of  alumina  precipitated  contaminated  with  soda.  If 
hydi’ochloric  acid  in  quantity  sufiicient  to  neutralize  the  soda  be 
added  to  a solution  of  the  aluminate,  the  alumina  is  precipitated 
in  a form  in  which  it  may  be  washed  ; but  the  precipitate  is  sim- 
ply dried  when  it  is  to  be  used  in  the  preparation  of  aluminum, 
for  which  it  is  chiefiy  required ; the  presence  of  chloride  of 
sodium  being  advantageous  in  the  subsequent  operations.  A curi- 
ous reaction  occurs  when  solutions  of  aluminate  of  sodium  and 
chloride  of  aluminum  are  mixed  in  equivalent  proportions ; chlo- 
ride of  sodium  is  formed,  and  the  alumina  from  both  compounds 
is  precipitated  in  the  form  of  hydi'ate  ; 2 Qs  agAlOg)  -f  Al^Clg^  2 Al^ 

Og-f-6  Isa-Gl. 

(664)  Chloride  of  ALrwrxrw  (AhCle=268) ; Sp.  Gr.  of 
Yapour^  9*34 : Mol.  Yol.  | | | ; or  (AlgClg^^lSI). — The  anhydi’ous 
chloride  of  aluminum  cannot  be  formed  directly  by  dissolving  alu- 
mina in  hydi’ochloric  acid,  and  evaporating  to  dr;smes3 ; since  dur- 
ing the  expulsion  of  the  water,  a great  part  of  the  acid  is  also 
driven  ofi*.  It  may  be  procured  as  a yellow,  anhydrous,  volatile 
sublimate,  by  a process  devised  by  Oersted  : — alumina,  mixed  with 
charcoal  powder,  is  made  up  into  paste  with  starch  or  oil,  and  sub- 
divided into  pellets  : these  pellets  are  charred  in  a covered  cruci- 
ble, and  then  exposed  to  ignition  in  a current  of  dry  chlorine. 
In  this  operation,  carbon,  in  a very  finely  divided  state,  is  mixed 
with  the  alumina ; when  the  mass  is  heated  with  chlorine,  the 
carbon  unites  with  the  oxygen  of  the  alumina,  and  the  chlorine 
seizes  the  liberated  aluminum ; Al^Og  -f-  3 O -f  3 Cl,  = Al^Clg  -f 
3 -00,  The  chloride  of  aluminum  condenses  in  the  cool  part  of 
the  tube  in  a crystalline,  somewhat  translucent  mass,  or  as  an 
amorphous  powder. 

In  preparing  the  chloride  of  aluminum  in  the  laboratory,  an 
apparatus  similar  to  that  shown  in  fig.  338  may  be  used  : 5 is  a 
vessel  containing  a mixture  of  black  oxide  of  manganese  and  hy- 
drochloric acid,  for  generating  chlorine  ; a is  a water-jacket,  for 
appl}ung  a moderate  heat  ; c is  a wash-bottle  containing  water ; 
d contains  sulphimc  acid : ^ is  a bent  tube  filled  with  pumice- 
stone  soaked  with  oil  of  vitriol,  to  remove  the  last  traces  of  moist- 
ure ; ^ is  an  earthen  retort  filled  with  the  mixtm*e  of  charcoal 
and  alumina,  heated  by  a charcoal  fire.  The  chlorine  is  conveyed 
nearly  to  the  bottom  of  this  retort  by  means  of  a porcelain  tube, 
y,  luted  into  the  tubulure  : the  gas  reacts  upon  the  mixture  in  the 
retort,  forming  carbonic  oxide  and  chloride  of  aluminum ; and 


FLTJOKIDE  OF  ALUiyirNTJM. 


429 


the  chloride  of  aluminum  condenses  in  the  gas-jar,  A,  which  is 
placed  for  its  reception  : the  open  mouth  of  this  jar  is  closed  by 
means  of  a funnel,  luted  on  with  a strip  of  pasted  paper ; and 
the  carbonic  oxide  escapes  through  the  open  tube,  i,  into  the 

Fig.  338. 


chimney.  In  order  to  purify  the  crude  chloride  of  aluminum 
from  the  small  quantity  of  volatile  ferric  chloride  which  usually 
accompanies  it,  tlie  compound  is  redistilled  from  iron  wire,  by 
which  the  ferric  chloride  is  converted  into  ferrous  chloride  which 
is  much  less  volatile,  and  the  chloride  of  aluminum  sublimes  near- 
ly in  a state  of  purity. 

Deville  prepares  this  chloride  on  a large  scale  from  a mixture 
of  coal  tar  and  alumina,  which  is  heated  in  a clay  retort,  such  as 
is  used  in  gas  making ; a current  of  chlorine  is  sent  over  the 
ignited  mass,  and  the  product  of  the  operation  is  received  in  a 
chamber  lined  with  glazed  brickwork.  (See  also  par.  660.) 

If  chloride  of  aluminum  be  heated  in  considerable  mass,  it 
melts  at  a dull  red  heat,  and  near  its  fusing-point  sublimes  rapidly  ; 
when  exposed  to  the  air  it  emits  fumes  of  hydrochloric  acid : it 
is  very  deliquescent,  and  when  thrown  into  water  hisses  from  the 
heat  developed  by  the  violence  of  the  combination.  Tliis  solution, 
when  concentrated  l)y  a very  moderate  heat,  yields  crystals  with 
the  formula  Al^Clg . 12  II^O.  It  is  soluble  in  alcohol.  By  sub- 
liming chloride  of  aluminum  in  a current  of  sulphuretted  hydro- 
gen it  forms  a combination  with  this  gas  : this  compound  is  de- 
composed by  resublimation,  or  by  solution  in  water.  Tlie  chlo- 
ride may  so  be  made  to  combine  with  phosphuretted  hydrogen, 
and  with  ammonia. 

(665)  Fluoride  of  Aluminum  occurs  native,  combined  with 
fluoride  of  sodium,  forming  cryolite  (3  KaF,AlF3).  It  may  be 
obtained  in  large  quantity  from  Greenland,  and  as  it  is  easily  de- 


430 


SESQUISULPHATE  OF  ALTJMINITM AETJM. 


composed  by  sodium,  it  lias  been  employed  as  a source  of  metallic 
aluminum,  of  which  it  contains  13  per  cent.  Another  highly 
prized  aluminous  mineral,  containing  fluorine,  is  the  topaz^  which 
is  extremely  hard ; the  colourless  variety  of  it  has  a lustre  which 
has  sometimes  caused  it  to  be  mistaken  for  the  diamond.  Its 
composition  may  be  represented  by  the  formula  [2  (Al20-3,Si02) 
:^l.e3,SiFJ. 

(666)  Sesquisulpiiate  of  Aluminum  (Al^  3 . 18  Il20= 

343  + 324),  or  Al303,3  SO, . 18  HO  = 171'5  + 162.— This  salt  is 
formed  by  dissolving  alumina  in  sulphuric  acid.  It  is  now  manu- 
factured on  a large  scale  in  the  north  of  England,  by  mixing 
flnely-powdered  clay  or  shale,  after  it  has  been  gently  roasted,  with 
about  half  its  weight  of  crude  sulphuric  acid  from  the  chambers, 
heating  it  gradually  until  fumes  of  acid  begin  to  escape  ; this  di- 
gestion is  continued  for  3 or  4 days,  after  which  the  mass  is  lixivi- 
ated, and  the  solution  thus  obtained  is  freed  from  iron  by  the 
addition  of  ferrocyanide  of  sodium  so  long  as  it  occasions  a blue 
precipitate ; the  clear  liquid  is  decanted  and  evaporated,  and  the 
residue  is  sold  under  the  name  of  concentrated  alum.  It  crystal- 
lizes in  thin  flexible  scales  which  are  soluble  in  twice  their  weight 
of  cold  water : this  solution  may  be  used  as  a test  for  potassium, 
for  by  mixing  it  with  a solution  containing  a salt  of  this  metal, 
and  evaporating,  octohedral  crystals  of  alum  are  deposited.  Sul- 
phate of  aluminum  has  a strong  tendency  to  form  double  salts 
with  monobasic  sulphates,  of  which  those  with  the  sulphates  of 
potassium  and  ammonium,  constituting  potash  and  ammonia-alum 
respectively,  are  the  most  important.  A remarkable  anhydrous 
sulphate  of  aluminum  wdiich  assumes  the  form  of  a wdiite  mealy 
powder,  insoluble  in  cold  Avater,  but  which  may  be  rendered  solu- 
ble, and  converted  into  the  ordinary  sulphate,  by  prolonged  boil- 
ing, is  obtained  by  boiling  either  cryolite,  or  ordinary  alum,  with 
from  three  to  ten  times  its  w^eight  of  oil  of  vitriol,  and  distilling 
off  about  three-fourths  of  the  sulphuric  acid ; the  acid  sulphate 
of  potassium  or  of  sodium  may  be  removed  by  washing,  and  the 
anhydi’ous  sulphate  is  left  as  a white  powder,  analogous  to  the 
corresponding  modiflcation  of  the  ferric  and  chromic  sulphates 
(Persoz). 

A basic  sulphate  of  aluminum,  soluble  in  water,  and  of  a yellow 
colour,  may  be  obtained ; the  yellow  is  not  due  to  the  presence  of 
ferric  sulphate  (Siewert). 

(667)  Alum;  Sulphate  of  Aluminum  and  Potassium  (KAl  2 
SO, . 12  H30=258-5  + 216),  or  (K0,S03,Al303,  3 SO3 . 24  Aq) : 
Sp.  Gr.  amhydrous.,  2*228  ; crystallized.^  1*726. — this  valuable  salt 
is  occasionally  found  native  in  volcanic  districts,  in  the  form  of  a 
white  efflorescence,  produced  by  the  action  of  the  sulphuric  acid  of 
the  volcano  upon  the  alumina  and  potash  contained  in  the  lava  and 
trachytic  rocks.  For  the  purposes  of  commerce,  however,  alum  is 
manufactured  artiflcially.  Three  principal  methods  are  adopted : — 

1. — In  the  flrst  the  alum  is  procured  by  the  addition  of  sul- 
phate of  potassium  to  the  crude  sulphate  of  aluminum  prepared 
from  clay  by  the  process  just  described. 


MMUFACTIJRE  OF  ALUM. 


431 


2.  — A still  simpler  method  is  practised  in  Italy,  where,  espe- 
cially in  the  neighbourhood  of  Civita  Y ecchia,  the  alum-stone  is 
abundant.  This  rock  contains  the  elements  of  alum,  with  an  ex- 
cess of  hydrate  of  alumina,  mixed  with  a variable  proportion  of 
siliceous  matter.  The  ore  is  first  roasted  at  a gentle  heat  in  kilns, 
avoiding  direct  contact  with  the  fuel : water  is  thus  expelled,  and 
the  mass  is  rendered  spongy ; the  hydrate  of  alumina  is  decom- 
posed, and  the  formation  of  a basic  sulphate  of  alnminnm  and 
potassium,  which  is  insoluble  in  water,  is  thereby  prevented : the 
roasted  ore  is  then  arranged  in  long  heaps  or  ridges  upon  a firm 
clay  fioor,  where  it  is  frequently  moistened  with  water ; in  the 
course  of  two  or  three  months  the  mass  crumbles  down  into  a sort 
of  mud,  which  is  lixiviated : and  the  solution  when  evaporated 
yields  crystals  of  almn,  which  after  a second  crystallization  are 
fit  for  the  market.  This  variety  of  alum,  known  as  Roman  alum^ 
crystallizes  in  opaque  cubes,  which  retain  basic  sulphate  of 
alnminnm. 

3.  — A third  process  is  resorted  to  in  England  and  Germany  for 
the  purpose  of  turning  alum  schist,  or  alum  ore,  as  it  is  termed,  to 
good  account.  This  mineral  is  abundant  at  Whitby,  in  Yorkshire, 
and  in  the  neighbourhood  of  Glasgow : it  is  a bituminous  shale, 
found  amongst  the  lower  beds  of  the  coal-measures,  and  it  con- 
tains a large  quantity  of  very  finely  divided  iron  pyrites,  disse- 
minated through  its  mass,  which  is  composed  chiefly  of  a siliceous 
clay.  The  mineral  is  decomposed  either  by  exposure  to  the  air, 
or,  as  is  more  usually  practised,  by  a slow  roasting,  conducted 
upon  the  ore  arranged  with  alternate  layers  of  fuel  in  long  heaps 
or  ridges,  which  are  covered  more  or  less  completely  with  spent 
ore,  in  order  to  regulate  the  heat  and  to  absorb  the  excess  of  sul- 
phuric acid.  In  this  operation  the  pyrites,  or  bisulphide  of  iron, 
is  converted  into  the  protosulphide  of  iron,  losing  half  its  sulphur, 
which  absorbs  oxygen  and  is  converted  into  sulphuric  anhydride ; 
this  at  the  moment  of  its  formation  unites  with  the  alumina,  while 
the  protosulphide  of  iron,  gradually  combining  wuth  more  oxygen, 
is  converted  into  ferrous  sulphate,  or  green  vitriol : 2 FeS^  + 3 

= 2 FeS + 2 SO3 ; and  FeS  -f  2 = FeSO^.  Great  care  is  required 

to  prevent  the  temperature  from  rising  too  high,  a circumstance 
which  would  be  attended  with  decomposition  of  the  sulphate  of 
aluminum  and  loss  of  sulphuric  acid.  By  the  time  that  the  roast- 
ing is  complete,  the  mass  has  become  greatly  reduced  in  bulk,  and 
is  rendered  porous  and  freely  permeable  to  the  air ; in  this  con- 
dition the  heap  is  allowed  to  lie  exposed  to  the  atmosphere,  and 
is  moistened  from  time  to  time ; it  is  then  lixiviated,  the  liquor  is 
digested  on  metallic  iron  to  reduce  any  ferric  salt  to  the  state  of 
ferrous  sulphate,  and  the  green  sulphate  of  iron  is  se])arated  froin 
the  sulphate  of  aluminum  by  crystallization  of  the  li(pior.  The 
mother-liquors  often  yield  sulphate  of  magnesium  when  concen- 
trated further. 

In  the  Whitby  alum  works,  in  which  the  quantity  of  the  sul- 
phate of  aluminum  much  exceeds  that  of  the  sulphate  of  iron  in 
solution,  the  concentration  is  completed  in  leaden  pans ; being 


MAXrTACTUPwE  OF  ALOI. 


43ii 

earned  so  far  as  that  the  liquid  shall,  when  cold,  be  perfectly 
satni’ated.  but  shall  deposit  no  crystals.  The  liqnid  is  then  mn 
off  into  the  precipitating  tank,  where  it  is  mixed  with  a saturated 
solution  of  sulphate  of  potassium,  or.  what  is  better,  of  chloride  of 
potassium,  in  quantity  sufficient  (as  found  by  trial  on  the  small 
scale)  to  yield  the  maximum  proportion  of  alum.  The  mixture  is 
briskly  agitated,  and  the  double  sulphate  of  almninum  and  potas- 
simn.  which  is  sparingly  soluble  in  cold  water,  is  deposited  in 
minute  crystals,  technically  termed  alum  meal  or  ffour.  ^Vlien 
chloride  of  potassium  is  used  the  siffphate  of  ii'on  is  decomposed, 
siffphate  of  potassium  is  produced,  and  the  veiw  soluble  fen*ous 
chloride  is  retained  in  the  liquor ; 2 KCl  — FeSO^  = FeCl, 

To  produce  100  parts  of  crystallized  alum,  between  IS 
and  19  parrs  of  sulphate  of  potassium  are  required,  or  about  16 
parts  of  the  chloride  of  p(»tassium.  The  mother-liquor  is  drained 
off"  and  preserved,  and  the  ciystals.  which  have  a reddish-brown 
colour  from  adhering  iron,  are  twice  washed  by  sul:>sidence  with 
a small  quantity  of  cold  water,  being  well  drained  after  each 
washing.  The  crystals  are  then  dissolved  by  heat  in  as  small  a 
quantity  of  water  as  possible,  and  the  solution  is  rim  off"  into  crys- 
tallizing barrels,  which  in  ten  days  or  a fortnight  are  taken  to 
pieces  ; the  crystalline  mass  is  broken  into  fi*agments,  drained, 
and  sent  into  the  market. 

In  the  Scotch  alum  works  at  Campsie.  in  the  neighbom’hood 
of  Glasgow,  alum  meal  is  not  formed;  but  the  hot  liquor  from 
the  evaporating  pan  is  run  into  a stone  cooler,  in  which  the  neces- 
sary quantity  of  dry  chloride  of  potassium  has  been  placed.  The 
liquid  is  thoroughly  agitated  and  left  to  cool ; on  the  sides  of  the 
vessel  large  crystals  of  alum  are  formed  in  four  or  five  days.  The 
mother-Hquor  is  then  drained  off",  and  the  crystals  are  afterwards 
washed  and  recrvstallized  twice. 

'Where  sulphate  of  ammonium  can  be  obtained  sufficiently 
cheap,  it  is  substituted  for  sulphate  of  potassium  in  the  manufac- 
ture of  alum,  as  the  double  salt  which  it  forms  with  sulphate  of 
aluminum  crystallizes  with  almost  as  much  facility  as  the  potas- 
sium salt;  it  constitutes  what  is  known  as  ammonia,  alum.  In 
England  at  present  the  greater  part  of  the  alum  which  is  made 
is  ammonia  alum.  Indeed,  for  the  purposes  to  which  alum  is 
applied,  neither  the  sulphate  of  potassium  nor  that  of  ammonium 
is  essential ; the  object  proposed  in  the  manufacture  of  alum  being 
to  obtain  a salt  of  aluminum  which,  by  the  facility  with  which 
it  crystallizes,  can  be  freed  from  iron  and  from  earthy  impurities. 

A number  of  other  salts  may  be  procured  which  have  the 
same  crystalline  form  as  potassimn  alum,  and  are  similar  to  it  in 
constitution  ; thus,  sulphate  of  potassium  may  be  displaced  by 
sulphate  of  sodium,  and  a sodium  alimi  may  be  formed,  but  the 
compoimd  is  much  more  soluble  than  potassium  alum : in  like 
manner  the  place  of  the  sulphate  of  aluminum  may  be  supplied  by 
ferric,  chromic,  or  manganic  sulphate,  forming  a remarkable  series 
of  isomorphous  compounds,  some  of  which  are  enumerated  in  the 
annexed  table  : — 


PROPERTIES  OF  ALTTM. 


433 


Potassium  alum  KAl  2 . 12  H2O 

Sodium  alum  l^aAl  2 SO^  . 12  H^O 

Ammonium  alum,  H^lSTAl  2 SO4 . 12 

Iron  alum  KPe  2 . 12 

Chrome  alum  KOr  2 . 12  H2O 

Manganese  alum  KMn  2 . 12 

Besides  these  true  alums,  a number  of  double  salts  of  aluminum 
may  be  formed  with  the  sulphates  isomorphous  with  that  of  mag- 
nesium ; they  crystallize  in  hne  silky  needles.  A native  sulphate 
of  aluminum  and  manganese  was  stated  by  Kane  and  by  Apjohn 
to  contain  25  atoms  of  water.  A similar  salt  of  iron  has  been 
met  with  in  the  native  state.  These  fibrous  salts,  according  to 
How,  contain  only  22  H2O,  so  that  the  formula  of  the  manganese 
salt  would  be  MnAl2  4 . 22  H20'. 

Ordinary  alum  has  a sweetish,  astringent  taste ; it  is  soluble 
in  about  18  parts  of  cold  water,  and  in  less  than  its  own  weight 
of  boiling  water.  The  solution  has  a strongly  acid  reaction,  and 
dissolves  iron  and  zinc  with  evolution  of  hydrogen.  When  heated, 
this  salt  first  melts  in  its  water  of  crystallization,  which  amounts 
to  45 ’53  per  cent,  of  its  weight ; as  it  loses  water  it  froths  up,  and 
forms  a tough,  tenacious  paste,  which  is  ultimately  converted 
into  a voluminous,  white,  infusible,  porous  mass  of  anhydrous  or 
'buT7it  alum.  If  crystallized  alum  be  submitted  to  a regularly 
increasing  heat,  a certain  proportion  of  the  water  contained  in  it 
is  readily  driven  ofi’:  thus  by  a temperature  of  212°,  5 atoms  out 
of  the  12  are  expelled,  and  5 more  at  248°.  If  the  salt  be  now 
heated  to  392°,  it  is  rendered  anhydrous  and  insoluble  in  water 
(Gerhardt).  By  ignition,  alum  loses  a great  part  of  its  acid. 

Alum  is  largely  employed  in  dyeing : when  used  in  this  pro- 
cess its  solution  is  gradually  mixed  with  carbonate  of  sodium,  so 
long  as  the  precipitate  is  redissolved  on  agitation,  which  happens 
till  two-thirds  of  the  acid  have  been  neutralized.  The  solution 
employed,  tlierefore,  contains  a mixture  of  3 salts,  viz.,  Al^OgSOj 
-f  1X28^4  + 2 ISra2S04.  Cloths  dipped  into  this  liquid  remove  the 
alumina  thus  redissolved,  and  contract  an  intimate  mechanical 
combination  with  it,  by  which  they  are  enabled,  as  already  men- 
tioned, to  retain  the  colours  of  the  dye-stuffs  employed.  Upon 
evaporation,  cubic  crystals  of  alum  are  deposited  from  this  solu- 
tion, and  the  excess  of  alumina  separates.  A hydrated  basic  sul- 
phate of  aluminum  (Al20a,  SO3 . 0 Tl20),  containing  the  same  pro- 
portion of  sulphuric  anhydride  and  alumina  as  that  formed  in  the 
mordanting  liquid  just  described,  is  obtained  by  precipitating  the 
normal  sulphate  of  aluminum  incompletely  by  caustic  ammonia ; 
it  is  a white  insoluble  powder.  A white  earthy-looking  mineral, 
termed  aluminite,  said  to  have  the  same  composition  as  this  basic, 
sulphate,  is  found  near  Newhaven. 

(GG8)  Phosphates  of  Aluminum. — Several  minerals  occur, 
into  the  composition  of  which  phosphate  of  aluminum  enters. 
The  blue  tuvfjuoise  is  a hydrated  native  phosphate,  AfiPjOjj . 5 IIjO^ 
or  2 AljOj,,  POg  . 5 iVq,  coloured  by  copper  and  iron.  Gibbsite 
28 


434 


SILICATES  OF  ALOIINTIM. 


which  was  formerly  considered  to  be  a hydrate  of  alumina,  was 
found  by  Hermann  to  consist  of  a hydrated  phosphate  of  the 
metal,  mixed  with  variable  proportions  of  hydrate  of  alumina. 
Pliosphate  of  aluminum  (AlPOJ  may  be  prepared  artificially  by 
mixing  a solution  of  phosphate  of  sodium  with  one  of  alum ; the 
precipitate  must  be  well  washed.  If  this  precipitate  be  redis- 
solved in  an  acid,  and  ammonia  be  added,  the  precipitate  thus 
occasioned  has,  according  to  Kammelsberg,  the  composition 
(4  AI2O3,  3 P2O5  . 18  H^O).  Wavellite  is  a mineral  which  crystal- 
lizes in  radiating  tufts  of  needles : according  to  Berzelius,  it  is  a 
combination  of  fluoride  of  aluminum  with  the  last-mentioned  basic 
phosphate  of  aluminum,  3 (4  AI2O3,  3 P2O5  . 18  H^O),  Al^Pg. 
The  mineral  arnblygonite  is  a combination  of  fiuoride  and  basic 
phosphate  of  aluminum  with  phosphate  of  lithium.  Lazulite^ 
2 (3  [■0aHgPe]O,P205),(4  1^1203,  3 P303),6  H^O,  is  a blue  mine- 
ral composed  of  another  double  phosphate  which  contains  the 
same  phosphate  of  almninum,  coloured  by  basic  phosphate  of 
iron  (Pammelsberg). 

Phosphate  of  aluminum,  in  its  hydrated  form,  is  readily  soluble 
in  hydrochloric  acid.  Its  solution  may  be  precipitated  by  hydrate 
of  potash,  but  the  precipitate  is  redissolved  by  an  excess  of  the 
alkali.  In  the  operations  of  analysis  it  is  often  necessary  to  sepa- 
rate phosphoric  acid  from  alumina : this  is  most  readily  effected 
by  Chancel’s  method,  in  which  the  solution  in  nitric  or  acetic  acid, 
perfectly  freed  both  from  hydrochloric  and  sulphuric  acid,  is  mixed 
with  an  acid  solution  of  nitrate  of  bismuth  (448).  Phosphoric 
acid  is  thus  precipitated  as  the  phosphate  of  bismuth  (Bi'^HO^), 
and  the  whole  of  the  aluminum  remains  in  solution. 

(669)  Silicates  of  Alttmixoi. — The  compounds  of  silica  with 
aluminum  are  numerous  and  important.  All  the  varieties  of  clay 
consist  of  hydrated  silicate  of  aluminum  more  or  less  mixed  with 
other  matters  derived  from  the  rocks  which,  by  their  disintegra- 
tion, have  formed  the  clay.  Clay  is,  in  fact,  the  result  of  the 
combined  action  of  air  and  water  upon  felspathic  and  siliceous 
rocks,  and  therefore  necessarily  varies  considerably  in  composition. 
The  fundamental  constituent  of  the  more  important  varieties  of 
clay,  according  to  the  researches  of  Brongniart,  Malaguiti,  and 
others,  is  represented  by  the  formula  (Al^Og,  2 SiO^  . 2 H^O),  or 
(AI2O3,  2 SiOj . 2 HO).  This  appears  to  be  the  composition  of  the 
fire-clay  of  the  Stafibrdshire  coal-measures.  The  ordinary  varieties 
of  clay,  however,  contain  fragments  of  undecomposed  rock,  a cer- 
tain proportion  of  potash,  and  variable  amounts  of  silica  in  the 
hydrated  condition,  mixed  with  oxide  of  iron,  lime,  and  magnesia ; 
the  character  of  the  clay  is  materially  modified  according  as  one 
or  other  of  these  ingredients  predominates. 

Pure  clay,  before  it  has  been  ignited,  forms,  when  kneaded,  a 
tenacious,  plastic  paste,  which  is  insoluble  in  water,  but  may 
readily  be  difiused  through  it  in  particles  which  are  in  an  extreme 
state  of  subdivision ; the  deposit,  when  freed  from  tlie  excess  of 
water,  as  it  subsides,  resumes  its  plastic  character.  This  paste, 
when  slowly  di’ied,  and  exposed  to  a higher  temperature,  shi'inks 


VARIETIES  OF  CLAY. 


435 


very  mncli,  and  splits  into  masses  which  are  extremely  hard,  hnt 
they  do  not  undergo  fusion  in  the  furnace.  Pure  hydrated  sili- 
cate of  aluminum  is  very  slowly  acted  upon  by  hydrochloric  or 
by  nitric  acid  ; hut  it  is  decomposed  when  heated  with  concen- 
trated sulphuric  acid  ; and  upon  this  fact  one  of  the  processes  for 
preparing  alum  (667)  is  founded.  A gentle  roasting  of  the  clay, 
previous  to  the  addition  of  the  acid,  frequently  favours  its  disin- 
tegration ; hut  ignition  at  a high  temperature  renders  it  proof 
against  the  action  of  acids,  except  the  hydrofluoric.  Strong  solu- 
tion of  caustic  potash  dissolves  unhurnt  clay  very  slowly  ; but  if 
the  hydrated  alkali  in  excess  be  fused  with  clay,  the  resulting 
mass  is  easily  soluble  in  water. 

The  intermixture  of  lime,  magnesia,  or  oxide  of  iron,  in  any 
considerable  quantity,  with  the  clay,  greatly  increases  its  fusibility, 
diminishes  its  plasticity,  and  causes  it  to  be  more  readily  attacked 
by  acids : whilst  an  excess  of  silica  renders  it  less  fusible. 

Clay  emits  the  peculiar  odour  known  as  argillaceous  when 
breathed  upon  or  slightly  moistened : its  presence  in  any  soil  may 
be  roughly  but  readily  distinguished  by  the  absorbent  quality 
which  it  exhibits  when  applied  in  a dry  state  to  the  tongue  or 
the  lips  ; it  adheres  to  them  strongly,  and  absorbs  the  saliva  from 
their  surface.  This  absorbent  property  of  clay  causes  it  to  retain 
ammonia  in  the  soil  to  an  extent  which  is  of  great  importance  to 
growing  plants,  and,  as  Way  has  shown,  it  arrests  the  ammoniacal 
portions  of  the  manure  applied  to  the  surface,  and  thus  not  only 
ministers  to  the  growth  of  the  crop,  but  exerts  a very  important 
purifying  influence  upon  water  impregnated  with  organic  and 
other  substances,  which  find  their  way  slowly  through  the  soil. 
Indeed,  mere  agitation  of  such  water  with  finely  divided  clay  is 
sufficient  to  remove  a considerable  amount  of  the  organic  and 
saline  matter  previously  in  solution.  It  was  found  that  both  sul- 
phate and  cliloride  of  ammonium  were  partially  decomposed  by 
the  lime  of  the  clay,  the  ammonia  being  retained,  whilst  a corre- 
sponding amount  of  sulphate  or  of  chloride  of  calcium  was  formed 
in  the  solution.  A similar  decomposing  action  was  also  exerted 
by  clay  upon  nitrate  of  potassium. 

Vdrieties  of  Clay. — The  most  important  varieties  of  clay  are 
the  following : — 

1. — The  celebrated  Imolin^  or  porcelain  clay  of  China,  is  a very 
pure  white  clay,  which  is  furnished  by  the  decomposition  of  a 
granitic  rock,  the  constituents  of  which  are  quartz,  felspar,  and 
mica,  the  felspar  having  gradually  mouldered  into  this  substance. 
A very  similar  description  of  clay  is  obtained  near  St.  Austel,  in 
Cornwall,  and  at  St.  Yrieix,  near  Limoges,  in  France.  It  is  in 
these  cases  chiefly  produced  by  the  disintegration  of  a rock  known 
to  geologists  pegmatite.,  which  is,  in  fact,  a species  of  granite  in 
which  mica  is  almost  wanting,  and  quartz  present  in  but  small 
quantity.  The  Cornish  stone  used  by  the  porcelain-makers  is  tlie 
same  rock  in  a less  advanced  stage  of  disintegration.  The  j)las- 
ticity  of  kaolin  is  much  less  than  that  of  the  clay  derived  from 
disintegration  of  the  secondary  rocks. 


436 


ZEOLITES ALUMINOUS  MINEKALS. 


2.  — Pipeclay  is  a white  variety  of  clay,  which  is  nearly  free 
from  iron.  That  of  the  Isle  of  Purbeck,  in  Dorsetshire,  where  it 
occurs  nearly  at  the  base  of  the  clay  deposits,  is  preferred : it  is 
used  in  the  manufacture  of  tobacco-pipes  without  any  addition  ; 
before  the  oxyhydrogeii  blowpipe  it  melts  to  a transparent,  nearly 
colourless  glass. 

3.  — The  Hue  clay  of  Devonshire  and  Dorsetshire  is  highly 
prized,  as  it  is  eminently  plastic.  The  organic  matter  to  wliicli 
it  owes  its  colour  is  destroyed  when  heated,  and  it  yields  a white 
paste  when  tired.  It  is  employed  as  one  of  the  materials  in  the 
manufacture  of  porcelain.  The  upper  beds  of  this  clay  frequently 
contain  a large  proportion  of-  sand  mixed  with  the  plastic  mate- 
rial, and  are  well  suited  for  making  salt-glazed  stoneware  without 
further  admixture. 

4.  — When  the  proportion  of  carbonate  of  calcium  in  a clay  is 
considerable,  it  constitutes  what  is  known  as  a / if  the  alu- 
minous constituent  preponderate,  it  forms  an  aluminous  marl ; if 
the  carbonate  of  calcium  be  in  excess,  it  is  a calcareous  marl.  The 
aluminous  marls  are  extensively  used  in  the  manufacture  of  the 
coarser  and  more  porous  kinds  of  pottery. 

5.  — Loam  is  a still  more  mixed  substance,  belonging  to  the 
more  recent  alluvial  formations  : it  is  the  common  material  of 
which  bricks  are  made ; its  red  or  brown  colour  is  derived  from 
the  large  proportion  of  peroxide  of  iron  which  it  contains. 

6.  — Yellow  ochre  and  red  hole  are  clays  which  derive  their 
colour  from  oxide  of  iron,  which  is  present  in  them  in  large 
quantity. 

llalloysite  is  a white  hydrated  silicate  of  aluminum  which 
greatly  resembles  kaolin  in  appearance,  but  it  is  destitute  of  any 
plastic  character,  and  is  therefore  unfitted  for  the  manufacture  of 
porcelain.  Fuller'^ s earth  is  a porous  silicate  of  aluminum  which 
has  a strong  adhesion  to  oily  matters : if  made  into  a paste  with 
water,  and  allowed  to  dry  upon  a spot  of  grease  upon  a board  or 
a cloth,  it  removes  most  of  the  oil  by  capillary  action.  Amongst 
other  localities  in  England,  it  is  found  abundantly  near  Eeigate, 
in  Surrey. 

The  table  on  the  opposite  page  exhibits  the  composition  of 
some  of  the  more  important  varieties  of  clay  used  in  the  arts. 
The  first  two  are  results  obtained  by  Ebelmen  and  Salvetat ; the 
others  are  from  analyses  executed  in  Richardson’s  laboratory, 
and  are  quoted  in  the  second  volume  of  the  English  translation 
of  Knapp’s  Technological  Chemistry. 

Besides  these  amorphous  silicates  of  aluminum,  there  are  many 
which  occur  in  a crystalline  form.  Disthene^  or  cyanite^  is  a blue- 
coloured  soft  mineral  of  this  kind  (A]2O3,Si02). 

(670)  Other  aluminous  Minerals. — The  zeolites  are  hydrated 
double  silicates  in  which  the  principal  bases  are  alumina  and  lime. 
They  boil  up  when  heated  upon  charcoal  before  the  blowpipe,  and 
are  dissolved  by  acids,  leaving  the  silica  in  a gelatinous  state.  In 
these  minerals  the  lime  is  liable  to  displacement  more  or  less  com- 
X)lete  by  protoxide  of  iron,  by  magnesia,  or  by  the  alkaline  bases. 


FELSPAES ALLTrimOUS  ROCKS. 


437 


Washed  kaolin. 

Stour- 

bridge 

fire-clay 

Pipe- 

Sandy 

Blue 

Brick 

Chinese. 

St.Yrieix 

Cornish. 

•^lay. 

clay. 

clay. 

clay. 

Silica 

50-5 

48-3'7 

46-32 

64-10 

53-66 

66-68 

46-38 

49-44 

Alumina 

sst 

34-95 

39-74 

23-15 

32-00 

26-08 

38-04 

34-26 

Oxide  of  iron. . . 

1-8 

1-26 

0-27 

1-85 

1-35 

1-26 

1-04 

7-74 

Lime 

0.36 

0-40 

0-84 

1-20 

1-48 

Magnesia 

’o-8 

trace 

0-44 

0-95 

trace 

trace 

trace 

5-14 

Potash  and  soda 
Water 

1-9 

11-2 

2-40 

12-62 

1 12-67 

10-00 

12-08 

5-14 

13-57 

1-94 

99-9 

99-60 

99-80 

100-05 

99-49 

100-00 

100-23 

100.00 

They  are  often  very  beautifully  crystallized.  Analohne  (^7a.,0, 
SiOa  . ^^laOg,  3 SiO^  . 2 H2O)  is  one  of  these  minerals  ; it  crys- 
tallizes in  cubes.  Stilbite  crystallizes  in  radiated  needles,  and 
has  the  composition  of  hydrated  labradorite  (OaO,  3 SiO^ . Al^Og, 
3 SiOj  . 6 Prehnite  crystallizes  in  six-sided  prisms  ; it  may 

be  represented  by  the  formula,  2 (0a0-,Si02)  . • Il2^- 

The  varieties  oi felspar  (M^O,  3 SiO^  . Al^Og,  3 SiO^),  are  like- 
wise double  silicates  of  aluminum  with  potassium,  sodium,  lithium, 
or  calcium.  Potash-felspar,  the  adularia  or  orthoclccse  of  mine- 
ralogists, and  the  petuntze  of  the  Chinese  potters,  is  sufficiently  hard 
to  scratch  glass ; it  is  used  as  a glaze  in  the  manufacture  of  the 
finest  kinds  of  porcelain.  Felspar  requires  the  most  intense  heat 
of  the  porcelain  furnace  for  its  fusion,  when  it  forms  a white  milky 
glass.  Soda-felspar,  from  its  usual  white  colour,  has  received  the 
name  of  alhite.  The  felspar  containing  lithia  constitutes  petalite. 
Common,  or  potash-felspar,  crystallizes  in  oblique  rhombic  prisms. 
Labradorite  is  a double  silicate  of  aluminum,  analogous  to  felspar, 
but  it  contains  calcium  instead  of  the  alkaline  metals  : it  crys- 
tallizes in  doubly  oblique  prisms  belonging  to  the  sixth  system. 

These  minerals,  by  disintegration,  yield  the  2)orcelain  clay,  or 
kaolin. 

Felspar  not  only  forms  the  regularly  crystallized  minerals  just 
mentioned,  but  it  occurs  mingled  with  quartz  and  other  crystal- 
lized minerals  : it  is  indeed  one  of  the  most  abundant  constituents 
of  many  of  the  older  rocks.  Granite^  for  example,  is  a rock  con- 
sisting of  intermixed  crystals  of  quartz,  felspar,  and  mica.  When 
it  contains  hornblende  instead  of  mica,  the  term  syenite  is  given 
to  it.  Gneiss  contains  the  same  components  as  granite,  but  it 
has  a more  stratified  appearance,  as  the  mica  occurs  more  in 
layers.  Porphyry  consists  chiefly  of  compact  felspar,  witli  crystals 
of  felspar  disseminated  through  it ; it  is  often  red  or  green,  and 
takes  a fine  polish.  Basalt  is  a dark-coloured  volcanic  rock,  con- 
sisting of  compact  felspar  containing  crystals  of  augite.  AVhen 
the  place  of  the  felspathic  constituent  is  supplied  by  labradorite 
(or  lime-felspar),  the  basalt  is  called  dolerite.  Trap^  or  (jreenstone^ 
is  a very  tough,  compact,  igneous  rock,  of  a dark-greenish  or 
brownish-black  colour;  it  is  com])osed  of  an  intimate  mixture  of 
felspar  and  hornblende.  If  it  contain  soda-fels])ar  (albite),  the 
rock  is  known  under  the  name  of  diorite.  Trachyte  is  a volcaTiic 
rock  also  consisting  chiefly  of  felspar,  less  compact  than  either 


438 


MICA YAEIETIES  OF  SLATE POTTEKT-WAEE. 


porphyry  or  basalt.  The  pumice  stone  of  yolcanic  districts 

is  probably  altered  felspar ; it  contains  a much  smaller  proportion 
of  alkali  than  the  crystallized  mineral.  Melted  pumice  consti- 
tutes obsidian^  or  yolcanic  glass. 

Garnet^  which  commonly  crystallizes  in  rhombic  dodecahedra, 
and  idocrase^  which  crystallizes  in  square  prisms,  are  basic  double 
silicates  of  calcium  and  aluminum,  in  which  part  of  the  lime  is 
displaced  by  other  protoxides,  and  the  alumina  by  sesquioxide  of 
iron  [3  (0aMgFeMn)''0,  2Si02  • (^lFe)'"203,  SiO^].  \\\ pyrope^ 
which  is  a species  of  garnet  found  in  Bohemia,  the  colouring 
matter  is  partly  sesquioxide  of  chromium.  These  minerals  have 
a hardness  greater  than  that  of  quartz. 

The  different  forms  of  mica  are  also  double  silicates  of  alumi- 
num, which  contain  in  addition  a small  quantity  of  water  and 
some  alkaline  fluoride.  Uniaxal  mica  consists  chiefly  of  silicate 
of  magnesium  and  silicate  of  aluminum,  2 [2  (MgKFe)0,Si02]  . 
(AlFej^Og,  2 Si02.  In  hiaxal  mica  (KFe)O,  3 Si02 . 3 [(iklFe)2 
03,Si02],  on  the  other  hand,  silicate  of  potassium  predominates. 
LepAdolite  is  a variety  of  biaxal  mica  in  which  silicate  of  lithimn 
takes  the  place  of  silicate  of  potassium. 

Another  important  double  silicate  of  aluminum  and  magnesium 
constitutes  chlorite  [4  (MgFe)0,Si02  . (AlFe)203,Si02 . 3 H2O], 
v/hich  occurs  both  massive  and  in  crystals  with  a granular  frac- 
ture ; it  is  of  a green  colour.  In  the  massive  form  of  chlorite  slate 
it  occurs  as  one  of  the  primitive  rocks  which  is  widely  distributed. 
There  are  many  varieties  of  slate.  Hoofing  slate  is  an  argillaceous 
rock  which  splits  readily  into  thin  lamime.  Mica  slate^  as  its 
name  implies,  contains  particles  of  mica,  to  which  it  owes  its  glis- 
tening appearance.  Ilovnljlende  slate  contains  hornblende  in 
place  of  mica,  and  has  little  lustre. 

(6T1)  Porcelain  and  Pottery-Mare. — In  the  preparation  of 
earthenware  tlie  material  employed  is  required  to  possess  a plas- 
ticity equal  to  that  of  red-hot  glass,  and  yet  to  be  capable  of  being 
rendered  by  heat  sufiiciently  firm  and  hard  to  resist  the  mechani- 
cal violence  necessarily  inflicted  on  it  by  daily  use. 

The  basis  of  earthenware,  porcelain,  and  china,  is  silicate  of 
aluminum  : it  possesses  the  plasticity  required,  and  when  heated 
assumes  a great  degree  of  hardness.  Pure  silicate  of  aluminum, 
however,  contracts  greatly  and  unequally  on  drying  : the  utensils 
made  from  it  would  consequently  be  liable  to  crack  during  their 
desiccation  ; in  order,  therefore,  to  diminish  the  amount  of  this 
contraction,  an  addition  of  some  indiflerent  poAvder,  such  as  ground 
flint,  is  made  ; while  to  compensate  for  the  loss  of  tenacity  thus 
occasioned,  and  which  is  particularly  experienced  in  the  use  of  the 
fine  clays  employed  for  porcelain,  some  fusible  material  is  added, 
which,  at  the  temperature  required  for  tiring,  undergoes  Autrifica- 
tion,  and  greatly  assists  in  binding  the  mass  together.  According 
to  the  greater  or  less  proportion  of  these  fusible  materials,  the 
AAmre  is  more  or  less  semi-transparent,  and  more  or  less  subject, 
like  glass,  to  fly  on  the  application  of  sudden  changes  of  tempera- 
ture. 


VARIETIES  OF  EAETHEiq'WAEE ^PORCELAIN,  OR  CHINA. 


439 


The  articles  which  have  passed  once  through  the  kiln,  and  have 
thus  acquired  firmness,  are  rough  and  uneven,  and  the  coarser 
kinds  of  ware  are  very  porous.  It  is  usual,  after  the  first  firing, 
in  order  to  give  smoothness  and  uniformity  to  the  surface,  as  well 
as  to  render  the  body  of  the  ware  impermeable  to  moisture,  to 
cover  it  with  a kind  of  flux  or  glaze,  which  melts  at  a lower  tem- 
perature than  the  material  composing  the  ware  itself ; and  in  order 
to  melt  the  glaze  the  articles  are  a second  time  passed  through  the 
kiln. 

The  materials  employed  in  the  fabrication  of  porcelain  and 
earthenware  are,  clays  of  various  degrees  of  purity  and  fineness, 
ground  felspar,  calcined  flints  or  sand,  burnt  bones,  chalk,  and 
carbonate  of  sodium  or  of  potassium  ; they  do  not,  therefore,  difter 
very  greatly  from  those  which  are  employed  in  glass-making  except 
in  the  great  preponderance  of  silicate  of  aluminum.  The  varieties 
of  pottery  or  earthenware  are  numerous : the  following  include 
those  which  are  of  most  importance  ; — 

1.— Porcelain^  or  China.  — T\\\^  is  the  finest  and  most  valuable 
description  of  ware  : it  is  distinguished  from  ordinary  earthenware 
by  the  composition  of  the  paste  from  which  it  is  formed.  The 
materials  are  selected  with  great  care,  in  order  that  they  may  give 
a colourless  mass  after  firing.  Porcelain  consists  mainly  of  two 
classes  of  materials,  one  of  which,  the  clay,  is  plastic,  and  is  infu- 
sible at  the  temperature  employed  to  fire  it ; the  other  (chiefly 
silicate  of  calcium  and  potassium)  softens  and  becomes  vitrified, 
forming  a kind  of  cement  which  binds  the  clay  firmly  together, 
and  thus  produces  a translucent  mass,  which  when  broken  appears 
to  be  of  a uniform  texture  throughout,  and  is  impervious  to  liquids. 
Much  judgment  is  required  in  the  due  proportioning  of  the  fusible 
and  infusible  materials. 

The  celebrated  Sevres  porcelain  resembles  the  original  Chinese 


ware,  of  which  indeed  it  is  an  imitation. 


Pegnault  states  the 


composition  of  the  paste  used  at  Sevres  for  ornamental  purposes 
to  be  the  following  : — Washed  kaolin,  62  parts  ; Bougival  chalk,  4 ; 
Aumont  sand,  17 ; quartzose  felspar,  17.  These  ingredients  are 
carefully  levigated  and  then  thoroughly  incorporated.  As,  liow- 
ever,  the  composition  of  the  kaolin  varies,  tlie  proportion  of  the 
other  materials  is  necessarily  varied  likewise,  so  as  to  obtain  a 
porcelain  of  uniform  composition. 

In  order  to  give  a smooth  surface  to  the  ware,  a glaze  similar 
in  composition  to  the  fusible  material  is  used.  The  glaze  employed 
at  Sevres  consists  of  a mixture  of  felspar  and  quartz.  It  is  trans- 
7)arent,  and  rather  more  fusible  than  the  body  of  the  ware,  but 
becomes  thoroughly  incorporated  with  it,  and  from  its  similarity 
in  composition  it  expands  and  contracts  by  heat  uniformly  with 
the  paste  which  it  covers  ; hence  it  is  not  liable  to  crack  ands])lit 
in  all  directions  in  the  manner  which  is  so  commoidy  observed  in 
the  glaze  of  the  more  ordinary  kinds  of  earthenware. 

The  china  of  Berlin  and  Meissen  is  very  similar  in  composition 
to  that  of  Sevres  : these  constitute  what  is  termed  hard,  or  true, 
l)orcelain. 


440 


6TONEWAEE EAKTHEXWARES PORCELAIX. 


English  porcelain  contains,  in  addition  to  tlie  Cornish  clay  and 
felspar  or  hint,  a large  proportion  of  burnt  bones  ; the  glaze,  which 
is  transparent,  nsiiallj  contains  both  borax  and  oxide  of  lead  to 
increase  its  fusibility.  English  porcelain  is  softer  than  the  Chinese, 
French,  or  German  porcelain,  and  constitutes  oneyarietyof  what 
the  French  ievm.  parcelaine  tendre^  the  manufacture  of  which  in 
France  is  now  rarely  practised. 

2.  — Stoneware  is  a species  of  porcelain  in  which  the  body  of 
the  ware  is  more  or  less  coloured,  less  care  being  taken  with  re- 
gard to  tlie  purity  of  the  material.  It  generally  contains  more 
oxide  of  iron,  and  consequently  is  somewhat  more  fusible  than  the 
best  porcelain,  and  is  usually  salt-glazed  in  a manner  shortly  to  be 
described.  Wedgvjood-ware  is  a fine  description  of  stoneware. 

3.  — Fine  Earthenware. — Articles  of  this  description  are  yery 
extensiyely  manufactured  in  the  Stafibrdshire  Potteries,  and  con- 
stitute the  ordinary  table-seryice  of  this  country.  The  Deyonshire 
and  Dorsetshire  clays  are  those  chiefiy  made  use  of;  they  are 
mixed  with  a large  proportion  of  ground  flints,  and  yield  an  infu- 
sible paste  which  burns  nearly  white.  The  body  of  the  ware  is 
not  fused  in  the  firing,  but  it  is  rendered  imperious  to  liquids  by 
means  of  a fusible  lead  glaze. 

4.  — Common  Earthenioare  is  made  of  an  inferior  and  more 
fusible  description  of  clay  ; both  this  kind  of  ware  and  the  forego- 
ing one  crack  easily  on  the  sudden  application  of  heat. 

5.  — The  coarsest  description  of  clay  goods  are  bricks,  tiles, 
fiowerpots,  and  similar  articles. 

6.  — Articles  which  are  required  to  stand  a high  temperature, 
such  as  fire-bricks  for  lining  furnaces,  muffies,  pots  for  the  fusion 
of  glass,  crucibles  for  melting  steel,  and  the  Hessian  crucibles  so 
largely  in  demand  in  the  laboratory,  are  made  of  a pure,  infusible 
siliceous  clay,  the  shrinking  of  which  during  drying  is  diminished 
by  the  addition  either  of  burnt  clay  of  the  same  description,  or  of, 
what  amounts  to  the  same  thing,  broken  pots  of  the  same  material, 
which  are  reduced  to  a fine  powder  and  incorporated  with  the 
paste.  Good  fire-ware  is  nearly  white  : if  coloured,  the  presence 
of  oxide  of  iron  would  be  indicated,  and  this  would  render  it 
fusible. 

The  table  on  the  opposite  page  giyes  the  composition  of 
some  of  the  more  important  yarieties  of  china  and  pottery  ware. 

(672)  Mamifactiire  of  Porcelain. — For  the  finer  kinds  of 
porcelain  much  care  is  taken  to  ensure  the  purity  and  minute 
subdivision  of  the  constituents,  as  well  as  their  intimate  admixture. 
The  clay  is  first  ground  between  horizontal  stones  under  water  ; 
it  is  next  leyigated  in  water,  to  allow  the  coarser  particles  to  sub- 
side while  the  lighter  ones  remain  in  suspension.  The  finer  sus- 
pended particles  are  then  formed  into  a mixture  of  the  consistence 
of  thin  cream,  a wine  pint  of  this  being  made  to  weigh  24  or  26 
ounces  : in  this  state  the  cream  or  pulp  is  mixed  with  the  ground 
felspar,  fiint,  or  other  material.  Suppose,  for  example,  that  the 
pulp  is  to  be  mixed  with  ground  fiints  ; the  fiints  are  heated  to 
redness,  suddenly  quenched  in  cold  water,  and  then  reduced  by 


MANUFACTURE  OF  EARTHENWARE.  441 


Porcelain. 

Wedg- 

wood 

ware. 

Lambeth 

stone 

ware. 

Hessian 

Chinese. 

Berlin. 

English. 

Sevres. 

Meissen. 

crucible. 

C.  Cowper 

Wilson. 

Cowper. 

Laurent. 

Laurent. 

Salvetat. 

Salvetat. 

Berthier. 

Silica 

71*04 

71*34 

40*60 

58*0 

57*7 

66*49 

74-00 

71 

Alumina  ] 
Oxide  of  >• 

22*46 

23*76 

24*15 

34*5 

36*0 

26-00 

22*04 

25 

iron ) 

1*74 

0*8 

6*12 

2*00 

4 

Lime 

3*82 

0*57 

14*22 

4-5 

0*3 

1*04 

0*60 

Alkali 

2*68 

2*00 

5*28 

3*0 

5*2 

0*20 

1*06 

Magnesia. . . 
Bone  earth  ) 

0*20 

0*43 

trace 

0*15 

0*17 

and  oxide  V 
of  iron . . . ) 

15*32 

100*00 

99*61 

100*00 

100*0 

100*0 

100*00 

99-87 

100*0 

stamping  and  grinding  them  under  water  to  an  impalpable  pow- 
der ; this  also  is  suspended  in  water,  a wine  pint  of  the  mixture 
being  made  to  weigh  32  ounces.  The  two  ingredients  are  easily 
mixed  in  the  necessary  proportions  by  taking  a given  measure  of 
each  pulp  and  thoroughly  incorporating  them.  The  mixture  thus 
obtained  is  technically  termed  slip.  The  slip  is  well  agitated  and 
allowed  to  subside  ; the  deposit  is  drained  (carefully  mixing  it 
from  time  to  time),  and  dried,  until  it  has  acquired  sufficient  con- 
sistence to  allow  of  its  being  wrought  by  the  potter.  Much  labour 
is  afterwards  bestowed  in  'working  this  clay  in  such  a manner  as 
to  render  it  of  uniform  composition  throughout,  and  to  preserve  it 
free  from  air-bubbles.  The  mixture  is  found  to  be  greatly  im- 
proved in  quality  by  being  allowed  to  remain  for  some  months 
before  it  is  worked  up,  the  mass  being  occasionally  turned  over  and 
beaten.  During  this  process  of  ripening  the  massjundergoes  a slow 
change,  in  tlie  course  of  which  traces  of  organic  matter  which  it 
contains  gradually  become  oxidized,  reducing  the  sulphates  to  sul- 
phides, in  consequence  of  which  it  evolves  a slight  odour  of  sul- 
phuretted hydrogen,  and  the  colour  of  the  paste  becomes  somewhat 
darker  from  the  formation  of  traces  of  sulphide  of  iron.  It  is  of 
great  importance  in  the  finer  specimens  of  ware  to  avoid  the  pre- 
sence of  organic  matter : a single  hair  might  spoil  a delicate  work 
of  art  by  the  disengagement  of  gas,  and  the  formation  of  bubbles 
in  the  interior  of  the  mass  when  heated. 

Less  labour  is  expended  upon  the  coarser  kinds  of  pottery.  After 
the  raw  clay,  brought  from  Devonshire  or  Dorsetshire  in  idocks  of 
about  30  pounds  weight,  has  been  dried,  it  is  ground  aiid  mixed 
with  a certain  proportion  of  ground  flints ; it  is  then  tempered  with 
water  into  a stiff  paste,  and 'passed  between  rollers  to  complete  the 
process  of  fitting  it  for  the  wheel. 

The  mechanical  operations  are  of  the  same  nature  in  every  case  ; 
and,  for  fashioning  the  clay,  \\\q potter's  v^heel  is  in  general  use. 
This  consists  of  a circular  slab,  whicli  can  be  made  to  revolve  in  a 
horizontal  plane,  eitlier  by  a treddle  or  by  a winch  turned  by  al)oy 
or  girl.  A mass  of  clay  of  tlie  size  required  is  dashed  upon  the 
moistened  slab,  and  is  'v(mrked  by  the  hands,  the  wheel  revolving 


PAESTDsG  OX  POECELATX. 


U2 

during  tlie  whole  time,  so  that  the  operation  is  a compound  of 
moulding  and  turning ; the  article  is  finally  trhnmed  up  with  a 
wooden  tool,  and  the  work  is  detached  fi’om  the  wheel  by  passing 
a wire  between  the  slab  and  the  yessel.  The  moulded  articles  are 
then  allowed  to  diw  for  a day  or  two  in  a room  heated  from  90°  to 
100°  F.,  in  order  to  give  them  firmness  sufficient  to  permit  them, 
when  necessary,  to  be  carefully  turned  on  a lathe.  After  this  ope- 
ration has  been  completed,  the  handles  and  ornaments  may  be  at- 
tached ; these  are  made  in  moulds,  and  adhere  readily  by  means  of 
slip  when  pressed  against  the  moulded  mass,  which  is  still  moist. 
The  articles  have  at  this  stage  received  the  form  which  they  are  in- 
tended to  retain,  and  are  next  subjected  to  heat  in  the  hiscuit  fur- 
nace. It  is  necessary  that  the  temperature  be  at  first  very  gra- 
dually and  carefully  raised,  lest  the  aqueous  vapour,  being  extri- 
cated too  suddenly,  should  deface  the  vessel  or  injure  its  texture. 
By  this  first  firing  the  difierent  articles  acqume  a greater  degree  of 
firmness,  and  can  be  handled  without  danger  of  breakage,  but  they 
are  in  a very  porous  state,  technically  termed  biscuit.  The  ware 
in  this  stage  readily  absorbs  any  solution  that  may  be  placed  upon 
its  surface,  and  this  is  the  period  chosen  for  printing^ the  patterns 
or  designs  which  the  finished  goods  are  to  exhibit.  The  colouring 
matter  generally  consists  of  some  metallic  oxide  ground  up  with  oil 
of  turpentine  or  with  boiled  linseed  oil.  Blue  is  usually  given  by 
oxide  of  cobalt ; green  by  oxide  of  chromium ; brown  by  a mixture 
of  oxides  of  iron  and  manganese  ; black,  by  the  black  oxide  of 
mnniiun ; and  a pink,  which  is  much  esteemed,  by  a combination 
of  oxide  of  tin,  lime,  and  a minute  quantity  of  oxide  of  chromium. 
In  order  to  apply  the  colouring  material,  it  is  printed  from  copper 
plates  on  a thin  unsized  paper  made  for  the  purpose ; this  paper, 
while  the  colour  is  still  moist,  is  applied  to  the  sinface  of  the  bis- 
cuit ; the  design  is  soon  absorbed  by  the  ware,  and  the  paper  is 
washed  off.  The  ware  is  now  subjected  to  another  baking  or  firing, 
for  the  pm’pose  of  fixing  the  colour  and  burning  ofi'  the  oil.  For 
decorating  the  finer  kinds  of  porcelain  the  metallic  colour  is  mixed 
with  a fusible  glaze  containing  quartz,  boracic  acid,  and  oxide  of 
lead,  and  melted.  The  coloured  glass  thus  obtained  is  then  re- 
duced by  levigation  to  a fine  power,  and  ground  up  with  some 
volatile  oil,  in  which  form  it  is  laid  on  in  the  desired  pattern  by 
means  of  a hair  pencil.  After  the  glazing  has  been  completed,  it 
is  fired  at  a moderate  heat  in  a muffie.  In  the  finer  kinds  of  decora- 
tion, the  application  of  the  colouring  matter  requires  the  nicest 
management.  For  details  upon  this  point  (and  indeed  upon  most 
others  connected  with  the  art  of  Pottery),  the  reader  is  referred  to 
Brongniart’s  great  work/S'^r  les  A'rts  Ceramiques.  After  the  ap- 
plication of  the  colouring  material,  the  ware  still  remains  far  too 
porous  for  use,  and  it  further  undergoes  the  process  of  glazing. 

The  glaze  for  fine  porcelain  is  prepared  by  levigating  quartz  and 
felspar  with  water,  so  as  to  form  a mixture  of  the  consistence  of 
cream  ; to  this  a little  vinegar  is  added,  to  favour  the  suspension 
of  the  finely  divided  particles.  Each  article  is  then  dipped  sepa- 
rately into  the  mixtm’e.  The  porous  mass  quickly  absorbs  the  mois* 


GLAZING  OF  STONEWARE. 


443 


ture,  leaving  a tliin  uniform  film  of  glaze  upon  the  surface.  The 
goods  thus  prepared  are  then  enclosed  in  vessels  made  of  fire-clay, 
termed  seggars,  and  ai^e  exposed  to  the  most  intense  heat  attainable 
in  the  porcelain  furnace. 

In  glazing  ordinary  earthenware  a similar  process  is  adopted, 
but  the  temperature  of  firing  is  below  that  required  in  the  biscuit 
furnace.  The  glaze  usually  consists  of  a fusible  material  contain- 
ing a considerable  quantity  of  oxide  of  lead  : a mixture  of  felspar, 
fiint,  Hint  glass,  and  white  lead,  is  in  common  use. 

The  glazing  of  stoneware  depends  upon  a peculiar  mode  of 
decomposition  of  common  salt.  Chloride  of  sodium  is  not  decom- 
posed by  heat  alone,  and  if  heated  with  dry  silica  no  decomposi- 
tion occurs ; but  in  the  presence  of  silica  and  some  substance 
capable  of  imparting  oxygen  to  the  sodium,  and  at  the  same  time 
of  removing  the  chlorine  with  which  it  is  united, — such,  for  in- 
stance as  steam,  or  oxide  of  iron — the  salt  is  susceptible  of  decom- 
position at  an  elevated  temperature ; silicate  of  sodium  and  hydro- 
chloric acid,  or  silicate  of  sodium  and  perchloride  of  iron,  as  the 
case  may  be,  being  formed.  The  various  utensils,  having  been 
dipped  into  sand  and  water,  are  placed  in  tlie  kiln,  and  are 
gradually  raised  to  an  intense  heat.  A certain  quantity  of  moist 
salt  is  then  thrown  in : the  chloride  of  sodium  is  quickly  con- 
verted into  vapour,  and  the  salt  is  decomposed  by  tlie  silica,  and 
the  oxide  of  iron  in  the  clay,  aided  by  the  steam  produced  in  the 
combustion  of  the  fuel  in  the  furnace.  The  perchloride  of  iron 
and  hydi’ochloric  acid  pass  off  in  vapour  with  the  excess  of  salt 
employed,  whilst  the  silicate  of  sodium  fuses  upon  the  ware,  and 
renders  it  impervious  to  liquids.  The  reactions  may  be  thus  re- 
presented : — 

H,e  -f  2 IN^aCl  -f  SiO,  2 HCl  + Na,0,Sie, ; and 
Fe,e3  + 6 IlaCl  + 3 SiO^  = Pe^Cl,  + 3 

It  is  worthy  of  remark,  that  although  clay  contracts  very 
evenly  by  heat  when  its  density  is  uniform  throughout,  yet  if  its 
density  be  unequal  in  different  parts,  the  contraction  is  also  un- 
equal ; hence  though  a vessel  may  issue  smooth  and  well  finished 
from  the  workman’s  hands,  it  often  assumes  a striated  and  uneven 
appearance  during  the  process  of  firing ; and  if  a stamp  be  im- 
pressed upon  clay  while  soft,  and  the  whole  surface  be  shaved 
away  until  no  further  impression  is  visible,  the  mark  of  the  stamp, 
after  baking,  reappears  in  a manner  more  or  less  distinct. 

(G73)  TJltr amarine. — Alumina  enters  into  the  formation  of 
the  pigment  ultramarine,  so  higldy  prized  for  the  purity  and 
delicacy  of  its  blue  colour,  and  for  its  permanence  when  exposed 
to  light  and  air,  though  mixed  with  oils,  and  subjected  to  the 
action  of  lime  or  of  alkalies.  This  valuable  colouring  material 
was  formerly  obtained  exclusively  from  the  lapis  lazuli  by  a tedious 
process,  which  consisted  in  gently  calcining  the  stone,  broken  into 
fragments  of  the  size  of  hazel-nuts;  the  heated  fragments  were 
then  quenched  in  vinegar,  by  which  they  were  rendered  more  fri- 
able, and  were  deprived  of  adhering  carbonate  of  calcium : they 


444 


ULTEAMAKDs'E. 


were  next  subjected  to  a patient  levigation  with  a thin  syrup  of 
honey  and  dragon’s-blood ; were  then  made  into  a paste  with  a 
resinous  cement ; and  after  allowing  this  to  remain  undisturbed 
for  some  days,  the  ultramarine  was  extracted  from  it  by  suspension 
in  hot  water  and  subsidence.  Ultramarine  is  now,  however, 
manufactm*ed  artificially  upon  a large  scale ; and,  amongst  other 
applications,  it  is  extensively  used  in  paper-staining.  The  fol- 
lowing process  answers  well  upon  the  small  scale : — 100  parts  of 
finely  washed  kaolin,  100  of  carbonate  of  sodium,  60  of  sulphur, 
and  12  of  charcoal,  are  intimately  mixed,  and  ex|)osed  in  a covered 
crucible  to  a bright  red  heat  for  three  hours  and  a half.  The  re- 
sidue, which  shotild  not  be  in  a fused  condition,  is  of  a green  co- 
lom*.  It  must  be  well  washed,  di’ied,  and  mixed  with  a fifth  of 
its  weight  of  sulphur,  and  exposed  in  a thin  layer  to  a gentle  heat, 
little  above  that  required  to  burn  ofi*  the  sulphm'.  When  the  sul- 
phur has  all  been  burned  off,  a fr-esh  quantity  of  sulphur  must  be 
added,  and  the  roasting  repeated;  and  this  roasting,  with  fresh 
additions  of  sulphur,  must  be  repeated  two  or  three  times  until 
the  mass  acquires  a bright  blue  colour.  Other  proportions  of  the 
ingredients  may  be  used,  the  temperature  varying  with  the  com- 
position : the  heat  should  be  as  high  as  the  mass  will  bear,  pro- 
vided it  is  not  fused.  The  green  modification  of  ultramarine  is 
also  manufactured  for  the  market : by  oxidation  the  green  may  be 
converted  into  the  blue  form.  Blue  ultramarines  vary  in  tint, 
some  being  pure  blue,  others  greenish  blue,  and  others  violet  blue, 
with  a roseate  refiex.  The  violet  ultramarines  are  well  adapted 
for  use  in  paper-stauiing,  as  they  withstand  the  action  of  the  alum 
used  in  sizes,  which  the  two  other  tints  do  not. 

Considerable  doubt  still  exists  as  to  the  true  nature  of  the 
colouring  matter  of  ultramarine,  which  has  been  made  the  subject 
of  study  by  many  chemists.  According  to  the  experiments  of 
Wilkens, — who  has  made  careful  analyses  of  a variety  of  samples 
of  the  artificial  product,  both  from  his  o^vn  manutactory  and  from 
other  sources — ultramarine  is  composed  of  two  portions,  one  of 
which  is  constant  in  composition ; and  which  he  regards  as  the 
essential  colomfing  body ; it  is  attacked  with  facility  by  hydro- 
chloric acid,  evolving  sulphuretted  hydrogen : the  other  portion 
is  not  soluble  in  the  acid,  and  contains  a variable  amount  of  sand, 
clay,  oxide  of  iron,  and  sulphuric  acid.  His  analyses  of  the  pure 
blue  pigment  correspond  nearly  with  the  formula  (2  AfiOg,  3 SiO, 
. AlgOg,  4 SiOg  . XagSgHgO^  . 3 ^ a^S) , which  would  contain,  in 
100  parts : — 

By  calculation.  By  experiment. 


SiOa  = 

37-6 

40-25 

39-39 

40-19 

ztlaOj  = 

27’4 

26-62 

26-40 

25-85 

s = 

14'2 

13-42 

12-69 

13-27 

200 

19-89 

21-52 

20-69 

and  he  regards  the  blue  colouring  principle  as  a compound  of 
hyposulphite  and  sulpliide  of  sodium.  lie  states  that  the  pre- 
sence of  iron  is  found  not  to  be  essential  to  the  production  of  the 
colour,  but  tills  is  still  a matter  of  doubt.  According  to  Brunner, 


CHAKACTERS  OF  THE  COMPOUNDS  OF  ALUMINUM GLUCINUM.  445 

a corresponding  compound,  in  which  sulphide  of  potassium  is  sub- 
stituted for  sulphide  of  sodium,  is  colourless. 

Ultramarine,  if  heated  in  the  air,  gradually  assumes  a dull 
green  hue  ; when  heated  with  sulphur,  it  is  not  changed  ; if  melted 
with  borax,  sulphur  and  sulphurous  anhydride  escape,  and  a 
colourless  glass  remains.  Sulphuric,  nitric,  and  hydrochloric 
acids  decompose  it,  and  the  colour  is  quickly  destroyed.  Chlorine 
acts  still  more  rapidly,  dissolving  everything  but  the  silica,  and 
completely  discharging  the  colour. 

(674)  Characters  of  the  Compounds  of  Aluminum. — The 
ordinary  salts  of  aluminum,  with  the  exception  of  the  chloride, 
are  colourless.  They  have  a sweetish,  strongly  astringent  taste, 
and  an  acid  reaction  upon  litmus. 

Before  the  blowpipe  the  compounds  of  aluminum  are  distin- 
guished by  the  formation  of  a pale  azure  blue  if  moistened  with 
nitrate  of  cobalt  and  gently  ignited. 

In  solution  they  give  with  hydrosulphate  of  ammonium  a white 
precipitate  of  hydrate  of  alumina,  with  evolution  of  sulphuretted 
hydrogen.  Ammonia  produces  a bulky,  semi-transparent,  gela- 
tinous precipitate  of  hydrate  of  alumina ; it  is  nearly  insoluble  in 
excess  of  ammonia  or  of  its  carbonate.  Hydrate  of  potash  dis- 
solves it  readily  ; and  it  is  reprecipitated  on  adding  solution  of 
chloride  of  ammonium  in  excess.  The  carbonates  of  the  alkaline 
metals  produce  the  same  precipitate  under  disengagement  of  car- 
bonic anhydride,  but,  according  to  Muspratt,  it  retains  a portion 
of  carbonic  acid.  Sxdphate  of  potassium  and  sulphuric  acid  in 
slight  excess  added  to  solutions  of  the  salts  of  aluminum,  and 
evaporated,  furnish  well-marked  octohedral  crystals  of  alum. 

Estimation  of  Alumina. — Tlie  quantity  of  alumina  in  the 
course  of  an  analysis  is  always  estimated  from  the  precipitate  by 
ammonia,  or  its  carbonate  or  hydrosulphate ; when  thoroughly 
w'ashed  (an  operation  which,  from  its  gelatinous  nature,  is  tedious), 
and  then  ignited,  it  consists  of  the  pure  earth  only. 

(675)  Reparation  of  Alumina  from  the  Alkalies  and  Alkaline 
Earths. — Supposing  a salt  of  magnesium  to  be  present  in  the 
liquid,  a solution  of  chloride  of  ammonium  is  first  added  to  it, 
unless  it  be  powerfully  acid ; on  the  addition  of  caustic  ammonia 
in  slight  excess,  pure  hydrate  of  alumina  is  precipitated.  Hydro- 
sulphate of  ammonium  is  a still  better  precipitant,  if  the  liquid 
has  been  first  nearly  neutralized  by  ammonia ; the  preci])itate  is 
extremely  voluminous,  and  requires  persevering  washing.  On 
ignition  it  yields  pure  alumina.  The  alkalies  and  alkaline  earths 
remain  in  the  solution  which  has  been  filtered  from  the  alumina, 
and  their  amount  may  be  determined  by  methods  hereafter  to  be 
detailed  (694  et  seq^i). 

§ II.  Glucinum:  G"=:9’5.  Sp.  Gr.  2T.  Atomic  Yol.  solid^  4*44. 

(676)  Glucinum,  \\\q  beryllium  oi  German  writers,  is  extracted 

from  the  emerald  or  the  beryl,  which  consist  chiefly  of  silicate 
of  aluminum  and  glucinum  [3  (G-OjSiO^)  . 3 SiO  1.  The 


446 


GLrCINA. 


metal  is  procured  from  its  chloride  in  the  same  way  as  alu- 
minum. 

Glncinnm,  according  to  the  experiments  of  Dehray  {^Ann.  de 
Chimie^  III.  xliv.  5),  is  a white,  malleable  metal,  fusible  below  the 
melting-point  of  silver.  It  does  not  burn  in  air,  oxygen,  or  the 
vapour  of  sulphur,  but  it  combines  readily  with  chlorine  and 
iodine,  and  also  with  silicon.  The  vapour  of  water  is  not  decom- 
posed by  it,  even  when  the  metal  is  heated  to  full  redness  and 
exposed  to  it.  Glucinnm  is  easily  dissolved  by  diluted  hydro- 
chloric and  sulphuric  acids  ; nitric  acid,  whether  diluted  or  con- 
centrated, acts  but  feebly  upon  it.  It  is,  however,  readily  dis- 
solved by  a solution  of  potash,  with  evolution  of  hydrogen,  but  is 
not  acted  upon  by  ammonia.  Glucinnm  forms  but  one  oxide ; 
there  is  some  doubt  whether  this  should  be  regarded  as  a prot- 
oxide or  as  a sesquioxide.  Berzelius  adopted  the  latter  view, 
but  later  researches  favour  the  supposition  that  it  is  a prot- 
oxide. 

(677)  Glucixa  (GO=25-5 ; Sjp.  Gr.  2-967)  is  extracted  from 
the  beryl,  of  which  it  constitutes  13*6  per  cent. : the  mineral  is 
reduced  to  a very  tine  powder,  fused  with  carbonate  of  potassium 
treated  with  hydrochloric  acid,  evaporated  to  dryness,  again  moist- 
ened with  acid  and  treated  with  ^vater ; in  this  way  everything 
except  the  silica  is  dissolved : the  filtered  liquid  is  mixed  with  an 
excess  of  a solution  of  ammonia,  which  occasions  a voluminous 
precipitate  containing  both  alumina  and  gliicina ; this  precipitate 
is  well  washed,  and  the  glucina  is  dissolved  out  from  the  alumina 
by  digesting  the  mass  in  a solution  of  carbonate  of  ammonium. 
It  is  again  filtered,  and  upon  boiling  the  clear  liquid,  carbonate 
of  glucinnm  is  deposited  as  a white  powder,  which,  when  ignited, 
leaves  pure  glucina.  Freshly  precipitated  glucina  forms  with 
water  a somewhat  tenacious  mass,  but  it  does  not  harden  like 
alumina  when  ignited.  Ebelmen  obtained  it  in  crystals,  by  ope- 
rating at  a high  temperature,  as  upon  alumina  (72) ; it  formed 
minute  six-sided  prismatic  crystals  of  the  same  form  as  those  of 
oxide  of  zinc.  The  fixed  alkalies  and  their  carbonates  dissolve 
glucina  readily ; but  the  dilute  solution  in  caustic  potash  deposits 
glucina  when  boiled.  Hydrate  of  glucina  yields  a bulky,  white, 
gelatinous  mass,  which  absorbs  carbonic  acid  from  the  air.  "When 
heated  with  solutions  of  the  salts  of  ammonium  it  displaces  am- 
monia, and  is  gradually  dissolved.  The  cliloAde  (GCl2=80-5)  is 
prepared  in  the  same  way  as  the  chloride  of  aluminum : it  sub- 
limes in  white,  brilliant,  fusible  needles,  which  are  very  deli- 
quescent ; a hydrated  chloride  may  be  obtained  in  crystals. 
Glucinnm  yields  several  sulphates  ; one  of  these  (GSO^,  4 II^O) 
crystallizes  in  octohedra ; the  other  sulphates  are  amorphous 
sub-salts.  It  does  not  form  an  alum  with  sulphate  of  potassium, 
but  yields  a double  salt,  in  which  the  proportion  of  acid  is  di- 
vided equally  between  the  two  bases  (Iv^G  2 SO,).  An  alummate 
of  ghccinum  coloured  with  peroxide  of  iron  occurs  native  in 

* Debray  finds  it  advantageous  to  substitute  for  the  carbonate  of  potassium 
quicklime,  in  proportion  of  half  the  weight  of  the  beryl  employed. 


■ CHARACTEES  OF  THE  SALTS  OF  GLUCIHUM. 


447 


the  gem  chrysoberyl  (€r0,Al203).  Carbonate  of  ghicinnm  forms 
double  salts  with  the  carbonate  of  potassium  and  of  ammonium. 

(678)  Characters  of  the  Salts  of  Glucinijm. — The  salts  of 
glucinum  have  a sweet  taste  (whence  the  name  glucinmn  was  de- 
rived, from  /Xux’jV,  sweet),  with  a slight  astringency,  and  have  an 
acid  reaction  upon  litmus.  They  are  colourless,  and  are  distin- 
guished from  those  of  aluminum  by  not  yielding  an  alum  with 
sulphate  of  potassium ; nor  a blue  when  heated  before  the  blow- 
pipe with  nitrate  of  cobalt : and  by  giving  with  carbonate  of  am.- 
moniiom  a white  precipitate  of  carbonate  of  glucinum,  easily 
soluble  in  excess  of  the  alkaline  salt.  Ferrocyanide  of  potassium 
gives  no  precipitate  in  their  solutions : a white  precipitate  of  hy- 
drate of  glucina  is  produced  by  sulphide  of  potassium^  with  ex- 
trication of  sulphuretted  hydrogen.  If  a hot  solution  of  fluoride 
of  potassium  in  excess  be  added  to  a hot  solution  of  a glucinum 
salt,  scales  of  a sparingly  soluble  double  fluoride  of  glucinum  and 
potassium  are  formed. 

Glucinum  is  always  estimated  in  the  form  of  the  anhydrous 
earth. 

§ III.  Zirconium:  Zk''=89-5. 

(679)  Zirconium  is  the  elementary  base  of  an  earth  contained 
in  the  zircon  and  the  hyacinth^  which  are  silicates  of  zirconium. 
The  metal  is  procured  by  heating  the  fluoride  of  potassium  and 
zirconium  with  potassium,  and  treating  the  residue  when  cold  with 
diluted  hydrochloric  acid,  by  which  everything  except  the  zirco- 
nium is  dissolved : it  is  thus  left  in  a pulverulent  form,  and  must 
be  washed,  first  with  a solution  of  chloride  of  ammonium,  and 
then  with  alcohol ; if  water  be  used  for  tlie  wasliing,  the  finely 
divided  zirconium  passes  through  the  filter  in  suspension  in  the 
water.  As  thus  obtained  it  is  in  the  form  of  a black  powder,  which 
does  not  conduct  a feeble  voltaic  current : under  the  burnisher  it 
assumes  a slightly  metallic  lustre.  Zirconium  has  not  been  fused : 
when  heated  in  the  air  or  in  oxygen,  it  takes  fire  below  redness 
and  burns  brilliantly,  forming  zirconia  of  snowy  whiteness : diluted 
sulphuric  and  hydrochloric  acids  do  not  act  on  it.  Hydrofluoric 
acid  dissolves  it  with  extrication  of  hydrogen,  forming  a fluoride 
closely  resembling  fluotitanic  acid : it  yields  a number  of  fluozir- 
conates  with  the  fluorides  of  the  basylous  metals,  which  have  the 
general  formula  2 MF,ZrF4.  Boiling  water  gradually  oxidizes 
zirconium  ; if  heated  with  sulphur  in  vacuo  it  forms  a brown  pul- 
verulent sulphide^  which  is  not  decomposed  by  sulphuric  or  hydro- 
chloric acid,  and  is  but  slowly  attacked  by  aqua  regia.  Zirconium 
is  intermediate  in  properties  between  silicon  and  titanium,  to 
which  latter  body  it  is  more  allied  than  to  any  other  element,  as 
is  particularly  seen  in  the  properties  of  the  fluoride  of  zirconium, 
and  of  the  fluozirconates. 

(680)  Zirconia  (Zr03=121*5);  Sp.  Gr.^i'Z. — Zirconium  forms 
but  one  oxide,  which  Berzelius  regarded  as  the  sesquioxide,  though 
most  chemists  now  adopt  the  view  of  Dumas  and  of  I)e  Marignac, 
who  consider  it  to  be  a binoxide,  like  silica.  It  may  be  obtained 


44:8 


ZmCONIA THOEINUM. 


by  fusing  very  finely  powdered  zircon  witli  hydrate  of  potasli  or 
of  soda,  and  saturating  with  hydrochloric  acid.  The  excess  of 
acid  and  moisture  is  expelled  by  evaporating  nearly  to  dryness ; 
on  the  addition  of  water,  the  chloride  of  zirconium  is  dissolved, 
leaving  the  silica ; the  solution  is  decomposed  by  excess  of  ammo- 
nia : hydrate  of  zirconia  is  tlms  precipitated  and  is  washed  and 
ignited.  Upon  appljdng  heat,  it  glows  brilliantly  just  before  igni- 
tion, and  becomes  much  denser.  Zirconia  fofms  a white  infusible 
powder,  which,  after  ignition,  is  insoluble  in  acids,  with  the  ex- 
ception of  strong  sulphuric  acid.  The  hydrate  is  a gelatinous, 
bulky,  white  precipitate,  very  sparingly  soluble  in  carbonate  of 
ammonium.  It  is  insoluble  in  the  caustic  alkalies.  If  the  salts  of 
zirconium  be  precipitated  by  an  alkaline  carbonate,  the  precipitate 
becomes  redissolved  if  agitated  with  excess  of  the  carbonate ; a 
bicarbonate  takes  up  still  more,  and  by  boiling  the  solution,  a por- 
tion of  the  earth  is  deposited.  If  a neutral  solution  of  sulphate 
of  zirconium  to  which  sulphate  of  potassium  has  been  added  be 
boiled,  a characteristic  decomposition  occurs,  and  a basic  sulphate 
of  zirconium  falls,  whilst  acid  sulphate  of  potassium  is  formed  and 
remains  dissolved.  The  chloride  of  zirconixim,  (ZrCl^^  231*5  ; 
Mol.  Yol.  Ill;  Sj).  Gr.  of  vajooiir^  8*15)  crystallizes  in  needles: 
it  is  soluble  in  water  and  in  alcohol : the  crystals  effloresce  in  the 
air,  and  lose  water  and  hydrochloric  acid,  leaving  an  oxychloride, 
which  is  soluble. 

Zirconia  is  distinguished  from  alumina  and  glucina  by  its  in- 
solubility in  the  caustic  alkalies.  Its  salts  have  a purely  astrin- 
gent taste  ; when  their  neutral  solutions  are  boiled  with  the  sul- 
jphate  of  jpotassium^  a sparingly  soluble  subsulphate  of  the  earth 
is  formed.  Tincture  of  galls  gives  a yellow  precipitate  in  their 
solutions  ; ferrocyanide  of  yjotassium  does  not  produce  a precipi- 
tate with  them. 

§ lY.  Thoeixu^i,  Yttrioi,  Erbium,  Terbium. 

(681)  Thorixoi  (Th=119*0)  was  discovered  in  1829,  by  Ber- 
zelius, in  a rare  black  mineral  termed  thorite.^  found  in  a syenitic 
rock  in  Uorway.  This  metal,  like  aluminum,  is  procured  from  its 
chloride,  which  is  a volatile  compound  obtained  by  heating  an 
intimate  mixture  of  thorina  and  finely  divided  charcoal  in  a cur- 
rent of  dry  chlorine.  Thorinum  much  resembles  aluminum,  but 
takes  fire  considerably  below  redness,, and  burns  with  great  bril- 
liancy ; the  resulting  oxide  shows  no  traces  of  fusion.  Thorina  is 
considered  to  be  a protoxide,  and  is  remarkable  for  its  high  spe- 
cific gravity  (9*402).  It  is  insoluble  in  solutions  of  the  caustic 
alkalies,  but  is  dissolved  without  difflculty  in  those  of  their  car- 
bonates. After  it  has  been  ignited  it  is  no  longer  soluble  in  any 
acid  except  the  concentrated  sulphuric.  Its  salts  have  an  astrin- 
gent taste,  and  their  solutions  give  a white  precipitate  with  ferro- 
cyanide of  potassium.  Sulphate  of  thorinum  forms  with  sulphate 
of  potassium  a double  sulphate  of  potassium  and  thorinum,  which 
is  soluble  in  water,  but  is  precipitated  by  a saturated  solution  of 


YTTEITM YTTEIA CEEITJM. 


449 


sulphate  of  potassium.  The  sulphate  of  thorinum  exhibits  the 
characteristic  peculiarity  of  being  precipitated  by  boiling  its  solu- 
tion, but  it  is  redissolved  slowly  on  cooling.  Its  crystals,  like 
those  of  sulphate  of  yttrium,  when  heated,  become  milk-white 
without  altering  in  form.  Oxalic  acid  gives  with  salts  of  thori- 
num, even  in  acid  solutions,  a white  insoluble  oxalate  of  the  metal. 

(682)  Ytteiltvi  is  obtained  by  a method  similar  to  that  em- 
ployed for  aluminum  and  glucinum.  This  metal  is  not  oxidized 
when  heated  to  redness  either  in  air  or  in  aqueous  vapour ; in 
oxygen  it  burns  with  superb  scintillations  ; solutions  of  the  alka- 
lies and  the  dilute  acids  dissolve  it  slowly. 

Yttria  is  a very  rare  earth,  found  in  gadolinite^  a mineral 
wdiich  occurs  at  Ytterby,  in  Sweden,  and  which  is  a silicate  of 
yttrium,  glucinum,  cerium,  and  iron  : it  occurs  also  in  yttrotan- 
talite  combined  with  tantalum,  and  in  one  or  two  other  very  rare 
minerals.  It  is  considered  to  be  a protoxide,  and  forms  a white 
earthy  powder  of  sp.  gr.  4*842  ; it  is  insoluble  in  the  caustic  alka- 
lies, but  the  carbonates  of  the  alkaline  metals  dissolve  it ; carbo- 
nate of  ammonium  dissolves  it  still  more  freely. 

Its  salts  are  colourless  ; they  have  a sweetish  astringent  taste  ; 
their  solutions  yield  a white  precipitate  with  ferrocyanide  of  po- 
tassium. The  most  characteristic  salt  of  yttrium  is  the  sulphate, 
the  crystals  of  which  lose  water  at  176°,  and  become  milk-white, 
without  change  of  form  ; on  being  put  into  water  they  do  not  re- 
sume their  transparency. 

Mosander  states  that  three  bases  have  been  confounded  under 
the  name  of  yttria : to  the  more  abundant  of  these  he  gives  the 
name  of  yttria : the  other  two  he  distinguishes  as  erbia  and  ter- 
bia.  The  oxide  of  erbium  has  a yellowish  tint,  but  its  salts  are 
colourless  ; the  salts  of  terbium  have  a pale  rose  colour. 

§ y.  Ceeium,  Lanthanum,  and  Didymium. 

(682  a)  Closely  allied  to  the  metals  of  the  earths  are  three 
other  metals,  the  oxides  of  which,  being  more  or  less  coloured, 
have  not  generally  been  considered  as  belonging  to  the  earths 
proper.  They  need  no  lengthened  description,  as  they  have 
hitherto  been  found  only  in  a few  rare  minerals,  of  which  cerite^ 
a hydrated  basic  silicate  of  cerium,  is  the  most  common.  Till  re- 
cently they  were  all  confounded  together  under  the  name  cerium.. 

Ceeium  appears  to  form  two  oxides — a protoxide,  and  a sesqui- 
oxide,  both  of  wliich  yield  salts  with  acids.  Tlie  best  known  of 
these  are  the  oxalate  and  the  double  sulpliate  of  ])rotoxide  of 
cerium  and  potassium,  which  latter  salt  is  insoluble  in  a solution 
of  potassium.  The  oxalate  (OeO^O^,  3 H^O)  lias  been  given  in 
doses  of  from  2 to  4 grains,  with  good  effect,  in  some  cases  of  ob- 
stinate vomiting,  and  in  some  forms  of  pyrosis.  The  sesqui  oxide 
of  cerium  has  a yellowish  tinge,  and  its  salts  are  yellow  or  red. 

Lanthanum  (so  named  from  Xav^avw,  to  lie  hid)  was  discov- 
ered by  Mosander,  in  1841.  It  forms  only  one  oxide,  which  is 
buff-coloured,  and  freely  soluble  in  diluted  nitric  acid.  It  forms 
29 


450 


LAl^THANTJM DIDYMITJM 3»IAGNESIUM. 


colourless,  astringent  salts,  which  give  a white  precipitate  with 
the  soluble  oxalates. 

Didymium  (so  named  from  ^i5u(xo?,  twin,  in  reference  to  its  close 
association  with  lanthanum)  also  furnishes  hut  a single  oxide,  which 
is  of  a dark-hrovm  colour,  when  anhydrous : in  the  hydrated  state 
it  is  insoluble  in  solutions  of  potash  and  ammonia ; but  it  absorbs 
carbonic  acid  from  the  air.  It  furnishes  a sparingly  soluble  white 
oxalate,  and  yields  rose-white  double  sulphates  with  the  sulphates 
of  potassium,  sodium,  and  ammonium.  Its  solutions,  when  viewed 
through  a prism  by  transmitted  light,  show  a strong  absorption 
line  in  the  yellow,  and  another  in  the  green  (Part  I.  p.  140).  Its 
salts  are  pink  or  violet-coloured,  and  are  not  precipitated  at  ordi- 
nary temperatures  by  sulpliide  of  ammonium. 


CHAPTER  XY. 

G E O U P I V. MAGNESIAN  METALS. 


Magnesium — Zinc — Cadmium. 


Metal. 

Symbol. 

Atomic 

weight. 

Atomic 

vol. 

Specific 

heat. 

F using- 
point  F° 

Boiling- 
point  F° 

Specific 

gravity. 

Electric 

condnc- 

tivitv 
at  32'=’  F. 

Magnesium  .... 

Mg 

24 

13-76 

0-2499 

1-743 

25-47* 

Zinc 

Zn 

65 

9-12 

0-0955 

773 

1904 

7-146 

29-02 

Cadmium 

m 

112 

12-96 

0-0567 

442 

1580 

8-604 

23-72 

These  metals  are  all  volatile,  and  burn  in  air  with  a powerful 
flame  when  strongly  heated.  They  furnish  but  one  basic  oxide, 
and  yield  very  soluble  chlorides  and  sulphates : the  sulphide  of 
magnesium  is  to  some  extent  soluble ; those  of  zinc  and  cadmium 
are  insoluble.  These  metals  have  a strong  tendency  to  form  basic 
carbonates  ; their  corresponding  salts  are  isomorphous. 

§ I.  Magnesium:  Mg"=24,  or  Mg  = 12.  Sj?.  Gr.  1-743. 

(683)  Magnesiiim  is  usually  classed  with  those  metals  the  oxides 
of  which  furnish  the  alkaline  earths,  but  it  is  much  more  analo- 
gous to  zinc  in  its  properties  than  to  any  other  element.  Magne 
slum  is  an  abundant  ingredient  of  the  crust  of  the  earth.  It  is 
found  in  combination  in  large  quantities  as  a double  carbonate 
with  calcium,  forming  magnesian  limestone,  or  dolomite.  It  is 
contained  abundantly  in  sea-water  as  chloride,  and  in  many 
springs  as  sulphate.  It  likewise  enters  more  or  less  extensively  into 
the  formation  of  many  rocks,  and  of  a great  variety  of  minerals. 

Prejparation.  1. — Hussy  obtained  it  in  the  metallic  form  by 
heating  its  anhydrous  chloride  with  potassium  in  a porcelain  or 
platinum  crucible.  AVhen  cold,  the  contents  of  the  vessel  were 
digested  in  cold  water,  by  which  the  chloride  of  potassium  and  un- 

* At  62°  -6. 


MAGNESniM. 


451 


decomposed  chloride  of  magnesium  were  dissolved  out.  The  metal 
was  left  as  a grey  powder,  which  could  be  melted  into  globules. 

2.  — Deville  and  Caron  {Corrvptes  rendus^  xliv.  394)  obtain  the 
metal  as  follows  : — 9000  grains  of  pure  chloride  of  magnesium  are 
mixed  with  1500  grains  of  fused  chloride  of  sodium  and  1500 
of  pure  fluoride  of  calcium,  both  in  fine  powder.  1500  grains 
of  sodium  in  small  fragments  are  carefully  mingled  with  the 
powder,  and  the  whole  is  thrown  into  a clay  crucible  at  a full  red 
heat,  and  it  is  then  instantly  covered.  When  the  mixture  has 
become  tranquil,  the  cover  is  removed,  and  the  fused  mass  is 
stirred  with  an  iron  rod,  in  order  to  render  it  homogeneous 
throughout,  and  to  obtain  a clean  surface  upon  the  liquid.  Glob- 
ules of  magnesium  are  then  distinctly  visible.  The  crucible  is 
allowed  to  cool  partially,  and  the  metallic  globules  are  united  by 
means  of  the  iron  rod ; the  melted  mass  is  then  poured  upon  a 
shovel,  and  the  magnesium,  amounting  to  about  675  grains,  is 
separated  from  the  slag.  The  magnesium  may  be  placed  in  a 
porcelain  tray  and  collected  into  one  mass  by  melting  it  in  a cur- 
rent of  hydrogen ; after  which  it  may  be  purified  by  remelting 
in  a bath  of  mixed  chloride  of  magnesium,  chloride  of  sodium, 
and  fluoride  of  calcium.  It  still,  however,  usually  retains  portions 
of  carbon,  silicon,  and  nitrogen,  from  which  it  may  be  purified 
by  careful  distillation  in  a current  of  hydrogen.  Sonstadt  has 
recently  prepared  it  on  a considerable  scale  by  this  method,  for 
commercial  purposes. 

3.  — Bunsen  (^Liebig's  Annal.  Ixxxii.  137)  prepares  magnesium 
by  the  electrolytic  decomposition  of  the  chloride  of  magnesium  ; 
this  salt  he  melts  in  a deep  covered  porcelain  crucible  divided  by 
a vertical  diaphragm  of  porcelain,  which  extends  half-way  down 
the  crucible ; the  electrodes  are  made  of  carbon,  and  are  intro- 
duced through  two  openings  in  the  lid,  the  negative  electrode 
being  notched  to  receive  the  reduced  magnesium  which  lodges  in 
the  cavities : the  crucible  is  brought  to  a red  heat,  and  is  filled 
with  the  melted  chloride,  which  then  is  readily  decomposed  by 
10  cells  of  the  zinc  carbon  battery  (266).  The  principal  difficulty 
in  this  operation  arises  from  the  small  density  of  the  reduced 
metal,  which  rises  to  the  surface  of  the  fused  salt,  and  is  liable  to 
reoxidation. 

Properties. — Magnesium  is  a malleable,  ductile  metal  of  the 
colour  of  silver,  which  takes  a high  polish,  and  preserves  it  nearly 
as  well  as  zinc  at  ordinary  temperatures  in  dry  air  ; but  in  a moist 
atmosphere  it  becomes  slowly  oxidized.  Its  fracture  appears  some- 
times to  be  crystalline,  at  other  times  fibrous.  It  has  about  tlie  same 
degree  of  hardness  as  calc-spar.  At  a moderate  red  heat  it  may 
be  melted.  Wlien  ignited  in  dry  air  or  in  oxygen  gas,  it  takes  fire 
and  becomes  oxidized  ; in  the  form  of  wire  it  burns  easily,  emitting 
a light  of  dazzling  brilliancy,  which  has  lately  been  employed  as 
an  artificial  light  for  photogra})hic  purposes;  the  magnesia  wliich 
is  produced  exhibits  no  sign  of  fusion.  Deville  and  (Jaron  have 
shown  that  magnesium  is  nearly  as  volatile  as  zinc,  and  that  it  may 
be  distilled  by  heating  it  strongly  in  a current  of  hydrogen.  A 


452  MAGNESIA SULPHIDE  AND  CHLOKIDE  Oi'  MAGNESIUM. 

portion  of  the  metal  is  carried  away  in  suspension  by  the  gas,  and 
if  the  latter  be  kindled  as  it  issues  from  the  apparatus,  it  burns  with 
a beautiful  and  highly  luminous  flame.  Magnesium  is  but  slowly 
acted  upon  by  cold  water,  but  it  is  rapidly  dissolved  if  the  water 
be  slightly  acidulated.  It  is  also  freely  soluble  in  a solution  of  sal 
ammoniac.  When  thro^vn  into  strong  hydrochloric  acid  it  bursts 
into  flame  ; yet  a mixture  of  concentrated  sulphuric  and  fuming 
nitric  acid  has  no  action  upon  it  unless  it  be  heated.  When  heated 
in  chlorine  and  in  the  vapour  of  bromine,  of  iodine,  or  of  sulphur, 
it  burns  brilliantly.  Magnesium  unites  directly  with  nitrogen, 
forming  a transparent  crystallized  nitride  (MggX^)  which  is  decom- 
])Osed  rapidly  by  water  into  magnesia  and  ammonia  (Deville). 
Geuther  and  Briegleb  obtained  a greenish-yellow  amorphous 
nitride  of  similar  composition,  by  heating  the  metal  in  pure  and 
dry  nitrogen.  It  is  immediately  decomposed  by  water. 

(684)  Magnesia  (MgO=40,  or  MgO=20) ; Sp.  Gr.  3.6 ; Com.- 

position  in  parts ^ Mg,  60  ; O,  40. — The  only  known  oxide  of 

magnesium  is  a bulky,  white,  tasteless,  infusible,  and  nearly  in- 
soluble powder,  which  when  placed  upon  moistened  turmeric-paper 
turns  it  distinctly  brown.  It  is  usually  procured  by  strongly 
igniting  the  artificial  carbonate  in  a crucible,  but  it  may  also  be 
obtained  by  ignition  of  the  nitrate  of  magnesium  ; in  this  case  it 
assumes  a much  denser  form.  Magnesia,  when  mixed  with  water, 
gradually  combines  with  it,  and  forms  a hydrate  (H^MgO^)?  which 
absorbs  carbonic  acid  slowly  from  the  air : no  sensible  elevation 
of  temperature  occurs  during  the  process  of  hydration.  A native 
hydrate  of  similar  composition  occurs  in  crystalline  scales. 

(685)  Sulphide  of  Magnesium  (MgS=56)  is  but  sparingly 
soluble  in  water.  It  may  be  obtained  as  a hydrate  by  precipitat- 
ing a boiling  solution  of  sulphate  of  magnesium  with  sulphide  of 
potassium,  when  it  falls  as  a white  mucilaginous  mass. 

(686)  Chloride  of  Magnesioi  (MgCl2=95,  or  MgCl=4T'5  ; 
Sp.  Gr.  2 '77,  cryst.  vnth  6 H^O,  1'562)  is  contained  abundantly  in 
sea  water.  It  may  be  obtained  in  the  anhydrous  condition  by  dis- 
solving 1 part  of  magnesia  in  hydrochloric  acid,  and  adding  3 parts 
of  sal  ammoniac  in  solution,  after  which  the  mixture  is  evaporated 
to  dryness  ; by  this  means  a double  chloride  of  magnesium  and 
ammonium  is  formed  (II^XCl,MgCl2),  which  may  be  evaporated 
wdthout  loss  of  acid,  whilst  the  solution  of  mere  chloride  of  mag- 
nesium is  partially  decomposed  during  evaporation  : when  the 
double  salt  is  ignited  in  a covered  crucible,  the  sal  ammoniac  is 
expelled,  and  pure  chloride  of  magnesium  remains.  At  a red  heat 
it  fuses  to  a transparent  liquid,  which  forms  a silky-looking  mass 
of  confused  crystals  on  cooling.  Chloride  of  magnesium  is  deli- 
quescent, and  gives  out  heat  whilst  undergoing  solution  in  water ; 
by  evaporation  at  a low  temperature  it  may  be  obtained  in  crystal- 
line needles  with  6 H^O.  It  is-  soluble  in  alcohol : it  forms  double 
chlorides  with  the  chlorides  of  the  metals  of  the  alkalies.  If  heated 
strongly  in  a current  of  dry  ammoniacal  gas,  the  chloride  of  mag- 
nesium is  volatilized,  and  a white  sublimate  of  (MgCl^,  4H,Is)  is 
obtained  (Clark). 


SULPHATE,  KTTKATE,  AND  CARBONATE  OF  MAGNESIUM.  453 


(687)  Sulphate  OF  Magnesium  (MgSO^,  7 Il2O=:120  + 126,  or 
Mg0,S03,H0. 6 HO  = 60 + 63);  Sp.  Gr.  anhydrous^  2-706,  cryst, 
1*660  ; Composition  in  parts ^ dry,  MgO,  33*33  ; SO3,  66-67  ; 
cryst.  MgO,  16*26  ; SO3,  32*52  ; H2O,  51*22. — This  is  the  most 
important  salt  of  magnesium.  It  is  made  in  very  large  quantities 
from  sea  water,  either  by  precipitating  the  magnesia  hy  means  of 
lime,  and  then  dissolving  it  in  sulphuric  acid ; or  by  first  crystal- 
lizing out  the  greater  part  of  the  common  salt,  after  which,  on 
evaporation,  crystals  of  the  sulphate  are  obtained.  Native  car- 
bonate of  magnesium  is  also  sometimes  acted  upon  with  diluted 
sulphuric  acid,  and  the  salt  obtained  by  evaporation.  Tlie  sul- 
phate is  also  procured  in  considerable  quantities  from  magnesian 
limestone : the  rock  is  burned,  slaked,  and  largely  washed  with 
w'ater  to  remove  part  of  the  lime ; it  is  then  treated  with  sul- 
phuric acid,  and  the  sulphate  of  magnesium  is  separated  from  the 
sparingly  soluble  sulphate  of  calcium  by  solution  and  recrystal- 
lization. It  is  also  obtained  in  considerable  quantity  from  the 
mother-liquors  of  the  alum  works.  Sulphate  of  magnesium  is  a 
common  ingredient  in  mineral  waters.  Its  trivial  name  of  Epsom 
salts  is  derived  from  the  circumstance  of  its  being  abundantly 
contained  in  many  springs  in  the  neighbourhood  of  Epsom,  from 
the  waters  of  which  it  was  at  one  time  obtained.  Sulphate  of 
magnesium  is  soluble  in  3 times  its  weight  of  water  at  60°,  and 
1^  at  212°.  Its  solution  has  a bitter,  disgusting  taste.  It  crys- 
tallizes readily  in  right  rhombic  prisms,  which  are  slightly  efflo- 
rescent: when  lieated  moderately,  they  lose  their  water  of  crys- 
tallization ; if  the  heat  be  intense  and  long  continued,  a part  of 
the  acid  also  escapes.  If  crystallized  from  a liot  solution,  oblique 
rhombic  prisms,  with  6 Il^O  are  deposited,  and  the  ordinary  crys- 
tals, when  heated  to  125°,  become  opaque  and  lose  1 H^O.  Crys- 
tallized sulphate  of  magnesium  loses  6 of  its  7 atoms  of  water  at  a 
temperature  below  300°,  but  it  retains  1 atom  even  at  400°.  This 
last  atom  may  be  displaced  by  an  equivalent  of  an  anhydrous  salt, 
such  as  sulphate  of  potassium,  with  which  it  forms  a double  salt, 
])Ossessed  of  the  same  crystalline  form  as  sulphate  of  magnesium 
(MgSO^K^SO^  . 6 II2O)  of  sp.  gr.  2*076.  Sulpliate  of  ammoni- 
um forms  with  the  sulphate  of  magnesium  a similar  double 
salt. 

(688)  Nitrate  of  Magnesium  (Mg  2 NO3  . 6 II2O  = 148  + 
108;  Sp.  Gr.  1*464)  is  deliquescent,  and  soluble  in  alcohol;  it 
crystallizes  with  difficulty. 

(689)  Carbonate  OF  Magnesium  (MgC03=84,  orMgO,C02= 
42;  Sp.  Gr.  3*056)  occurs  native  as  a white,  hard,  am()r]i)hous  mi- 
neral, called  7na(jnesite.  It  is  procured  artificially  by  ])reci])itat- 
ing  a boiling  solution  of  a salt  of  magnesium  with  carbonate  of 
potassium,  and  dissolving  the  ])reci])itate  in  carbonic  acid  water; 
as  the  gas  escapes,  the  salt  is  deposited  as  a terhydrate,  in  trans- 
])arent  hexagonal  prisms  (Mg003 . 3 ir2H):  by  ex])osure  to  air 
the  crystals  effloresce  and  are  converted  into  a })rotoliydrate 
(MgCOg  . II2O).  The  anhydrous  carbonate  may  be  obtained  by 
introducing  a test-tube  containing  a solution  of  sulpliate  of  mag- 


4:54: 


CAEBOXATE,  BOEATE,  AXD  SILICATES  OF  MAGNESIUM. 


nesiiim  into  a strong  glass  tube  containing  a solution  of  carbonate 
of  sodium,  sealing  the  tube,  and  then  allowing  the  two  solutions 
to  mix.  Crystals  of  carbonate  of  magnesium  are  deposited  slowly. 

JIagnesia  aJha^  the  common  white  magnesia  of  the  shops,  is 
made  by  precipitating  a boiling  solution  of  the  sulphate  of  mag- 
nesium by  a hot  solution  of  carbonate  of  sodium.  The  sulphate 
of  magnesium  is  allowed  to  remain  slightly  in  excess,  otherwise 
the  precipitate  contains  a little  carbonate  of  sodium.  It  is  depo- 
sited as  a white,  light,  bulky  powder,  which  is  composed  of  hy- 
drate of  magnesia  (MgH^OJ  combined  with  a quantity  of  hydrated 
carbonate  (5dEgC-0-3,H2O),  the  amount  of  which  may  vary  from  2 
to  4 atoms  to  1 atom  of  the  hydrate  of  magnesia ; it  is  very  spar- 
ingly soluble  in  water.  A quantity  of  carbonic  acid  is  expelled 
from  the  mixture  during  the  preparation  of  this  compound. 

Dolomite^  when  its  structure  is  crystalline,  usually  consists  of 
carbonate  of  magnesium  and  carbonate  of  calcium  in  the  propor- 
tion of  1 atom  of  each  (Mg'Oa  2 003),  though  sometimes  the  pro- 
portion of  carbonate  of  calcium  considerably  exceeds  1 atom.  A 
solution  of  sulphate  of  calcium  decomposes  carbonate  of  magne- 
sium at  ordinary  temperatm’es,  and  thus  spring  water  originally 
charged  with  sulphate  of  calcium  may,  by  filtration  through  a 
bed  of  dolomite,  become  impregnated  with  sulphate  of  magnesium. 

A very  pure  carbonate  of  magnesium  is  manufactured  from 
dolomite  by  a process  introduced  by  Pattinson.  In  this  operation 
the  mineral  is  finely  ground  and  sifted,  and  exposed  to  a low  red 
heat  for  2 or  3 hours,  by  which  the  carbonate  of  magnesium  is 
decomposed.  It  is  then  introduced  into  a strong  iron  cylinder 
lined  with  lead,  where  it  is  mixed  with  water,  and  carbonic  anhy- 
dride is  forced  in  under  a pressure  of  2 or  3 atmospheres,  till  it 
ceases  to  be  absorbed ; the  carbonate  of  magnesium  becomes  dis- 
solved as  acid  carbonate,  leaving  the  carbonate  of  calcium ; the 
clear  liquid,  when  boiled,  deposits  the  carbonate  of  magnesiimi, 
which  is  drained,  and  dried  in  a stove  at  a low  temperature. 

By  mixing  a solution  of  nitrate  of  magnesium  with  an  excess 
of  a saturated  solution  of  tlie  acid  carbonate  of  potassium,  and 
allowing  the  solution  to  stand  for  some  days,  a remarkable  double 
salt  is  deposited  in  regular  crystals,  composed  of  (Mg003,lAH003 
. 4 11,0),  but  which  is  decomposed  by  redissolving  it  in  water. 
The  corresponding  salt  of  sodium  is  more  stable. 

A native  homte  of  magnesium  [3  (Mg  2 BO,),  B2O3,  or  3 MgO, 
4 BO3],  named  horacite^  is  found  crystallized  in  cubes;  it  is  ren- 
dered electric  by  heat. 

(690)  Silicates  of  Magneskai. — Silica  and  magnesia  may 
be  artificially  combined  in  many  proportions.  A large  number 
of  minerals  are  formed,  either  wholly  or  partially,  of  the  silicates 
of  magnesium.  Olivine  or  chrysolite  [2  (MgFe)O,  SiO,]  is  a 
crystallized  orthosilicate,  usually  of  a green  colour,  obtained  from 
basaltic  and  volcanic  rocks ; it  frequently  accompanies  masses  of 
meteoric  iron.  Talc  is  a very  soft  slaty  mineral,  which  has  a 
fonnula  [2  (MgO,  SiOj)  . 2 MgO,  3 SiO^].  Steatite^  French 
Chalky  or  Soapstone ^ is  (MgO,  SiOj  . 2 MgO,  3 SiO,).  Pieros- 


CHABACTEES  OF  THE  SALTS  OF  MAGNESmM. 


455 


mine  is  a hydrated  metasilicate,  (2  MgSiOg  . Meer- 

schaum is  another  hydrated  silicate,  of  which  the  formula  is 
(2  MgO,  3 SiO, . 4 Ii;e).  Serpentine  (2  [(MgPe)e,Siej  . MgO, 
2 HJO)  is  another  hydrated  silicate  of  magnesium,  in  which  a 
portion  of  the  magnesia  is  often  displaced  by  protoxide  of  iron. 
Serpentine  frequently  occurs  in  compact  masses,  which  take  a 
high  polish,  and  from  the  beauty  of  its  variegated  colours,  it  is 
often  employed  for  ornamental  purposes.  It  is  readily  attacked 
by  acids,  and  occurs  in  sufficient  abundance  to  be  employed  as  a 
source  of  the  salts  of  magnesium. 

The  double  silicates  of  magnesium  are  still  more  numerous. 
Aicgite  or  pyroxene  is  one  of  these : it  is  a crystalline  mineral, 
often  found  in  basalt  and  lava,  and  is  a silicate  of  calcium  and 
magnesium,  portions  of  which  metals  are  often  displaced  by  iron 
and  manganese  [(-0aMgFeMn)0,  SiOj.  Hornblende  or  amphi- 
bole  is  a silicate  and  aluminate  of  magnesium,  calcium,  and  iron, 
with  a variable  proportion  of  the  fluorides  of  calcium  and  potas- 
sium, (3  [(Mg'GaFe)O,  SiOJ  . 2 (MgOaFeMn)  O,  3 SiO^ . x (KOa) 
F^).  It  occurs  sometimes  in  dark  green  or  black  crystals,  at  other 
times  massive,  disseminated  through  many  rocks,  such  as  syenite 
and  porphyry,  and  frequently  in  basalt  and  lava.  Asbestos  and 
amiantMos  commonly  consist  of  a fibrous  variety  of  amphibole. 

(691)  Triphospthate  of  magnesium  and  hydrogen  (II,Mg'', 

PO4  . Y or  HO,  2 MgO,  PO5  . 14  Aq)  is  an  efflorescent, 

sparingly  soluble  salt,  which  crystallizes  in  fine  tufts  of  six-sided 
acicular  prisms,  when  a solution  of  a magnesian  salt  is  mixed 
with  the  solution  of  the  common  phosphate  of  sodium. 

Triphosphate  of  Magnesium  and  Ammonium  (Mg'TI^H,PO^ 
. 6 II2O,  or  2 MgO,  H,H0,P05 . 12  Aq=13Y -1-108),  or  triple 
phosphate^  as  it  was  formerly  called,  is  a more  important  compound 
than  the  foregoing  one.  ‘‘  It  is  prepared  by  mixing  phosphate  of 
sodium,  mingled  with  chloride  of  ammonium,  with  a salt  of  mag- 
nesium ; by  agitation  tliis  compound  is  deposited  in  minute  crys- 
talline grains  : ” it  furnishes  a very  delicate  test  of  the  presence  of 
magnesium  : it  is  insoluble  in  water  containing  free  ammonia  or 
muriate  of  ammonia,  but  it  is  taken  up  in  appreciable  quantities 
by  pure  water.  It  is  frequently  met  with  as  a constituent  of 
urinary  calculi,  both  in  man  and  in  the  lower  animals.  Phos- 
phate of  magnesium  and  ammonium  is  readily  soluble  in  acids ; 
ammonia  precipitates  it  from  such  solutions  unchanged  ; when 
ignited,  it  parts  with  its  water  and  ammonia,  and  glows  like 
alumina  and  zirconia  as  it  suddenly  contracts  its  bulk.  The 
ignited  residue  contains  35’Y  per  cent,  of  MgO,  and  64‘3  of  P^O^. 
It  is  frequently  employed  for  the  determination  of  the  amount  of 
magnesia  in  the  course  of  analysis. 

(692)  Characters  of  the  Salts  of  Magnesium. — The  salts 
of  magnesium  are  colourless  and  have  a bitter  taste.  Many  ot 
the  magnesian  minerals  possess  a silky  lustre,  and  feel  unctuous  to 
the  touch.  Compounds  of  magnesium  may  be  recognised  before 
the  blowpipe^  by  the  pink  tinge  which  they  acquire  when  heated 
with  nitrate  of  cobalt. 


ESTOIATIOX  OF  THE  SALTS  OF  POTASSIOI  AXD  SODIOT. 


45  ?3 


In  solution  tliev  give  no  precipitate  with  the  acid  carhonatcs 
of  the  cdl'ali-metals  till  boiled ; but  a white  basic  carbonate  of 
inagnesiuin  when  mixed  with  the  normal  carbonate  of  potassium 
or  sodium^  unless  a salt  of  ammonium  be  present,  which  interferes 
with  the  precipitation.  Phosphate  of  ammonium  gives  with  them 
a white  crystalline  granular  precipitate  of  double  phosphate  of 
magnesium  and  ammonium,  which  is  easily  soluble  in  acids. 
Oxalate  of  ammonium^  mixed  with  sal  ammoniac,  gives  no  pre- 
cipitate with  the  magnesium  salts,  neither  do  the  soluble  sulphates. 
T\\q  fixed  alPalies  throw  down  a white  gelatinous  hydrate  of  the 
earth,  which  is  insoluble  in  excess  of  the  precipitant.  Lime-ioater 
produces  a similar  precipitate.  Ammonia  produces  but  a very 
incomplete  precipitation  of  magnesia  from  its  solutions  ; the  gela- 
tinous precipitate  which  it  occasions  becomes  redissolved  on  the 
addition  of  a solution  of  chloride  of  ammonium,  and  a double 
salt  of  magnesium  and  ammonium  is  formed. 

(693)  Chaeacteks  of  the  Metals  of  the  First  Gkoup 
('Metals  of  the  Alkalies). — The  salts  of  these  metals  when  in  solu- 
tion are  distinguished  by  the  following  characters : — 1.  By  the 
absence  of  any  precipitate  on  the  addition  of  a solution  of  car- 
bonate of  potassium,  or  of  sodium  : in  the  case  of  lithium,  if  the 
salt  exceed  two  per  cent,  of  the  solution,  a precipitate  of  carbon- 
ate of  lithium  is  liable  to  occur.  2.  By  the  absence  of  any  pre- 
cipitate when  sulphuretted  hydrogen  or  hydrosulphate  of  ammo- 
nium is  added  to  the  solution.  3.  By  the  occurrence  of  a precip- 
itate with  chloride  of  platinum  in  the  case  of  salts  of  ammonium 
or  of  potassium  f and  by  the  formation  of  prismatic  crystals  of 
the  double  chloride  of  sodium  and  platinum  when  evaporated  in 
the  presence  of  salts  of  sodium. 

(694)  Estimation  of  Potassium  and  Sodium. — If  the  relative 
proportions  of  the  potassium  and  sodium  be  not  required,  their 
combined  weight  is  usually  ascertained  in  the  form  of  sulphates. 
They  may  in  most  cases  be  readily  obtained  in  this  condition  by 
treating  the  solution  with  sulphuric  acid,  evaporating  to  dryness, 
and  fusing  the  mass  in  a platinum  crucible  in  which  a fragment 
of  carbonate  of  ammonium  is  suspended.  Tlie  excess  of  sulphuric 
acid  is  thus  readily  dissipated,  and  the  amount  of  the  acid  com- 
bined with  the  potassium  and  sodium,  is  determined  by  precipita- 
tion with  chloride  of  barium.  Mhen  ammonium  salts  are  present 
with  those  of  potassium  and  sodium,  its  amount  may  be  deter- 
mined by  distilling  off  the  ammonia  in  the  manner  already  de- 
scribed (626). 

In  order  to  determine  the  quantity  of  potassium  and  sodium 
in  a mixture  of  the  salts  of  the  two  metals,  they  should  be  con- 
verted into  the  state  of  chlorides,  and  heated  to  low  redness  to 
expel  moisture  and  all  ammoniacal  salts,  allowed  to  cool,  and 
weighed  ; a certain  proportion  of  these  mixed  chlorides  (ten  or 
twelve  grains  will  suffice)  is  then  mixed  with  an  excess  of  the 
double  chloride  of  platinum  and  sodium,  evaporated  to  dryness 

* Rubidium  and  coesium  -^ould  also  be  found  in  this  precipitate  (607,  608),  if  either 
of  these  metals  were  present. 


CHAHACTEES  OF  THE  METALS  OF  THE  SECOND  GKOHP.  457 

over  a steam  bath,  and  the  excess  of  the  chloride  of  platinum  and 
sodium  removed  by  washing  with  alcohol  of  specific  gravity  0’860. 
The  crystalline  residue  i-s  collected  on  a filter  and  weighed.  One 
hundred  parts  contain  30‘53  of  chloride  of  potassium,  and  cor- 
respond to  15*98  of  potassium,  or  to  19*26  of  anhydrous  potash. 
The  quantity  of  chloride  of  sodium  is  obtained  by  deducting  the 
weight  of  the  chloride  of  potassium  from  that  of  the  mixed  chlo- 
rides employed. 

(695)  The  conversion  of  the  alkaline  metals  into  the  condition 
of  chlorides^  previous  to  precipitation  by  the  perchloride  of 
platinum,  if  they  are  not  already  in  that  form,  is  rather  trouble- 
some. They  may  be  first  converted  into  sulphates  by  evaporat- 
ing the  solution  with  a slight  excess  of  sulphuric  acid,  and  ignit- 
ing the  residue  ; the  sulphates  thus  obtained  are  to  be  dissolved  in 
water  and  mixed  with  a solution  of  chloride  of  barium  in  slight 
excess.  The  sulphuric  acid  is  thus  precipitated  as  sulphate  of 
barium,  and  the  alkalies  are  converted  into  chlorides  ; but  the  ex- 
cess of  barium  in  the  liquid  must  still  be  got  rid  of.  A mixture 
of  caustic  ammonia  and  of  the  sesqui  carbon  ate  of  ammonium  is 
therefore  added  to  the  solution  after  it  has  been  filtered  from  the 
sulphate  of  barium.  The  excess  of  barium  is  thus  thrown  down 
as  carbonate,  and  the  carbonate  of  barium  may  then  be  removed 
by  filtration.  Once  more  the  solution  is  to  be  evaporated  to  dry- 
ness in  a platinum  dish,  and  the  residue  gently  ignited  to  expel 
the  ammoniacal  salts.  The  remaining  mass  now  contains  nothing 
but  the  mixed  chlorides  of  sodium  and  potassium. 

(696)  Characters  of  the  Metals  of  the  Second  Group 
(Metals  of  the  Alkaline  Earths,  including  Magnesium) : — 1.  The 
salts  of  these  metals  when  in  solution  give  a wdiite  precipitate  on 
the  addition  of  solution  of  carbonate  of  sodium  or  of  potassium. 
— 2.  They  yield  no  precipitate  with  hydrosulphate  of  ammonium 
nor  with  sulphuretted  hydrogen. — 3.  Lime-water  occasions  no 
precipitate,  except  in  cases  in  which  the  magnesian  salts  are  pre- 
sent, or  in  wliich  the  solution  contains  free  carbonic  acid. 

(697)  Separation  of  the  Alkaline  Earths  from  the  Alkalies. — 
Supposing  a solution  to  contain  salts  of  the  alkalies  and  of  the 
alkaline  earths,  the  quantities  of  each  base  may  be  determined  in 
the  following  manner : — An  excess  of  a mixture  of  ammonia  and 
sesquicarbonate  of  ammonium  is  added  to  the  solution ; tlie  am- 
monium thus  combines  with  the  radicle  of  the  acid  previously  in 
union  with  the  earths,  whilst  tlie  carbonic  acid  converts  the  earths 
into  carbonates;  the  liquid  is  filtered  from  tlie  precipitate,  tlien 
evaporated  to  dryness,  and  heated  to  expel  the  ammoniacal  salts. 
The  dry  residue  is  then  washed  with  water,  which  dissolves  out 
the  salts  of  the  alkali-metals  : and  from  this  liquid  the  proportions 
of  potassium  and  sodium  can  be  ascertained  in  the  manner  already 
described  (694).  A little  magnesia  is  apt  to  acconi])any  the  salts 
of  the  alkali-metals : its  presence  may  be  detected  and  its  quantity 
determined  by  the  addition  of  lime-water  to  the  solution  ; hydrate 
of  magnesia  is  precipitated,  and  may  be  collected,  weighed,  and 
added  to  the  amount  obtained  from  tlie  portion  which  was  preci- 


458  SEPAEATION  OF  THE  ALKALINE  EARTHS  FROM  EACH  OTHER. 

pitated  as  carbonate.  The  precipitation  must  be  effected  in  a 
stoppered  bottle,  to  exclude  the  carbonic  acid  of  the  atmosphere, 
which  would  precipitate  a portion  of  lime  with  the  magnesia. 
The  excess  of  lime  may  be  got  rid  of  by  the  addition  of  oxalic 
acid,  which  occasions  a precipitate  of  oxalate  of  calcium  that  can 
be  separated  on  a filter,  but  need  not  be  weighed.  The  earthy 
carbonates  must  now  be  dealt  with  in  the  following  manner : — 

(698)  Separation  of  Barium^  Strontium^  Calcvum^  and  Mag- 
nesium from  each  other. — The  alkalies  having  been  separated  in 
the  manner  just  described,  the  carbonates  of  the  metals  which  in 
the  preceding  operation  were  not  dissolved  by  water  are  taken  up 
with  diluted  nitric  acid,  and  the  liquid  is  largely  diluted.  Sul- 
phuric acid  is  then  added  so  long  as  it  occasions  a precipitate. 

If  the  liquid  originally  contained  no  alkaline  salts,  it  will  not 
be  necessary  to  convert  the  earths  into  carbonates,  but  the  solu- 
tion may  be  simply  diluted,  acidulated  with  nitric  acid,  and 
mixed  with  sulphuric  acid,  as  before. 

This  precipitate  may  consist  of  the  sulphates  of  barium  and 
strontium.  It  must  be  collected,  washed  with  boiling  water  and 
weighed,  then  fused  with  thrice  its  weight  of  carbonate  of  sodium, 
by  which  it  will  be  decomposed  ; double  decomposition  occurs,  car- 
bonates of  barium  and  strontium  and  sulphate  of  sodium  being 
formed.  The  carbonates  of  barium  and  strontium,  being  in- 
soluble, are  separated  from  the  soluble  sulphate  of  sodium  by 
washing,  and  the  carbonates  of  the  two  earths  are  converted  into 
chlorides  by  the  action  of  diluted  hydrochloric  acid.  The  chlo- 
rides of  barium  and  strontium  are  evaporated  to  dryness,  weighed, 
and  may  then  be  separated  with  tolerable  exactness  by  the  action 
of  alcohol,  which  dissolves  the  chloride  of  strontium,  but  leaves 
that  of  barium  unacted  upon.  Hydrofluosilicic  acid  may  also 
be  employed  to  separate  the  two  earths ; in  the  course  of  two  or 
three  hours  the  whole  of  the  barium  is  precipitated  by  it,  whilst 
the  strontium  remains  in  solution. 

The  acid  liquid  from  which  the  barium  and  strontium  have 
been  separated  is  rendered  slightly  alkaline  by  ammonia,  and  the 
calcium  precipitated  as  oxalate,  by  means  of  oxalate  of  ammo- 
nium : this  precipitate,  after  being  well  washed,  is  heated  to  dull 
redness,  and  is  estimated  as  carbonate  of  calcium.  If  the  propor- 
tion of  magnesium  be  large,  a little  of  the  salt  of  calcium  is  re- 
tained in  solution. 

The  filtrate,  which  may  still  contain  magnesium,  is  mixed 
with  phosphate  of  sodium,  briskly  stirred,  and  allowed  to  stand 
for  twelve  hours,  to  give  time  for  the  granular  crystalline  phos- 
phate of  magnesium  and  ammonium  to  subside:  it  is  collected 
on  a filter,  washed  with  water  which  contains  free  ammonia,  and 
estimated,  after  ignition,  as  pyrophosphate  of  magnesium. 

(699)  Collection  of  Precipitates. — It  will  generally  be  found 
more  convenient  in  separating  the  metals  of  the  alkaline  earths 
from  those  of  the  alkalies,  in  the  first  place  to  precipitate  the 
barium  and  strontium  by  sulphuric  acid  from  the  dilute  acidulated 
solution;  then  to  neutralize  by  ammonia,  and  separate  the  cal- 


MANIPIJXATION  OF  FILTEES  AND  PEECIPITATES.  459 

cinm  by  the  addition  of  oxalate  of  ammonium ; to  evaporate  the 
solution  containing  the  salts  of  magnesium  and  of  the  metals  of 
the  alkalies  to  dryness,  heating,  to  expel  salts  of  ammonium ; then 
to  redissolve  the  residue  in  water,  and  separate  the  whole  of  the 
magnesia  at  once  by  the  addition  of  lime-water  in  a stoppered 
bottle,  in  the  manner  already  described. 

Certain  precautions  in  manipulation  are  required  in  transfer- 
ring a solution  to  a filter,  in  order  to  avoid  loss.  In  pouring  a 
liquid  from  one  vessel  to  another,  a glass  rod  should  be  moistened 
with  distilled  water  and  brought  against  the  edge  of  the  vessel 
from  which  the  liquid  is  to  be  poured,  as  shown  in  fig.  339.  By 
this  means,  when  the  pouring  is 
ended,  if  the  rod  be  still  kept  in 
contact  with  the  edge,  the  last 
drop  is  prevented  from  running 
down  the  outside  of  the  jar  or 
basin : the  rod  may  then  be 
placed  in  the  vessel  until  a 
similar  operation  is  again  re- 
quired. After  the  whole  of  the 
liquid  has  been  poured  off,  the 
portion  which  adheres  to  the 
rod  and  to  the  sides  of  the  ves- 
sel is  washed  down  by  a jet  of 
water  from  the  washing  bottle, 
fig.  340,  and  the  washings  are 
added  to  the  rest  of  the  decanted  liquid. 

(700)  Washing  of  Precipitates, — In  washing  precipitates,  the 
use  of  a flask  provided  wdth  two  tubes 
passing  through  the  cork,  as  represented 
in  fig.  340,  facilitates  the  operation.  The 
tube  (2^,  passes  just  through  the  cork;  the 
longer  tube,  J,  reaches  almost  to  the  bot- 
tom of  the  flask ; it  terminates  at  in  a 
fine  orifice ; on  forcing  air  from  the  lungs 
through  the  tube  <3^,  the  water  is  expelled 
at  c,  and  may  be  directed  upon  the  filter. 

It  is  necessary  that  the  filter  should  fall 
completely  within  the  funnel,  and  that 
before  any  of  the  liquid  for  filtration  is 
poured  into  it,  the  paper,  after  it  has  been 
placed  in  the  funnel,  should  be  moistened 
with  distilled  water.  In  washing  a precipitate,  the  stream  of 
water  should  be  directed  upon  the  upper  edges  of  the  filter,  so  as 
to  wash  down  the  saline  particles,  which,  by  evaporation  of  the 
liquid,  have  a tendency  to  accumulate  there  as  the  solution  rises 
under  the  influence  of  capillary  action. 

In  cases  where  gelatinous  ])recipitates,  like  hydrated  oxide  of 
iron  or  alumina,  are  to  be  washed  continuously  for  a long  period, 
a simple  contrivance  by  Gay-Lussac  will  be  found  very  useful ; it 
is  merely  a bottle  of  distilled  water,  a,  fig.  341,  which  by  means 


Fig.  340. 


Fig.  339. 


460 


WASHCsG  AXD  COLLECTESTG  PKECTPITATES. 


of  a siphon,  supplies  the  water  at  a regulated  level  in  the  funnel, 
d\  h represents  a tube  open  at  both  "ends,  which  reaches  nearly 
to  the  bottom  of  the  bottle,  a ; c is  a siphon  with  limbs  of  equal 
length,  which  passes  a little  deeper  into  the  bottle  than  h ; the 

Fig.  341. 


limb  which  dips  into  the  funnel  has  its  lower  extremity  a little 
recurved,  to  direct  the  pui-e  water  upwards,  and  the  siphon  can 
be  filled  by  blowing  gently  into  the  bottle  through  the  tube  h. 
The  funnel,  cZ,  is  placed  so  that  the  upper  edge  of  the  filter  shall 
be  a little  above  the  level  of  the  lower  end  of  c.  Under  these 
circumstances  the  filter  can  never  overflow.  As  soon  as  the  sur- 
face of  the  liquid  in  the  funnel  falls  just  below  the  level  of  the 
lower  extremity  of  Z»,  the  siphon  carries  over  a small  quantity  of 
water,  and  bubbles  of  air  rise  in  the  bottle,  a,  to  supply  its  place. 
This  process  goes  on  continuously  as  the  water  flows  from  the  fil- 
ter, until  A is  empty. 

In  order  to  ascertain  whether  a precipitate  has  been  sufliciently 
washed,  a drop  of  the  liquid  which  passes  through  is  evaporated  on 
a slip  of  glass : it  ought  to  leave  no  appreciable  stain  or  residue. 

In  collecting  a precipitate  from  a filter,  the  paper  should 
be  dried  thoroughly ; after  which  the  portion  that  can  be  readily 
detached  from  the  paper  should  be  allowed  to  fall  into  the  pla- 
tinum or  porcelain  capsule  in  which  it  is  intended  to  perform  the 
ignition.  The  capsule  is  to  be  placed  upon  a smooth  sheet  of 
paper,  and  the  filter  being  held  at  one  corner  with  a pair  of 
forceps,  is  burned  in  such  a way  that  the  ashes  shall  fall  into  the 
platinum  capsule ; any  particles  of  ash  which  may  fall  upon  the 
paper  are  carefully  transferred  to  the  capsule. 


ZINC. 


461 


It  must  not  be  forgotten  that  filtering-paper  itself  leaves 
traces  of  ash  when  burnt ; but  the  amount  of  this  in  good  speci- 
mens should  not  exceed  about  3 grains  in  1000.  Before  using 
any  paper  for  the  purposes  of  analysis,  the  quantity  of  ash  (usually 
consisting  of  silica,  lime,  and  traces  of  oxide  of  iron)  which  a 
given  weight  of  it  afibrds  when  burnt  must  be  ascertained.  In 
each  analytical  experiment  the  weight  of  the  filter  employed  being 
approximatively  known,  it  is  easy  to  estimate  the  amount  of  ash 
wBich  it  would  yield  (at  most  but  a few  hundredths  of  a grain) 
and  to  deduct  this  from  the  gross  weight  of  the  precipitate. 

§ II.  Zinc  : Zn''  = 65*0,  or  Zn=32*5.  Sp.  Gr.  6*8  to  7*1 ; 

Boiling  Pt.  1904°  F. 

(701)  Zinc,  or  spelter^  as  it  is  often  called  in  commerce,  has 
been  known  in  the  metallic  form  since  the  time  of  Paracelsus. 
Its  ores  occur  in  considerable  abundance,  though  it  is  never  met 
with  in  the  native  state.  Much  of  the  zinc  of  commerce  is  sup- 
plied from  Silesia,  where  the  ore  wrought  is  calamine  ; the  com- 
mon or  rhomboidal  calamine,  a carbonate  of  zinc,  is  the  most 
important  variety,  though  the  prismatic  or  electric  calamine,  a 
hydrated  basic  silicate  of  zinc,  is  found  often  in  the  Carinthian 
ores : it  is  much  more  difficult  of  reduction.  Carbonate  of  zinc 
is  also  extensively  worked  in  Belgium,  where  it  is  found  mixed 
with  clay.  In  the  Mendip  Hills,  in  Somersetshire,  the  carbonate 
of  zinc  is  associated  wdth  magnesian  limestone.  Blende^  or  sul- 
phide of  zinc,  is  worked  in  England  to  some  extent ; it  usually 
accompanies  the  sulphide  of  lead  (or  galena)  in  the  mountain 
limestone.  In  Hew  Jersey  red  oxide  of  zinc  has  been  found 
in  large  quantities  both  massive  and  crystallized;  the  colour  is 
due  to  admixture  with  oxides  of  manganese  and  iron.  It  forms 
a valuable  ore,  and  is  easily  reduced.  In  the  year  1860,  4357 
tons  of  zinc  were  extracted  from  English  mines. 

(702)  Extraction  of  Zinc  f ro7n  its  Ores. — In  the  extraction 
of  zinc,  whether  from  blende  or  from  calamine,  the  ore  is  crushed 
between  rollers,  and  undergoes  a process  of  roasting ; in  the  case 
of  blende  a preliminary  mechanical  treatment  is  required,  in 
order  to  separate  the  galena  as  completely  as  possible,  as  the 
])resence  of  lead  would  occasion  rapid  destruction  of  the  crucibles 
during  the  subsequent  reduction  of  the  metal.  The  roasting  of 
l)lende  is  tedious,  and  requires  to  be  carefully  performed  ; the 
sulphur  burns  away  as  sulphurous  anhydride,  and  the  zinc  be- 
comes oxidized ; 2 ZnS  -h  3 yield  2 ZnO  -|-  2 SO^.  Calamine 
also  yields  oxide  of  zinc  when  roasted,  whilst  carbonic  aidiydride 
and  water  are  expelled.  The  roasted  ore  from  either  source 
is  mixed  with  half  its  weight  of  powdered  coke  or  antliracite,  and 
introduced  into  crucibles  of  peculiar  construction.  Tlic  metliod 
of  reduction  practised  in  England  offers  one  of  the  few  instances 
in  which  distillation  per  descensum  is  still  practised : — a circular 
furnace,  somewhat  similar  to  tliat  used  in  making  glass,  is  em 
ployed:  in  this  furnace  six  large  clay  crucibles,  (three  of  which 


4G2 


EXTRACTION  OF  ZINC  FROM  ITS  ORES. 


are  represented  in  the  section  at  a,  a,  a,  fig.  342,)  each  4 
feet  high  and  2-|-  feet  in  diameter,  are  arranged,  three  on  each  side 
of  the  firebars ; one  of  these  crucibles  is  shown  in  section  in  the 
figure.  In  the  bottom  of  each  crucible  is  an  opening,  and  to  this 
is  attached  a short  iron  pipe,  which  passes  out  through  the 

bottom  of  the  fur- 
nace ; to  this  iron 
tube  a second  wider 
tube,  about  eight 
feet  long,  is  fastened 
in  such  a manner  as 
to  be  readily  remov- 
able ; beneath  the 
open  end  of  this  tube 
a sheet-iron  vessel,  c, 
is  placed  to  receive 
the  zinc.  The  bot- 
tom of  the  crucible 
is  then  loosely  plug- 
ged with  large  pieces 
of  coke,  and  a charge 
containing  from  4 to 
5 cwt.  of  the  mixture 
of  calcined  ore  and 
coal  is  introduced 
into  each  pot,  and 
the  cover  is  carefully 
luted  on.  Carbonic 
oxide  is  first  evolv- 
ed abundantly,  and 
burns  with  a blue 
fiame  at  the  mouth 
of  the  short  iron  tube ; 
in  a few  hours  the  colour  of  the  fiame  changes  to  brown,  when 
the  cadmium,  which  is  more  volatile  than  zinc,  comes  over,  and 
may  be  condensed.  When  the  colour  of  the  fiame  changes 
to  bluish-white  the  zinc  is  distilling  nearly  pure.  The  fiame 
is  then  extinguished  by  attaching  the  longer  tube,  and  the  metal 
becomes  condensed  partly  in  pow^der,  partly  in  stalactitic  masses, 
and  falls  down  into  the  iron  vessels,  c,  c,  placed  for  its  reception. 
The  zinc,  being  volatile  at  very  high  temperatures,  boils  and  dis- 
tils as  the  operation  proceeds.  In  order  to  prevent  the  pipe, 
from  becoming  choked,  it  is  occasionally  removed,  and  the  zinc 
detached  from  it.  The  crude  metal  is  mingled  with  a good  deal 
of  oxide  ; it  is  therefore  re-melted,  skimmed,  and  cast  into  ingots  ; 
or  (if  intended  for  rolling)  into  sheets,  and  then  laminated  at  a 
temperature  of  about  250°.  Calamine,  which  contains  52  per 
cent,  of  metal,  does  not  yield  on  an  average  above  30;  the 
greater  part  of  the  silicate  of  zinc,  which  calamine  almost  always 
contains,  escaping  decomposition. 

(703)  In  Silesia  the  distillation  is  efiected  in  muffle-shaped 


EXTRACTION  OF  ZINC  IN  SILESIA  AND  BELGIUM.  463 

eartlien  retorts,  wliicli  are  ranged  in  two  rows  on  the  same  plane 
in  a long  furnace,  back  to  back : the  outer  end  of  each  retort  is 
provided  with  two  apertures ; the  lower  one  is  employed  for  in- 
troducing the  charge,  and  is  afterwards  carefully  luted  up,  whilst 
the  upper  one  is  for  receiving  a bent  earthen  pipe  which  carries 
off  the  metal  as  it  distils. 

(704)  In  Belgium  the  distillation  is  managed  quite  differently. 
The  ores  treated  in  that  country  are  of  two  kinds,  both  occurring 
in  a matrix  of  clay  above  a bed  of  dolomite : one  is  a red  variety, 
containing  about  33  per  cent,  of  zinc,  with  a good  deal  of  oxide 
of  iron,  but  admitting  of  reduction  at  a moderate  temperature ; 
the  other  is  a white  ore,  also  a calamine,  which  contains  about  46 
per  cent,  of  zinc,  and  requires  a much  higher  temperature  for  its 
reduction.  These  two  species  of  ore  are  kept  distinct  from  each 
other  during  the  process  of  smelting.  The  calamine,  having  been 
washed  to  remove  the  clay,  is  roasted,  during  which  operation  it 
loses  about  25  per  cent,  of  w^ater  and  carbonic  anhydride.  After 
this  it  is  reduced  to  a ffne  powder,  and  thoroughly  mixed  with 
half  its  weight  of  coal  dust : this  mix- 
ture is  then  introduced  into  clay 
retorts  about  three  feet  eight  inches 
long  and  six  inches  in  diameter; 
each  retort  is  charged  with  about 
40  lb.  of  the  mixture  of  coal  and 
roasted  ore.  Forty-two  of  these  re- 
torts are  arranged  in  an  arched  fur- 
nace, in  rows  of  six,  placed  one  above 
another.  The  backs  of  the  retorts 
rest  on  notches  in  the  wall,  e,  ffg. 

343,  and  are  supported  on  a slightly 
higher  level  than  the  open  extremi- 
ties, which  rest  in  front  upon  iron 
plates,  To  each  retort  an  open, 

somewhat  conical,  cast-iron  pipe,  c,  is 
luted  ; tliis  serves  as  a receiver  for  the 
distilled  metal,  and  upon  each  of 
these  receivers  is  fitted  a second  re- 
ceiver of  sheet-iron,  d,  with  an  open- 
ing at  the  extremity  for  the  es- 
cape of  gas.  The  fire  by  which 
the  retorts  are  heated  is  shown  at 
A.  In  such  a furnace  two  charges 
may  be  worked  off*  in  twenty-four 
liours.  During  the  operation  the  small 
adapters,  d,  d,  are  withdrawn  once  in 
two  hours,  and  the  liquid  zinc  which 
lias  condensed  in  the  receivers  is  raked 
out  into  a large  ladle  and  cast  into 
ingots.  When  the  distillation  is  com- 
]dete,  the  residues  in  the  retorts  still 
retain  nearly  25  per  cent,  of  zinc,  which  is  chiefly  in  the  form 


464 


PEOPEETIES  AND  ESES  OF  ZINC. 


of  silicate;  this  portion  is  entirely  wasted  (Plot  and  Mni'aillie, 
Ann.  des  Mines^  lY.  v.  165). 

The  retorts  in  the  upper  part  of  snch  a furnace  necessarily 
receive  less  heat  than  those  in  the  lower  part,  and  hence  this  pro- 
cess is  particularly  well  adapted  to  the  Belgian  ores,  because  the 
poorer  ones,  which  require  less  heat,  can  be  employed  in  charg- 
ing the  upper  retorts. 

(705)  Preparation  of  Pure  Zinc. — Commercial  zinc  contains 
a small  amount  of  lead  and  of  mon ; minute  quantities  of  tin  and 
cadmium  are  also  often  present,  besides  occasionally  traces  of 
arsenic  and  of  copper.  Carbon  is  also  mentioned  among  its  impu- 
rities, but  Eliot  and  Storer,  in  their  elaborate  examination  of  the 
ordinary  impurities  of  this  metal,  did  not  find  it  in  any  of  the  13 
specimens  which  they  examined,  though  traces  of  sulphur  were 
always  present.  The  best  method  of  obtaining  the  metal  in  a 
state  of  purity  consists  in  transmitting  sulphuretted  hycbogen 
through  a strong  and  somewhat  acid  solution  of  sulphate  of  zinc, 
filtering  from  any  precipitate  which  may  be  formed ; and  after 
boiling  the  solution,  in  order  to  expel  the  sulphuretted  hydrogen, 
precipitating  the  zinc  in  the  form  of  carbonate  by  the  addition  of 
carbonate  of  sodium.  The  carbonate  is  to  be  washed  and  redis- 
solved in  pure  sulphuric  acid  and  submitted  to  electrolytic  decom- 
position, or  else  the  dried  carbonate  may  by  ignition  be  convert- 
ed into  oxide  of  zinc,  which  must  be  distilled  in  a porcelain 
retort  with  charcoal  prepared  from  loaf  sugar. 

(706)  Properties. — Zinc  is  a hard,  bluish-white  metal,  which, 
when  a mass  of  it  is  broken  across,  exhibits  a beautiful  crystalline 
fracture.  It  is  rather  brittle  at  ordinary  temperatures,  but  between 
200°  and  300°,  it  is  possessed  of  considerable  ductility  and  malle- 
ability, and  it  may  be  laminated  and  wrought  with  ease  : at  a tem- 
perature a little  higher  than  this,  it  again  becomes  so  brittle  that 
it  may  be  pulverized  in  a mortar.  It  fuses  at  773°,  and  at  a bright- 
red  heat  it  may  be  volatilized : the  temperature  of  its  boiling- 
point  i.s  estimated  by  Deville  at  1904°  F. : if  its  vapour  be  exposed 
to  the  air,  it  bimis  with  great  splendour  and  is  converted  into 
oxide,  which  is  deposited  in  copious  white  flocculi.  Zinc  soon 
tarnishes  when  exposed  to  a moist  atmosphere,  and  becomes  cov- 
ered with  a thin,  closely-adhering  film  of  oxide,  by  whicli  the  metal 
beneath  is  protected  from  further  change.  This  property  renders 
zinc  valuable  for  a variety  of  economical  and  domestic  purposes. 
It  combines,  however,  readily  at  ordinary  temperatures  with  chlo- 
rine, bromine,  and  iodine,  if  moistened  with  water ; it  is  also  easily 
attacked  by  all  the  mineral  acids,  and  is  employed  to  decompose 
diluted  sulphuric  acid  when  hydrogen  is  required.  A strong  solu- 
tion of  potash  likewise  acts  upon  zinc  if  boiled  upon  it ; hydrogen 
being  liberated,  whilst  the  zinc  is  dissolved  in  the  alkaline  solu- 
tion ; Zn  + 2 KIIO  becoming  II,  Iv20,Zn0.  Zinc  precipitates 
most  of  the  basylous  metals  less  oxidizable  than  itself  in  the 
metallic  state  from  their  solutions. 

(707)  Uses. — The  uses  of  zinc  are  daily  extending.  From  its 
durability,  cheapness,  and  lightness,  it  is  frequently  employed  as 


OXIDE  OF  ZINC. 


465 


a substitute  for  lead  in  roofing.  It  is  employed  as  the  oxidizable 
metal  in  the  construction  of  the  voltaic  battery.  Sheet  iron  coated 
with  zinc,  or  galvanized  iron  as  it  is  often  called,  is  also  used  for 
roofing ; the  iron  gives  strength,  whilst  the  zinc  protects  it  from 
oxidation,  and  it  is  not  combustible  like  zinc  alone.  Galvanized 
iron  is  prepared  by  cleaning  sheet  iron  thoroughly  as  in  making 
tin  plate  (811),  and  plunging  the  metal  into  a bath  of  molten  zinc, 
covered  with  sal  ammoniac ; the  surface  of  the  zinc  is  by  this 
means  kept  free  from  oxide,  which  is  dissolved  by  the  sal  ammo- 
niac, and  the  two  metals  unite  readily.  A tougher  and  superior 
article  is  obtained  by  first  coating  the  iron  plate  with  a very  thin 
film  of  tin  by  a voltaic  action,  and  then  immersing  the  metal  in 
the  melted  zinc. 

Zinc  has  a considerable  power  of  dissolving  iron,  in  consequence 
of  which  it  corrodes  the  iron  pots  in  which  it  is  melted : an  alloy 
of  zinc  with  a small  proportion  of  iron  is  formed,  which  is  less 
fusible  than  zinc,  and  crystallizes  in  large  plates  on  cooling. 

Zinc  forms  several  valuable  alloys.  Of  these,  brass  is  the  most 
important : it  consists  of  about  2 parts  of  copper  to  1 of  zinc. 
German  silver  is  brass  containing  a portion  of  nickel,  to  which  its 
white  colour  is  due.  Of  late  years  zinc  in  powder  has  been  em- 
ployed as  the  basis  of  a pigment  well  adapted  to  resist  the  action 
of  the  weather.  Oxide  of  zinc  has  likewise  been  substituted  for 
red  lead  wfith  advantage  in  the  preparation  of  glass  for  optical 
purposes  (599). 

(708)  Oxide  of  Zinc  (ZnO=81,  or  ZnO=40-5);  Sjp.  Gr. 
5*612  : Composition  in  100  jmHs^  Zn,  80*39  ; O,  19*61. — It  is  pos- 
sible that  the  film  which  is  formed  upon  the  surface  of  metallic 
zinc  by  exposure  is  a suboxiOe ; but  only  one  well  ascertained 
oxide  of  the  metal  is  known,  and  this  is  regarded  as  a protoxide : 
this  oxide  is  occasionally  deposited  in  furnace  flues  in  yellowish 
six-sided  prisms;  but  it  is  generally  obtained  in  the  form  of  a 
white  flocculent  powder.  If  zinc  be  thrown  in  small  quantities  at 
a time  into  a capacious  clay  crucible  previously  heated  to  white- 
ness, it  burns  with  a brilliant  flame  and  deposits  large  white  flakes 
of  the  oxide ; but  when  thus  prepared,  it  is  mechanically  mixed 
with  particles  of  the  metal,  from  wdiich  it  may  be  separated  by 
levigation  with  water;  the  heavier  metallic  portions  subside 
quickly  and  leave  the  oxide  in  suspension.  The  process  of  manu- 
facturing this  oxide  when  it  is  required  as  a pigment  known  as 
zinc  white ^ consists  in  distilling  zinc  from  clay  retorts  into  cli am- 
bers through  which  a current  of  air  is  maintained.  The  volatilized 
metal  burns  at  the  high  temperature  to  which  it  is  exposed  under 
these  circumstances,  and  the  oxide  is  deposited  in  a series  of  con- 
densing chambers.  It  has  been  attempted  to  introduce  this  white 
pigment  as  a substitute  for  white  lead,  but  though  the  colour  is 
permanent,  and  of  a pure  white,  it  does  not  combine  chemically 
with  the  oil  necessary  as  vehicle  for  distributing  the  colour,  and 
hence  it  soon  peels  otf,  and  allows  moisture  to  ])enetrate.  An 
impure  oxide,  sold  under  the  name  of  tutty^  is  obtained  from  the 
flues  of  furnaces  in  which  brass  is  melted. 

30 


466 


SULPHIDE,  CHLOEIDE,  AND  SULPHATE  OF  ZINC. 


Oxide  of  zinc  becomes  yellow  when  heated,  but  recovers  its 
whiteness  as  the  temperature  falls.  It  is  readily  soluble  in  acids. 
The  hydrated  oxide  (Zn0,H.,0)  is  precipitated  from  the  solutions 
of  the  salts  of  zinc  by  the  addition  of  hydrate  of  potash  or  of  soda, 
as  well  as  by  ammonia ; it  is  redissolved  by  an  excess  of  the  alka- 
line liquid. 

(709)  Sulphide  of  Zinc:  Blende  (ZnS=97,  or  ZnS  = 48‘5); 
8p.  Gr.  4T  : Comp,  in  parts Zn,  67T4;  S,  32'86. — This  com- 
pound is  one  of  the  most  abundant  minerals  of  zinc.  When  pure 
it  is  of  a pale-brown  colour,  but  generally  it  is  nearly  black  from 
admixture  with  sulphide  of  iron.  It  sometimes  occurs  massive, 
but  is  usually  crystallized  in  rhombic  dodecahedra,  though  it  oc- 
curs in  other  forms  of  the  regular  system.  Metallic  zinc  does  not 
unite  readily  with  sulphur : but  if  heated  rapidly  in  mixture  with 
cinnabar  (or  sulphide  of  mercury),  the  mercury  is  volatilized,  and 
sulphide  of  zinc  is  formed  with  almost  explosive  violence.  Sul- 
phide of  zinc  does  not  fuse  when  heated : when  roasted  in  the  air 
it  absorbs  oxygen ; at  a low  temperature  a large  portion  of  it  is 
converted  into  sulphate  of  zinc,  but  at  a higher  temperature  sul- 
phurous anhydride  is  formed,  and  oxide  of  zinc  is  left.  The  sul- 
phide is  only  slightly  attacked  by  sulphuric  and  hydrochloric 
acids,  but  nitric  acid  and  aqua  regia  dissolve  it  readily.  When 
the  salts  of  zinc  are  mixed  with  sulphide  of  ammonium,  a white, 
gelatinous,  hydrated  sulphide  of  zinc  is  precipitated,  which  absorbs 
oxygen  quickly  from  air,  and  is  readily  dissolved  by  acids. 

(710)  Chloride  of  Zinc  (ZnCl2=136,  or  ZnCl  = 68) ; Sp.  Gr. 
2*753. — This  salt  may  be  procured  by  heating  the  metal  in  chlo- 
rine gas,  but  it  is  generally  obtained  by  dissolving  the  metal  in 
hydrochloric  acid ; the  acid  is  decomposed,  its  chlorine  unites  with 
the  zinc,  forming  chloride  of  zinc,  which  is  retained  in  solution, 
whilst  its  hydrogen  escapes  in  the  gaseous  form.  When  this  solu- 
tion is  heated,  it  loses  water  till  the  temperature  rises  to  480°  ; it 
then  becomes  anhydrous,  but  remains  fluid,  and  may  be  heated  to 
above  700°  without  emitting  an  inconvenient  amount  of  fumes; 
hence  it  is  sometimes  employed  as  a hot-bath  for  maintaining 
objects  at  a high  but  measurable  and  regulated  temperature.  At 
a red  heat  it  distils.  Pure  chloride  of  zinc  is  a white,  very  deli- 
quescent substance,  fusible  at  about  212°  ; it  is  powerfully  corro- 
sive when  applied  to  the  skin.  Under  the  name  of  Burnettes  Dis- 
infecting Fluids  its  solution  has  been  largely  used  as  an  antiseptic, 
and  as  a preservative  of  wood  and  vegetable  fibre  against  decay. 
Chloride  of  zinc  is  soluble  in  alcohol. 

Chloride  of  zinc  absorbs  ammoniacal  gas  freely.  It  also  unites 
with  oxide  of  zinc  in  several  proportions,  and  forms  a number  of 
oxychlorides.  Chloride  of  zinc  forms  double  salts  with  the  chlo- 
rides of  the  alkaline  metals ; a concentrated  solution  of  the  double 
chloride  of  zinc  and  ammonium  (2  Il4UCl,ZnCl2)  is  used  for  the 
purpose  of  removing  the  film  of  oxide  from  the  surface  of  metals, 
such  as  zinc,  iron,  or  copper,  which  are  to  be  united  by  the  ope^ 
ration  of  soldering. 

(711)  Sulphate  of  Zinc  (ZnSO^,  7 = 161  + 126,  or 


CARBONATE,  AND  CHARACTERS  OF  THE  SALTS  OF  ZINC.  467 


ZnOjSOg  . 7 no  = 80*5  + 63;  Sp.  Gr.,  anhydrous^  3*681 ; cryst. 
1*931)  is  obtained  in  large  quantities  as  a residue  in  the  ordinary 
process  of  procuring  hydrogen  by  the  action  of  diluted  sulphuric 
acid.  It  may  also  be  prepared  by  roasting  sulphide  of  zinc  at  a 
low  temperature,  lixiviating  the  mass  and  crystallizing.  It  crys- 
tallizes in  colourless  four-sided  prisms,  which  constitute  the  white 
vitriol  of  commerce.  In  a dry  air  it  is  efflorescent ; it  is  soluble 
in  2|-  parts  of  w^ater  at  60°,  and  melts  in  its  water  of  crystalliza- 
tion when  heated ; it  may  be  obtained  crystallized  with  6,  5,  2, 
and  1 atom  of  water,  by  varying  the  temperature  at  which  the 
crystals  are  allowed  to  be  formed.  Sulphate  of  zinc  is  used  medi- 
cinally in  small  doses  ; it  is  likewise  prepared  largely  for  the 
calico  printer.  It  forms  double  sulphates  with  potassium  and 
with  ammonium,  which  crystallize  with  6 H^O.  Several  basic 
sulphates  of  zinc  may  also  be  obtained.  . 

(712)  Carbonate  of  Zinc  (ZnOOg— 125,  or  ZnO, 00^=62*5  ; 
Sp,  Gr.  4*4:  Composition  in  100  ZnO,  64*8;  OO^,  35*2  ; or 
Zn,  52 ; OO3,  48)  is  found  native,  both  massive  and  crystallized, 
in  forms  derived  from  the  rhombohedron.  It  is  usually  of  a 
greyish  or  yellowish  colour,  forming  one  variety  of  ccdarnine^  which 
is  so  named  from  its  property  of  adhering,  after  fusion,  in  the 
form  of  reeds,  to  the  base  of  the  furnace.  It  readily  loses  car- 
bonic anhydride  when  ignited.  Ho  neutral  carbonate  of  zinc  can 
be  obtained  from  the  salts  of  the  metal  by  double  decomposition. 
When  a hot  solution  of  a salt  of  zinc  is  precipitated  by  a boiling 
solution  of  an  alkaline  carbonate,  a hydrated  oxycarbonate  is 
formed,  consisting  of  (8  Zn0,300-2 . 6 II^O ; Schindler).  Several 
other  basic  carbonates  of  zinc  may  be  formed. 

The  other  variety  of  calamine  becomes  electric  by  heat ; it  is 
a hydrated  orthosilicate  (Zn^SiO^jIIjO,  or  2 ZnO,  Si 63  . IIO). 

(713)  Characters  of  the  Salts  of  Zinc. — The  salts  of  zinc 
are  colourless  ; their  solutions  have  an  astringent,  metallic  taste, 
and  act  rapidly  and  powerfully  as  emetics. 

They  are  distinguished  by  giving  no  precipitate  in  acid  solu- 
tions with  sidplinretted  hydrogen^  though  the  acetate,  even  when 
acidulated  with  acetic  acid,  gives  a white  hydrated  sulphide  when 
the  gas  is  transmitted : they  yield  a white  hydrated  sulpliide  of 
zinc  with  sulphide  of  ammonitim  ; a white  hydrated  oxide  with 
potash^  soda^  or  ammonia^  soluble  in  excess  of  the  alkali ; a white 
basic  carbonate  of  zinc  with  the  carbonates  of  the  alhali-metals^ 
soluble  in  excess  of  tlie  solution  of  carbonate  of  ammonium,  but 
not  in  that  of  the  carbonates  of  potassium  or  sodium  ; they  also 
yield  a white  precipitate  ^ii\\  ferrocyanide  of  jwtassium. 

Before  the  blovjpipe^  in  the  reducing  dame  on  charcoal,  the 
metal  is  reduced  and  volatilized,  burning  into  white  fumes  of  oxide 
of  zinc.  If  ])laced  on  charcoal  and  moistened  with  a solution  of 
nitrate  of  cobalt,  the  compounds  of  zinc  when  heated  in  the  oxi- 
dating flame  leave  a green  residue,  which  is  not  fusible. 

(714)  Estimation  of  Zinc, — Zinc  is  best  precipitated  for  ana- 
lysis by  carbonate  of  potassium,  the  whole  solution  l)eing  evaj)0- 
rated  down  to  dryness  ; the  residue,  which  contains  the  carbonate 


468 


CADMITTM. 


of  zinc,  is  washed  with  boiling  water,  dried,  and  converted  by 
ignition  into  oxide  of  zinc,  which  is  weighed.  The  oxide  con- 
tains, in  100  parts,  80 '39  of  zinc.  If  ammoniacal  salts  be  present, 
an  excess  of  the  carbonate  of  potassium  should  be  used  sufficient  to 
decompose  the  salts  of  ammonium  completely,  the  ammonium  being 
wholly  expelled  as  carbonate  during  the  process  of  evaporation. 
The  foregoing  process  is  not  applicable  to  the  separation  of  zinc 
from  any  but  the  alkaline  metals. 

(715)  Separation  ofzinofrom  the  A Ikalies  and  Alkaline  Earths. 
— This  may  be  effected  by  the  addition  of  sulphide  of  ammonium 
to  the  solution  after  it  has  been  neutralized  by  ammonia ; the  zinc 
is  thus  precipitated  as  hydrated  sulphide  : it  must  be  washed  with 
a solution  of  sulphuretted  hydi’ogen,  to  prevent  its  oxidation,  then 
redissolved  in  hydrochloric  acid,  and  evaporated  to  dryness  with 
excess  of  carbonate  of  sodium  : the  soluble  salts  must  be  washed 
from  the  carbonate  of  zinc,  Avhich  is  to  be  converted  into  oxide 
by  ignition,  and  then  weighed. 

The  separation  of  zinc  from  aluminum  omd  glucinum  may  be 
effected  by  dissolving  all  the  bases  by  means  of  an  excess  of  caustic 
potash,  and  adding  sulphide  of  ammonium  : in  this  case  sulphide 
of  zinc  is  alone  precipitated : it  may  be  collected  and  its  amount 
determined  in  the  manner  just  described. 

§ III.  Cadmiuxi:  Od"=112,  or(Cd=56);  Sp.  Gr.  8*6  to  8'69 ; 

Boiling-pt.  1580°  ; calculated  Sp.  Gr.  of  vapour.^  3*869  ; observed 

Sp.  Gr.  3*94 ; Atomic  and  ALol.  Vol.  of  Vapour.^  | | 

(716)  Cadmiuw  was  discovered  by  Strome^^er,  in  1818.  It  is 
occasionally  found  as  sulphide  of  cadmium,  accompanjdng  the  ores 
of  zinc,  and  is  obtained  as  an  accidental  product  during  the  ex- 
traction of  the  latter  metal.  Being  more  volatile  than  zinc,  the 
greater  part  of  the  cadmium  sublimes  among  the  first  portions  of 
the  distilled  metal,  from  which  it  may  be  extracted  by  dissolving 
them  in  sulphuric  acid,  and  precipitating  the  cadmium  as  sulphide 
by  means  of  sulphuretted  hydrogen  ; the  sulphide  may  be  dissolved 
in  strong  hydrochloric  acid,  precipitated  by  carbonate  of  ammo- 
nium, and  reduced  in  an  earthern  retort  by  ignition  with  charcoal; 
the  metal  distils  over  at  a heat  below  redness. 

Cadmium  is  of  a white  colour,  resembling  tin,  and,  like  it, 
creaks  when  a rod  of  it  is  bent ; it  is  so  soft  that  it  leaves  its 
traces  upon  paper,  and  possesses  considerable  malleability  and  duc- 
tility : when  heated  to  about  180°,  it  becomes  very  brittle,  and 
may  be  powdered  in  a mortar  with  facility.  Cadmium  fuses  at 
442°,  and  may  be  obtained  in  octohedral  crystals  as  it  cools.  In 
the  atmosphere  it  undergoes  little  change,  but  when  thrown  into 
a red-hot  crucible  it  takes  fire,  depositing  brownish-yellow  fumes 
of  oxide.  It  is  dissolved  with  evolution  of  hydrogen  when  heated 
in  sulphuric  or  hydrochloric  acid  slightly  diluted  ; nitric  acid  dis- 
solves it  still  more  freely. 

* This  vapour  (as  well  probably  as  that  of  zinc  and  the  other  metallic  dyads)  is 
anomalous  in  volume,  1 atom  of  each  metal  yielding  2 volumes  instead  of  1 volume. 


CIIAHACTEKS  OF  THE  SALTS  OF  CADMIEAI.  4:69 

The  addition  of  cadmium  to  the  more  fusible  metals  generally 
yields  an  alloy  of  low  fusing-point,  without  destroying  the  tough- 
ness or  malleability  of  the  compound.  An  alloy  consisting  of  15 
parts  of  bismuth,  8 of  lead,  4 of  tin,  and  3 of  cadmium  fur- 
nishes a silver-white  alloy  of  sp.  gr.  9'4 : it  softens  between  131° 
and  140°,  and  at  about  140°  F.  is  completely  liquid ; it  expands 
a little  as  it  solidifies.  This  alloy  is  somewhat  ductile,  and  may 
be  filed  readily  without  clogging  the  tool : it  preserves  its  brilliancy 
in  the  air.  An  alloy  consisting  of  1 part  of  cadmium,  6 parts  of 
lead,  and  7 of  bismuth,  melts  at  180°. 

(717)  Oxide  of  Cadmium  (OdO=128,  or  CdO  = 64;  Sp.  Gr. 
6'93)  : Comp,  in  100  parts^  Od,  87*5;  0, 12'5. — This  oxide  is  ob- 
tained as  a brown  anhydrous  powder,  by  burning  the  metal  in  air, 
or  by  igniting  the  nitrate  of  cadmium  ; it  is  not  fusible  or  volatile 
in  the  furnace.  A white  hydrated  oxide  of  cadmium,  ■0dO,Il2O, 
may  be  obtained  by  decomposing  its  salts  by  a fixed  alkali ; am- 
monia in  excess  redissolves  it,  but  the  hydrates  of  potash  and  soda 
have  no  such  effect ; even  the  anhydrous  oxide  is  soluble  in  am- 
monia. Carbonate  of  ammonium  does  not  dissolve  oxide  of  cad- 
mium either  in  the  anhydrous  or  the  hydrated  form. 

Sulphide  of  Cadmium  (OdS^ldd,  or  CdS  = 72)  constitutes 
the  mineral  known  as  Greenockite^  which  occurs  crystallized  in 
six-sided  prisms.  It  may  be  formed  artificially  by  transmitting  a 
current  of  sulphuretted  hydrogen  through  a solution  of  a salt  of 
cadmium ; it  greatly  resembles  orpiment  in  appearance,  but  is 
distinguished  from  it  by  its  w^ant  of  volatility  when  heated,  and 
by  its  insolubility  in  ammonia  and  in  the  sulphides  of  the  alka- 
line metals.  It  forms  a bright  yellow  pigment  highly  valued  both 
for  the  purity  and  permanence  of  its  tint. 

Chloride  of  Cadmium  (OdCh,  2 H^O,  or  CdCl,  2 HO)  crys- 
tallizes easily.  The  (sp.  gr.  4*576)  may  be  also  obtained 

without  difficulty  in  crystals  which  have  a pearly  lustre.  It  is 
anhydrous,  and  fuses  readily  on  the  application  of  heat.  This 
salt  is  easily  obtained  by  digesting  metallic  cadmium  in  water 
with  free  iodine,  and  evaporating  the  solution  ; it  is  employed  for 
iodizing  collodion  for  photographic  purposes  (1018) 

(718)  Characters  of  the  Salts  of  Cadmium.  — The  salts  of 
cadmium  are  colourless,  and  resemble  those  of  zinc.  Tliey  may 
be  readily  distinguislied  by  the  yellow  precipitate  of  sulphide  of 
cadmium  wliich  they  yield  with  s'ldphuretted  hydrogen  in  acid 
solutions  ; this  precipitate  is  insoluble  either  in  ammonia  or  in  the 
alkaline  sulphides,  or  in  cyanide  of  potassium,  but  soluble  in 
boiling  diluted  sulphuric  acid.  Hydrates  of  potash  and  soda 
give  a precipitate  of  white  hydrated  oxide,  insoluble  in  excess  ; 
arnmoma.^  a similar  precipitate  very  soluble  in  excess  ; carhonates 
of  potassium.^  sodium.,  and  ammonium.,  a white  carbonate,  inso- 
luble in  excess;  oxalic  acid.,  a white  precipitate,  soluble  in  am- 
monia \ ferrocyanide  of  potassium,  a yellowish-white  precipitate, 
soluble  in  hydrochloric  acid. 

Before  the  hlowpipe  they  are  decomposed,  and  on  the  cool 
part  of  the  charcoal  a ring  of  brown  oxide  of  cadmium  is  depos- 


470 


COBALT. 


ited,  due  to  the  reduction  and  subsequent  combustion  of  the 
metal. 

Estimation  of  Cadmium. — Cadmium  is  readily  separated  from 
all  the  foregoing  metals  by  the  action  of  sulphm-etted  hydrogen, 
which  caus"es  a precipitate  of  the  yellow  sulphide  of  cadmium 
from  an  acidulated  solution  of  its  salts.  This  precipitate  is  redis- 
solyed  in  nitric  acid,  decomposed  by  an  excess  of  carbonate  of 
sodinm,  eyaporated  to  dryness,  washed  from  the  soluble  salts,  and 
the  resulting  carbonate  of  cadmium  is  heated  to  redness,  bj  which 
it  is  conyerted  into  oxide ; it  is  then  weighed : 100  grains  of  ox- 
ide of  cadmium  contain  S7’5  of  the  metal. 


CHAPTEK  XVI. 

GROUP  y.  METALS  MORE  OR  LESS  ALLIED  TO  IRON. 


Metals. 

Symbol 

Atomic 

weight. 

i ! 

Atomic  1 Specific  ! 
Tol.  heat. 

! ' 

Specific 

grarity. 

Electric 
conductivity 
32^  F. 

Cobalt 

Uo 

59 

6-94-  0-1069  . 

8 950 

} i 

1 i 

Nickel 

Ni  1 

59 

694  0-1086  : 

8-820 

13-11 

Uranium 

U 

' 120 

' 

1 

1 Iron  

Fe 

56 

7-10  0-1138  i 

7-844 

16-81  1 

1 Chromium 

Ur  i 

52-5 

7-00 

6-810 

1 

j Mansranese 

Mn 

55 

7-00  0-1217 

1 8-013 

! 

i 

The  metals  of  this  class  include  those  which  are  distinctly 
magnetic ; uranium,  howeyer,  appears  to  be  diamagnetic.  They 
decompose  water  at  a red  heat,  and  are  soluble  with  eyolution  of 
hydrogen  in  hydrochloric  and  diluted  sulphuric  acid.  They  form 
seyeral  oxides,  two  at  least  of  which,  except  in  the  case  of  cobalt 
and  nickel,  are  soluble  in  acids.  Sulphuretted  hydi’ogen  in  solu- 
tions acidulated  with  the  mineral  acids  does  not  precipitate  the 
metals  of  this  group.  Corresponding  salts  of  these  metals  are 
isomorphous  (see  page  291). 

§ I.  Cobalt  : Oo"  = 59,  or  Co  = 29-5.  Sp.  Gr.  8-95. 

(719)  Cobalt  appears  to  haxe  been  first  recognised  as  a dis- 
tinct metal  by  Brandt,  in  1733.  It  generally  occurs  in  combina- 
tion with  arsenic,  as  speiss-cobalt  or  tin-white  cobalt  (^oAs,),  but 
occasionally  it  is  found  as  cobalt  glance,  which  is  a compound  of 
the  ai-senide  and  the  sulphide  of  the  metal  (0oS2,-0oAs,).  Cobalt 
is  neyer  met  with  in  the  natiye  state,  except  as  an  ingredient  in 
meteoric  iron  in  small  proportion.  The  black  oxide  has  been 
found  to  some  extent  in  the  IV estern  States  of  America,  mixed 
with  the  sulphide  of  cobalt  and  with  yariable  proportions  of  the 
oxides  of  nickel,  manganese,  iron,  and  copper.  The  ores  of  tliis 


EXTRACTION  OF  COBALT. 


471 


metal  occur  cliietly  in  the  primitive  rocks,  and  are  usually  very 
complicated;  they  contain  nickel,  iron,  and  often  bismuth  and 
copper,  mineralized  either  by  sulphur  or  by  arsenic,  or  by  both 
together. 

Exi/raction. — It  is  not  easy  to  obtain  cobalt  in  a state  of  purity. 
On  a small  scale  the  ore  may  be  treated  as  follows : — It  is  first 
roasted  at  a low  but  gradually  rising  temperature,  in  order  to 
expel  the  greater  portion  of  the  arsenic  ; after  which  it  is  dissolved 
in  aqua  regia,  and  evaporated  to  dryness  to  expel  the  excess  of 
acid  ; it  is  then  redissolved  in  water,  and  a current  of  sulphuretted 
hydrogen  is  transmitted  through  the  solution.  Bismuth,  copper, 
and  the  remainder  of  the  arsenic  are  thus  precipitated  as  sulphides. 
The  filtered  liquid  is  boiled  to  expel  the  excess  of  the  gas,  and  a 
slight  excess  of  nitric  acid  is  added  to  the  boiling  liquid,  to  con- 
vert the  ferrous  into  ferric  salts  ; when  cold,  it  is  diluted  and 
supersaturated  with  ammonia ; the  iron  is  precipitated  as  per- 
oxide, carrying  with  it  a little  cobalt,  but  the  bulk  of  the  cobalt 
remains  dissolved,  with  any  nickel  which  the  ore  may  have 
contained. 

The  exact  separation  of  cobalt  from  nickel  is  tedious.  Two 
methods  have  been  proposed,  one  by  Bose,  the  other  by  Liebig 
(737).  Bose’s  method  is  the  following : — The  two  metals  are 
thrown  down  from  the  ammoniacal  liquid  as  sulphides,  by  the 
addition  of  sulphide  of  ammonium.  The  sulphides  are  redissolved 
in  nitric  acid,  the  solution  is  then  largely  diluted,  and  acted  upon 
by  a current  of  chlorine ; after  this  it  is  digested  in  a closed 
vessel  for  12  hours  upon  powdered  carbonate  of  barium.  The 
chlorine  converts  the  cobalt  into  sesquioxide,  which  is  gradually 
precipitated  by  the  barium,  and  remains  mixed  with  the  excess  of 
carbonate  of  barium  employed.  This  precipitate  is  again  dis- 
solved in  hydrochloric  acid ; the  barium  is  removed  by  adding 
sulphate  of  sodium,  and  the  cobalt  precipitated  as  protoxide  by 
caustic  soda  : the  precipitate  must  then  be  well  w^ashed  with 
boiling  water,  and  reduced  in  a current  of  hydrogen  gas,  which 
leaves  the  metal  in  the  form  of  a black,  highly  magnetic  powder. 
When  nickel  is  to  be  separated  from  cobalt  for  purposes  of  ana- 
lysis, T.  II.  Henry  recommends  the  substitution  of  a solution  of 
bromine  for  chlorine  gas  in  the  foregoing  process.  Bromine  may 
be  used  instead  of  chlorine  in  many  analogous  cases  with  great 
convenience. 

If  oxide  of  cobalt  be  reduced  in  a crucible  lined  with  charcoal, 
a carbide  of  cobalt  is  formed,  which  may  be  obtained  in  a well- 
fused  button.  The  crucible  may  be  lined  with  charcoal  for  this 
purpose  by  dipping  it  into  water,  and  filling  it  completely  with 
charcoal  finely  powdered,  and  sufficiently  moistened  to  render  it 
coherent  when  firmly  beaten  into  the  crucible ; a cylindrical 
cavity  is  then  scooped  out  of  the  middle  of  the  mass,  and  its  inte- 
rior is  carefully  smoothed  with  a glass  rod,  after  which  the 
crucible  is  allowed  to  dry  slowly.  Cobalt  nearly  ])U]*e  may  be 
procured  by  heating  the  oxalate  in  a covered  })orcelain  crucible, 
enclosed  in  a second  earthen  one,  with  the  cover  luted  down ; 


472 


OXIDES  PROTOXIDE  OF  COBALT. 


the  crucibles  are  then  exposed  for  an  hour  to  the  most  intense 
heat  of  a forge : a vrell-fnsed  button  of  cobalt  may  generally  be 
obtained  in  this  manner. 

Properties. — Metallic  cobalt  is  nearly  as  infusible  as  iron.  It 
is  of  a reddish-grey  colour,  is  hard,  and  strongly  magnetic.  De- 
ville  states  that  by  reducing  the  oxalate  in  a crucible  lined  with 
lime,  he  obtained  a metallic  button  which  yielded  a wire  of  a tena- 
city nearly  double  that  of  an  iron  wire  of  the  same  diameter.  It 
is  dissolved  slowly,  with  evolution  of  hydi’ogen,  by  hydi*ochloric 
and  diluted  sulphuric  acids,  and  it  is  freely  attacked  by  nitric  acid  ; 
when  exposed  to  the  atmosphere,  it  becomes  slowly  converted  into 
oxide.  Cobalt  is  not  used  in  the  metallic  state  in  the  arts.  Many 
of  the  compounds  of  cobalt  are  remarkable  for  the  beauty  and 
brilliancy  of  their  colour,  and  are  used  as  pigments. 

The  alloys  of  cobalt  are  unimportant.  Its  compounds  with 
arsenic  are  interesting,  as  they  supply  the  greater  part  of  the  cobalt 
employed  in  the  arts.  Tin-white  cobalt  (OoAs^),  when  pm’e,  con- 
tains 28 '5 7 per  cent,  of  cobalt  and  71 ‘43  of  arsenic  ; but  portions 
of  the  cobalt  are  frequently  displaced  by  nickel  and  iron.  The 
purest  specimens  of  this  mineral  are  obtained  from  Tunaberg ; the 
ore  from  this  locality  is  the  best  material  to  employ  in  preparing 
the  compounds  of  cobalt.  Arsenide  of  cobalt  melts  at  a moderate 
red  heat.  Bright  white  cobalt^  or  cobalt  glance  (-0oS2,C-oAs2),  cor- 
responds in  composition  to  mispickel : it  crystallizes  in  cubes, 
octohedra,  or  dodecahedra,  and  contains  35*54  per  cent,  of  cobalt, 
45 ‘18  of  arsenic,  and  19 ‘28  of  sulphur.  These  minerals  are  vio- 
lently decomposed  by  nitric  acid  or  by  aqua  regia,  and  are  readily 
attacked  when  heated  in  a current  of  gaseous  chlorine.  They  are 
also  decomposed  when  roasted  in  a current  of  air. 

(720)  OxroES  OF  Cobalt. — There  are  two  well-marked  oxides 
of  cobalt,  the  protoxide,  -CoO,  which  is  the  salifiable  base  of 
the  metal,  and  the  sesquioxide,  -Co^Og ; these  two  oxides  are 
capable  of  uniting  with  each  other  in  difi“erent  proportions. 
According  to  Schwarzenberg,  an  acid  oxide,  O03O5,  may  be 
obtained  in  combination,  by  strongly  igniting  the  protoxide  or 
the  carbonate  with  hydi’ate  of  potash,  in  which  case  a crystalline 
compound  is  formed,  which  when  dined  at  212°,  consists  of  K^O, 
3 -BOaOs.  3 H^O. 

Protoxide  (BoO=75.  orCoO  = 37‘5). — This  oxide,  when  dried 
at  a low  temperature,  is  of  a greenish-grey  colour  ; when  heated 
to  dull  redness  in  the  air  it  absorbs  oxygen,  and  becomes  black, 
forming  an  oxide  (OOgO,)  corresponding  to  the  black  or  magnetic 
oxide  of  iron,  but  if  more  strongly  heated  it  again  loses  oxygen, 
and  becomes  reconverted  into  the  protoxide,  which  is  of  a brovui 
colour,  and  which  may  be  cooled  in  a current  of  carbonic  anhy- 
dride without  absorbing  oxygen  (Kussell).  Protoxide  of  cobalt  is 
soluble  in  acids,  and  forms  solutions  which,  when  concentrated, 
are  of  a beautiful  blue  colour,  but  they  become  pink  on  dilution. 
The  oxide  forms  an  important  article  of  commerce,  from  its  em- 
ployment for  the  production  of  a blue  colour  in  painting  on  porce- 
lain. 'When  describing  the  preparation  of  nickel,  a process  will 


ZAFFRE SMALT. 


473 


be  detailed  wliicli  furnishes  the  oxide  of  cobalt  lit  for  this  purpose 
(729).  Protoxide  of  cobalt  combines  with  bases  as  well  as  with 
acids.  If  fused  with  hydrate  of  potash  it  forms  a blue  compound, 
which  is  decomposed  by  the  free  addition  of  water  ; when  heated 
with  nitrate  of  magnesium,  a pale  pink  residue,  formed  by  the 
combination  of  the  magnesia  with  oxide  of  cobalt,  is  obtained  ; 
with  alumina  it  forms  the  bine  pigment  known  as  Thenard’s 
blue,  and  with  oxide  of  zinc  the  compound  constitutes  Pinman’s 
green. 

The  zoffre  of  commerce  is  a very  impnre  oxide  of  cobalt,  pro- 
cm’ed  by  imperfectly  roasting  cobalt  ore,  mingled  with  2 or  3 times 
its  weight  of  siliceous  sand. 

Smalt  is  a beautiful  blue  glass  coloured  by  oxide  of  cobalt ; it 
is  chiefly  manufactured  in  Saxony.  In  preparing  smalt,  the  cobalt 
ore  is  first  roasted  ; but  the  roasting  is  arrested  at  a particular 
stage,  the  object  being  to  oxidize  the  cobalt,  whilst  the  nickel, 
copper,  and  iron  remain  in  combination  with  arsenic  and  sulphur  ; 
it  is  necessary  to  leave  a sufficient  amount  of  arsenic  in  the 
mass  to  retain  these  metals,  as  the  admixture  of  a very  small 
quantity  of  the  oxides  either  of  iron,  nickel,  or  copper  with 
the  glass,  seriously  injures  the  purity  of  its  colour.  From  4 
to  5 parts  of  the  roasted  ore  in  powder  are  next  mingled  with 
10  parts  of  ground  calcined  quartz  and  4 parts  of  carbonate  of 
potassium,  and  the  mixture  is  slowly  melted  in  pots  arranged  in 
a furnace  resembling  that  used  in  making  ordinary  glass.  The 
oxide  of  cobalt  combines  with  the  fused  silicate  of  potassium  ; 
a deep  blue  glass  is  thus  formed,  whilst  the  mixed  arsenides  and 
sulphides  of  nickel,  copper,  and  iron  fuse,  and  collect  at  the 
bottom  of  the  pot,  in  the  form  of  a brittle  mass  of  metallic 
appearance,  commonly  known  as  speiss.  The  pot  is  then 
skimmed  and  the  glass  is  ladled  out,  and  poured  into  cold  water, 
by  which  means  it  is  split  into  innumerable  fragments : the 
speiss  is  cast  into  ingots  and  used  in  the  manufacture  of  nickel. 
The  broken  glass  is  stamped  to  powder,  and  subsequently  ground 
between  granite  stones,  which  are  caused  to  revolve  under  water, 
in  a vessel  through  which  a gentle  stream  of  water  is  continually 
flowing.  The  water  as  it  flows  carries  off  with  it  the  powdered 
smalt  in  suspension : it  is  made  to  pass  through  a number  of 
depositing  vessels,  so  arranged  tliat  the  overflow  from  the  first 
shall  pass  into  the  second,  that  from  the  second  into  the  third, 
and  so  on : each  of  these  vessels  is  successively  larger  than  tlie 
one  wliicli  precedes  it,  so  that  the  period  for  which  tlie  washings 
are  retained  in  each  goes  on  progressively  increasing,  and  the 
particles  deposited  progressively  increase  in  the  minuteness  of 
their  subdivision ; the  colour  becoming  less  intense,  the  greater 
the  degree  of  subdivision  of  its  particles.  Smalt  is  used  largely 
by  paper-stainers,  to  produce  a bine  colour,  and  it  is  employed 
to  some  extent  by  laundresses,  for  correcting  the  yellow  tinge  in 
linen. 

Another  valuable  pigment  into  the  composition  of  which  cobalt 
enters  is  of  a pale  blue  colour,  and  is  known  as  Thtnardh  Hue. 


474  SESQTJIOXIDE  OF  COBALT BASES  WHICH  CONTAIN  AmiONIA. 

The  most  approved  method  of  preparing  it  consists  of  precipitating 
nitrate  of  cobalt  by  means  of  phosphate  of  potassium,  and  mixing 
the  precipitate  whilst  still  moist  with  four  or  five  times  its  hulk  of 
the  gelatinous  mass  obtained  by  adding  carbonate  of  sodium  to 
a dilute  solution  of  alum  perfectly  free  from  iron.  The  mixture 
is  dried  and  then  exposed  to  a dull  red  heat  in  a covered  crucible. 
The  brilliancy  of  the  colour  is  much  impaired  by  the  reducing 
action  of  the  combustible  gases  of  the  fuel.  The  best  preventive 
of  this  efiect  is  found  to  consist  in  placing  a little  red  oxide  of 
mercury  at  the  bottom  of  each  crucible  ; by  the  decomposition  of 
this  oxide  an  atmosphere  of  oxygen  is  obtained,  and  the  metallic 
mercury  is  dissipated  in  vapour  (Regnault,  Gouts  Elem.  de  Chimie^ 
vol.  iii.  p.  150). 

RinmaEs  green  is  a pigment  of  analogous  composition,  con- 
taining oxide  of  cobalt  combined  with  oxide  of  zinc. 

Hydrated  oxide  of  cobalt  (OoO,  H^O)  is  precipitated  by  the 
addition  of  solution  of  potash  or  of  soda  to  solutions  of  any  of  its 
salts.  The  pale  blue  precipitate  which  is  first  formed  is  a basic 
salt  of  cobalt,  but  if  an  excess  of  alkali  be  used,  it  quickly  becomes 
violet,  and  finally  rose-coloured,  which  is  the  true  colour  of  the 
hydrated  oxide  : these  changes  occur  most  rapidly  if  the  liquid  be 
warmed.  It  becomes  of  a dingy  green  if  exposed  while  moist  to 
the  air,  owing  to  the  gradual  absorption  of  oxygen.  The  hydrated 
protoxide  is  readily  dissolved  by  a solution  of  carbonate  of  am- 
monium, and  also  by  excess  of  ammonia,  especially  in  the  presence 
of  a neutral  salt  of  ammonium. 

Sesquioxide  of  cobalt  (-00203=166,  or  Co203=:83)  maybe  pre- 
pared by  suspending  the  hydrated  protoxide  of  the  metal  in  water, 
and  transmitting  a current  of  chlorine  through  the  liquid ; chloride 
of  cobalt  is  formed  and  dissolved,  whilst  a black  hydrated  sesqui- 
oxide of  cobalt  is  precipitated,  OOgO^,  3 H2O.  The  reaction  may  be 
thus  expressed  : 3 (0oO,H2O)  + CI2 =00303,  3 H2O  -f  0OCI2.  If 
the  oxide  of  cobalt  he  suspended  in  a solution  of  potash  instead 
of  in  pure  water,  the  whole  of  the  cobalt  is  converted  into  sesqui- 
oxide. It  may  be  rendered  anhydrous  by  a careful  application  of 
heat,  hut  if  strongly  heated  it  becomes  converted  into  a black 
oxide  (0oO,  0O2O3),  corresponding  with  the  magnetic  oxide  of 
iron.  This  magnetic  oxide  is  sometimes  deposited  in  small,  hard, 
anhydrous,  brilliant,  steel-grey  octohedra  when  a pure  aqueous 
solution  of  chloride  of  roseocobaltia  (721)  is  boiled.  In  this  form 
it  is  insoluble  in  nitric  acid,  in  hydrochloric  acid,  and  in  aqua 
regia : it  is  but  slowly  attacked  by  heating  it  with  oil  of  vitriol 
or  with  acid  sulphate  of  potassium.  The  basic  powers  of  the 
sesquioxide  are  extremely  feeble.  Cold  sulphuric,  nitric,  hydro- 
chloric, phosphoric,  and  acetic  acids  dissolve  the  hydrated  oxide, 
but  the  salts  are  gradually  converted  at  ordinary  temperatures 
into  those  of  the  protoxide,  and  this  change  is  immediately  effected 
if  the  solutions  are  heated. 

(721)  Ai^imonlacal  Compounds  of  Cobalt. — ^When  a solution 
of  a salt  of  cobalt  in  ammonia  is  exposed  to  the  air,  it  absorbs 
oxygen  rapidly,  although  the  hydrated  protoxide  of  cobalt  alone 


A^IMOXIACAL  COMPOUNDS  OF  COBALT.  475 

exhibits  this  tendency  to  a small  extent  only.  If  the  hydrated 
oxide  be  dissolved  in  a solution  of  chloride  of  ammonium  contain- 
ing free  ammonia,  the  absorption  of  oxygen  proceeds  quickly,  and 
a remarkable  violet-red  colour  gradually  developes  itself  in  the 
liquid.  If  at  this  stage  the  liquid  be  supersaturated  with  hydro- 
chloric acid  in  the  cold,  a heavy  brick-red  crystalline  powder  is 
precipitated,  the  chloride  of  roseocohaltia  (O0CI3,  5 H3N,Il20,  or 
CO2CI3,  5 IlghI,  2 HO,  Genth  and  Gibbs) ; and  this  compound,  if 
boiled,  is  converted  into  a purple  precipitate  of  chloride  of  ^tor- 
2?ureocobaltia  (-00013  5 H3N,  Genth  and  Gibbs),  which  separates 
in  crystals,  leaving  the  solution  nearly  colourless  : this  precipitate 
may  be  dissolved  by  heating  it  in  water  slightly  acidulated  with 
hydrochloric  acid,  and  as  the  liquid  cools,  beautiful  ruby-red  octo- 
hedral  crystals  are  formed  (F.  Claudet).  This  remarkable  com- 
pound is  quite  insoluble  in  boiling  hydrochloric  acid,  and  may  be 
employed  as  a means  of  obtaining  chemically  pure  cobalt : at  a 
red  heat  it  loses  ammonia  and  hydrochlorate  of  ammonia,  leaving 
chloride  of  cobalt.  The  latter  may  be  reduced  to  the  metallic 
state  by  passing  a current  of  hydrogen  gas  over  it  in  a tube 
heated  to  redness.  AYhen  digested  with  water  upon  oxide  of 
silver,  the  chlorine  is  withdrawn  from  the  new  compound,  whilst 
the  oxygen  of  the  oxide  takes  its  place ; a red  strongly  alkaline 
liquid,  oxide  of  purpureocobaltia,  is  thus  produced,  which  unites 
with  acids,  and  forms  a peculiar  class  of  salts : this  alkaline  solu- 
tion emits  no  smell  of  ammonia. 

Fremy,  in  an  elaborate  series  of  researches  on  the  ammoniacal 
compounds  of  cobalt,  has  shown  {Ann.  de  Chimie^  III.  xxxv.  257) 
that,  independently  of  the  ammoniacal  compounds  obtained  with 
the  ordinary  salts  of  the  metal,  and  of  the  above  compounds 
described  by  Claudet,  three  other  sets  of  salts  may  be  procured, 
wliich  he  regards  as  compounds  of  different  oxides  of  cobalt  with 
various  proportions  of  ammonia : the  first  of  these  bases  he  names 
oxycobaltia.  Its  salts  crystallize  readily  ; they  have  for  the  most 
part  an  olive  colour,  and  may  be  dissolved  in  a solution  of  ammo- 
nia without  change,  but  when  placed  in  cold  water  they  are  decom- 
posed with  evolution  of  oxygen  and  deposition  of  a green  basic  salt : 
the  salts  of  this  base  appear  to  contain  a binoxide  of  cobalt,  which, 
however,  cannot  be  isolated.  The  second  base,  from  the  yellow 
colour  of  its  salts,  he  terms  luteocobaltia  ‘ this  base  has  been  isolat- 
ed ; it  has  a strongly  alkaline  reaction,  and  its  salts  crystallize  easily. 
The  third  base  is  iarmeA  fuscohaltia  j it  forms  brown  uncrystal- 
lizable  salts.  The  base  of  Claudet’s  salts,  which  Fremy  termed, 
from  the  red  colour  of  its  compounds,  roseocohaltia^  is,  according 
to  Gibbs  and  Genth,  a mixture  of  two  isomeric  bases,  one  of 
wliicli,  roseocobaltia,  neutralizes  3 atoms  of  a monobasic  acid  ; tlie 
other,  purpureocobaltia,  neutralizes  only  2 atoms  of  acid.  Further 
details  regarding  the  preparation  of  these  difierent  compounds  are 
also  contained  in  a paper  by  Gibbs  and  Genth  {Chem.  Gaz.  1857, 
]).  181),  wlio  have  described  an  additional  series,  to  wliich  they 
give  the  name  of  salts  of  xanthocobalt,  from  the  brilliant  yellow 
colour  of  these  compounds.  The  chloride  of  xanthocobaltia 


470 


SCLPHIDES  OF  COBALT. 


(eo.eci,  10  II3X  2 NO  . or  Co,OCl„  5 . IIO)  may 

1)6  obtained  in  crystals  by  decomposing  the  sulphate  of  this  base 
with  a solution  of  chloride  of  barium ; and  the  sulphate  (Oo^Og, 
10  H3X,  2 XO5  2 SO3  . or  CO2O3,  5 Il3]S',]Sr02,  2 SO3  . HO)  is 
easily  procured  by  transmitting  a rapid  current  of  nitrous  acid 
through  an  ammoniacal  solution  of  sulphate  of  cobalt,  taking  care 
to  preserve  the  alkalinity  of  the  liquid  by  the  occasional  addition 
of  ammonia.  The  solution  gradually  assumes  a dark  yellowish- 
brown  colour,  and  if  left  to  evaporate,  spontaneously  deposits  the 
sulphate  of  the  new  base  in  the  form  of  thin  plates  derived  from 
the  right  rhombic  prism. 

All  the  compounds  of  each  of  these  bases,  when  boiled  with 
a solution  of  caustic  potash  or  of  soda,  are  decomposed,  and 
hydrated  sesquioxide  of  cobalt  is  precipitated,  Avhilst  ammonia  is 
expelled. 

The  following  table  will  afford  a general  comparative  view  of 
these  different  classes  of  salts,  including  the  double  salts  which 
ammonia  forms  wdtli  the  protoxide  of  the  metal ; they  are  probably 
compounds,  of  very  complex  constitution,  formed  on  the  ammonium 
type 

1.  Double  Salts  of  Ammonia  and  Protoxide  of  Cohalt. 

Hitrate Oo  2 HO3,  6 H3H,  2 H2O 

Chloride HoCh,  6 H3H,  3 H^O. 

2.  Salts  of  Oxycobaltia. 

Hitrate (HoO^,  5 H3H,  H^O 

Sulphate 2 [(OoO^,  m,)  5 H3H],  3 H^O. 

3.  Salts  of  Luteocobaltia. 

Nitrate Ho  3 ^03,  6 H3N 

Chloride OoCh,  6 H3K 

4.  Salts  of  Fuscobaltia. 

Nitrate ^0303,  2 N^O^,  8 H3N,  3 H^O 

Chloride Oo^Che,  8 H3N,  3 H^O. 

5.  Salts  of  Xantliocobaltia. 

Nitrate 00^03,  2 N^O^,  10  H3N,  2 NO  . H^O 

Chloride Oo^OCl,,  10  H3N,  2 NO  . H^O. 

6.  Salts  of  Roseocobaltia  {Gibbs  and  Genth). 

Nitrate Oo^  6 Ne3,  10  H3N,  2 

Chloride Oo^Cl^,  10  H3N,  2 H^O. 

7.  Salts  of  Purpureocobaltia. 

Acid  sulphate  O02O3,  4 SO3,  10  H3N  . 5 

Chloride eo^Cl^,  10  H3N. 

(722)  SuLpnroES  of  Cobalt. — Three  sulphides  of  this  metal 
may  be  procured, — a protosulphide,  OoS ; a sesquisulphide,  Oo^Sj ; 
and  a bisulphide,  OoS,.  The  latter  may  be  obtained  by  heating 
carbonate  of  cobalt  with  sulphur,  not  allowing  the  temperature  to 


CHLORIDE,  SULPHATE,  AND  NTTRATE  OF  COBALT. 


477 


rise  too  liigh.  The  most  important  of  these  is  the  protoml])liide^ 
whicli  may  be  procured  in  a hydrated  condition  by  precipitating 
a solution  of  acetate  of  cobalt  by  sulphuretted  hydrogen,  or  by 
mixing  any  neutral  solution  of  a salt  of  cobalt  with  sulphide  of 
ammonium.  In  this  form  it  speedily  absorbs  oxygen  from  the 
air,  and  becomes  converted  into  sulphate  of  cobalt.  If  a mixture 
of  oxide  of  cobalt  with  persulphide  of  potassium  (the  liver  of 
sulphur)  be  fused  in  a covered  crucible,  fused  sulphide  of  cobalt 
is  obtained  at  the  bottom  of  the  crucible.  The  sesquisulphide, 
which  is  occasionally  met  with  in  octohedra  of  a grey  colour,  may 
be  obtained  by  heating  sesquioxide  of  cobalt  to  about  500°  in  a 
current  of  sulphuretted  hydrogen. 

(723)  Chloride  of  Cobalt  (OoCl2=130,  or  CoCl=65  ; Sp.  Gr. 
2'937)  is  obtained  as  a lilac-coloured  anhydrous  mass,  by  passing 
chlorine  over  metallic  cobalt ; it  is  volatile  at  a high  temperature. 
By  dissolving  the  oxide  or  the  carbonate  of  cobalt  in  hydrochloric 
acid,  the  hyilrated  chloride  may  be  obtained  in  ruby-red  octohe- 
dral  crystals  with  6 H^O,  of  sp.  gr.  1*84,  which  are  readily  soluble 
in  water  and  in  alcohol ; its  aqueous  solution  when  concentrated, 
or  when  mixed  with  an  excess  of  strong  hydrochloric  acid,  is  of  a 
deep  blue  colour,  but  on  dilution  it  becomes  pink.  This  dilute 
solution  may  be  used  as  a sympathetic  ink ; characters  traced  with 
it  on  paper,  though  invisible  when  cold,  become  blue  by  heat,  and 
again  fade  as  the  hygroscopic  moisture  of  the  paper  is  restored 
from  the  air:  the  colours  of  this  ink  may  be  varied  at  pleasure; 
the  addition  of  a small  proportion  of  a ferric  salt  renders  it  green ; 
zinc  produces  a red,  and  copper  a yellow  tint.  Anhydrous  chlo- 
ride of  cobalt  absorbs  4 atoms  of  ammonia,  and  if  its  solution  be 
mixed  with  an  excess  of  ammonia  it  deposits  crystals,  consisting 
of  OoCl,,  3 [(H,A),0]. 

(724)  Sulphate  of  Cobalt  (OoSO^,  7 II2O  = 155  + 126,  or 
CoO,S03 . 7 HO=77‘5  + 63  ; Sp.  Gr.  arJiydrous^  3*531)  is  isomor- 
phous  with  sulphate  of  magnesium.  The  anhydrous  salt  contains 
38*06  of  metallic  cobalt  or  48*38  of  the  protoxide. 

ISTtrate  of  Cobalt  (Oo  2 hlOg  . 6 II^O  = 183 -f  108,  or 
CoO,N05 . 6 IIO=:91*5-f-54;  Sp.  Gr.  1*83)  is  prepared  by  dissolv- 
ing the  oxide  in  nitric  acid.  It  is  a deliquescent  salt,  which  is 
sometimes  employed  as  a reagent  for  the  blowpipe  : a fragment 
of  the  compound  under  examination  is  supported  either  upon 
charcoal,  or  upon  a bent  platinum  wire,  and  moistened  wdth  a 
minute  quantity  of  a strong  solution  of  the  nitrate  of  cobalt. 
When  treated  in  this  way,  many  of  the  compounds  of  magnesium 
yield  a pale  pink-coloured  mass  after  ignition  ; those  of  zinc  give 
a green  residue,  and  tliose  of  aluminum  a blue. 

If  a concentrated  solution  of  nitrite  of  ])otassium  be  gradually 
added  to  a solution  of  nitrate  of  cobalt  acidulated  with  nitric  or 
with  acetic  acid,  a beautifid  orange-yellow  compound  is  precipi- 
tated in  microscopic  four-sided  prisins  with  pyramidal  summits ; 
it  is  sparingly  soluble.  According  to  A.  Stromeyer,  it  consists  of 
[OoA,  2 NA,6  (KNO^) . 2 11,0],  or  [Co^\,2  NO3,  3 (KO,NO,)  . 
2 110],  and  contains  13*6  of  metallic  cobalt. 


478 


ESTIMATION  OF  COBALT. 


A hydrated  arseniate  of  cobalt  (Oog  2 AsO^  . 8 or 

3 CoOjAsOg,  8 HO)  is  found  native,  in  minute  crystals,  and  is 
known  as  cobalt  bloom. 

(725)  Cauboxates  of  Cobalt. — Cobalt  resembles  magnesium, 

zinc,  nickel,  and  copper,  in  the  circumstance  that  when  solutions 
of  its  normal  salts  are  mixed  with  a solution  of  carbonate  of 
sodium  or  potassium,  the  precipitate  which  falls  is  not  a normal 
carbonate,  but  a mixture  of  normal  carbonate  with  hydrated  oxide 
of  cobalt.  If  the  two  solutions  be  mixed  when  hot,  the  red  pre- 
cipitate is  said  to  have  the  formula  (5  OoO,  2 . 4 IlgO).  If  the 

salts  be  mixed  at  the  ordinary  temperature,  the  precipitate  is  of  a 
brighter  red,  and  has  a composition  (4  -CoO,  2 -GO,  . 7 H^O).  If 
either  of  these  precipitates  be  boiled  with  an  excess  of  carbonate 
of  sodium,  it  assumes  an  indigo-blue  colour,  and  is  converted  into 
the  compound  4 GoO,  GO^  . 4 HgO,  which  absorbs  oxygen  and 
becomes  green  during  washing. 

A true  normal  carbonate  [3  -Go-GOg  . 2 HoO,  or  3 (CoO,C02)  . 
2 HO]  is  formed  by  digesting  either  of  the  basic  carbonates  of 
cobalt  with  the  acid-carbonate  of  sodium  or  ammonium. 

(726)  Chakacters  of  the  Salts  of  Cobalt. — The  crystal- 
lized salts  of  cobalt  are  red;  when  anhydrous  they  are  usually 
lilac-coloured.  Their  solutions  when  in  a very  concentrated  form 
are  blue ; at  a particular  stage  of  dilution  they  are  red  when  cold, 
but  become  blue  on  heating  them,  the  red  colour  returning  as  the 
liquid  cools  : when  mixed  with  a larger  proportion  of  water  they 
exhibit  a delicate  rose  colour,  and  this  tint  is  perceptible  even 
when  the  solution  is  very  much  diluted.  They  have  an  astringent 
metallic  taste. 

Before  the  bloicpijpe  the  compounds  of  cobalt  are  easily  recog- 
nised by  the  intense  blue  colour  which  they  communicate  to  a 
bead  of  borax  in  the  oxidating  flame. 

In  solution  the  salts  which  this  metal  forms  with  the  mineral 
acids  give  no  precipitate  with  sulphuretted  hydrogen^  if  the  liquid 
be  slightly  acidulated  with  sulphuric  or  hydrochloric  acid ; but  the 
cobalt  is  completely  precipitated  by  it  from  a dilute  neutral  solu- 
tion of  the  acetate.  With  sulphide  of  ammonium  they  yield  a 
black  sulphide.  Carbonate  of  potassium  gives  a rose-coloured 
basic  carbonate,  which  is  soluble  in  carbonate  of  ammonium. 
Hydrate  of  potash  gives  a blue  basic  salt,  which  by  excess  of  the 
alkali  becomes  rose-coloured.  Ammonia  produces  a similar  eflect, 
but  readily  dissolves  the  precipitate,  forming  a brownish  solution 
which  rapidly  absorbs  oxygen  from  the  air,  and  becomes  red.  The 
soluble  oxalates  give  a sparingly  soluble  pink  oxalate  of  cobalt, 
which  is  soluble  in  nitric  acid  and  in  ammonia.  Ferrocyanide  of 
potassium  gives  a dirty  green,  and  ferricyanide  of  potassium  a 
bulky  reddish-brown  precipitate ; the  latter  reaction  occurring 
even  in  ammoniacal  solutions. 

(727)  Estimation  of  Cobalt. — Cobalt  may  be  estimated  with 
accuracy  in  the  metallic  form.  Supposing  that  no  compound  of 
any  other  metal  susceptible  of  precipitation  by  sulphuretted  hy- 
drogen be  present,  the  solution  is  to  be  neutralized  by  means  of 


ESTEVIATION  OF  COBALT. 


479 


carbonate  of  potassium,  mixed  with  a solution  of  acetate  of  j^otas- 
sium,  and  the  cobalt  precipitated  as  sulphide  by  a current  of  sul- 
phuretted hydrogen,  the  precipitate  allowed  to  settle  in  a beaker 
closed  by  a glass  plate,  then  collected  on  a filter  and  washed.  The 
alkalies  are  prevented  from  effecting  the  complete  precipitation 
of  cobalt,  as  well  as  of  iron,  of  nickel,  of  copper,  and  of  many 
other  metals,  by  the  presence  of  certain  kinds  of  organic  matter, 
such  as  that  derived  from  the  paper  of  the  filter ; special  precau- 
tions are  therefore  required  to  avoid  this  accident.  For  this  pur- 
pose the  neck  of  the  funnel  with  the  filter  and  its  contents  is  in- 
troduced into  a small  flask,  a hole  is  made  with  a glass  rod  in  the 
bottom  of  the  filter,  and  the  precipitate  is  washed  into  the  flask  ; 
the  filter  after  being  moistened  with  concentrated  nitric  acid,  is 
again  washed ; it  is  then  dried,  burnt,  and  the  ash  added  to  the 
contents  of  the  flask,  which  are  now  boiled  with  nitric  acid  until 
the  sulphide  of  cobalt  is  dissolved.  The  liquid  so  obtained  is  di- 
luted and  poured  off  from  any  particles  of  undissolved  sulphur, 
and  the  solution  of  cobalt  may  be  evaporated  to  dryness,  then 
mixed  with  sulphuric  acid  to  convert  it  into  sulphate,  and  the  ex- 
cess of  acid  expelled  by  a moderate  heat.  100  parts  of  sulphate 
of  cobalt  indicate  38*06  of  the  metal.  After  the  sulphide  has 
been  brought  into  solution  by  the  nitric  acid,  the  cobalt  may  also 
be  precipitated  in  the  form  of  hydrated  oxide  by  an  excess  of  pure 
potash  ; the  oxide  is  then  thoroughly  washed  with  boiling  water, 
dried,  ignited  and  weighed : the  black  oxide  thus  procured  con- 
sists of  OOgO^,  and  corresponds  to  73*44  of  metallic  cobalt.  Some 
chemists,  however,  prefer  to  reduce  this  oxide  in  a current  of  dry 
and  pure  hydrogen  in  the  manner  shown  in  fig.  344.  The  tube, 
is  weighed  when  empty ; then  a certain  proportion  of  the  oxide 
of  cobalt  is  introduced  into  the  bulb,  and  the  tube  is  again 
weighed ; hydrogen  is  generated  in  the  bottle,  <2,  and  allowed  to 
traverse  the  vessels,  c,  and  d : h contains  a solution  of  potash, 
and  G one  of  nitrate  of  silver,  which  are  designed  to  arrest  any 
traces  of  arseniuretted  hydrogen ; oil  of  vitriol  is  placed  in  d for 
the  purpose  of  drying  the  gas  : a dull  red  heat  is  next  applied  to 
the  bulb,  e ; under 
these  circumstances 
the  hydrogen  enters 
into  combination 
with  the  oxygen  of 
the  oxide,  and  the 
water  which  is  pro- 
duced passes  on  as 
vapour.  As  soon  as 
water  ceases  to  be 
formed,  the  reduc- 
tion is  complete : 
the  lamp  may  then  be  removed  from  the  bulb,  but  the  current  of 
hydrogen  must  be  maintained  till  the  tube  is  quite  cold.  The 
tube  and  its  contents  are  finally  weighed  a third  time,  and  the 
proportion  of  metallic  cobalt,  wliich  a given  weight  of  the  oxide 


Fig.  344. 


480 


SEPARATION  OF  COBALT NICKEL. 


under  trial  contained,  is  thus  ascertained ; but  the  process  is  not 
to  be  recommended,  as,  if  the  tube  be  weighed  full  of  hydrogen, 
the  weight  is  too  little,  and  if  the  hydi’ogen  be  displaced  by  at- 
mospheric air,  the  finely  divided  reduced  metal  is  apt  to  become 
partially  oxidized. 

(728)  Separation  of  Cobalt  from  the  Metals  of  the  Alkalies  and 
Alkaline  Earths^  and  from  Aluminum. — This  is  readily  effected 
by  converting  the  cobalt  into  acetate,  and  transmitting  sulphu- 
retted hydrogen,  as  has  been  already  mentioned  in  the  preceding 
paragraph.  Another  plan  consists  in  the  addition  of  sulphide  of 
ammonium  to  the  solution  previously  neutralized  by  ammonia. 
If  alumina  be  present,  it  will  accompany  the  cobalt,  but  if  this 
precipitate  be  redissolved  in  acid,  and  again  thrown  down  by 
means  of  caustic  potash  in  excess,  the  alumina  will  be  retained  ; 
the  oxide  of  cobalt  is,  however,  apt  to  carry  down  traces  of  alum- 
ina ; these  may  be  removed  by  treating  the  precipitated  oxide  by 
means  of  a mixture  of  ammonia  and  chloride  of  ammonium,  which 
dissolves  the  cobalt,  but  leaves  any  traces  of  alumina  which  may 
have  accompanied  it.  The  cobalt  is  again  precipitated  by  sul- 
phide of  ammonium. 

The  separation  of  cobalt  from  zinc  is  not  easy.  One  of  the 
best  methods  consists  in  precipitating  the  two  metals  together  in 
the  form  of  sulphides,  dissolving  this  precipitate  in  nitric  acid, 
and  then  adding  an  excess  of  carbonate  of  potassium,  and 
evaporating  to  dryness.  After  the  mixed  carbonates  of  zinc  and 
cobalt  have  been  well  washed,  they  are  heated  in  a bulb-tube  in 
a current  of  dried  hydrochloric  acid : in  this  process  the  carbonic 
acid  is  expelled,  and  the  metals  are  converted  into  chlorides,  whilst 
water  is  formed.  The  open  end  of  the  tube  is  in  this  case  bent 
downwards  at  a right  angle,  and  the  aperture  is  made  to  dip  into 
a small  quantity  of  water  contained  in  a flask : the  chloride  of 
zinc,  which  is  volatile,  is  carried  forward  in  the  current  of  gas ; a 
portion  of  it  is  condensed  in  the  bend  of  the  tube,  and  the  re- 
mainder is  dissolved  in  the  water  placed  for  its  reception.  Chlo- 
ride of  cobalt  alone  remains  in  the  bulb.  The  portion  of  the 
tube  in  which  the  chloride  of  zinc  has  been  condensed  is  cut  oif 
when  the  operation  is  complete,  and  is  allowed  to  fall  into  the 
flask.  The  zinc  and  the  cobalt  are  then  easily  determined  sepa- 
rately by  the  usual  methods. 

§ II.  Nickel:  Ni"=59,  or  Ni— 29*5.  Sp.  Gr.  8*82. 

(729)  Nickel  is  a metal  the  peculiar  characters  of  which 
were  first  recognised  in  1751  by  Cronstedt : it  has  a remarkable 
analogy  with  cobalt,  and  always  occurs  associated  with  it  in  nature, 
both  as  a constituent  of  meteoric  iron,  and  in  its  ores,  which 
present  a composition  similar  to  those  of  cobalt.  It  is  most 
abundant  in  the  form  of  kupfernickel  (arsenide  of  nickel),  and  is 
extracted  either  from  this  ore  or  from  speiss.,  which  is  an  impure 
arseniosulphide  of  nickel,  formed  during  the  manufacture  of  smalt 
(720). 


NICKEL PKOPEETIES. 


481 


Preparation. — As  the  metal  itself  is  now  extensively  used  in 
alloys,  of  which  German  silver  is  one  of  the  most  important,  great 
pains  have  been  taken  to  procure  it  in  a state  of  comparative 
purity,  and  several  processes  have  been  proposed. 

1.  — According  to  Louyet,  the  method  by  which  nickel  is 
extracted  from  speiss  at  Birmingham  on  the  large  scale  is  as 
follows  : — The  speiss  is  first  fused  with  chalk  and  fiuor-spar,  the 
metalliferous  mass  so  obtained  is  reduced  to  powder,  and  roasted 
for  twelve  hours  to  expel  the  arsenic : the  residue  is  next  dissolved 
in  hydrochloric  acid ; the  solution  is  diluted,  and  the  iron  con- 
verted into  a ferric  salt  by  the  cautious  addition  of  bleaching 
powder.  Milk  of  lime  is  then  carefully  added  so  long  as  per- 
oxide of  iron  falls,  which  carries  down  with  it  the  last  portions 
of  arsenic ; this  precipitate  is  well  washed,  and  the  liquid,  which 
contains  all  the  cobalt  and  nickel,  is  treated  with  a current  of 
sulphuretted  hydrogen ; the  sulphides  of  copper,  bismuth,  and 
lead,  are  thus  precipitated,  and  are  thoroughly  washed.  All  the 
nickel  and  cobalt  still  remains  in  the  liquid ; this  liquid  is  boiled 
to  expel  sulphuretted  hydrogen,  neutralized  with  lime,  and  is 
again  treated  with  chloride  of  lime  : the  whole  of  the  cobalt  is 
thus  thrown  down  as  peroxide ; after  whicli  the  whole  of  the 
nickel  is  separated  from  the  solution  in  the  form  of  hydrated 
oxide  by  adding  milk  of  lime  so  long  as  any  precipitate  is  pro- 
duced. 

2.  — Nickel  may  be  obtained  pure  upon  a small  scale,  by  dis- 
solving the  roasted  ore  in  aqua  regia,  evaporating  to  expel  the 
excess  of  acid,  redissolving  in  water,  and  transmitting  a current 
of  sulphuretted  hydrogen.  The  filtered  liquid  is  boiled  with 
nitric  acid,  to  convert  the  iron  into  a ferric  salt ; the  solution  is 
precipitated  by  an  excess  of  caustic  ammonia,  filtered  from  the 
oxide  of  iron,  and  to  the  blue  liquid  caustic  potash  is  added  until 
the  blue  tint  nearly  disappears ; a pale  green  precipitate,  consist- 
ing of  hydrated  oxide  of  nickel  and  potash  is  thus  obtained,  which 
must  be  well  washed  with  hot  water  to  remove  the  potash,  and 
then  reduced  by  ignition  in  a current  of  hydrogen  gas  : when 
obtained  in  this  manner  it  is  generally  pyrophoric.  If  heated  for 
an  hour  by  means  of  a blacksmith’s  forge,  in  a crucible  lined  with 
charcoal,  a well-fused  button  of  carbide  of  nickel  is  produced.  A 
button  of  the  pure  metal  may,  however,  be  procured  by  heating 
the  oxalate  of  nickel  intensely  in  a crucible  with  a luted  cover, 
without  any  other  reducing  agent  than  the  carbonic  oxide  fur- 
nished by  its  own  decomposition. 

3.  — It  may  also  be  obtained  in  laminge  by  the  electrolysis  of 
a solution  of  the  double  sulphate  of  nickel  and  ammonium. 

Properties. — Pure  nickel  is  a brilliant,  silver-white,  hard,  but 
ductile  metal,  little  more  fusible  than  iron,  which,  according  to 
Deville,  it  even  surpasses  in  tenacity.  At  ordinary  temperatures 
it  is  susceptible  of  magnetism,  but  it  loses  this  property  almost 
entirely  if  heated  to  a point  exceeding  030°,  though  it  recovers 
its  magnetic  power  on  cooling.  Nickel  becomes  oxidized  by  ex- 
posure to  a current  of  air  at  a high  temperature.  The  metal  is 
31 


482 


ALLOTS  AND  OXIDES  OF  NICKEL. 


easily  attacked  at  ordinary  temperatures  by  chlorine  or  bromine 
if  suspended  in  water.  It  is  also  readily  dissolved  by  nitric  acid 
and  by  aqua  regia,  and  is  dissolved  slowly  with  evolution  of 
hydrogen  by  diluted  sulphuric  or  by  hydrochloric  acid.  Owing 
to  the  remarkable  whitening  power  which  nickel  exerts  on  brass, 
it  is  now  much  used  in  the  manufacture  of  packfong^  or  German 
silver,  a compound  of  zinc,  nickel,  and  copper,  in  which  the  pro- 
portions of  the  metals  may  vary  considerably.  A good  alloy  con- 
sists of  5 equivalents  of  copper,  3 of  zinc,  and  2 of  nickel,  or  in 
100  parts,  of  51  of  copper,  30*6  of  zinc,  and  18'4  of  nickel.  Pack- 
fong  is  of  a yellowish-white  colour,  and  when  freshly  polished 
closely  resembles  silver  in  appearance.  Tutenag  is  the  name 
given  by  the  Chinese  to  a similar  alloy,  consisting  of  8 parts  of 
copper,  6|-  of  zinc,  and  3 of  nickel. 

The  native  arsenides  of  nickel  are  important,  as  they  form 
the  principal  ores  of  the  metal.  Kupfernickel  (?^iAs)  is  arsenide 
of  nickel : it  contains  44  parts  of  nickel  to  56  of  arsenic  ; part  of 
the  arsenic  in  this  ore  is  sometimes  displaced  by  an  equivalent 
amount  of  antimony.  It  has  a reddish  colour,  and  a metallic 
lustre.  It  is  not  attacked  by  hydrochloric  acid,  but  is  soluble  in 
nitric  acid,  and  is  decomposed  when  heated  in  air  or  in  a cmTent 
of  chlorine.  Arsenical  nickel  (xviAs^)  is  another  native  compound 
of  the  two  metals : by  ignition  in  closed  vessels  it  loses  half  its 
arsenic,  and  becomes  converted  into  kupfernickel.  A compound 
of  nickel  with  arsenic  and  sulphur,  corresponding  to  mispickel, 
and  known  as  nickel  glance  (??iSAs,  or  IsiS2,IIiAs),  is  also  found 
native. 

(730)  OxroES  OF  Hickel. — ^Kickel  forms  two  oxides ; a prot- 
oxide, xfiO,  and  sesquioxide, 

Protoxide  of  Nickel  (57iO=T5,  or  ]S’iO=37'5) ; Sjp. 
Composition  in  parts ^ ^i,  78*67  ; O,  21*33. — This  oxide  may 
be  obtained  in  the  anhydrous  form  by  igniting  the  nitrate  or  the 
carbonate  of  the  metal  in  a covered  crucible,  when  it  is  left  of  an 
olive-green  colour.  It  may  be  precipitated  from  its  salts  by  hy- 
drate of  potash,  as  a bulky  light-green  hydrate  (x^iO,!!^^  ?),  and 
may  be  obtained  crystallized  by  decomposing  the  solution  of  car- 
bonate of  nickel  in  ammonia  by  ebullition.  Oxide  of  nickel  is 
readily  soluble  in  acids,  forming  salts  which  have  a pale  green 
colour.  It  yields  insoluble  compounds  with  potash  and  with  soda, 
which,  however,  may  be  decomposed  by  frequent  washings  with 
boiling  water.  Baryta,  strontia,  and  several  other  bases  also 
form  with  it  insoluble  compounds ; ammonia  dissolves  it,  forming 
a deep  blue  solution.  A solution  of  chloride  of  ammonium  also 
dissolves  it  slowly. 

The  sesquioxide  (?vi203=166,  or  ]Sri203=83),  is  a black  powder 
which  may  be  procured  as  a hydrate  with  3 H^O,  by  treating  the 
hydrated  protoxide  with  a solution  of  chloride  of  soda.  It  does 
not  combine  with  acids,  and  gives  off  a portion  of  its  oxygen  by 
ignition,  or  by  heating  it  with  nitric  or  sulphuric  acids,  which 
form  with  it  salts  of  the  protoxide. 

(731)  Sulphides  of  INickel. — Tliree  of  these  compounds  are 


CHAEACTEKS  OF  THE  SALTS  OF  NICKEL. 


483 


known ; a snbsnlpliide,  a protosnlpliide,  and  a bisnlpliide.  The 
jprotosulpliide  (5^iS=91)  occurs  native  as  millerite  in  greyish  or 
yellowish  capillary  crystals,  which  are  insoluble  in  hydrochloric, 
but  soluble  in  nitric  acid : it  may  be  formed  artihcially  by  fusion 
of  sulphur  with  nickel.  It  may  also  be  procured  by  fusing  a per- 
sulphide of  one  of  the  alkaline  metals  with  biarsenide  of  nickel, 
and  is  left  in  yellow  crystalline  scales.  A black  hydrate  of  this 
sulpliide  is  produced  when  a salt  of  nickel  is  precipitated  by  sul- 
phide of  ammonium  ; in  this  form  it  absorbs  oxygen  from  the  air, 
and  is  gradually  converted  into  sulphate  of  nickel.  The  sicbsul- 
jphide  (x^i^S)  may  be  formed  by  reduction  of  the  sulphate  of  nickel 
by  means  either  of  charcoal  or  of  hydrogen  gas.  The  histdphide 
(i^iSj)  is  left  as  a steel-grey  powder  on  treating  with  water  the 
mass  obtained  by  heating  to  redness  an  intimate  mixture  of  car- 
bonate of  nickel,  carbonate  of  potassium,  and  sulphur. 

(732)  CiiLOEiDE  OF  hTicKEL  (57iCl2=130,  or  h7iCl=:65)  is 

formed  by  dissolving  the  oxide  in  hydrochloric  acid.  Its  solution 
on  evaporation,  yields  green  hydrated  crystals  with  9 ; by 

heat  it  may  be  obtained  as  a yellowish-brown  anhydrous  mass, 
which  at  a high  temperature  is  volatile,  and  condenses  in  yellow 
crystalline  scales,  which  are  dissolved  slowly  by  boiling  water. 
If  heated  in  a current  of  air,  a portion  of  the  chlorine  is 
expelled,  and  a corresponding  quantity  of  oxide  of  nickel  is 
formed. 

(733)  Sulphate  of  Nickel  (NiS04,7  H20=155-hl26,  or  NiO, 
SOg . 7 H0=77'54-63). — This  salt  maybe  obtained  by  dissolving 
metallic  nickel,  or  its  oxide  or  carbonate,  in  sulphuric  acid.  It 
crystallizes  in  green  rhombic  prisms,  which  require  3 parts  of  cold 
water  for  solution ; the  prismatic  crystals,  when  exposed  to  light, 
are  converted  into  small  regular  octohedra,  aggregated  together 
in  the  form  of  the  original  crystal,  which  becomes  opaque.  It 
may  be  obtained  in  octohedra  at  once  with  6 II2O  {sp.  gr.  2‘037), 
by  crystallizing  at  a temperature  between  60°  and  80°.  A do\d)le 
sulphate  of  potassium  and  nickel  (NiSO^K.^SO^ . 6 II^O  ; Sp.  Gr. 
anhydrous.^  2’897,  cryst.  2T90)  may  be  formed  by  adding  caustic 
potash  to  the  impure  solution  of  speiss,  and  by  repeated  crystal- 
lizations may  be  freed  from  all  impurities  except  traces  of  iron 
and  cobalt : it  was  at  one  time  used  as  a means  of  purifying  nickel 
for  commercial  purposes.  Other  double  sulphates  of  nickel  may 
be  formed.  Sulphate  of  nickel  in  the  solid  form  absorbs  6 atoms 
of  arnmoniacal  gas.  An  insoluble  basic  sulphate  is  obtained  by 
addiiig  to  a solution  of  the  normal  sulphate  a quantity  of  hydrate 
of  potash  insufficient  for  its  complete  deconq)Osition. 

(734)  Carijonates  of  Nickel. — There  are  several  basic  carbo- 
nates of  nickel,  of  a green  colour.  The  normal  carbonate  is  })re- 
cipitated  as  a crystalline  powder,  when  a solution  of  nitrate  of 
nickel  is  poured  into  a large  excess  of  a solution  of  the  acid  car- 
bonate of  sodium. 

(735)  Characters  of  the  Salts  of  Nickel.  — Tlie  salts  of 
this  metal  are  of  a delicate  green  colour,  both  wlien  in  tlie  solid 
state  and  when  in  solution  ; they  redden  blue  litmus  feebly.  They 


4:84 


NICKEL SEPARATION  FROM  COBALT. 


have  a sweetish  astringent  metallic  taste,  and  when  taken  inter- 
nally excite  vomiting. 

Before  the  hlowpipe^  salts  of  nickel  give  in  the  oxidating  flame 
with  borax  a reddish-yellow  glass,  which  becomes  much  paler  as 
it  cools.  The  addition  of  a salt  of  potassium  colours  the  bead 
blue.  In  the  reducing  flame,  greyish  particles  of  reduced  nickel 
are  disseminated  through  the  bead. 

In  solution,  sulphuretted  hydrogen  gives  no  precipitate  if  the 
liquid  be  acidulated  with  sulphuric  acid ; but  it  precipitates  a 
diluted  solution  of  acetate  of  nickel,  if  nearly  neutral,  very  per- 
fectly when  aided  by  a gentle  heat.  Sulphide  of  ammonium  gives 
a black  sulphide  slightly  soluble  in  excess  of  the  precipitant, 
forming  a dark-brown  solution.  Ammonia  gives  a pale  green 
precipitate,  soluble  in  excess  of  ammonia,  forming  a bright  blue 
solution,  from  which  an  excess  of  potash  precipitates  a green  com- 
pound of  oxide  of  nickel  and  potash.  Hydrates  of  potash  and 
soda  throw  down  a pale-green  bulky  hydrated  oxide  of  nickel, 
insoluble  in  excess  of  the  alkali.  The  carbonates  of  the  alkaline 
metals  give  a pale  apple-green  precipitate  of  basic  carbonate  of 
nickel,  which  is  readily  soluble  in  carbonate  of  ammonium.  Fer- 
rocyanide  of  potassium  gives  a greenish  white,  and  ferricyanide 
of  potassium  a yellowish-green  precipitate,  both  of  which  are 
soluble  in  hydrochloric  acid.  Acid  oxalate  of  potassium  in  a 
neutral  solution,  if  not  too  dilute,  causes  the  deposition  of  a green- 
ish-white sparingly  soluble  double  oxalate  of  nickel  and  potassium, 
soluble  in  excess  of  ammonia. 

(736)  Estimation  of  Nickel. — Nickel  is  best  estimated  in  the 
form  of  protoxide  which,  when  precipitated  by  means  of  caustic 
potash,  requires  patient  washing  with  hot  water  to  remove  the 
adhering  alkali : 100  parts  of  protoxide  of  nickel  contain  78*67 
of  the  metal. 

Separation  of  Nicked  from  the  Alkalies  and  Earths^  and  from 
Zinc. — For  this  purpose  the  same  processes  as  those  adopted  for 
the  separation  of  cobalt  (728)  may  be  employed. 

(737)  Separation  from  Cobalt. — The  following  method,  advised 
by  Liebig  and  slightly  modified  by  Hadow,  is  the  best  for  this 
purpose.  The  nitric  solution  of  the  cobalt  and  nickel  having  been 
freed  from  all  other  metals  except  potassium  or  sodium,  after  being 
nearly  neutralized  with  carbonate  of  potassium,  is  mixed  with  an 
excess  of  hydrocyanic  acid,  and  then  with  pure  caustic  potash,  after 
which  the  mixture  is  left  exposed  to  the  air  in  a shallow  open  dish 
for  a few  hours.  During  this  time  oxygen  is  absorbed,  and  the 
liquid  acquires  a pale  yellow  colour.  A cobalticyanide  of  potas- 
sium (KgOoCye)  is  formed,  and  a double  cyanide  of  nickel  and 
potassium  (2  KCy,NiCy2)  is  produced  at  the  same  time.  The  for- 
mation of  the  cobalticyanide  may  be  traced  as  follows  : cyanide 
of  cobalt  is  first  formed;  2 HCy-f OoO=-0oCy,  + HgO,  aiid  this 
cyanide  of  cobalt,  by  exposure  to  air  with  an  excess  of  cyanide  of 
potassium  and  hydrocyanic  acid,  yields  cobalticyanide  of  potassium, 
whilst  oxygen  is  absorbed  and  water  is  separated ; 4 OoCyg  4-12  KCy 
4-4  IICy-f-Dg  = 4 KgOoCyg  4-  2 II^O.  The  double  cyanide  of 


mANIUM. 


485 


nickel  and  potassium  is  very  simply  formed  ; for  with  nickel  no 
compound  corresponding  to  the  cohalticyanide  is  obtained  ; 4 KCy 
+ me  + H,e= 2 KCy,^iCy,  + 2 Klie.  If  the  strongly  alkaline 
solution  be  now  boiled  and  a solution  of  mercuric  nitrate  be  added 
in  slight  excess,  so  as  to  produce  a precipitate  which,  from  its 
yellowish  colour,  shows  that  the  oxide  of  mercury  is  in  excess,  the 
nickel  salt  is  decomposed,  hydrated  oxide  of  nickel  is  precipitated, 
and  cyanide  of  mercury  is  produced  ; 2 KCy,5?iCy2  + iIg0+H20 
= 2I&y,HgCy,  + ifie,H,0. 

The  cohalticyanide  ot  potassium  is  not  decomposed  by  the 
oxide  of  mercury,  but  remains  in  solution,  and  may  be  filtered 
from  the  oxide  of  nickel,  which  requires  to  be  carefully  ignited  in 
a platinum  crucible  till  it  ceases  to  lose  weight.  After  cautiously 
neutralizing  the  filtrate  with  nitric  acid,  the  cobalt  may  then,  by 
the  addition  of  a solution  of  mercurous  nitrate,  be  precipitated  as 
a wdiite  mercurous  cohalticyanide : the  precipitate  is  collected, 
dried,  and  ignited,  w^hen  pure  oxide  of  cobalt  is  left. 

If,  instead  of  precipitating  the  mixed  cyanides  by  means  of 
mercury,  a solution  of  chloride  of  soda  be  added  in  excess  to  the 
boiling  alkaline  liquid,  in  quantity  sufficient  to  destroy  the  free 
cyanide  of  potassium,  the  nickel  is  precipitated  of  an  intense  black 
as  sesquioxide  ; in  this  form  it  may  be  readily  washed,  and  by 
ignition  it  may  be  converted  into  the  protoxide,  in  which  state  it 
may  be  weighed.  Traces  of  nickel  which  escape  discovery  by 
other  methods  may  thus  often  be  detected  in  cobalt.  Care  must 
be  taken  to  ascertain  the  absence  of  manganese,  as  it  would  go 
down  with  the  nickel,  accompanied  by  traces  of  iron,  if  the  latter 
metal  were  present. 

§ III.  Uranium:  U=:120,  or  U=60.  Sp.  Gr.  18*4. 

(738)  Uranium  is  a metal  the  compounds  of  which  are  but 
sparingly  distributed  over  the  surface  of  the  earth.  It  was  origi- 
nally discovered  by  Klaproth,  \\\  pitchblende^  which  contains  nearly 
80  per  cent,  of  the  black  oxide  of  uranium  (2  U0,U203) ; the  re- 
mainder of  the  mass  consists  of  variable  quantities  of  copper,  lead, 
iron,  arsenic,  and  frequently  of  cobalt  and  nickel.  Uranite^  wdiich 
is  a mineral  of  micaceous  structure,  of  rarer  occurrence,  consists 
of  a hydrated  double  phospliate  of  calcium  and  uranium  (Oa'' 
2 {e,e,)"  2 pe„  8 Il^e,  or  CaO,  2 U203,P0„  8 IIO).  Chcdcolite 
(e\i"  2 (UjOj)^'  2 PO4,  8 1120)  is  a similar  mineral,  in  which 
copper  takes  the  place  of  calcium. 

In  order  to  extract  uranium  from  pitchblende,  the  mineral  is 
heated  to  redness,  and  thrown  whilst  red-hot  into  water,  after 
which  it  admits  of  being  readily  pulverized  : Ebelmen  then  treats 
the  ore  in  the  following  manner  : — The  fine  powder  is  washed  with 
diluted  hydrochloric  acid,  heated  with  charcoal,  and  digested  in 
strong  hydrochloric  acid,  ihy  which  the  earthy  matters  and  most 
of  the  iron,  arsenic,  and  sulphur  are  removed  : the  washed  residue 
is  roasted  and  then  treated  with  nitric  acid  ; the  solution  thus  ob- 
tained is  evaporated  nearly  to  dryness,  to  expel  the  excess  of  acid, 


483 


OXIDES  OF  IJRAXnJM. 


and  is  diluted,  by  which  means  most  of  the  arseniate  of  iron  is  pre- 
cipitated. Sulphuretted  hydrogen  is  then  transmitted  through  the 
filtered  solution,  and  the  liquid  is  filtered  from  the  sulphides  of 
copper,  lead,  and  arsenic  thus  tlirown  down  ; after  which  it  is 
again  evaporated  until  crystals  of  uranic  nitrate  begin  to  be  formed. 
This  salt  is  decomposed  by  heating  it  to  redness,  and  the  oxide  of 
uranium  which  is  left  is  mingled  with  charcoal  and  heated  in  a 
glass  tube  through  which  a current  of  dry  chlorine  is  passing  ; car- 
bonic anhydride  and  carbonic  oxide  are  thus  formed,  and  a volatile 
green  chloride  of  uranium  (dfCl^)  sublimes.  This  chloride,  when 
heated  with  potassium  in  a platinum  crucible,  yields  chloride  of 
potassium  and  metallic  uranium  : intense  heat  is  evolved  during 
the  reaction  of  the  potassium  on  the  chloride  of  uranium,  and  the 
resulting  metal  is  partially  fused.  The  isolation  of  metallic  uranium 
is  due  to  Peligot  {Ann.  de  Chimie.^  III.  v.  5),  the  substance  origi- 
nally supposed  to  be  the  metal  having  been  proved  by  him  to  be 
its  protoxide. 

Uranium  as  thus  obtained  is  of  a steel- white  colour : it  appears 
to  be  slightly  malleable  ; it  is  not  oxidized  by  exposure  to  air  or  to 
water  at  ordinary  temperatures  ; but  if  heated  in  the  air  it  burns 
brilliantly : sulphuric  and  hydrochloric  acids  dissolve  it  with  extri- 
cation of  hydrogen  gas.  In  its  chemical  relations  it  is  somewhat 
analogous  to  iron  and  manganese. 

(739)  Oxides  of  Uranium. — Uranium  forms  two  principal  ox- 
ides, a protoxide.^  or  uranous  oxide^  UO,  and  a sesquioxide^  or  ura- 
nic oxide^  U2O3 : two  intermediate  oxides  may  also  be  obtained,  the 
hlach  oxide ^ 2 U0,U203,  and  the  green  oxide U0-,U2O3. 

T\\q  protoxide.,  or  uranous  oxide  (UO=:136,  or  UO=68),  may 
be  obtained  in  several  ways  : one  of  the  easiest  consists  in  igniting 
uranic  oxalate  in  closed  vessels,  or  in  a current  of  hydrogen.  In 
its  anhydrous  state  the  dilute  acids  are  without  action  upon  it,  but 
its  hydrate,  which  may  be  obtained  in  reddish-brown  fiocculi,  by 
adding  ammonia  to  a solution  of  the  chloride,  UCl^,  is  readily  so- 
luble in  the  acids  ; it  forms  green  cry stalliz able  salts,  which  have 
a strong  tendency  to  absorb  oxygen. 

The  hlacJc  oxide  (2  U-0-,U2O3)  may  be  procured  by  heating  the 
protoxide  to  bright  redness,  and  suddenly  cooling  it,  or  by  igniting 
uranic  nitrate.  It  furnishes  a pure  and  intense  black,  highly  prized 
for  colouring  porcelain. 

The  green  oxide  (UO,U2^3  5 9^-  which  corresponds 

in  composition  to  the  magnetic  oxide  of  iron,  is  procured  by  heat- 
ing the  black  oxide  moderately  in  a current  of  oxygen  or  in  the 
open  air  ; by  more  intense  ignition  it  becomes  re-converted  into 
the  black  oxide,  and  is  again  partially  re-oxidized  as  it  cools.  It 
is  soluble  in  hot  concentrated  sulphuric  acid,  but  does  not  form 
distinct  salts. 

The  sesquioxide^  or  uranic  oxide,  (U2O3)  partakes  of  the  cha- 
racter both  of  an  acid  and  of  a base.  It  is  with  difficulty  obtained 
in  a pure  state.  By  exposing  uranic  oxalate  to  the  sun’s  rays,  a 
brownish- violet  powder,  which  is  a hydrate  of  the  green  oxide, 
(U3O4,  3 HjO)  is  deposited,  while  carbonic  anhydidde  makes  its 


OXIDES  AXD  CHLOEIDES  OF  TJEANIUM. 


487 


escape  : this  precipitate  absorbs  oxygen  on  exposure  to  the  air,  and 
becomes  converted  into  a greenish-yellow  mass,  which,  according 
to  Ebelmen,  is  a hydrate  of  the  sesqnioxide  2 H^O).  The 

sesqnioxide  may  be  obtained  in  the  anhydrons  state  as  a brick-red 
powder,  by  heating  this  hydrate  to  a temperature  not  exceeding 
572°.  Uranic  oxide  reacts  readily  with  acids,  and  forms  salts  of  a 
bright  yellow  colour.  Peligot  found  that  the  oxide  (UO)  evinced 
a strong  tendency  to  unite  with  elementary  bodies  like  a metal, 
and  hence  he  proposed  to  call  it  uranyl^  and  he  explained  the  fact 
that  the  normal  uranic  salts  are  all  formed  by  the  action  of  uranic 
oxide  upon  two  atoms  of  monobasic  acid  instead  of  on  six  atoms. 
Uranic  nitrate,  for  instance,  which  furnishes  long  striated  prisms, 
consists,  even  when  crystallized  from  a strongly  acid  solution,  of 
(U2O2)''  2 UO3,  6 H^O.  Numerous  uranic  double  salts  have  also 
been  formed  ; uranic  sulphate  of  potassium  consists  of  (K2(U202)'' 
2 SO^,  2 H2^)-  If  an  attempt  be  made  to  procure  uranic  oxide 
by  decomposing  the  solutions  of  these  salts  by  the  addition  of  an 
alkali,  an  insoluble  yellow  precipitate,  consisting  of  a compound 
of  the  sesqnioxide  with  the  alkali,  frequently  called  a tti^anate  of 
the  base,  falk  ; uranate  of  potassium  has  the  formula  K2^j  ^ U2O3, 
and  the  other  similar  compounds  have  a corresponding  composi- 
tion ; this  compound  cannot  be  decomposed  even  by  boiling  water : 
the  commercial  yellow  oxide  is  a hydrate  retaining  about  2 per 
cent,  of  ammonia,  from  which  heat  expels  the  water  and  ammonia, 
and  also  converts  the  sesqnioxide  into  the  black  or  the  green  oxide. 
The  compounds  of  uranic  oxide  with  the  earths,  however,  stand  a 
strong  heat  without  decomposition,  and  are  employed  to  commu- 
nicate a beautiful  and  peculiar  yellow  to  glass. 

(740)  Chlorides  of  Uranium. — The  bichloride  (UCI2),  uranous 
chloride  (Peligot’s  protochloride,  UCl)  is  a green,  volatile,  deli- 
quescent compound,  which  is  decomposed  by  water ; the  method 
of  preparing  it  has  already  been  described  (738).  If  dry  hydro- 
gen gas  be  transmitted  over  the  uranous  cldoride,  while  it  is  being 
heated  to  redness  in  a glass  tube,  a chloride  (U2CI3)  is  produced, 
wliich  crystallizes  in  slender  dark-brown  needles,  which  are  but 
slightly  volatile : they  are  very  soluble  in  water,  and  form  a deep 
purple  solution,  from  which  ammonia  throws  down  a brown  sub- 
oxide ; this  oxide  absorbs  oxygen  from  the  air  rapidly.  An  oxy- 
chloride  (UOCl),  or  (U-203,UCl3),  somewhat  analogous  to  chloro- 
chromic  acid  (789),  is  formed  by  passing  chlorine  over  tlie  protoxide 
of  the  metal,  constituting  Peligot’s  chloride  of  uranyl : it  is  deli- 
(juescent,  and  forms  a yellow  solution  with  water ; with  tlie  clilo- 
rides  of  tlie  alkaline  metals  it  forms  remarkable  double  salts ; the 
double  salt  with  chloride  of  potassium  consists  of  (KCl,UOCl . 
UgO),  and  crystallizes  in  rhombic  tables  of  a greenish-yellow 
colour. 

(741)  Characters  of  the  Compounds  of  Uranium. — 1.  The 
ur(mou8  salts  have  a green  colour,  and  have  a strong  tendency  to 
form  double  salts  with  salts  of  the  alkaline  metals  which  contain 
the  same  acid  as  themselves.  In  solutions  of  the  uranous  salts, 
ammonia  and  the  alkalies  give  a gelatinous,  blackish-brown  pre- 


488 


TTKAXIUM 


cipitate  of  hydrated  oxide:  this  precipitate  absorbs  oxygen  and 
becomes  yellow  from  the  formation  of  sesquioxide  of  nraniiim, 
which  unites  with  the  excess  of  alkali.  Sulphuretted  hydrogen 
produces  no  precipitate ; but  sidphide  of  ammonium  occasions  a 
black  deposit  of  sulphide  of  uranium.  Oxalate  of  ammonium  gives 
a greenish-white  precipitate  of  uranous  oxalate.  Solutions  of  the 
green  salts  of  uranium  absorb  oxygen  rapidly,  and  are  converted 
by  nitric  acid  into  uranic  salts,  even  without  the  aid  of  heat. 

2.  The  uranic  salts  are  yellow.  Their  solutions  give  with 
ammonia  precipitate,  consisting  of  uranate  of  ammonium ; 

^T\^ferrocyanide  of  potassium  they  yield  a hair-brown  precipitate. 
By  the  action  of  ammonia  they  are  distinguished  at  once  from  the 
compounds  of  copper,  wdiich  give  a blue  solution  on  the  addition 
of  an  excess  of  ammonia,  though  they  yield  a precipitate  with  the 
ferrocyanide  similar  in  colour  to  that  furnished  by  the  salts  of 
uranium.  Sulphuretted  hydrogen  produces  no  precipitate,  but 
sidphide  of  ammonium  gives  a yellowish-brown  sulphide.  Car- 
honates  of  the  cdJcaline  metals  give  a yellow  granular  precipitate, 
soluble  in  excess  of  the  precipitant ; these  precipitates  are  double 
carbonates  of  uranium  and  of  the  alkaline  metal  employed.  With 
infusion  of  nut-galls  a dark-brown  precipitate  is  produced. 

(742)  Estimation  of  Uranium. — Uranium  is  usually  estimated 
in  the  form  of  protoxide,  to  which  it  is  reduced  by  heating  the 
sesquioxide  to  redness  in  a glass  tube  in  a current  of  hydrogen ; 
the  tube  must  be  sealed  up  whilst  full  of  hydrogen,  and  weighed 
in  this  condition,  to  jmevent  the  oxide  from  reabsorbing  oxygen 
from  the  air. 

Uranium  is  separated  from  the  alkalies  by  converting  it  into 
a uranic  salt  by  nitric  acid,  if  not  already  in  that  condition,  and 
then  precipitating  it  in  the  form  of  yellow  uranate  of  ammonium. 
If  barium,  strontium,  calcium,  or  magnesium  be  present,  the  addi- 
tion of  sulphuric  acid  separates  the  first  two  in  the  form  of  sul- 
phates ; if  calcium  or  magnesium  be  present,  the  solution  is  fil- 
tered from  the  precipitate,  the  filtrate  evaporated  to  drjmess,  and 
then  heated  with  alcohol  of  specific  gravity  0'900 ; the  sulphates 
of  calcium  and  magnesium  remain  unacted  upon,  whilst  the  uranic 
sulphate  is  dissolved. 

Aluminum,  glucinum,  zinc,  cobalt,  and  nickel  may  be  sepa- 
rated from  uranium  by  adding  acid-carbonate  of  potassium  in 
excess  to  the  acidulated  solution : a double  carbonate  of  potassium 
and  uranium  remains  in  the  liquid,  whilst  the  earths,  and  other 
metallic  oxides,  are  precipitated.  For  the  success  of  this  experi- 
ment, it  is  necessary,  if  salts  of  ammonium  be  present,  that  they 
should  be  expelled,  by  evaporating  the  solution  to  dryness  and 
igniting  the  residue,  before  effecting  the  precipitation  of  the 
various  bases  with  the  acid-carbonate  of  potassium. 

§ lY.  Iron  : Fe"  = 56,  or  Fe  = 28.  Sp.  Gr.  7*844. 

(743)  Condition  of  Iron  in  Nature. — Iron  is  more  extensively 
diffused  than  any  other  metal : not  only  is  it  abundant  in  the  in  or- 


METEOEITES ORES  OF  IRON. 


489 


ganic  creation,  but  it  is  an  essential  constituent  in  tlie  blood  of 
the  vertebrate  animals. 

Iron  has  been  occasionally  found  in  the  native  form  accom- 
panying the  ores  of  platinum ; but  when  it  occurs  in  the  metallic 
state  it  is  generally  met  with  in  the  meteoric  masses  associated 
with  nickel,  cobalt,  and  small  quantities  of  other  metals,  among 
which  are  copper,  manganese,  and  chromium.^  Some  of  these 
masses  which  have  fallen  in  an  ignited  state  from  the  atmosphere 
are  of  very  considerable  size.  One  discovered  in  Siberia,  by 
Pallas,  weighed  1600  lb.,  and  a block  found  in  the  district  of 
Chaco-Gualamba,  in  South  America,  is  estimated, at  between  13 
and  14  tons  weight.  These  extraordinary  bodies  are  unimportant 
as  sources  of  iron. 

The  ores  of  iron  are  numerous.  The  most  valuable  are  the 
following : — 

1. — ^fagnetic  Iron  Ore,  or  Loadstone  (Pe0,Pe203 ; S][>.  Gr. 
5 ‘09). — This  is  found  in  enormous  masses,  or  even  mountains, 
amongst  the  primary  formations.  Much  of  the  best  Swedish  iron 
is  obtained  from  this  material,  which  is  also  abundant  in  Hortli 
America.  Occasionally  it  is  found  in  detached  octohedral  crys- 
tals. Coal  is  absent  in  those  formations  in  which  this  mineral 
occurs ; hence  charcoal  is  the  fuel  ordinarily  employed  in  smelt- 


* Aerolites,  or  meteoric  stones,  may  be  subdivided  into  three  principal  groups, 
the  first  of  which  consists  of  metallic  masses,  and  these  are  the  most  common ; the 
second  variety  contains  no  metallic  iron,  but  consists  often  of  crystalline  minerals ; 
and  the  third  not  uncommon  form  is  composed  of  a mixture  of  the  metallic  and 
earthy  variety  in  the  same  specimen.  These  different  kinds  of  aerolites  are  inclosed 
in  a thin  crust  or  rind  of  a few  hundredths  of  an  inch  in  thickness,  presenting  a glossy, 
pitch-like,  or  veined  surface.  The  crystalline  minerals  which  have  been  observed 
are  of  a basaltic  nature,  and  consist  of  olivine,  varieties  of  augite  and  leucite,  anor- 
thite  and  labradorite ; in  addition  to  these,  chrome  iron,  tinstone,  magnetic  iron  ore,  and 
magnetic  pyrites,  besides  nickeliferous  metallic  iron. 

The  masses  of  meteoric  iron  themselves  also  display  crystalline  structure.  When 
a polished  surface  of  one  of  these  metallic  masses  is  immersed  in  nitric  acid,  the  dif- 
ferent portions  of  the  surface  are  unequally  acted  upon,  as  was  first  noticed  by  Wid- 
mannstatt ; and  a series  of  lines  crossing  each  other  in  three  different  directions  be- 
come developed ; between  them  are  broad  shallow  spaces,  less  deeply  etched,  and 
narrow  bands  between  these  retain  their  pohsh  and  resist  the  acid ; these  bands  con- 
tain more  nickel  than  the  rest  of  the  mass. 

The  origin  of  these  meteorites  is  unknown;  but  it  is  an  opinion  generally  received, 
that  they  are  asteroids  or  planetary  dust,  fragments  of  which  from  time  to  time  come 
within  the  sphere  of  the  earth’s  attraction : these,  by  friction  in  their  rapid  flight 
through  the  earth’s  atmosphere,  become  ignited,  and  ultimately  reach  the  surface  of 
the  earth. 


Amongst  the  constituents  of  these  meteorites  twenty-two  elementary  substances 
have  been  found,  but  no  element  not  previously  known  to  be  of  terrestrial  origin  has 
been  discovered.  The  following  are  the  meteoric  elements,  partly  in  the  earthy, 
partly  in  the  metallic  portions  : — 


Iron. 

Cobalt. 

Nickel. 

Chromium. 

Manganese. 

Copper. 

Tin. 


Magnesium. 

Calcium. 

Potassium. 

Sodium. 

Aluminum. 

Titanium. 

Silicon. 

Carbon. 


Arsenic. 

Phosphorus. 

Nitrogen. 

Sulphur. 

Oxygen. 

Chlorine. 

Bromine. 


The  metallic  portions  consist  chiefly  of  native  iron,  which  contains  sulphur,  phos- 
phorus, carbon,  manganese,  magnesium,  nickel,  cobalt,  tin,  and  copper. 


490 


ORES  OF  IRON. 


iiig  it.  This  fuel  contains  a smaller  amount  of  ash  than  coal ; 
fewer  impurities  are  therefore  introduced  by  it  during  the  smelt- 
ing than  when  coal  is  used ; and  as  the  ore  itself  is  generally  very 
pure,  the  metal  which  it  furnishes  is  of  excellent  quality.  The 
iron  sand  found  at  Nellore,  in  India,  and  employed  in  the  manu- 
facture of  wootz,  consists  chiefly  of  magnetic  oxide  of  iron. 

2.  — Specular  Iron  Ore^  or  Fer  Oligiste  ' Sp.  Gr.  5'2. — This  is 
an  anhydrous  sesquioxide  of  iron  (Fe^Og) : it  occurs  in  the  primary 
rocks.  The  principal  part  of  the  celebrated  Elba  iron,  and  also  a 
large  quantity  of  Eussian  and  of  Swedish  iron,  are  obtained  from 
this  source.  Charcoal  is  in  this  case  also  the  fuel  employed. 

3.  — Fed  Hcematite  (EegOg,  sp.  gr.  about  5’0)  is  another  form 
of  the  anhydrous  sesquioxide : it  is  sometimes  found  massive ; 
but  more  generally  in  fibrous  crystalline  nodules.  This  ore  is 
largely  raised  in  Lancashire  and  in  some  parts  of  Cornwall.  It 
is  seldom  smelted  alone ; but  it  forms  a valuable  addition  to  the 
clay  iron-stone  of  the  coal-measures. 

4.  — Brown  Hcematite  (2  Ee^Og,  3 H^O) ; Sp.  Gr.  about  3*9. — 

This  is  a hydrated  sesquioxide  of  iron,  which  generally  occurs  in 
fibrous  or  in  compact  masses.  It  is,  however,  also  met  with  in 
the  oolitic  strata,  in  some  parts  of  France,  in  the  form  of  rounded 
masses  termed  ore^  mixed  with  a small  proportion  of  clay. 

Much  of  the  French  iron  is  obtained  from  this  source.  Brown 
haematite  is  readily  soluble  in  hydrochloric  acid ; it  is  less  refrac- 
tory in  the  furnace  than  the  preceding  variety.  The  brown  hae- 
matite, when  roasted,  becomes  porous  from  the  loss  of  its  water, 
and  is  thus  rendered  more  manageable.  Mixed  with  variable  pro- 
portions of  earth  or  clay,  and  sometimes  with  oxide  of  manganese, 
this  oxide  of  iron  forms  the  varieties  of  umber  and  ochres.  It 
occurs  principally  in  the  secondary  and  tertiary  deposits. 

5.  — Spathic  Iron^  or  Carbonate  of  Iron  (PeOOg) ; Sp.  Gr.  3*8. 
— This  is  found  in  crystalline  masses  often  combined  with  carbo- 
nate of  magnesium  and  with  a considerable  portion  of  manga- 
nese, as  in  the  Saxony  ores.  Much  of  the  so-called  natural  steel 
is  made  from  this  ore. 

6.  — Clay  ironstone  is  the  chief  source  of  the  enormous  quan- 
tity of  iron  manufactured  in  Great  Britain.  It  is  an  impure 
carbonate  of  iron,  containing  generally  from  30  to  33  per  cent,  of 
metallic  iron,  mingled  with  varying  proportions  of  clay,  oxide  of 
manganese,  lime  and  magnesia.  This  argillaceous  ironstone 
occurs  in  bands  broken  up  into  nodules,  or  in  continuous  seams, 
from  two  to  fourteen  inches  thick,  alternating  with  beds  of  coal, 
clay,  shale,  or  limestone,  in  the  coal-measures  diffused  over  large 
areas  in  South  Staffordshire,  South  Wales,  and  some  other  parts 
of  Great  Britain.  It  is  also  found  in  the  United  States,  and  in 
Bohemia  and  other  countries  of  central  Europe.  It  has  a specific 
gravity  ranging  between  2*7  and  3*47. 

7.  — The  black  band  of  the  Scotch  coal-fields  is  also  a car- 
bonate of  iron,  but  the  principal  foreign  matter  in  this  mineral, 
which  often  amounts  to  25  or  30  per  cent.,  is  of  a bitmninous  or 
combustible  nature. 


BLAST  FURNACE. 


491 


8.  — A siliceous  ironstone  has  been  found  abundantly  in  the  oolite 
in  the  neighbourhood  of  IN’orthampton.  It  yields  an  inferior  iron, 
owing  to  the  presence  of  a large  quantity  of  phosphates  in  the  ore. 

9.  — Another,  but  comparatively  an  unimportant  ore,  of  a brown 
colour,  known  as  hog-iron  ore,  is  a mixture  of  hydrated  sesqui- 
oxide  and  phosphate  of  iron  in  variable  proportions.  It  occurs  in 
marshy  alluvial  districts,  near  the  surface. 

Iron  pyrites  though  a very  abundant  mineral,  is 

wrought  only  for  the  sake  of  its  sulphur,  because  the  iron  which 
it  furnishes  is  not  pure  enough  for  use. 

(744)  Smelting  of  Clay  Ironstone. — After  the  ore  has  been 
broken  up  into  masses  about  the  size  of  two  fists,  it  is  roasted,  in 
order  to  expel  water  and  carbonic  acid  ; the  mass  is  thus  left  in 
a porous  state,  highly  favourable  to  its  subsequent  reduction  in 
the  furnace.  The  roasting  is  sometimes  performed  in  kilns,  but 
usually  in  heaps  in  the  open  air.  If  this  operation  is  to  be  ef- 
fected in  the  open  heaj),  a plat  of  ground  is  leveled  and  covered 
with  a layer  of  coal  in  lumps  to  tlie  depth  of  10  or  12  inches  ; this 
is  succeeded  by  alternate  layers  of  the  mineral  and  of  small  coal. 
The  quantity  of  coal  required  in  the  case  of  the  black  band  is 
often  very  small,  as  the  ore  itself  frequently  contains  sufficient  in- 
fiammable  matter  to  con- 
tinue burning  when  once 
well  lighted.  The  heap, 
when  finished,  is  14  or  15 
feet  wide,  8 or  10  high, 
and  of  great  length.  The 
fire  is  kindled  at  the 
windward  extremity,  and 
allowed  to  spread  gra- 
dually through  the  mass. 

Tills  preliminary  ope- 
ration occupies  some 
months  for  its  comple- 
tion. The  roasted  ore 
is  then  ready  for  the 
smelting. 

The  blast  furnace 
employed  for  this  pur- 
pose is  represented  in 
section  in  fig.  345.  The 
internal  cavity  in  shape 
resembles  a long  narrow 
funnel  inverted  upon  the 
mouth  of  another  shorter 
funnel.  These  furnaces 
are  usually  about  50  feet 
high,  and  from  14  to  17 
feet  in  diameter  in  the 
widest  part  of  the  cavity. 

The  lowest  portion,  f,  or  neck  of  the  funnel,  is  termed  the 


492 


THEORY  OF  THE  BLAST  FURNACE. 


crucihle  or  hearth^  and  is  made  of  very  refractory  gritstone. 
In  the  front,  8 or  10  inches  from  the  floor  ii,  is  a longitudinal  aper- 
ture above  the  tymp-stone,  l,  for  the  overflow  of  the  slag,  and  on 
the  sides  are  the  openings  for  the  tuyeres^  i,  i,  or  blast-pipes, 
which  are  connected  with  powerful  blowing  machines  for  supply- 
ing air  under  a pressure  of  from  2 lb.  to  3 lb.  upon  the  inch.  A 
steady  and  most  intense  heat  is  thus  uniformly  maintained.  At 
the  lowest  point  of  the  furnace  is  the  tap-hole^  for  drawing  off  the 
melted  metal  at  suitable  intervals,  and  which,  except  at  such 
times,  is  closed  with  sand  and  clay  : k,  k,  are  galleries,  which 
allow  the  workmen  free  access  to  the  tuyeres  and  lower  portion 
of  the  furnace,  the  base  of  which  is  kept  dry  and  well  drained  by 
the  arched  channels,  m.  Above  the  crucible  the  furnace  suddenly 
widens,  forming  the  hoshes^  n ; the  lining,  c,  is  formed  of  fire- 
bricks, which  are  continued  up  to  the  throat,  a,  of  the  furnace : 
the  whole  is  cased  in  solid  masonry,  e,  e,  and  supported  by  iron 
bands.  When  working  regularly,  such  a furnace  is  charged 
through  the  opening,  b,  near  the  top,  at  intervals,  first  with  coal, 
and  then  with  a suitable  mixture  of  roasted  ore  and  of  a limestoe 
flux  broken  into  small  fragments.  As  the  fuel  burns  away,  and 
the  materials  sink  down  gradually,  fresh  layers  of  fuel,  and  of  ore, 
are  added  ; so  that  the  furnace  becomes  filled  with  alternate  lay- 
ers of  each. 

The  principal  substances  which  are  acted  upon  in  such  a fur- 
nace are  the  following  : — 

1st,  the  oxygen  contained  in  the  air  of  the  blast ; 2nd,  the 
roasted  ore, — consisting  of  oxide  of  iron,  silica  in  the  shape  of 
sand  or  quartz,  clay  or  silicate  of  aluminum,  and  a little  magnesia 
and  oxide  of  manganese ; 3rd,  coal  or  coke, — composed  chiefly 
of  carbon,  with  a small  proportion  of  hydrogen ; and  4th,  car- 
bonate of  calcium,  which  in  the  heat  of  the  furnace  soon  becomes 
quicklime. 

(745)  Theory  of  the  Blast  Furnace. — The  chemical  changes 
may  be  traced  as  follows,  beginning  at  the  bottom  of  the  fur- 
nace : — The  oxygen  contained  in  the  air  of  the  blast,  as  soon  as 
it  comes  into  contact  with  the  fuel  in  the  crucible,  combines  with 
the  carbon  and  forms  carbonic  anhydride,  attended  with  a com- 
bustion of  intense  activity.  The  blast  is  thus  soon  deprived  of 
all  its  free  oxygen ; nearly  the  whole  of  the  nitrogen  escapes 
unchanged,  but  the  carbonic  anhydride,  in  its  passage  over  the 
ignited  fuel,  is  decomposed ; each  atom  of  the  anhydride  combines 
with  an  additional  atom  of  carbon,  and  becomes  converted  into 
carbonic  oxide  ; for  each  volume  of  carbonic  anhydride  2 volumes 
of  carbonic  oxide  are  produced.  This  formation  of  carbonic  oxide 
is  attended  with  a large  absorption  of  heat,  so  that  the  tempera- 
ture of  the  furnace,  above  the  crucible,  becomes  rapidly  reduced, 
and  a quantity  of  highly  combustible  gas  is  thus  formed.*  This 

* Bunsen  and  Playfair,  in  their  examination  of  the  gases  produced  in  a hot-hlast 
furnace  at  Alfreton,  found  that  a considerable  amount  of  cyanide  of  potassium  was 
formed  in  the  hotter  portions  of  the  furnace  {British  Association  Reports,  1845,  p,  182): 
part  of  the  nitrogen,  derived  probably  both  from  the  blast  and  from  the  coal,  had 


GASEOUS  PKC>DUCTS  OF  THE  BLAST  FUKNACE. 


493 


carbonic  oxide  becomes  mingled  with  carbnretted  hydrogen  and 
free  hydrogen,  which  are  derived  from  the  fuel  contained  in  the 
upper  part  of  the  charge,  as  it  gradually  descends  towards  the 
focus  of  intense  heat  below.  A proportion  of  the  gases  which 
escape  from  the  opening  at  the  top  of  the  furnace,  varying  from 
35  to  40  per  cent.,  is  combustible  ; the  remainder  consists  princi- 
pally of  nitrogen,  with  a small  amount  of  carbonic  anhydride. 
The  ore  having  been  rendered  porous  by  the  previous  roasting,  is 
easily  penetrated  by  these  ascending  gases,  by  contact  with  which 
the  iron  becomes  reduced  in  the  upper  part  of  the  boshes,  where 
the  heat  is  comparatively  moderate.  By  degrees  the  reduced 
metal,  mixed  with  the  earthy  matter  of  the  ore,  sinks  down  to  the 
hotter  region.  Here  the  earthy  matters  melt  and  become  vitri- 
fied ; whilst  the  iron,  in  a minutely  divided  state,  being  brought 
into  contact  with  the  carbon  of  the  fuel,  combines  with  it  and 
forms  the  fusible  compound  well  known  as  cast  iron.  This  car- 
bide of  iron  melts,  sinks  down  below  the  tuyeres  through  the 
lighter  vitrified  slags,  and  is  protected  by  them  from  the  further 
action  of  oxygen.  The  bulk  of  the  slag  is  5 or  6 times  as  great 
as  that  of  the  iron  produced : it  floats  above  the  melted  metal, 

therefore  entered  into  combination  with  carbon,  and  had  united  with  the  potassium 
contained  in  small  quantities  in  the  ore  and  in  the  ashes  of  the  coal. 

The  furnace  in  which  these  experiments  were  made  was  40  feet  deep  from  the 
top  of  the  charge  to  the  hearthstone,  and  was  charged  every  twenty  minutes  with 
420  lb.  of  calcined  clay  ironstone,  containing  about  60  per  cent,  of  oxide  of  iron, 
390  lb.  of  coal,  and  170  lb.  of  limestone:  each  charge  yielded  140  lb.  of  pig-iron. 
The  blast  was  under  a pressure  of  6-75  inches  of  mercury,  and  had  a temperature  of 
626°. 

These  chemists  state  that  at  a depth  of  2f  feet  from  the  tuyere,  or  34  feet  from 
the  top  of  the  furnace,  the  gases  which  they  collected  contained  1'34  per  cent,  of 
cyanogen.  The  following  table  furnishes  a summary  of  the  results  which  they 
obtained: — 

Analysis  of  Gases  from  a Ilot-Uast  Furnace. 


Depth  from  the  top 
Height  from  tuyere 

5 feet. 
32 

8 

29 

14 

23 

17 

20 

20 

17 

24 

13 

34 

n 

Nitrogen 

55-35 

54-77 

50-95 

55-49 

60-46 

56-75 

58-05 

Carbonic  anhydride 

7-77 

9-42 

9-10 

12-43 

10-83 

10-08 

0-00 

Carbonic  oxide .... 

25-97 

20-24 

19-32 

18-77 

19-48 

25-19 

37-43 

Marsh  gas 

3-75 

8-23 

6-64 

4-31 

4-40 

2-33 

0-00 

Hydrogen 

6-73 

6-49 

12-42 

7-62 

4-83 

5-65 

3-18 

Olefiant  gas 

0-43 

0-85 

1-57 

1-38 

0-00 

0-00 

0-00 

Cyanogen 

0-00 

0-00 

0-00 

0-00 

0-00 

trace 

1-34 

100-00 

100-00 

100-00 

100-00 

100-00 

loO-OO 

100-00 

The  process  of  coking,  which  is  effected  in  the  upper  part  of  the  furnace,  did 
not  appear  to  be  complete  until  the  charge  had  readied  a depth  of  24  feet,  but  was 
most  active  at  a depth  of  14  feet;  the  principal  reduction  of  the  ore  seemed  to  take 
place  just  below  the  point  at  which  the  coking  was  completed : the  maximum  heat 
of  this  furnace  occurring  between  about  3 and  4 feet  above  the  tuyere,  or  33  from 
the  top. 

In  a furnace  fed  with  charcoal,  Bunsen  found  the  reduction  of  the  ore  to  com- 
mence nearer  the  throat  of  the  furnace,  for  in  this  case  no  absorption  of  heat 
occurred  similar  to  that  occasioned  by  the  process  of  coking  the  coal,  which  takes 
place  in  the  upper  part  of  the  hot-blast  furnace.  The  body  of  a charcoal  furnace 
consequently  did  not  require  to  be  so  high  as  that  of  a furnace  in  which  coal  is  used. 
Similar  experiments  by  Ebelmen  load  to  conclusions  substantially  the  same. 


49i 


SLAGS SMELTING  OF  CLAY  IRONSTONE. 


and  is  allowed  to  flow  over  continiiallv  at  tlie  opening  left  for 
the  purpose  ; whilst  the  iron  is  run  off  at  intervals  of  12  or  24 
hours,  by  withdrawing  the  stopping  of  clay  and  sand  from  the 
tap-hole  at  the  bottom. 

The  furnace  slags  constitute  an  imperfect  species  of  glass, 
which  is  sometimes  more  or  less  distinctly  crystalline,  and  which 
varies  in  colour  with  its  composition,  being  grey,  blue,  green, 
brown,  or  black.  They  consist  principally  of  silicates  of  calcium, 
magnesium,  and  aluminum,  with  generally  a small  proportion  of 
silicates  of  manganese  and  iron.  In  the  formation  of  these  slags 
the  siliceous  matters  of  the  ore  react  upon  the  earthy  bases, 
lime,  magnesia,  and  alumina,  and  really  neutralize  them. 

The  general  composition  of  these  slags  may  be  seen  from  the 
subjoined  analyses  : I.  A slag  obtained  from  Merthyr  Tydvil, 
by  Berthier.  II.  A cold-blast  slag,  Tipton,  Staffordshire,  by 
D.  Forbes.  III.  A hot-blast  slag,  from  coke-furnace,  by  Percy. 
lY.  Average  of  slag  from  13  blast  furnaces  at  Dowlais,  by  Piley ; 
the  last  three  quoted  from  Percy’s  Metallurgy^  vol.  ii.  pp.  497  and 
499. 


I. 

IL 

III. 

lY. 

Silica 

40-4 

39-52 

37-91 

43-07 

Alumina 

11-2 

15-11 

13-01 

14-85 

Ferrous  oxide 

3-8 

2-02 

0-93 

2-53 

Manganous  oxide 

2-89 

2-79 

1-37 

Lime 

38-9 

32-52 

31-43 

28-92 

Magnesia 

5-2 

3-49 

7-24 

5-87 

Potash 

1-06 

2-60 

1-84 

Sulphide  of  calcium. . . 
Phosphoric  anhydr 

traces 

2-15 

3-65 

1-90 

traces 

99*1 

98-76 

99-56 

100-35 

The  oxygen  in  the  bases  of  these  slags  is  nearly  equal  in 
amount  to  that  contained  in  the  silica.  Those  quoted  from 
Percy  approach  the  formula,  6 [2(0aMgMnFe)0,Si0J,  2 Al^Og, 
3 SiOj. 

The  composition  of  Ho.  I.  may  be  represented  by  the  formula, 
5 [3  (eaMgFe)e,2Siej  . (2  Al,e3,  SiO^). 

There  are  several  points  which  require  nice  adjustment  in  this 
process  of  reduction.  The  sla^  must  not  be  of  too  fusible  a 
description,  otherwise  the  iron  falls  to  the  bottom  before  it  has 
thoroughly  combined  with  the  carbon,  and  is  not  completely 
melted ; a sufficiency  of  lime  should  always  be  present  to  neutral- 
ize the  whole  of  the  silica,  for  unless  this  be  attended  to,  a ferrous 
silicate  is  formed,  and  iron  runs  off  in  waste.  Indeed,  a small 
excess  of  lime  is  advantageous,  as  it  removes  sulpliur,  if  present, 
in  the  shape  of  sulphide  of  calcium.  At  the  same  time  the  cal- 
careous matter  must  not  be  too  abundant,  otherwise  the  working 
of  the  furnace  is  obstructed ; the  slags  which  are  formed  being  of 
a less  fusible  character  are  but  imperfectly  melted,  the  iron  is 
entangled  within  them,  it  is  again  partially  oxidated  by  the  blast, 
and  the  product  of  the  furnace  is  greatly  diminished.  Experience 


THE  HOT  BLAST. 


495 


has  shown  that  the  slags  (which  are  chiefly  composed  of  the  mixed 
silicates  of  aluminum  and  calcium)  are  most  fusible  when  the 
oxygen  of  the  silica  amounts  to  double  that  in  the  bases  with 
which  it  is  combined,  and  when  the  proportion  of  lime  employed 
as  a flux  is  such  as  would  be  furnished  by  adding  2 parts  of  lime- 
stone for  every  three  of  clay  contained  in  the  ore  ; the  ratio  of  lime 
to  alumina  being  6 OaO  : Al^Og.  A slag  of  this  kind,  however, 
can  only  advantageously  be  formed  when  the  ore  is  smelted  with 
charcoal,  a fuel  which  contains  but  little  sulphur,  and  which  allows 
the  reduction  to  be  €;^ected  at  a comparatively  moderate  tempe- 
rature. When  coal  or  coke  is  used  as  the  fuel,  an  excess  of  lime 
is  recpiired  to  carry  off  the  sulphur  introduced  by  the  pyrites  of 
the  coal,  and  the  slag  which  is  produced  under  these  circumstances 
is  found  to  work  most  advantageously  when  the  proportion  of 
oxygen  in  the  bases  is  nearly  equal  to  that  of  the  silica.  The 
temperature  of  a blast-furnace  fed  with  coal  or  coke  is  much  higher 
than  that  of  one  in  which  charcoal  is  used.  Slags  containing 
several  bases  are  more  fusible  than  when  one  or  two  only  are 
present,  the  different  silicates  aiding  the  fusibility  of  each  other. 
For  a summary  of  an  extensive  experimental  inquiry  into  the 
composition  and  properties  of  slags,  the  reader  is  referred  to 
Percy’s  Metallurgy^  vol.  i.  pp.  20 — 49,  and  vol.  ii.  loc.  cit. 

In  the  process  of  smelting  it  is  also  necessary  to  proportion 
the  supply  of  air  rightly  ; if  too  much  be  thrown  in,  the  furnace 
becomes  unduly  cooled ; if  too  little,  the  supply  of  oxygen  is  in- 
sufficient for  the  maintenance  of  a proper  temperature  by  a due 
amount  of  combustion.  These,  however,  are  points  the  successful 
regulation  of  which  can  only  be  acquired  by  experience.  The 
stream  of  air  for  the  blast  is  not  supplied  in  intermitting  gusts, 
but  is  equalized  as  much  as  possible  : where  the  cold  blast  is  used, 
this  object  is  attained  by  employing  an  air-chamber  or  reservoir ; 
and  where  the  hot  blast  is  employed,  the  long  pipes  required  for 
heating  the  air  answer  the  same  purpose. 

(746)  The  Hot  Blast. — The  mass  of  air  which  passes  through 
one  of  these  furnaces  is  enormous,  being  not  less  than  160,000 
cubic  feet,  or  about  6 tons  weight,  per  hour.  It  is  evident,  there- 
fore, that  tliis  immense  volume  of  air  must  exercise  an  extraordi- 
nary cooling  effect  upon  the  contents  of  tlie  furnace.  This  evil 
lias  been  much  reduced  of  late  years  by  the  introduction  of  air 
which  has  been  previously  lieated.  In  this  contrivance,  wliich  is 
known  as  the  hot  hlast^  the  air,  before  it  reaches  the  furnace,  is 
made  to  pass  through  a series  of  pipes  which  are  maintained  at  a 
liigli  temperature,  either  by  means  of  a separate  furnace,  or  by  a 
]>ortion  of  the  waste  heat  of  the  blast  furnace  itself:  in  tlie  latter 
case  the  hot  gases  are  conveyed  through  flues  which  pass  from  the 
upper  part  of  the  furnace  into  the  cliamlier  which  contains  the 
pipes:  the  necessary  draught  being  maintained  by  a chimney  fur- 
nished with  a damper.  A jet  of  the  blast  as  it  enters  the  furnace 
should  have  a temperature  sufficiently  high  to  melt  a strip  of  lead 
when  held  in  it.  The  temperature  of  such  a jet  as  it  issues  from 
the  tuyere  is  somewhat  higher  than  600°.  Mr.  Siemens  has  im- 


4:96 


THE  HOT  BLAST. 


proved  npon  this  plan  by  transmitting  the  gases  which  escape 
from  the  furnace,  tlirongh  what  he  terms  a regenerator.  It  is 
simply  a chamber  of  brickwork  filled  with  fire-bricks  so  arranged 
as  to  allow  the  heated  gases  to  circulate  freely  around  them.  Two 
such  chambers  are  prepared ; as  soon  as  the  bricks  in  one  of  these 
chambers  are  red-hot,  the  current  of  gas  from  the  furnace  is  cut 
ofi‘,  and  directed  into  the  other  chamber,  in  order  to  heat  it.  In 
the  meantime  a current  of  cold  air  is  forced  through  the  heated 
chamber,  and  a hot  blast  of  from  1200°  to  1300°  is  thus  obtained. 
Each  chamber  is  worked  alternately ; the  one  becoming  heated 
whilst  the  other  is  employed  in  heating  the  blast.  In  this  way  a 
large  proportion  of  the  heat  of  the  waste  gases  may  be  econo- 
mized.^ 

The  saving  of  fuel  effected  by  the  employment  of  the  hot  blast 
is  immense,  and  is  much  greater  than  was  at  first  anticipated ; 2f 
tons  of  coal  are  now  amply  sufficient  for  the  production  of  a ton 
of  iron,  from  ore  wdiich  wmuld  have  required  8 tons  when  the  cold 
blast  was  used.  This  saving  is  effected  owing  to  the  operation  of 
several  causes,  one  of  which  is,  that  raw  coal  may  now  be  used  in 
the  furnace  instead  of  coke  : moreover  as  a smaller  quantity  of 
fuel  is  required  in  the  furnace  to  raise  the  injected  air  to  the  ne- 
cessary temperature,  so  also  a smaller  quantity  of  air  is  needed  to 
maintain  the  combustion  : combustion  takes  place  within  a short 
time,  so  that  the  maximum  heat  of  the  furnace  is  obtained  lower 
down  in  the  ^ crucible,’  and  the  upper  portions  of  the  furnace  do 
not  become  so  intensely  heated : the  reduction  of  the  ore  conse- 
quently takes  place  nearer  to  the  bottom,  and  the  heat  is  thus 
concentrated  and  economized. 

In  every  metallurgical  process  a particular  temperature  must 
be  attained  in  order  to  secure  the  occurrence  of  the  reaction,  or  of 
the  fusion  which  is  desired.  All  fuel  consumed  at  temperatures 
below  that  point  is  ineffective,  and  is  therefore  burned  to  waste. 
It  must  be  remembered  that  in  every  case  of  combustion  where 
the  same  chemical  compounds  are  produced,  a definite  weight  of 
fuel  always  emits  a definite  amount  of  heat ; consequently  it  will 
raise  a definite  weight  of  air,  and  of  materials  in  the  furnace, 
through  a definite  number  of  degrees  of  temperature : — Say  that 
a certain  weight  of  fuel  will  raise  the  temperature  of  a given 
charge  in  the  furnace  from  60°  to  2500°.  How,  the  same  weight 
of  fuel  (if  we  neglect  the  quantity  of  heat  absorbed  by  alteration 

* This  process,  as  its  value  becomes  appreciated,  will  no  doubt  come  into  very  ex- 
tensive use  in  a great  variety  of  operations  in  metallurgy.  In  many  cases  it  effects 
an  economy  of  one-half  of  the  fuel  employed,  and  it  is  possible  to  obtain  by  its  means 
a steady  and  uniform  temperature  not  exceeding  that  of  a full  red,  up  to  the  heat  re- 
quired for  welding  iron.  It  is  now  employed  with  great  success  in  welding  the  joints  of 
wrought-iron  tubes.  Messrs.  Siemens  prefer  to  distil  the  coal  in  furnaces  through  which 
a regulated  supply  of  air  is  transmitted,  thus  furnishing  a mixture  of  gaseous  hydrocar- 
bons with  carbonic  oxide  and  the  nitrogen  of  the  spent  atmospheric  air,  and  these  com- 
bustible gases  are  conveyed  by  a flue  and  burned  at  the  spot  where  the  heat  is  required. 
The  gases  after  having  done  their  work  are  passed  through  the  regenerator  above  de- 
scribed ; and  in  the  furnace  where  the  combustion  is  effected  a temperature  can  thus 
be  obtained,  limited  at  present  only  by  the  powers  of  the  flre-brick  to  resist  its  fusing 
action.  The  gas  furnace,  for  such  it  is,  has  already,  in  some  cases,  superseded  the  old 
coal  furnace  in  glass-making. 


COISIPOSITION  AKD  PEOPEETIES  OF  CAST  lEON. 


497 


of  the  specific  heat  with  rise  of  temperature)  will  also  raise  the 
same  charge  from  660°  to  3100°.  Suppose,  now,  that  iron  re- 
quired a temperature  of  2800°  for  its  fusion,  no  amount  of  fuel 
burned  so  as  to  produce  a temperature  of  2500°  would  he  of  any 
avail  in  effecting  the  fusion  of  the  metal,  whilst  a comparatively 
small  quantity,  starting  from  the  initial  temperature  of  660°, 
would  produce  the  desired  result. 

Even  in  a hot-blast  furnace,  however,  the  quantity  of  fuel  which 
is  wasted  is  enormous.  Bunsen  and  Playfair,  from  their  elaborate 
experiments  at  Alfreton,  make  the  almost  incredible  estimate  that 
somewhat  more  than  |-ths  of  the  total  quantity  of  heat  producible 
from  the  fuel  consumed  is  lost,  owing  to  the  escape  of  unburned 
combustible  matter  in  the  form  of  gases,  such  as  carbonic  oxide, 
carburetted  hydrogen,  and  hydrogen,  which  are  still  fit  for  use. 
Since  the  publication  of  these  researches,  Mr.  Budd  and  other 
iron-masters  have  economized  a portion  of  the  heat  contained  in 
the  escaping  gases,  in  heating  the  blast  and  in  generating  steam. 

The  iron  obtained  by  the  use  of  the  hot  blast  is  inferior  in 
tenacity  to  cold-blast  iron ; a circumstance  which  appears  to  be 
partially  due  to  the  fact  that  the  proportion  of  silicon  is  greater 
in  hot-  than  in  cold-blast  iron ; it  is  also  to  be  noticed,  that  in  the 
employment  of  the  hot  blast  uncoked  coal  is  used,  a fuel  which 
contains  more  sulphur,  and  possibly  also  more  phosphorus,  than 
coke,  which  is  required  in  working  with  the  cold  blast. 

A furnace  in  full  work  requires  an  hourly  supply  of  rather 
more  than  ton  of  solid  material,  consisting  of  an  average  of 
5 parts  of  coal,  5 of  roasted  ore,  and  2 of  limestone.  The  roasted 
clay-iron  ore  yields  on  an  average  35  per  cent,  of  iron,  and  each 
furnace  when  in  full  activity  furnishes  from  8 to  10  tons  of  metal 
in  the  24  hours.  Every  morning  and  evening  it  requires  to  be 
tapped : on  these  occasions  the  iron  is  run  into  shallow  groves  in 
the  sand,  and  forms  the  cast  iron,  or  pig-iron  of  commerce.  A 
good  furnace,  if  well  managed,  may  be  made  thus  to  work  unin- 
terruptedly without  repair  tor  many  years.* 

(747)  Varieties  of  Cast  Iron. — The  iron  as  it  runs  from  the 
furnace,  however,  is  not  a pure  carbide  or  carburet,  for  in  the 
intense  heat,  not  only  is  the  iron  reduced,  but  portions  also  of 
silicon,  aluminum,  and  calcium,  and  occasionally  other  bodies  de- 
rived from  the  fiux  and  from  the  fuel.  These  bodies  enter  in 
small  quantity  into  combination  with  the  iron,  the  properties  of 
which  they  materially 'modify.  Manganese  generally  accompanies 
the  ores  of  iron  in  greater  or  less  quantity,  and  frequently  com- 

* The  production  of  iron  in  Grreat  Britain,  in  1862,  amounted  to  about  3,943,000 
tons.  It  was  estimated  in  1855,  by  Mr.  Blackwell,  that  the  annual  production  of  iron 
in  different  countries  was  then  as  follows : — 

Tons.  1 Tons. 

England 3,000,000  I Belgium 200,000 

France 750,000  Russia 200,000 

North  America 750,000  I Sweden 150,000 

Prussia 300,000  Germany 100,000 

Austria 250,000  1 Other  States 300,000 

In  all,  six  millions  of  tons,  of  which  Great  Britain  supplied  one-half. 

32 


498  COMPOSITION  AND  PEOPEETIES  OF  CAST  IRON. 

bines  with  the  reduced  metal.  Cast  iron  differs  greatly  in  quality ; 
the  differences  observed  in  it  depend  in  part  upon  differences  in 
the  proportion  of  carbon  and  silicon  which  it  contains.  The 
composition  of  these  carbides  varies  considerably  within  certain 
limits ; but  it  does  not  appear  that  iron  is  capable  of  combining 
with  more  than  about  5 per  cent,  of  carbon.  A compound  of 
carbon  having  the  composition  of  Fe^O,  or  the  tetracarbide^  would 
consist  of  94*92  of  iron,  and  5*08  of  carbon ; and  this  is  very  nearly 
the  composition  of  the  hardest  and  most  fusible  kind  of  white  cast 
iron,  which,  from  the  circumstance  of  its  crystallizing  in  flat  bril- 
liant tables,  is  termed  by  the  Germans  spiegdeisen  (or  mirror  iron) : 
according  to  Giirlt,  the  specific  gravity  of  this  carbide  is  7*65. 
Spiegeleisen  is,  however,  not  a pure  carbide  of  iron,  but  always 
appears  to  contain  manganese  in  amount  varying  form  4 to  10  or  12 
per  cent.  Faraday  and  Stodart  found  the  most  highly  carburetted 
iron  which  they  could  produce  to  consist  of — iron,  94*36 ; carbon, 
5*64.  Gurlt  {Chem.  Gaz.^  1856,  p.  231)  has  described  another  de- 
finite form  of  cast  iron  (FcgO),  the  octocarhide^  which  when  pure 
contains  2*63  per  cent,  of  carbon.  It  has  a sp.  gr.  7*75,  is  of  an 
iron-grey  colour,  and  has  a hardness  much  inferior  to  that  of  the 
tetracarbide,  being  slightly  malleable.  It  crystallizes  in  confused 
octohedral  groups,  and  according  to  Gurlt  is  the  principal  consti- 
tuent of  grey  cast  iron.  The  existence  of  this  compound  is  prob- 
able, but  cannot  be  regarded  as  absolutely  proved.  In  many 
varieties  of  cast  iron  the  carbon  exists  in  two  distinct  forms, — 
one  portion  being  chemically  combined  with  the  metal,  the  other 
being  mechanically  diffused  through  it  in  the  condition  of  graphite, 
the  scales  of  which  may  be  distinctly  seen  with  a magnifying  lens, 
when  the  surface  of  a freshly  fractured  bar  is  examined.  These 
scales  remain  unacted  upon  when  the  metal  is  dissolved  in  diluted 
acids  ; the  combined  carbon  under  such  circumstances  unites  with 
hydrogen,  and  forms  an  oily-looking  liquid  of  ill  odour. 

In  addition  to  carbon,  cast  iron  also  contains  silicon,  the  pro- 
portion of  which  is  equally  liable  to  variation ; the  quantities  of 
silicon  which  have  been  found  in  pig-iron  range  between  3*5  and 
0*25  per  cent.* 

The  table  on  the  opposite  page  will  serve  to  illustrate  the  gen- 
eral composition  of  some  varieties  of  cast  iron.  Gurlt’s  speci- 
mens were  all  made  in  the  same  furnace,  and  with  the  same 

* Karsten  found  that  when  cast  iron  was  melted  with  sulphur  in  a covered  clay 
crucible,  there  was  formed,  on  cooling,  a layer  of  sulphide  of  iron  upon  the  surface, 
then  a layer  of  graphite,  and  beneath  this  a layer  of  carbide  of  iron  in  the  maximum 
degree  of  carburation.  These  effects  may  be  thus  explained: — Carbon  is  incapable 
of  decomposing  sulphide  of  iron,  but  sulphur  can  displace  carbon  from  the  carbide. 
On  the  addition  of  sulphur  to  the  melted  cast  iron  the  carbon  gradually  becomes  con- 
centrated in  that  part  of  the  iron  not  combined  with  the  sulphur,  until  its  point  of 
saturation  with  carbon  is  reached,  and  then  the  graphite  is  separated.  According  to 
the  same  authority,  both  phosphorus  and  silicon  act  in  a similar  manner,  phosphide 
and  silicide  of  iron  being  formed,  whilst  the  carbon  becomes  concentrated  in  the 
remainder  until  the  excess  of  carbon  is  expelled  and  crystallizes  in  the  form  of  gra- 
phite. When  the  proportion  of  phosphorus,  of  silicon,  or  of  sulphur,  is  but  small, 
the  compounds  which  they  form  with  the  iron  remain  disseminated  through  the  mass 
of  cast  iron,  and  exert  an  important  influence  upon  its  texture  and  tenacity. 


COMPOSITION  AND  PKOPEKTIES  OF  CAST  IRON. 


499 


Gurlt. 

Bodemann. 

Abel. 

Grey. 

Coal. 

Mottled, 
hot  blast. 

White. 

Gart- 

sherrie. 

Grey, 
hot  blast. 

Mottled, 
cold  blast. 

Grey. 

French 

charcl. 

White. 
Silesian 
very  crys. 

Specific  gravity .... 

7-21 

7-21 

7-41 

7-166 

7-43 

7-000 

7-531 

Carbon,  combined  . 
Graphite 

1-021 

1-793 

2-457 

1-44 

2-78 

4-94 

2-641 

1-110 

0-871 

2-71 

1-99 

3-40 

Silicon 

3-061 

2-165 

1-124 

3-21 

0-71 

0-80 

0-75 

Sulphur 

1-139 

1-480 

2-516 

trace 

trace 

0-05 

trace 

Phosphorus 

0-928 

1-1.71 

0-913 

1-22 

1-23 

0-45 

0-12 

Iron 

90-236 

89-314 

89-863 

91-42 

93-29 

95-18 

88-57 

Manganese 

0-834 

1-596 

2-715 

trace 

trace 

5-38 

Copper  

. . . 

0-24 

Arsenic 

trace 

Cobalt 

. • • 

trace 

Chromium  

... 

trace 

99-860 

98-629 

100-459 

100-00 

100-00 

99-88 

100-00 

material ; the  grey  at  the  highest  temperature,  the  white  at  the 
lowest. 

The  fusing-point  of  cast  iron  varies  with  its  composition ; that 
of  an  average  specimen  was  estimated  by  Daniell  at  2786°  F. 

In  commerce  there  are  three  principal  varieties  of  cast  iron^ 
known  respectively  as  Hos.  1,  2,  and  3.  I7o.  1 is  called  grey  cast 
iron ; No.  2,  mottled  cast  iron ; and  No.  3,  white  cast  iron.  The 
first  two  contain  carbon  disseminated  in  an  uncomhined  form 
through  the  mass.  Grey  cast  iron  is  soft ; it  may  he  filed,  drilled, 
and  turned  in  the  lathe,  and  through  somewhat  less  fusible  than 
the  white,  is  preferred  for  casting,  since  when  melted  its  liquidity 
is  more  perfect.  This  variety  is  that  which  is  generally  produced 
from  a furnace  in  good  working  order ; if  cooled  suddenly,  it  is 
often  converted  into  white  cast  iron.*  The  fracture  of  the  mottled 
variety  is  in  large  coarse  grains,  among  which  points  of  graphite 
are  distinctly  visible ; it  is  very  tough,  and  is  valued  for  casting 
ordnance.  It  may  be  obtained  for  this  purpose  by  partially 
refining  good  grey  iron.  White  cast  iron  contains  about  the  same 
amount  of  carbon  as  the  mottled  iron,  but  the  whole  of  the  carbon 
appears  to  be  chemically  combined  with  the  metal.  The  white 
variety  passes  through  a pasty  condition  as  a preliminary  to  lique- 
faction ; it  is  more  fusible  than  either  of  the  others,  is  lighter  in 
colour,  very  hard  and  brittle,  has  a lamellar  crystalline  fracture, 
and  a specific  gravity  varying  between  7’2  and  7’6.  It  usually 
contains  less  silicon,  but  more  sulphur  and  pliosphorus  than  grey 
iron.  White  cast  iron  seems  in  some  cases  to  owe  its  colour  to 
the  presence  of  manganese.  A much  higher  temperature  in  the 
furnace,  and  consequently  a greater  consumption  of  fuel  is  required 
for  the  production  of  grey  than  of  white  iron.  This  may  probably 
arise  from  the  fact,  that  if  white  iron  be  melted  and  exposed  to  a 

* According  to  Le  Guen  {Ann.  de  Chimie,  III.  Ixix.  282),  if  good  grey  pig-iron  bo 
fused  with  2^  per  cent,  of  powdered  wolfram,  the  cast  iron  so  produced  is  rendered 
much  stronger  and  more  elastic,  the  tenacity  being  increased  from  3 to  4:  if  tho 
quantity  of  wolfram  be  increased  to  3 per  cent,  the  metal  becomes  still  harder,  but 
not  BO  tough. 


500 


REFINING  OF  CAST  IRON. 


temperature  considerably  higher  than  its  melting-point,  the  tetra- 
carbide  of  iron  is  decomposed,  and  if  it  be  allowed  to  cool  very 
gradually,  a portion  of  the  carbon  crystallizes  out  as  graphite,  and 
grey  cast  iron  is  produced.  In  the  process  of  casting  heavy  ar- 
ticles this  carbon  separates,  and  is  thrown  off  in  the  form  of  bril- 
liant scales,  termed  by  the  casters  Msh. 

The  peculiar  value  of  iron  for  castings  depends  upon  its  pro- 
perty of  expanding  at  the  moment  of  solidification.  It  thus  fur- 
nishes an  admirable  material  for  taking  the  most  minute  impres- 
sions, as  is  well  exemplified  in  the  beautiful  castings  obtained 
from  Berlin. 

Small  articles  made  of  cast  iron,  such  as  key-blocks,  stirrup- 
irons,  &c.,  may  be  rendered  malleable  by  packing  them  in  pow- 
dered luematite,  then  heating  them  to  redness  for  some  hours,  and 
allowing  them  to  cool  very  slowly.  In  this  case  the  oxygen  of  the 
oxide  removes  a portion  both  of  the  carbon  and  of  the  silicon,  by 
a process  of  cementation  the  reverse  of  that  which  takes  place 
during  the  manufacture  of  steel : the  carbon  is  gradually  removed 
from  the  outer  layer  of  the  metal,  and  is  slowly  transmitted  from 
particle  to  particle  through  the  solid  bar,  till  it  reaches  the  sur- 
face, where  it  undergoes  oxidation  at  the  expense  of  part  of  the 


Specific  gravity 

Iron  (by  loss) 

Brittle. 

Malleable. 

•P684 

7-718 

95-732 

2-217 

0-583 

0-951 

trace 

0-015 

trace 

0-502 

98-711 

0-434 

0-446 

0-409 

trace 

trace 

^ , ( combined 

ar  on  -j  uncombined 

Silicon 

Aluminum 

Sulphur 

Phosphorus 

Sand 

100-000 

100-000 

oxygen  of  the  haematite.  The  foregoing  analyses  contain  the 
results  furnished  by  a sample  of  iron  both  before  and  after  it  had 
been  thus  treated.  The  cast  iron  was  obtained  from  the  Lan- 
cashire brown  haematite. 

(748)  Conversion  of  Cast  Iron  into  Wrought  Iron. — 1.  Re- 
fining.— The  pig-iron  as  delivered  from  the  furnace  is,  as  already 
noticed,  far  from  pure  : it  contains  variable  quantities  of  carbon, 
silicon,  sulphur,  and  phosphorus,  besides  traces  of  other  metals, 
such  as  aluminum,  calcium,  and  potassium.  Before  it  can  be 
converted  into  the  wrought  iron  of  commerce,  it  has  to  undergo 
a process  for  the  removal  of  these  extraneous  matters.  Many 
castings  may  be  made  at  once  with  pig-iron,  but  it  cannot  be 
worked  at  the  forge. 

In  order  to  effect  the  purification  of  the  crude  pig-iron,  it  is 
necessary  to  expose  it  to  the  regulated  action  of  oxygen  at  a high 
temperature,  so  as  gradually  to  burn  off  these  oxidizable  substances. 


PUDDLING. 


501 


and  leave  the  iron.  The  pig-iron  is  nsnally  first  remelted  in 
cjuantities  of  from  25  to  30  cwt.,  upon  the  hearth  of  a sort  of 
forge,  termed  the  finery  or  refinery^  the  fire  of  which  is  animated 
by  a cold  blast  from  a double  row  of  blast-pipes.  The  sides  and  back 
of  the  hearth  are  formed  of  hollow  iron  castings,  through  which 
water  is  kept  continually  flowing.  During  this  operation,  wliich 
lasts  about  two  hours,  and  is  one  of  the  most  wasteful  both  of  fuel 
and  of  iron,  the  metal  loses  from  10  to  12  per  cent,  of  its  weight. 
The  silicon  is  more  readily  oxidized  than  the  carbon,  so  that  it  is 
the  impurity  which  is  first  attacked  in  the  refining  process,  but  at 
the  same  time  a small  portion  of  the  carbon  contained  in  the  iron 
is  burned  off  as  carbonic  oxide ; part  of  the  iron  also  becomes 
converted  into  the  protoxide,  which  unites  with  the  silica  furnished 
by  the  oxidation  of  the  silicon,  and  with  the  sand  which  adhered 
to  the  surface  of  the  cast  metal : a fusible  slag  consisting  of  fer- 
rous ortho-silicate  (Fe/'SiO^)  is  thus  produced.  The  oxide  of 
iron  in  this  slag  again  reacts  upon  the  melted  metal,  and  by  im- 
parting a portion  of  its  oxygen  to  the  silicon  and  carbon  dissem- 
inated through  the  mass,  burns  off  an  additional  quantity  of  these 
substances ; portions  of  sulphur  and  phosphorus  are  also  sepa- 
rated by  oxidation  in  this  process,  and  accumulate  in  the  slag. 
The  melted  iron  is  then  run  off,  and  formed  into  a flat  cake  2 or  3 
inches  thick,  and  as  soon  as  it  begins  to  solidify  it  is  suddenly 
cooled  by  pouring  water  upon  it ; a hard,  white,  brittle  mass  is 
thus  obtained,  w^hich  is  broken  up  into  fragments.  In  this  opera- 
tion coke  is  the  combustible  generally  made  use  of,  but  where  iron 
of  superior  quality  is  required,  as  in  making  tin-plate,  charcoal  is 
employed.  Ordinary  coke  contains  sulphur  and  earthy  impurities 
which  injure  the  quality  of  the  iron. 

The  effect  of  the  operation  is  well  exhibited  by  the  following 
analysis  quoted  by  Regnault,  giving  the  composition  of  a portion 
of  cast  iron  before  refining,  and  a portion  of  the  same  metal  after 
it  had  passed  through  the  refinery  furnace. 


Before 

After 

refining. 

refining. 

Carbon 

30 

1-7 

Silicon 

4-5 

0-5 

Phosphorus 

0-2 

Iron 

92-3 

97-8 

100-0 

100-0 

(749)  Puddling. — The  refined  metal  still  retains  a considera- 
ble proportion  of  carbon  and  some  silicon.  In  order  to  remove 
tliem  it  is  next  introduced,  in  charges  of  from  4 to  5 cwt.,  into 
\\\Q picddlmg  furnace.  This  consists  of  a reverl)eratory  furnace, 
connected  with  a chimney  40  or  50  feet  in  lieight,  and  ca])al)le  of 
y)roducinga  powerful  draught,  which  is  under  conijdete  command 
by  means  of  a damper.  Fig.  346  represents  a section  of  tlie  pud- 
dling furnace;  a,  is  the  bed,  or  hearth,  upon  wliich  the  iron  for 


502 


PUDDLING  OE  BOILING. 


puddling  is  placed  ; b is  the  fire-place  with  the  aperture  for  stok- 
ing, which  is  closed  with  coal,  and  not  bj  a door  as  is  usual  in 
most  furnaces ; g is  the  bridge  which  separates  the  fuel  from  the 
metal : the  hearth,  a,  is  lined  with  cast-iron  plates,  e,  e,  which  are 
prevented  from  melting  by  the  free  circulation  of  air  beneath 
them  ; c is  the  flue  leading  to  the  chimney,  d,  at  the  top  of  which 
the  damper  is  shown  ; h is  the  plate  upon  which  the  iron  rests 
during  the  puddling  process ; it  is  protected  from  the  heat  by  a 
coating  of  powdered  haematite,  of  sand,  or  of  slag  ;*  f is  the 
working  door  of  the  furnace  through  the  upper  aperture  in  which 
the  puddler  works  ; the  lower  aperture  is  closed  by  sand  during 
the  operation,  and  is  opened  at  intervals  to  allow  the  slag  or  ta]) 
cinder  to  be  drawn  off,  and  i is  the  floss-hole  or  aperture  through 
which  the  overflow  of  slag  is  removed. 

For  the  coarser  kinds  of  iron  the  furnace  is  sometimes  charged 
partially,  or  even  wholly,  with  pig-iron  that  has  not  been  refined. 

Fig.  346. 


Iron  which  has  undergone  the  refining  process  never  becomes  so 
completely  liquid  in  puddling  as  when  crude  pig-iron  is  employed, 
but  the  product  is  a metal  of  finer  quality. 

Supposing  the  crude  pig-iron  to  be  used,  the  pigs  slowly  become 
melted,  and  the  metal  when  first  heated  forms  a thick  pasty  mass, 
which  gradually  becomes  fluid,  and  at  length  perfectly  liquid.  At 

* The  employment  of  lime  as  a lining  to  the  furnace  has  been  recommended ; it  is 
said  to  improve  the  quality  of  the  iron  by  removing  sulphur  more  completely,  and  at 
the  same  time  to  diminish  the  rate  of  oxidation. 


PUDDLING. 


503 


this  stage  the  metal  becomes  violently  agitated,  and  assumes  an 
appearance  of  boiling,  owing  to  the  escape  of  the  carbonic  oxide 
in  jets,  which  take  fire  and  burn  with  a blue  flame,  whilst  the 
melted  mass  swells  up  to  several  times  its  original  bulk.  It  is  now 
briskly  stirred  by  the  puddler  to  promote  oxidation. 

When  refined  iron  is  used  it  is  often  mixed  with  a certain  pro- 
portion ot  scales  of  oxide  from  the  forge,  and  is  then  gradually 
brought  into  complete  fusion,  carefully  avoiding  the  contact  of  fuel. 
The  mass  is  well  stirred,  so  as  to  incorporate  the  oxide  of  iron 
with  the  melted  metal ; oxygen  is  transferred  from  the  oxide  thus 
introduced,  to  the  carbon  of  the  melted  iron,  and  carbonic  oxide 
is  formed  abundantly ; but  the  appearance  of  boiling  is  less  marked 
than  when  crude  pig-iron  is  used.  In  either  case,  the  metal  by 
degrees  becomes  less  fusible  as  the  carbon  diminishes  in  quantity, 
and  at  length  it  is  converted  into  a granular,  sandy  mass.  The 
heat  is  now  raised  till  it  becomes  very  intense,  and  air  is  carefully 
excluded  by  closing  the  damper  and  doors.  The  metal  again  be- 
gins to  soften  and  agglomerate.  The  puddler  gradually  collects 
it  into  balls  or  hlooins  upon  the  end  of  an  iron  rod ; he  then  re- 
moves it  from  the  furnace  in  masses  weighing  about  three-quarters 
of  a hundred w^eight,  and  subjects  it,  whilst  still  intensely  hot,  to 
the  action  either  of  the  steam  hammer,  or  a powerful  press,  called 
the  shingling  press.  The  melted  slag  is  thus  forcibly  squeezed 
out,  the  particles  of  metal  are  brought  nearer  together,  and  the 
density  is  increased.  The  iron  is  then  fashioned  into  a bar  by 
passing  it  between  grooved  rollers,  and  the  bar  thus  obtained  is 
cut  into  lengths,  then  piled  up  in  a reverberatory  furnace  and  re- 
heated ; it  is  again  rolled,  doubled  upon  itself,  and  re-heated  and 
rolled.  Upon  the  best  qualities  of  iron  this  process  is  repeated 
several  times,  in  order  to  render  its  flbres  parallel  to  each  other, 
by  which  the  toughness  of  the  metal  is  much  increased.  The  iron 
is  now  nearly  pure ; it  contains  from  to  of  its  weight  of 
carbon,  and  about  -g-J-g-  of  silicon.  The  presence  even  of  this 
small  proportion  of  carbon  adds  materially  to  the  toughness  and 
hardness  of  the  metal.  The  process  of  puddling  occupies  about 
two  hours : and  provided  it  has  been  properly  reflned  previously, 
the  metal  loses  from  Y to  10  per  cent,  of  its  weight.* 

* Calvert  and  Johnson  {Phil.  Mag.  Sept.  1851)  have  made  a series  of  analyses  of 
the  iron  in  different  stages  of  the  process  of  hoiling.  They  employed  in  their  expe- 


Time  after 
charging^. 

Carbon. 

Silicon. 

Phos- 

phorus. 

Sulphur. 

Pig  iron 

2-275 

2-720 

0-645 

0-301 

1 St  sample 

40' 

2-726 

0-915 

‘2nd 

“ ... 

60' 

2-905 

0-197 

3rd 

U 

65' 

2-444 

0-194 

4th 

(( 

80' 

2-305 

0-182 

5th 

(( 

95' 

1-647 

0-183 

6th 

100' 

1-206 

0-163 

7th 

u 

105' 

0-963 

0-163 

8th 

(( 

110' 

0-772 

0-168 

9 Puddled  bar 

0-296 

0-120 

0-139 

0-134 

10  Wire  iron 

0-111 

0-088 

0-117 

0-O94 

504 


MAXrTACTTEE  OF  TVEOUGHT  lEOX. 


The  slag  produced  during  the  operations  of  puddling  and  re- 
fining consists  chiefly  of  ferrous  ortho-silicate  (Fe^SiO^),  and  con- 
tains upwards  of  60  per  cent,  of  the  metal.  This  slag  or  finery 
cinder  is  reduced  in  the  blast  furnace  in  the  same  manner  as  the 
original  ore,  but  it  is  always  found  to  produce  a defective  iron, 
technically  known  as  cold  short.  Such  iron  may  be  forged  well 
at  a red  heat,  but  when  cold  it  is  brittle  and  rotten.  This  defect 
is  attributed  to  the  presence  of  phosphorus,  which  is  separated 
from  the  crude  metal  in  the  form  of  phosphate  of  iron  during  the 
puddling.  AYlien  the  slag  is  reduced  in  the  blast  furnace,  both 
the  phosphorus  and  the  iron  are  deprived  of  their  oxygen,  and  by 
their  union,  as  phospliide  of  iron,  form  the  faulty  metal  in  question. 

Mr.  Bessemer  has  attempted  to  substitute  for  the  processes  of 
puddling  and  reflning  a method  of  purification  which  consists  in 
forcing  cold  air  at  a pressure  of  10  or  12  lb.  upon  the  square  inch 
through  melted  cast  iron,  which,  as  it  runs  from  the  furnace,  is 
received  into  a cylindrical  vessel  covered  with  an  arched  head  and 
lined  with  fire-clay,  the  air  being  driven  in  at  the  bottom,  through 
several  tuyeres.  An  intense  combustion  occurs,  attended  with 
remarkable  elevation  of  temperature,  owing  partly  to  the  oxida- 
tion of  the  iron,  and  partly  to  that  of  carbon ; the  latter,  being 
converted  into  carbonic  oxide,  escapes  at  all  points  of  the  mass, 
throwing  the  whole  into  violent  agitation,  which  subsides  as  soon 
as  the  carbon  is  burnt  off ; when  this  occurs  the  melted  iron  nearly 
freed  from  carbon  is  run  off  into  moulds.  A great  loss  of  iron  is, 
however,  incurred  in  this  operation  ; a copious  slag  of  oxide  of 
iron,  mixed  with  a little  silicate,  is  produced,  and  in  this  a large 
quantity  of  metallic  iron  is  entangled : not  less  than  20  per  cent, 
of  the  metal  is  thus  wasted,  and  the  malleable  iron  still  retains 
nearly  all  the  phosphorus  and  much  of  the  sulphur  originally 
present. 

riments  good  cold-blast  Staffordshire  grey  iron,  No.  3,  such  as  is  used  for  making 
iron  wire. 

A charge  of  2 cwt,  of  iron  was  introduced  into  the  bed  of  the  furnace,  without 
any  addition  of  oxide  of  iron:  in  40  minutes  it  became  fused,  and  on  cooling  the 
sample  suddenly,  it  yielded  a brittle  mass  like  white  iron.  It  will  be  seen  that  whilst 
the  carbon  increases  during  the  first  stage  of  the  process,  the  silicon  undergoes  a 
very  rapid  diminution.  The  3rd  sample  was  taken  just  before  the  beginning  of  the 
hoU.  when  the  iron  was  in  its  most  fluid  condition.  No.  4 was  taken  during  the  full 
boil,  and  consisted  of  small  detached  brittle  granules  surrounded  by  slag.  No.  5,  the 
boil  was  completed.  It  was  still  in  granules,  but  they  were  slightly  malleable.  No. 
6,  the  iron  was  eoUected  into  masses.  No.  7 was  taken  during  balling,  and  in  No.  8 
the  balls  were  just  ready  for  the  shingling  press.  The  ‘puddled  bar  ’ was  taken  from 
the  iron  after  it  had  been  hammered ; and  the  ‘ wire  iron  ’ was  the  same  after  it  had 
been  broken  up  into  billets,  reheated,  and  rolled  as  a preliminary  to  drawing. 

The  slag  which  was  separated  during  the  operation  was  found  to  have  the  fol- 
lowing composition : — 


Silica 16-53 

Protoxide  of  iron 66*23 

Sulphide  of  iron 6-80 

Phosphoric  acid 3-80 

Protoxide  of  manganese 4-90 

Alumina 1-04 

Lime 0-70 


100-00 


BESSE^klER’s  PROCESS — MANTJEACTERE  OF  STEEL. 


505 


But  though  the  process  of  Bessemer  has  not  been  attended 
with  the  important  results  which  were  anticipated  from  its  em- 
ployment in  refining  the  ordinary  pig-iron  obtained  by  the  smelt- 
ing of  clay  iron-stone  with  coal,  it  is  stated  to  have  been  eminent- 
ly successful  when  applied  to  the  pure  Swedish  charcoal  pig-iron, 
which  has  by  its  means  been  converted  by  a single  operation  of 
short  duration  into  cast  steel  of  the  finest  quality : as  much  as  5 
tons  of  iron  are  commonly  operated  on  at  one  fusion. 

(750)  Production  of  Wrought  Iron  direct  from  the  Ore. — The 
pure  ores,  w^hich  consist  of  magnetic  oxide,  or  of  peroxide  of  iron, 
are  frequently  converted  at  once  into  wrought  iron,  without  the 
production  of  cast  iron.  This  process  is  practised  in  the  Pyrenees, 
by  what  is  termed  the  Catalan  forge,  and  still  more  largely  by  the 
Vloomery  forges  of  hlorth  America.  In  the  American  bloomery 
forge  either  the  hot  or  the  cold  blast  may  be  employed : — The  ore 
having  been  first  reduced  by  stampers  to  a coarse  powder,  is  placed 
on  the  top  of  the  coal  in  the  forge  which  has  been  kindled  for  its 
reception ; a high  heap  of  coal  is  kept  on  the  fire,  and  a gradual 
supply  of  ore  is  maintained ; as  the  metal  is  reduced,  it  sinks  to 
the  bottom  in  a pasty  state ; when  sufficient  has  been  added  to 
form  a bloom,  or  ball,  the  metal  is  collected  on  an  iron  bar,  heated 
before  the  blast-pipe,  and  then  hammered,  rolled,  and  wielded,  as 
if  it  had  come  from  the  puddling  furnace  (Overman’s  Metallurgy., 
p.  544).  This  method  yields  a very  pure  iron  when  charcoal  is 
employed,  but  the  consumption  of  fuel  per  ton  of  metal  is  much 
greater  than  in  the  blast-furnace  ; a large  portion  of  the  ore  is 
also  wasted  in  the  form  of  slags  which  are  very  rich  in  oxide  of 
iron.  The  iron  produced  by  this  process  frequently  contains  suf- 
ficient carbon  to  give  to  it  some  of  the  properties  of  steel ; for 
instance,  it  becomes  much  harder  when  heated  and  suddenly 
cooled.  Iron  of  this  description  is  valuable  in  the  manufacture 
of  plough-shares,  and  heavy  articles  requiring  both  toughness  and 
hardness. 

(751)  Manufacture  of  Steel. — Iron,  when  combined  with  a 
smaller  proportion  of  carbon  than  is  contained  in  cast  iron,  fur- 
nishes the  valuable  compound  well  known  as  steely  of  which  there 
are  several  varieties.  The  quantity  of  carbon  in  good  steel  varies 
between  0-7  and  1*7  per  cent. ; but  steel  whicli  possesses  the  great- 
est tenacity  has  been  found  to  contain  from  1’3  to  1‘5  per  cent,  of 
carbon,  and  about  OT  of  silicon.  Natural  steel  is  produced  di- 
rectly from  the  best  cast  iron  by  heating  it  by  means  of  cliarcoal 
on  tlie  refining  hearth,  as  in  the  operation  which  precedes  the  pro- 
cess of  puddling ; the  oxygen  burns  off  a portion  of  the  carbon 
from  the  cast  iron,  and  steel  is  left.  In  some  of  the  Welsli  iron 
works  steel  is  now  made  upon  tlie  bed  of  the  puddling  furnace 
itself,  by  carefully  arresting  the  operation  at  a stage  short  of  the 
complete  oxidation  of  the  carbon.  The  preparation  of  natural  or 
y)uddled  steel  is,  therefore,  like  the  Bessemer  steel,  an  intermedi- 
ate stage  in  the  conversion  of  cast  into  wrought  iron.  Iron 
which  contains  manganese  is  best  fitted  for  the  ])rej)aration  of  this 
kind  of  steel.  The  mass  thus  obtained  is  rendered  homogeneous 


506 


MArnTFACTUEE  OF  STEEL. 


by  forging.  It  yields  a steel  of  inferior  quality,  which  is  employed 
for  making  agricultural  implements  and  springs  for  machinery. 

For  more  delicate  purposes  hlistered  steel  is  made  use  of ; this 
is  obtained  by  means  of  cementation^  which  is  an  operation  just 
the  reverse  of  that  by  which  natural  steel  is  formed.  This  process 
is  carried  on  in  a furnace  into  which  two  rectangular  boxes  of 
brickwork  or  stoneware,  for  the  reception  of  the  bars  of  iron 
which  are  to  be  converted  into  steel,  are  built ; the  fire-grate  is 
between  these  boxes,  around  which  the  flame  circulates  freely. 
This  conversion  is  effected  by  heating  the  iron  in  contact  with 
powdered  charcoal,  or  with  soot ; the  carbonaceous  matter  in 
either  case  is  usually  mixed  wdth  about  a tenth  of  its  weight  of 
common  salt  and  wood  ashes,  forming  what  is  technically  termed 
cement  powder.  In  preparing  a charge,  the  bottom  of  each  box  is 
covered  with  a layer  of  the  cement  powder  to  a depth  of  about  an 
inch,  and  upon  this  a layer  of  bars  of  the  best  malleable  iron  is 
placed.  The  bars  are  generally  about  3 inches  broad  and  f inch 
thick.  The  interstices  between  the  bars  are  also  filled  with  cement 
powder,  which  is  tightly  packed  around  the  iron ; above  this  is  a 
layer  of  the  powder,  then  another  layer  of  bars,  and  so  on  in 
succession  until  the  box  is  nearly  full,  when  it  contains  fi’om  5 to 
6 tons  of  iron.  The  remaining  space  is  now  covered  with  a layer 
of  damp  sand  of  from  3 to  6 inches  in  depth,  and  the  fire  is 
gradually  raised  to  a full  red  heat,  or  to  about  the  temperature  re- 
quired for  melting  copper ; at  this  point  it  is  steadily  maintained. 
One  of  the  bars  of  iron  is  so  placed  that  it  can  be  removed  from 
time  to  time  during  the  operation,  for  the  purpose  of  ascertaining 
the  process  of  the  carburation  by  inspection.  The  process  is  usually 
complete  in  six  or  eight  days ; but  the  time  required  necessarily 
varies  with  the  thickness  of  the  iron  bars  operated  on  ; the  fire  is 
then  gradually  reduced,  and  the  ffumace  is  suffered  to  cool  slowly, 
an  operation  which  lasts  ten  days  or  a fortnight.  The  steel  thus 
obtained  retains  the  form  of  the  iron,  but  it  is  covered  with  blebs 
or  blisters,  by  which  the  smfface  is  rendered  irregular  and  uneven. 
The  mass  is  found  to  have  been  penetrated  by  carbon  which  has 
been  transferred  from  particle  to  particle  of  the  metal,  the  pro- 
perties of  which  it  has  completely  changed.  In  some  cases  these 
blisters  probably  arise  from  the  combination  of  parts  of  the  car- 
bon with  oxygen  derived  from  particles  of  oxide  of  iron,  which 
are  apt  to  be  mechanically  retained  even  in  the  most  carefully 
prepared  bars.  Carbonic  oxide  would  thus  be  produced,  and  im- 
prisoned in  the  tenacious  metal,  which  in  its  softened  state  would 
be  raised  by  it  into  bubbles  or  blebs.  Great  care,  however,  is  gen- 
erally taken  to  exclude  slag  and  oxide  of  iron  from  bars  which  it 
is  intended  to  convert  into  steel ; so  that  in  the  majority  of 
instances  it  is  not  unlikely  that  the  blisters  are  occasioned  by  the 
combination  of  carbon  with  the  sulphur  which  is  still  retained  by 
the  iron,  and  which,  by  forming  the  volatile  bisulphide  of  carbon 
would  produce  the  effect  (T.  H.  Henry).  All  bar  iron  contains 
traces  of  sulphur;  but  in  steel  sulphur  is  seldom  present,  and 
there  appears  to  be  no  other  mode  of  accounting  for  its  general 


BLISTERED  STEEL  -CEMENTATION.  507 

absence  than  its  removal  during  the  process  of  carburation  in 
the  form  of  bisulphide  of  carbon. 

By  the  process  of  cementation  the  iron  has  been  combined 
with  about  1’5  per  cent,  of  carbon  ; it  is  now  much  more  fusible 
than  before."^  It  has  likewise  entirely  lost  its  fibrous  texture ; and 
when  broken  across  exhibits  a close,  fine-grained  fracture.  Steel 
may  also  be  made  without  direct  contact  with  carbon,  by  simply 
heating  the  bars  in  carburetted  hydi’ogen ; but  this  process  has 
not  come  into  general  use. 

Blistered  steel  is  never  homogeneous,  the  surface  being  always 
more  highly  carburetted  than  the  inner  portions  of  the  bars.  This 
variety  of  steel  is  employed  for  files,  tools,  and  hardware  of  all 
descriptions.  'When  blistered  steel  is  fused,  it  forms  cast  steely 
which,  from  being  more  uniform  in  texture,  is  of  superior  quality, 
as  the  carbon  is  more  equally  distributed  throughout  the  mass : it 
is  employed  for  cutlery  of  the  best  description.  Tilted  steel  Ya  also 
obtained  from  blistered  steel ; this  is  first  broken  up  into  lengths 
of  about  18  inches,  then  bound  into  fagots  and  raised  to  a welding 
heat  in  a wind  furnace,  where  it  is  covered  with  sand,  which  com- 
bines with  the  superficial  coating  of  oxide  of  iron  and  forms  a 
fusible  slag : the  red-hot  fagot  is  then  rolled,  and  forged,  by  means 
of  the  tilt-hammer,  into  smaller  bars.  All  steel  is  improved  by 
this  process  of  hammering.  These  tilted  bars,  when  broken  up 
and  welded  together,  form  shear  steel. 

Tor  many  purposes,  the  addition  of  a small  quantity  of  man- 
ganese is  an  improvement  to  the  quality  of  the  steel.  If  about 
1 per  cent,  of  carbide  of  manganese,  or  of  a mixture  of  charcoal 
and  oxide  of  manganese,  be  introduced  into  the  melting-pot,  a 
steel  is  obtained  of  fine,  close  grain,  which  admits  of  being  welded 
to  wrought  iron  ; a property  not  possessed  by  ordinary  steel.  The 
experiments  of  Faraday  and  Stodart  led  them  to  the  conclusion  that 
the  addition  of  small  quantities  of  chromium,  or  of  rhodium,  to  good 
steel,  furnished  a steel  of  a very  superior  kind.  They  found  that 
steel  may  be  alloyed  with  about  a five  hundredth  of  its  weight  of 
silver;  and  with  platinum,  as  well  as  with  rhodium,  and  with 
osmium  and  iridium  in  all  proportions.  The  combination  of  8 or 
9 per  cent,  of  tungsten  with  ordinary  steel  has  been  said  to  yield 

* According  to  Fremy,  steel  contains  also  as  a necessary  ingredient  a minute 
quantity  of  nitrogen,  which  it  has  been  suggested  may  be  in  the  form  of  cyanogen. 
Caron,  however,  maintains  that  this  trace  of  nitrogen  is  not  essential:  this,  how- 
ever, is  still  sui)  judice.  Rammelsberg  was  unable  to  detect  more  nitrogen  than  20 
parts  m a million  of  cast  iron.  Marchand  heated  both  cast  iron  and  steel  with  potas- 
sium in  an  atmosphere  of  hydrogen,  and  also  heated  the  metal  with  soda-lime ; he 
also  burned  the  metal  by  heating  it  with  oxide  of  copper,  but  did  not  obtain  more 
than  1 50  parts  of  nitrogen  from  a million  parts  of  the  metal,  and  often  a much  smaller 
quantity.  He  considered  it  due  to  the  accidental  presence  of  foreign  impurities; 
and  this  is  certainly  the  most  probable  opinion ; no  instance  is  known  in  which  so 
minute  a quantity  of  matter  is  an  essential  constituent  of  any  compound.  JBoussiu- 
gault  found  pure  iron  reduced  from  the  oxide  in  hydrogen  gave  no  trace  of  nitrogen, 
by  a method  of  analysis  which  indicated  in  soft  iron  50  millionths,  and  in  piano  wire 
from  70  to  86  millionths,  and  in  cast  steel  57  millionths;  this  steel  also  contained 
traces  of  sulphur.  The  difficulty  of  excluding  such  minute  traces  of  nitrogen  in  the 
course  of  the  analysis  is  extreme,  even  in  the  hands  of  one  who,  as  in  this  case, 
is  confessedly  a master.  (See  p.  529.) 


508 


QUALITIES  OF  STEEL TEJiIPEEING. 


a material  remarkable  for  hardness  and  elasticity,  but  experience 
does  not  seem  to  justify  the  expectations  of  its  utility.  (Percy’s 
Metallurgy^  toL  ii.  p.  193.)  A similar  remark  is  also  applicable 
to  titanium  steel  {II).  p.  168).  When  steel  is  to  be  used  for  the 
manufacture  of  dies  for  coining,  the  presence  of  a small  proportion 
of  phosphorus  is  beneficial  (Brande). 

When  diluted  nitric  acid  falls  upon  steel,  a dark  grey  spot  is 
produced,  owing  to  the  solution  of  the  metal  in  the  acid  whilst  its 
carbon  remains  unacted  upon : the  acid  produces  a green  spot 
upon  iron.  The  acid  acts  unequally  upon  different  parts  of  the 
surface  in  certain  of  the  finer  varieties  of  steel,  and  thus  produces 
a veined  appearance,  such  as  was  formerly  given  to  the  celebrated 
Damascus  blades.  The  Damascus  steel  is  more  highly  carburetted 
than  ordinary  steel,  and  if  allowed  to  cool  slowly,  it  separates 
into  layers  of  two  different  degrees  of  carburation  (Breant) ; hence 
certain  parts,  when  acted  on  by  diluted  acid,  leave  more  carbon 
than  others  ; the  form  and  direction  of  these  veins  vary  with  the 
mode  of  forging  adopted. 

^Vootz  is  a finely  damasked,  hard  cast  steel,  of  excellent 
quality,  which  is  obtained  from  India.  Faraday  found  aluminum 
in  a sample  of  this  steel  which  he  analysed,,  and  was  disposed  to 
refer  its  peculiar  qualities  to  the  presence  of  this  metal.  It  ap- 
pears, however,  from  the  experiments  of  Henry  {Phil.  Mag.,  July, 
1852),  that  aluminum  is  not  always  present  in  wootz.  He  gives 
the  following  as  the  composition  of  a bar  of  genuine  Indian  wootz, 
of  specific  gravity  T'T2T  : — 


Carbon  j 

Silicon. . 
Sulphur. 
Arsenic. 

Iron. . . . 


combined. . . 
uncombined, 


1-340 
0-312 
, 0 042 
, 0-170 
0-036 
98-100 


100-000 

Other  analysts  have  also  failed  in  finding  aluminum  in  wootz. 

The  physical  properties  of  steel  differ  materially  from  those  of 
iron.  As  already  mentioned,  steel  is  granular  in  texture,  brittle, 
and  more  easily  melted  than  iron.  Its  most  characteristic  pro- 
perty, however,  consists  in  its  power  of  assuming  a hardness 
scarcely  inferior  to  that  of  the  diamond  when  heated  to  redness 
and  then  suddenly  cooled  by  plunging  it  into  water,  mercury,  or 
oil.  After  this  treatment  it  is  rendered  extremely  brittle,  and 
almost  perfectly  elastic.  It  can  then  no  longer  be  attacked  by 
the  file. 

This  extreme  hardness  and  brittleness  may  be  removed  by  the 
process  of  tempering,  which  is  a peculiar  mode  of  annealing  ; it 
consists  in  heating  the  steel  moderately,  and  then  allowing  it  to 
cool.  The  tempering  of  steel  is  an  operation  of  great  practical 
importance,  as  from  the  variety  of  purposes  to  wliich  steel  is  ap- 
plied, it  is  required  of  very  different  degrees  of  hardness,  and  upon 
the  due  adjustment  of  this  quality  much  of  its  utility  depends. 


TEMPERING  OF  STEEL PREPARATION  OF  PURE  IRON.  509 

The  degree  to  which  the  temperature  is  raised  in  the  second  heat- 
ing, regulates  this  point : the  higher  the  heat,  the  softer  is  the 
steel.  In  practice,  the  workman  judges  with  sufficient  accuracy 
of  the  temperature  to  which  the  metal  has  been  exposed,  by  ob- 
serffing  the  colour  which  the  steel  assumes  owing  to  the  varying 
thickness  of  the  film  of  oxide  which  is  formed  upon  its  surface. 
It  is  easy  to  show  that  this  colour  is  due  to  the  formation  of  a 
film  of  oxide ; for  by  painting  on  the  surface  of  the  steel  various 
devices  in  oil  or  varnish,  and  then  exposing  it  to  heat,  the  surface 
of  the  blade  becomes  coloured  in  every  part  excepting  these  por- 
tions which  have  been  varnished,  and  these,  when  the  varnish  is 
removed,  retain  their  original  polish.  The  first  perceptible  tint  is 
a light  straw  colour,  which  is  produced  by  the  lowest  degree  of 
heat,  and  indicates  the  hardest  temper ; the  heat  required  is  from 
430°  to  450° ; it  is  used  for  lancets,  razors,  and  surgical  instru- 
ments : at  470°  a full  yellow  is  produced ; it  is  the  temper 
fitted  for  scalpels,  penknives,  and  fine  cutlery.  The  temperature 
of  490°  gives  a brown-yellow,  which  is  the  temper  for  shears  in- 
tended for  cutting  iron.  At  510°  the  first  tinge  of  purple  shows 
itself:  this  is  the  temper  employed  for  pocket-knives;  520° 
gives  a purple,  which  is  the  tint  for  table  and  carving-knives.  A 
temperature  from  530°  to  570°  produces  various  shades  of  blue, 
such  as  are  used  for  watch-springs,  sword-blades,  saws,  and  instru- 
ments requiring  great  elasticity  (Stodart).  The  different  degrees 
of  heat  may  be  exactly  regulated  by  heating  the  different  articles 
in  a fusible  metal-  or  oil-bath,  the  temperature  of  which  is  ascer- 
tained by  means  of  thermometers,  though  in  ordinary  cases  this 
degree  of  nicety  is  not  observed. 

Hardened  steel  is  somewhat  less  dense  than  wrought  steel. 
It  appears  that  a portion  of  the  carbon  contained  in  steel,  before 
the  alloy  has  been  hardened,  is  in  the  uncombined  state;  this 
portion  is  left  in  the  form  of  graphitic  scales  when  the  metal  is 
dissolved  in  hydrochloric  acid  : but  after  the  steel  has  been  hard- 
ened, the  whole  of  the  carbon  is  chemically  united  with  the  iron  ; 
and  when  treated  with  acids,  is  left  in  the  form  of  a liquid  hydro- 
carbon. Before  it  has  been  hardened  it  may  be  worked  as  easily 
as  iron,  and  in  certain  cases  may  be  welded  upon  that  metal. 
Instruments  are  completely  finished  in  the  soft  state,  and  are  then 
hardened  and  subsequently  tempered. 

It  is  sometimes  desirable  to  convert  articles  manufactured 
from  soft  iron  superficially  into  steel.  This  is  termed  case-harden- 
ing^ and  is  effected  by  lieating  them  in  contact  with  powdered 
cast-iron  turnings,  or  sometimes  with  powdered  charcoal.  The 
same  object  is  attained  if  they  are  sprinkled  when  red-hot,  with 
powdered  ferrocyanide  of  potassium. 

(752)  Preparation  of  pure  Iron. — In  order  to  obtain  iron 
chemically  pure,  Berzelius  recommends  that  filings  of  the  best  bar 
iron  be  intimately  mixed  with  one-fifth  of  their  weight  of  pure 
peroxide  of  iron,  and  placed  in  a Hessian  crucible,  covered  with 
pounded  glass  (free  from  lead) ; the  cover  is  then  to  be  carefully 
luted  on,  and  the  crucible  to  be  exposed  for  an  hour  to  the  strong- 


510 


PROPEETIES  OF  BAR  IRON. 


est  heat  of  a smith’s  forge.  By  this  means,  all  traces  of  carbon 
and  of  silicon  are  oxidized  at  the  expense  of  the  oxygen  of  the 
peroxide  of  iron,  whilst  the  excess  of  oxide  forms  a fusible  slag 
with  glass.  If  the  operation  be  successful,  the  iron  will  be  melted 
into  a button,  with  a lustre  approaching  that  of  silver.  Such  iron 
is  very  tough,  and  much  softer  than  ordinary  bar  iron : it  has  a 
sp.  gr.  of  T’84:39.  Pure  iron  may  also  be  obtained  in  the  state  of 
fine  powder,  by  decomposing  the  pure  peroxide  at  a red  heat  in  a 
current  of  hydrogen  gas.  Iron  has  been  obtained  in  hollow  tetra- 
hedra,  apparently  belonging  to  the  cubic  system,  by  reducing  fer- 
rous chloride  in  a current  of  pure  hydrogen.  It  may  be  deposited 
in  fiexible  laminae  from  a mixed  solution  of  ferrous  chloride  and 
chloride  of  ammonium,  by  the  action  of  the  voltaic  current. 

(753)  Properties  of  Bar  Iron. — The  bar  iron  of  commerce  is 
never  pure.  It  alwa^^s  retains  small  quantities  of  carbon,  varying 
from  0‘2  to  O’l  per  cent.,  and  traces  of  silicon  and  sulphur ; occa- 
sionally, also  of  phosphorus  and  arsenic.  The  presence  of  this 
small  quantity  of  carbon  much  increases  its  hardness  and  tenacity, 
but  the  other  ingredients  act  injuriously  upon  the  metal. 

Bar  iron  has  a bluish-white  or  grey  colour,  and  is  endowed 
with  considerable  lustre  and  hardness ; it  takes  a high  polish : 
its  texture  is  usually  fibrous,  and  when  broken  across  it  exhibits  a 
ragged  or  hackly  fracture ; when  rubbed,  it  emits  a peculiar  cha- 
racteristic odour.  The  average  specific  gravity  of  good  bar  iron 
is  7'7.  It  requires  the  most  intense  heat  of  a wind  furnace  for  its 
fusion.  Iron  passes  through  a soft  jiasty  condition  before  it  is 
completely  melted ; this  property  is  one  of  great  practical  impor- 
tance : if  two  pieces  of  iron  be  heated  to  whiteness,  sprinkled  with 
sand,  and  hammered  together,  they  may  be  united  or  welded  so 
completely,  that  the  junction  is  as  tough  as  any  other  part  of  the 
metal.  The  sand  is  used  as  a fiux  to  the  oxide  of  iron,  with 
which  it  forms  a slag  which  coats  each  piece  of  the  metal ; by 
the  blow  of  the  hammer  this  layer  of  melted  matter  is  forced 
out,  and  the  two  clean  surfaces  of  metal  become  united  together. 
At  a red  heat  iron  may  be  forged  into  any  shape  with  facility, 
but  at  ordinary  temperatures  it  possesses  but  little  malleability, 
as  compared  with  gold  and  silver.  It  however  admits  of  being 
rolled  into  very  thin  sheets.  In  ductility,  iron  stands  very  high 
in  the  scale,  and  in  tenacity  it  far  exceeds  all  other  known  sub- 
stances, with  the  exception  of  cobalt  and  nickel. 

If  compared  with  other  metals,  iron  is  inferior  to  many  of 
them  as  a conductor  of  heat  and  of  electricity.  Its  susceptibility 
to  magnetism  is  peculiar ; no  other  metal  exhibiting  this  property 
in  any  marked  degree,  excepting  cobalt  and  nickel,  and  in  them 
the  power  is  developed  to  a much  smaller  extent.  But  though 
iron  in  its  pure  state  is  susceptible  of  magnetic  induction,  it  cannot 
be  permanently  magnetized  unless  it  be  combined  with  carbon, 
as  in  steel ; with  oxygen,  as  in  the  loadstone  (¥e^O^) ; or  with 
sulphur,  as  in  certain  varieties  of  pyrites  (BejS,),  and  (Fe,Sg). 
It  is  especially  worthy  of  observation,  that  if  oxygen  or  sulphur 
be  present  in  quantity  either  greater  or  less  than  in  these  parti- 


AC'nON  OF  AIE  Am)  OF  WATER  UPON  IRON. 


511 


cular  compounds,  not  only  is  the  power  of  retaining  magnetism 
destroyed,  but  the  mass  becomes  almost  indifferent  to  the  action 
of  a magnet.  Iron  loses  its  magnetic  power  when  heated  to  red- 
ness, hut  recovers  it  again  on  cooling. 

At  a high  temperature  iron  burns  readily,  emitting  vivid 
scintillations,  as  may  he  seen  at  the  blacksmith’s  forge,  or  still 
more  brilliantly  when  a glowing  wire  is  introduced  into  a jar  of 
oxygen.  In  a very  finely  divided  state,  such  as  that  produced  by 
reducing  precipitated  oxide  of  iron  at  a low  temperature  in  a 
current  of  hydrogen  gas,  the  metal  takes  fire  by  mere  exposure 
to  the  atmosphere.  If  a small  quantity  of  alumina  be  precipitated 
with  the  oxide  of  iron,  so  as  to  interpose  some  foreign  matter 
between  the  particles  of  the  metal,  this  pyrophoric  property  is 
much  increased.  A polished  mass  of  the  metal,  however,  pre- 
serves its  lustre  unchanged  in  dry  air  at  ordinary  temperatures 
for  an  unlimited  time,  but  when  exposed  to  a moist  atmosphere, 
so  that  water  in  the  liquid  form  shall  be  deposited  upon  the 
metal,  its  surface  is  quickly  altered,  and  it  becomes  covered  with 
rust.  When  once  a spot  of  rust  begins  to  show  itself,  the  oxida- 
tion proceeds  rapidly ; moisture  is  absorbed  from  the  air  by  the 
oxide,  and  thus  a species  of  voltaic  action  is  produced,  the  oxide 
performing  the  part  of  an  electro-negative  element,  whilst  the 
iron  becomes  electro-positive,  and  the  atmospheric  moisture  acts 
as  the  exciting  liquid.  The  carbonic  acid  derived  from  the  air 
contributes  in  an  important  way  towards  increasing  the  rapidity 
with  which  this  change  occurs ; but  it  is  not  indispensable.  It 
appears  that  usually  hydrated  ferrous  carbonate  is  first  formed, 
and  is  afterwards  decomposed  by  the  further  absorption  of  oxygen, 
by  which  it  is  converted  into  the  hydrated  peroxide,  or  rust  of 
iron,  whilst  the  liberated  carbonic  acid  forms  a fresh  portion  of 
ferrous  carbonate : a portion  of  water  is  deoxidized  in  the  process, 
and  hydrogen  is  evolved ; if  a considerable  heap  of  iron  turnings 
be  moistened  and  exposed  to  air,  the  peculiar  odour  of  hydrogen, 
as  evolved  from  a metallic  carbide,  is  perceived,  and  the  tempera- 
ture of  the  mass  rises  considerably.  Iron  rust  always  contains 
ammonia,  derived  probably  from  the  reaction  of  the  hydrogen  of  the 
water  upon  the  nitrogen  of  the  atmosphere,  which  is  dissolved  in 
tlie  water  with  which  the  metal  is  moistened.  Even  the  native 
oxides  of  iron  invariably  contain  traces  of  ammonia  (Chevallier). 
Iron  may  be  kept  for  any  length  of  time  without  undergoing  any 
change  in  water  quite  free  from  air,  as  well  as  in  lime-water,  or 
in  water  containing  a little  caustic  or  carbonated  alkali,  but  the 
alkaline  bicarbonates  do  not  exert  this  protective  action.  At  a red 
heat  iron  decomposes  water  rapidly,  and  liberates  hydrogen  (345), 
whilst  the  iron  is  converted  into  minute  crystals  of  the  black  or 
magnetic  oxide  ; the  following  equation  illustrates  the  chemical 
change:  4 II,0-f  3 Ee=4II,-hEe30,. 

Chlorine,  bromine,  and  iodine  combine  quickly  with  iron,  and 
dissolve  it  easily  at  ordinary  temperatures,  if  the  metal  be  digested 
with  them  in  water.  Iron  is  soluble  in  diluted  sulphuric  and 
hydrochloric  acids,  with  extrication  of  hydrogen.  Even  carbonic 


612 


PASSIVE  CONDITION  OF  IRON. 


acid,  when  contained  in  water  trom  which  air  is  excluded,  slowly 
dissolves  this  metal  with  extrication  of  hydrogen,  and  the  car^ 
honate  of  iron  is  dissolved  in  the  excess  of  carbonic  acid.  Con- 
centrated sulphuric  acid  has  very  little  action  on  iron,  even  when 
boiled  upon  it, — a slow  solution,  attended  with  the  evolution  of 
sulphurous  anhydride,  occurring  : but  the  metal  is  rapidly  attacked 
by  nitric  acid,  with  abundant  evolution  of  nitric  oxide. 

(754)  Passive  Condition  of  Iron. — Under  certain  circum- 
stances iron  may  be  kept  in  concentrated  nitric  acid  for  weeks, 
without  the  slightest  action,  or  alteration  of  the  polish  of  its  sur- 
face. There  are  various  methods  of  producing  passive  con- 
dition of  iron  in  an  acid  of  a moderate  degree  of  concentration  ; 
some  of  these  seem  to  indicate  an  intimate  connection  with  its 
voltaic  relations.  This  will  be  rendered  evident  from  the  follow- 
ing statement  of  some  of  the  circumstances  under  which  this  re- 
markable phenomenon  is  manifested : — If  a piece  of  clean  iron  wire 
be  introduced  into  nitric  acid  of  a sp.  gr.  of  about  1’35,  imme- 
diate and  brisk  action  ensues ; but  if  the  metal  be  touched  be- 
neath the  surface  of  the  liquid  with  a piece  of  gold,  of  platinum, 
or  of  plumbago,  the  chemical  action,  contrary  to  what  might  have 
been  anticipated,  is  suddenly  arrested  if  the  temperature  of  the 
acid  has  not  been  alloAved  to  rise  too  high.  If  a second  iron 
wire  be  made  to  touch  the  first,  and  then  be  intoduced  into  the 
acid,  it  also  is  rendered  inactive.  This  second  wire  may  be  used 
in  like  manner  to  render  a third  inactive.  But  if  any  of  these 
inactive  wires  be  withdrawn  from  the  acid,  and  exposed  to  the  air 
for  a few  seconds,  it  will  be  found  to  be  rapidly  acted  on  upon 
again  introducing  it  into  the  acid.  If  whilst  in  the  acid  the  iron 
wire  be  made  the  zincode  of  a voltaic  arrangement,  oxygen  gas 
is  evolved  from  the  surface  of  the  iron,  but  does  not  combine  with 
it.  If,  on  the  contrary,  a piece  of  passive  iron  be  made  the 
platinode  or  negative  plate  of  the  arrangement,  it  is  immediately 
attacked  by  the  acid. 

By  heating  the  end  of  a clean  iron  wire  in  the  fiame  of  a 
spirit-lamp  so  as  to  give  it  a superficial  coating  of  oxide,  the  wire 
is  brought  into  the  passive  condition.*  If  into  acid  containing 
a passive  wire,  a second  ordinary  wire,  not  in  contact  with  the 
first,  be  introduced,  brisk  action  on  the  ordinary  wire  ensues  ; 
and  on  causing  the  passive  wire  to  touch  the  active  one,  imme- 
diate action  occurs  on  both. 

Strong  nitric  acid,  of  sp.  gr.  1*45,  renders  all  iron  passive ; 
the  metal  may  be  kept  in  it  for  years  without  losing  its  brilliancy 
or  showing  any  action  ; and  a wire  withdrawn  from  the  strong 
acid,  and  plunged  into  acid  of  1*35,  still  remains  passive.  If  it 
be  wiped  first,  and  then  plunged  into  the  weaker  acid,  it  imme- 

* Similar  effects  are  produced  with  wires  of  cobalt  or  of  nickel,  though  with  them 
the  action  is  less  strongly  marked  (Xickles.)  Such  wires,  if  placed  in  voltaic  relation 
with  an  active  wire  of  the  same  metal,  are  found  to  be  strongly  electro-negative 
towards  it ; but  passive  iron,  cobalt,  and  nickel  are  electro-positive  in  relation  to 
platinum.  Andrews  has  shown  that  bismuth  also  may  be  rendered  passive  in  con- 
centrated nitric  acid. 


OXroES  OF  IKON. 


513 


diately  begins  to  be  dissolved.  If  the  acid  be  diluted  below  a 
density  of  1‘35,  it  dissolves  the  metal  rapidly,  whatever  may  have 
been  its  previous  condition. 

(755)  Alloys  of  Iron.  — Iron  forms  alloys  with  most  of  the 
metals ; but  they  are  not  in  general  of  much  importance.  The 
presence  of  small  quantities  of  silver,  of  copper,  of  arsenic,  or  of 
sulphur,  in  iron,  is  said  to  occasion  a defective  quality  of  metal, 
technically  known  as  red  short.  Such  iron  is  tough  at  ordinary 
temperatures,  but  becomes  brittle  when  heated  to  redness  for 
forging.  The  presence  of  a quantity  of  antimony  not  exceeding 
0'23  per  cent,  was  found  by  Karsten  to  render  it  both  cold  short 
and  red  short. 

The  mode  of  preparing  zinc-plate,  or  galvanized  iron,  has  been 
already  described  (707).  Tin-plate  is  prepared  by  an  analogous 
process  ; it  consists  of  iron  superhcially  alloyed  with  tin. 

(756)  Oxides  of  Iron. — Iron  yields  four  definite  compounds 
with  oxygen  : 1.  The  protoxide  (PeO),  which  is  the  base  of  the 
green,  or  ferrous  salts  of  iron  : 2.  The  sesquioxide  (Fe203),  which 
is  the  base  of  the  red,  or  ferric  salts  : 3.  The  black,  or  magnetic 
oxide  (FcgO^),  which  may  be  viewed  as  a compound  of  the  two 
preceding  oxides,  or  (FeO,  Fe^Og) ; it  does  not  form  any  definite 
salts : 4.  Fei^ric  acid^  which  is  a weak  and  unstable  metallic  acid, 
and  as  such  it  reacts  with  the  alkalies,  forming  salts  like  ferrate 
of  potassium  K2F6^4- 

Protoxide  of  Iron  ; Ferrous  Oxide  (FeO:=72,  or  FeO=36) : 
Composition  in  100  parts,  Fe,  77*78  ; O,  22*22. — It  is  obtained  in 
the  form  of  a white  hydrate  by  dissolving  a pure  ferrous  salt  in 
water  recently  boiled,  and  precipitating  by  an  alkali  the  solution 
of  whicli  has  been  similiaiTy  treated*,  both  by  being  allowed  to  cool 
out  of  contact  with  air,  and  being  mixed  in  vessels  from  which 
air  is  excluded.  If  this  precipitate  be  boiled  in  a vessel  from 
which  oxygen  is  excluded,  it  loses  its  water  of  hydration,  like  the 
oxide  of  copper  under  similar  circumstances.  The  hydrated  oxide 
absorbs  oxygen  greedily  from  the  air,  passing  tlirough  various 
shades  of  light  green,  bluish  green,  and  black,  till  finally  it  as- 
sumes an  ochry  hue,  due  to  the  formation  of  the  hydrated  sesqui- 
oxide. It  is  insoluble  in  water,  but  is  somewhat  soluble  in  am- 
monia; this  solution  quickly  absorbs  oxygen  from  the  air,  and  a 
film  of  insoluble  sesquioxide  of  iron  is  formed  upon  its  surface. 
The  protoxide  is  readily  dissolved  by  acids,  and  forms  with  them 
salts  which  are  known  as  the  ferrous  salts  or  protosalts  of  iron  / 
they  have  a green  colour,  and  an  astringent,  inky  taste.  The 
solutions  of  these  salts,  when  exposed  to  the  air,  absorb  oxygen, 
and  are  decomposed ; in  which  case  ferric  salts  are  formed,  one 
portion  of  which  is  retained  in  solution  whilst  a basic  ferric  salt 
falls  as  a rusty  insoluble  precipitate.  For  example,  in  the  case 
of  the  green  sulphate  of  iron,  the  change  may  be  represented  as 
follows : — 

Ferrous 

sulphate. 

20  ¥e"m^  + 5 Oa  + 6 
33 


Soluble  ferric 
sulphate. 


Insoluble  ferric 
sulphate. 


= 6 [(Fe'F  3 804]  + 2 (2  Fe'''a03,Se3,  3 HaO). 


SESQnOXIDE  OF  IKOX. 


5U 


(757)  Peroxide^  Red  Oxide ^ or  Sesqiiioxide  of  Iron  ; Ferric 
Oxide  (Fe"'2O3=160,  or  Fe^Og^SO) : Comp,  in  parts.,  Fe,  70  ; 
O,  30.  — The  anhydi’oiis  sesqiiioxide  is  obtained  for  the  arts  by 
igniting  the  ferrous  sulphate  (767),  and  is  known  under  the  names 
of  colcothar^  crocus  of  Mars,  or  rouge,  according  to  the  degree 
of  levigation  to  which  it  has  been  submitted ; it  is  extensively 
employed,  amongst  other  uses,  for  polishing  glass,  and  by  jewellers 
for  putting  a finish  to  their  goods.  It  is  also  employed  as  a red 
pigment. 

T]ie  sesqiiioxide  occurs  native  in  great  abundance : several  of 
its  varieties  have  been  already  mentioned  as  among  the  most 
valuable  ores  of  iron.  The  specular  ore  of  Elba  (sp.  gr.  5*22) 
often  presents  natmal  facets  of  the  most  perfect  polish,  and  of 
remarkable  size  and  lustre.  It  occm’s  crystallized  in  forms  of  the 
rhombohedral  system,  and  is  isomorphous  with  alumina  in  co- 
rundum. Ked  haematite,  or  Uoodstone  (sp.  gr.  fi-om  I'S  to  5*0), 
another  of  its  varieties,  is  extremely  hard,  and,  when  polished,  is 
employed  for  burnishing  gilt  trinkets. 

Hydrates  of  Sesquioxide  of  Iron. — There  are  several  of  these. 
Brown  haematite  is  the  hydrate  (2  Fe^jOg,  3 H^O)  Sp.  Gr.  3’98. 
This  mineral  is  readily  dissolved  by  acids.  It  contains  59 ’89  per 
cent,  of  iron,  with  25*67  of  oxygen  and  II'II:  of  water.  Another 
native  hydrate  gothite  (H^OjEe^Og ; sp.  gr.  I:*12  to  4*37)  has  been 
found  crystallized  in  prisms.  Brown  haematite  gives  the  red  and 
yellow  colour  to  the  difierent  varieties  of  clay. 

The  sesquioxide  is  best  obtained  in  a state  of  purity,  by  pre- 
cipitating the  sesquichloride  of  iron  by  ammonia  in  excess.  It 
falls  as  a bulky  light-brown  flocculent  hydi’ate,  which  shrinks  re- 
markably as  it  dries : if  precipitated  in  a cold  solution,  and  dried 
without  heat  over  sulphuric  acid,  it  contains  2 FeaOg,  3 H^O  (St. 
Gilles),  but  it  is  apt  to  retain  a little  ammonia,  which  is  easily 
expelled  by  heat.  The  same  hydrate  is  also  formed  when  moist 
iron  is  allowed  to  become  oxidized  by  exposure  to  air.  If  the 
hydrate  be  not  dried,  but  allowed  to  remain  for  some  months 
under  water,  it  becomes  crystalline,  and,  according  to  Wittstein, 
is  converted  into  an  allotropic  hydrate  (2  Fe^Og,  3 HgO  1),  but  if 
dried  at  212°  it  retains  10*11  per  cent,  of  water,  corresponding 
in  composition  to  (Fe203,IIg0).  Hydrated  peroxide  of  iron  slowly 
parts  with  its  water  at  a prolonged  heat  of  600°,  and  if  subse- 
quently heated  to  dull  redness,  it  suddenly  contracts  in  bulk,  and 
glows  brightly  for  a few  moments  whilst  undergoing  molecular 
change ; after  this  it  is  dissolved  by  acids  with  difficulty,  but  is 
readily  attacked  by  a solution  of  ferrous  chloride  in  hydrochloric 
acid : at  a very  high  temperature  the  sesquioxide  loses  one-ninth 
of  its  oxygen,  and  is  converted  into  the  magnetic  oxide  of 
iron. 

Hydrated  sesquioxide  of  iron,  when  recently  precipitated  from 
cold  solutions,  is  easily  soluble  in  acids,  forming  the  persalts  of 
iron,  or  ferric  salts ; they  have  a strongly  acid  reaction,  and  do 
not  crystallize : many  of  them  are  deliquescent.  Their  concen- 
trated solutions  have  the  property  of  dissolving  a considerable 


HYDEATED  SESQUIOXIDE  OF  lEON. 


515 


excess  of  the  oxide,  in  which  case  they  assume  a deep  red  colour. 
If  these  basic  solutions  be  diluted  and  boiled,  the  iron  is  entirely 
separated  in  the  form  of  an  insoluble  ferric  subsalt.  If  well 
washed  and  freshly  precipitated  hydrated  peroxide  of  iron,  obtained 
by  the  action  of  ammonia  upon  the  sesquichloride  in  the  cold,  be 
boiled  in  water  for  a few  minutes  it  becomes  converted  into  the 
hydrate,  Fe203,Il20 ; but  if  the  ebullition  be  continued  for  8 or 
10  hours,  its  colour  l3ecomes  changed  from  ochry  brown  to  brick 
red,  and  it  is  converted  into  an  allotropic  modification  of  the  same 
hydrate,  and  by  prolonged  boiling  a portion  of  it  even  loses  all  its 
water.  This  modified  oxide  is  insoluble  in  strong  boiling  nitric 
acid,  and  only  slowly  soluble  in  hot  hydrochloric  acid.  Cold 
acetic  acid,  and  cold  diluted  hydrochloric  and  nitric  acids  dissolve 
it,  forming  a red  liquid  which  appears  to  be  turbid  by  reflected 
light;  concentrated  nitric  or  hydrochloric  acid  occasions  a red 
precipitate  in  this  solution,  but  it  becomes  redissolved  on  the  ad- 
dition of  water.  The  solution  is  also  precipitated  by  the  addition 
of  any  sulphate,  or  of  any  salts  of  the  alkali-metals.  If  the  ordi- 
nary hydrated  sesquioxide  of  iron  be  kept  long  in  water,  especially 
if  at  the  same  time  it  be  exposed  to  a low  temperature,  it  expe- 
riences a similar  modification  in  composition  and  properties.  An 
acetic  solution  of  this  oxide,  if  kept  for  some  time  in  a closed  ves- 
sel at  212°,  becomes  of  a brighter  red  colour.  It  appears  to  be 
turbid  when  viewed  by  reflected  light,  but  clear  by  transmitted 
light.  It  has  lost  its  astringent  metallic  taste.  The  addition  of  a 
soluble  sulphate  causes  an  immediate  precipitate,  and  so  do  the 
strong  acids  : it  is  no  longer  reddened  by  the  addition  of  a sulpho- 
cyanide,  and  does  not  give  a precipitate  of  Prussian  blue  with 
ferrocyanide  of  potassium  (Pean  de  St.  Gilles,  Ann.  de  Chiinie^  III. 
xlvi.  47).  Graham  found  that  if  a solution  of  ferric  chloride,  in 
which  a large  quantity  of  hydrated  ferric  oxide  had  been  dissolved 
by  prolonged  digestion  in  the  cold,  were  submitted  to  dialysis,  a 
solution  was  eventually  obtained  which  contained  a proportion  of 
08*5  of  the  oxide  and  1’5  of  hydrochloric  acid.  This  solution, 
however,  in  a few  weeks  became  gelatinous  spontaneously  in  the 
bottle  to  which  it  was  transferred. 

Hydrated  sesquioxide  of  iron  is  now  used  to  some  extent  for 
the  purpose  of  purifying  coal-gas  from  sulphuretted  hydrogen, 
which  is  always  produced  during  the  distillation  of  coal.  For  this 
purpose  the  oxide  is  mixed  with  sawdust,  and  placed,  in  layers  of 
10  or  12  inches  in  thickness,  upon  the  perforated  shelves  of  a dry 
lime  purifier:  hydrated  sesquisul])hide  of  iron  and  water  are 
formed  ; FeA,  a?  H A + 3 x HA  -f  3 HA-  After 

the  mixture  has  ceased  to  absorb  anymore  sulphuretted  hydrogen, 
it  is  oxidized  by  exposure  to  a current  of  air ; hydrated  ses(]ui- 
oxide  of  iron  is  thus  reproduced,  and  suljdiur  is  set  free ; 2Fe2B3, 
X H3O  + 3 0^=2  FeAs,  ^ IIA  + 3 The  mixture  may  again 
be  used  for  the  same  purpose  as  at  first,  and  this  process  may  be 
repeated  several  times  in  succession,  until  the  accumulation  of 
sulphur  mechanically  impairs  the  absorbent  powers  of  the  mixture. 
Considerable  elevation  of  temperature  attends  the  act  of  reoxida- 


516 


BLACK  OK  MAGXETIC  OXIDE  OF  EROX. 


tion,  Tvliicli  must  therefore  be  prevented  from  taking  place  with 
too  much  rapidity. 

Sesquioxide  of  iron  combines  with  some  of  the  more  powerful 
bases,  towards  which  it  acts  the  part  of  a feeble  acid.  The  com- 
pounds which  it  forms  by  heating  it  with  the  hydrates  of  potash 
and  soda  are  easily  decomposed  by  water,  but  the  oxide  retains 
traces  of  these  bases  with  great  obstinacy.  According  to  Pelouze, 
when  1 atoms  of  lime  and  1 atom  of  peroxide  of  iron  are  precipi- 
tated together  and  boiled,  they  unite  and  form  a white  compound 
(1  OaO-jFe^Og)  which  is  readily  decomposed  by  the  feeblest  acids. 
Sesquioxide  of  iron  occurs  native  combined  with  oxide  of  zinc  in 
crystals,  mixed  witli  oxide  of  manganese,  constituting  Frank- 
Unite.  IVith  protoxide  of  iron  it  forms  the  black  or  magnetic 
oxide  of  iron. 

(758)  Black  or  2LagnetiG  Oxide  of  Iron  {¥e^O^) ; Sp.  Or. 
5*09  : Composition  in  parts ^ Fe,  72‘11 ; O,  2T‘59. — This  oxide 
occurs  as  a well-known  mineral,  the  loadstone^  which  acquires  its 
magnetism  from  the  inductive  influence  of  the  earth.  It  is  found 
in  primitive  rocks  forming  beds,  or  sometimes,  as  in  Sweden, 
entire  mountains.  It  furnishes  a very  pure  and  excellent  iron, 
of  wliich  a large  quantity  is  annually  supplied  from  the  Swedish 
and  American  mines.  It  has  a black  colour  and  metallic  lustre : 
it  crystallizes  in  cubes,  octohedra,  or  rhombic  dodecahedra. 
Magnetic  oxide  of  iron  is  the  principal  constituent  of  the  scales 
of  oxide  which  are  detached  during  the  forging  of  wrought  iron. 
It  fuses  at  a high  temperature,  and  is  formed  when  iron  is  burned 
in  oxygen, — the  sesquioxide,  which  is  the  result  of  the  combina- 
tion, losing  part  of  its  oxygen,  owing  to  the  intensity  of  the  heat 
developed  during  the  combustion.  The  magnetic  oxide  is  also 
formed  by  passing  steam  over  heated  iron  turnings.  A hydi’ate 
of  this  oxide  (Fe30^,Il20)  may  be  procured  by  dividing  a freshly 
prepared  solution  of  ferrous  sulphate  into  three  equal  portions : 
two  of  these  are  acidulated  with  sulphuric  acid  and  heated  to 
the  boiling-point ; to  the  boiling  liquid  nitric  acid  is  added 
gradually  so  long  as  its  addition  causes  the  evolution  of  nitric 
oxide : when  this  point  is  reached,  the  whole  of  the  ferrous  salt 
will  have  been  converted  into  a ferric  salt ; 6 Fe'^SO^  + S H^SO^ 
-I-  2 11X03  = 3 {¥e"\  3 SO,)  + 2 XO  -fl  H^O:  the  remain- 
ing portion  of  the  solution  of  the  ferrous  sulphate  is  then  poured 
into  the  hot  liquid,  and  carbonate  of  sodium  or  caustic  ammonia 
is  added  in  slight  excess : the  solution  and  precipitate  are  boiled 
together,  and  the  black  oxide  is  formed  as  a heavy  crystalline 
powder.  The  magnetic  oxide  is  soluble  without  difficulty  in 
hydrochloric  acid,  as  well  as  in  nitric  acid  and  in  aqua  regia : 
this  oxide,  however,  does  not  form  specific  salts,  but  mixtures  of 
ferrous  and  ferric  salts;  ¥e^O^  -f-  I II^SO,  = Fe"SO,  + (Fe'")2 
3 SO,  + I H^O. 

If  recently  precipitated  hydrated  sesquioxide  of  iron,  obtained 
from  the  sesquichloride  by  ammonia,  be  well  washed,  and  without 
being  dried  be  boiled  with  water  and  iron  turnings  in  large 
excess,  hydrogen  is  evolved,  and  magnetic  oxide  of  iron  formed. 


NITEIDE  OF  IKON. 


517 


(759)  Ferric  acid  (H2Fe0-4  = 122,  or  HOjFeOg  = 9 + 52). — 
If  a mixture  of  1 part  of  sesquioxide  of  iron  and  4 parts  of  nitre 
be  heated  to  full  redness  for  some  time,  a brown  mass  is  obtained, 
which  with  water  gives  a beautiful  violet-coloured  solution,  due 
to  the  presence  of  ferrate  of  potassium.  In  this  compound  the 
iron  is  combined  with  a larger  quantity  of  oxygen  than  in  the 
sesquioxide,  but  the  ferric  anhydride  has  not  been  obtained  in 
an  isolated  form.  Ferrate  of  potassium  may  be  more  easily  pro- 
cured by  suspending  1 part  of  recently  precipitated  hydrated 
sesquioxide  of  iron  in  a concentrated  solution  of  potash,  consisting 
of  30  parts  of  hydrate  of  potash  and  50  of  water,  and  then  trans- 
mitting a current  of  chlorine  gas : the  ferrate  of  potassium  is 
insoluble  in  a concentrated  solution  of  potash,  and  is  deposited 
as  a black  powder,  which  may  be  drained  upon  a tile  (Fremy). 
This  compound  is  very  soluble  in  water,  but  is  precipitated  in 
black  flocculi  by  a large  excess  of  alkali.  It  is  a very  unstable 
salt : in  dilute  solutions  the  alkali  becomes  free,  hydrated  sesqui- 
oxide of  iron  subsides,  and  oxygen  escapes.  Organic  matter 
decomposes  it  speedily,  just  as  it  does  the  permanganate  of  potas- 
sium : a tenq^erature  of  212°  destroys  it  instantly  if  in  solution, 
and  the  addition  of  an  acid,  even  in  quantity  insufficient  to  neu- 
tralize the  whole  of  the  alkali,  causes  the  immediate  separation 
of  oxygen,  and  precipitation  of  the  sesquioxide  of  iron. 

Ferrates  of  barium,  strontium,  and  calcium  may  be  obtained 
in  the  form  of  red  insoluble  precipitates,  by  admixture  of  solu- 
tions of  the  salts  of  the  earths  with  a solution  of  the  ferrate  of 
potassium. 

W anklyn  and  Carius  have  described  a hydride  of  iron  procured 
by  the  action  of  iodide  of  iron  on  zinc  etliyl.  It  has  .not  been 
analysed,  but  is  described  as  a black  powder  wdiich  evolves  pure 
hydrogen  when  gently  heated : hydrochloric  acid  dissolves  it  with 
evolution  of  hydrogen. 

(760)  Nitride  of  Iron. — When  iron  wire  is  heated  in  a current 

of  dry  ammoniacal  gas  for  some  hours  it  becomes  brittle,  but 
does  not  usually  gain  in  weight  more  than  about  0-2  per  cent. 
Fespretz,  however,  obtained  a compound  of  iron  with  nitrogen  in 
which  100  parts  of  iron  increased  to  111 ‘5,  becoming  less  dense, 
brittle,  whitish,  and  less  oxidizable  than  pure  iron.  Sulphuric 
a^'id  dissolves  this  nitride  easily  with  evolution  both  of  hydrogen 
and  nitrogen,  whilst  sulphate  of  ammonium  is  retained  in  solution. 
If  lieated  to  redness  in  a current  of  dry  hydrogen  it  becomes 
reduced  to  metallic  iron,  wliilst  ammonia  is  generated.  Fremy 
found  tliat  it  becomes  easily  and  permanently  magnetized.  He 
found  the  best  mode  of  preparing  this  nitride,  to  wliicli  he 
attributes  a composition  expressed  by  the  formula  (Fe^N.^),  to 
consist  in  transmitting  a current  of  dry  ammonia  over  dried 
ferrous  chloride  heated  to  redness  in  a ])orcelain  tid)e.  If  pure 
ferric  oxide,  as  obtained  from  the  oxalate  by  ignition,  be  lieated 
in  a current  of  ammonia,  a brittle  nitride  is  tbrmed,  consisting 
of  (liogostadius),  wliich  is  with  much  probability  regarded 

by  the  last-named  chemist  as  the  only  definite  nitride  of  the  metal. 


518 


SULPHIDES  OF  IRON. 


(761)  Sulphides  of  Iron. — Sulphur  combines  with  iron  in 
several  proportions : the  protosulphide,  FeS,  and  the  bisulphide, 
FeSj,  are  the  most  important ; but  besides  these  a disulphide, 
Fe.^S,  has  been  obtained  bj  heating  sulphate  of  iron  to  redness  in 
a current  of  hydrogen  gas : a sesquisulphide,  FejSg,  maj  also  be 
formed  as  a hydrate  by  precipitating  the  persalts  of  iron  by  the 
protosulphides  of  the  alkaline  metals  ; and  two  magnetic  sulphides 
of  iron,  Fe.Sg,  and  FogS^,  are  found  native. 

Protosidjyhide^  or  Sidphuret  of  Iron  (FeS=88,  or  FeS=41:), 
may  be  prepared  by  heating  a bar  of  iron  to  whiteness  and 
bringing  it  into  contact  with  a roll  of  sulphur  : immediate  union 
takes  place,  and  the  resulting  sulphide  melts  and  runs  down  in 
drops  of  a reddish-brown  colour  : when  formed  in  this  manner  it 
usually  contains  an  excess  of  sulphur.  It  may  also  be  prepared 
by  projecting  in  successive  portions,  into  a red-hot  earthen  crucible, 
a mixture  of  7 parts  of  iron  tilings  with  4 parts  of  sulphur  in  fine 
powder ; vivid  deflagration  occurs  at  the  moment  of  combination, 
rrotosulphide  of  iron  dissolves  both  iron  and  sulphur  if  either  be 
present  in  excess  ; its  composition,  therefore,  is  variable.  Like 
carbon,  the  presence  even  of  a minute  portion  of  sidphur  alters 
the  cpiality  of  wrought  iron,  which  if  it  contains  even  of 

sulphur  is  rendered  ‘ red  short.’  Anhydrous  protosulphide  of 
iron  is  dissolved  by  diluted  sulphuric  or  hydrochloric  acid  with 
evolution  of  sulphuretted  hydrogen : this  decomposition  is  fre- 
quently employed  in  the  laboratory  as  a convenient  som'ce  of 
sulphuretted  hydrogen.  Xitric  acid  and  aqua  regia  decompose 
it  and  form  ferric  nitrate  or  ferric  chloride,  setting  part  of  the 
sulphur  free,  and  converting  the  residue  into  sulphuric  acid. 
When  heated  in  the  open  air,  this  sulphide  absorbs  oxygen  and 
becomes  converted  into  sulphate  of  iron ; at  a still  higher  tem- 
rature  it  is  decomposed,  sulphurous  and  sulphuric  anhydrides 
escape,  and  sesquioxide  of  iron  remains. 

Protosulphide  of  iron  may  be  obtained  as  a black  hydrate 
by  precipitating  a solution  of  a ferrous  salt  with  a solution  of  a 
protosulphide  of  one  of  the  alkaline  metals;  thus  2 KHS-f  FeSO^ 
=FeS  + Il2S-i-K2S04 ; in  this  condition  it  rapidly  attracts  oxygen 
from  the  air,  and  assumes  a brownish-red  colour,  sesquioxide  of 
iron  being  formed  and  sulphur  liberated.  When  iron  is  present 
in  very  minute  quantities  in  a solution,  and  is  precipitated  by  a 
solution  of  sulphide  of  ammonium,  the  very  finely  divided  particles 
of  sulphide  of  iron  are  apt  to  pass  through  the’ filter;  the  liquid 
then  has  a peculiar  green  tint. 

If  iron  tilings  be  mixed  with  two-thirds  of  their  weight  of  sul- 
phur in  powder,  and  moistened,  the  mixture  becomes  hot  when 
exposed  to  the  air,  and  absorbs  oxygen  with  sufficient  rapidity  to 
cause  it  in  many  cases  to  infiame;  sulphide  of  iron  is  at  first 
formed,  and  this  quickly  becomes  converted  into  sulphate.  A valu- 
able lute  for  the  joints  of  iron  vessels  is  composed  of  a mixture  of 
60  parts  of  iron  filings  sifted  fine,  and  2 of  sal  ammoniac  in  fine 
powder  intimately  blended  with  1 part  of  flowers  of  sulphur.  This 
powder  is  made  into  a paste  with  water,  and  applied  immediately ; 


BISULPHIDE  OF  IRON. 


519 


in  a few  minutes  it  becomes  hot,  swells,  disengages  ammonia  and 
sulphuretted  hydrogen,  and  soon  sets  as  hard  as  iron  itself. 

(762)  Bisulphide  of  Iron  {¥e^^=120,  or  reS2=60) ; /Sp.  Gr. 
4*98  : Composition  in  100  parts ^ Fe,  46*67 ; S,  53*33. — This  com- 
pound is  found  abundantly  in  the  native  state,  constituting  the 
iron  pyrites  of  mineralogists.  It  occurs  in  the  strata  of  every 
period  : when  found  in  the  older  formations  it  is  crystallized  in 
cubes,  and  sometimes  in  dodecahedra,  of  a brassy  lustre,  and  is 
hard  enough  to  strike  tire  with  steel ; but  in  the  tertiary  strata  it 
more  frequently  occurs  in  fibrous  radiated  nodules.  The  forma- 
tion of  iron  pyrites  may  occasionally  be  traced  to  the  slow  deoxi- 
dation of  sulphates  by  organic  matter  in  waters  containing  car- 
bonate or  other  salts  of  iron  in  solution;  it  is  then  frequently 
deposited  in  cubes  or  octohedra.  Tliis  appears  to  be  the  usual 
mode  of  its  formation  in  alluvial  soils.  Some  varieties  of  iron 
pyrites,  especially  those  found  in  the  tertiary  strata,  are  speedily 
decomposed  b}^  exposure  to  air ; oxygen  is  absorbed,  and  ferrous 
sulphate  formed.  This  decomposition  occurs  with  greater  facility 
if  the  bisulphide  be  mixed  with  other  substances,  as  is  the  case  in 
the  aluminous  schists  ; in  which,  by  the  further  action  of  air, 
a basic  ferric  sulphate  is  formed,  whilst  the  liberated  sulphuric 
acid  reacts  upon  the  alumina,  magnesia,  or  lime  of  the  soil,  and 
forms  sulphates ; those  of  aluminum  and  magnesium  may  be  ex- 
tracted by  lixiviation.  The  ordinary  crystallized  pyrites  from  the 
older  strata  is  not  thus  decomposed,  but  a variety  of  a whiter 
colour  is  rapidly  disintegrated  by  exposure  to  the  weather ; this 
form  of  pyrites  is  known  as  white  iron  pyrites  ; it  crystallizes  in 
right  rhomboidal  prisms,  but  it  possesses  the  same  chemical  com- 
position as  the  yellow  cubes. 

Iron  pyrites  is  not  acted  upon  by  cold  sulphuric  or  by  hydro- 
chloric acid,  but  is  rapidly  oxidized  and  dissolved  by  nitric  acid 
and  by  aqua  regia : boiling  oil  of  vitriol  dissolves  it  gradually  with 
evolution  of  sulphurous  anhydride.  When  heated  in  closed  ves- 
sels it  fuses,  and  sulphur  is  expelled.  If  heated  in  the  air  it  burns 
with  flame,  peroxide  of  iron  is  formed,  wdiilst  sulphurous  anhy- 
dride escapes  in  large  quantity.  This  circumstance  has  been 
turned  to  account  in  the  manufacture  of  oil  of  vitriol,  for  which 
purpose  enormous  quantities  of  mundic^  as  the  bisulidiide  is  termed 
by  the  workmen,  are  annually  consumed.  The  acid  obtained  from 
that  source  is  usually  contaminated  with  arsenic,  wliich  in  small 
quantity  is  a common  impurity  in  pyrites.  Iron  pyrites  may  be 
})re[)ared  artificially  by  exposing  a mixture  of  ])Owdered  ])rotosul- 
phide  of  iron  with  lialf  its  weight  of  flowers  of  sul})hur,  in  a cov- 
ered crucible  to  a heat  just  below  redness,  as  long  as  sulphurous 
fumes  escape. 

(763)  Maynetic  Sulphide  of  Iron  (Fe,Sg,  or  6 FeS,FeS3) ; Sp. 
Gr.  4*65. — Tliis  compound  exhibits  a brassy  lustre,  but  is  distin- 
guished from  ordinary  pyrites  by  its  solubility  in  hydrochloric 
acid.  It  is  often  formed  when  sul])hur  and  iron  are  heated  to- 
gether in  ■[)reparing  the  protosul])hide  for  use  in  the  laboratory. 
Another  variety  oi  magnetic  pyrites  consist  of  FCgS^. 


520 


SULPHIDES  ANT)  CHLORIDES  OF  IRON. 


MispicA'elj  or  arsenical  pyrites,  is  an  arsenio-siilphide  of  iron 
(FeSAs,  or  FeS^FeAs;  Sp.  Gr.  6*13)  which,  amongst  other  local- 
ities, occurs  abundantly  in  the  Hartz,  in  Saxony,  and  in  some  of 
the  Cornish  mines ; it  crystallizes  in  riglit  rhombic  prisms,  of  a 
steel-grey  colour  and  metallic  lustre.  AYhen  heated  in  closed 
vessels  it  is  partially  decomposed,  and  sulphide  of  arsenic  sublimes. 
If  exposed  to  a high  temperature  in  the  open  air,  it  produces  ses- 
quioxide  of  iron,  whilst  arsenious  and  sulphurous  anhydrides  es- 
cape. Analogous  compounds  of  cobalt  and  nickel  occm’  amongst 
the  ores  of  these  metals. 

A remarkable  class  of  compounds,  termed  by  Foussin,  who 
discovered  them,  nitrosulphides  of  iron^  may  be  obtained  by  the 
reaction  of  nitrite  of  potassium  and  sulphide  of  ammonium  upon 
the  salts  of  iron.  The  reaction  is  complicated,  and  their  properties 
will  be  better  examined  along  with  those  of  the  nitroprussides. 

BubpliospTiide  of  Iron  (Fe^P)  may  be  obtained  by  reducing  the 
phosphate  of  the  metal  with  charcoal : it  fuses  at  a red  heat,  and 
forms  an  extremely  hard,  brittle  mass,  which  unites  with  both 
phosphorus  and  iron  in  all  proportions. 

(761)  Chlorides  of  Iron. — Iron  forms  with  chlorine  two  com- 
pounds— ferrous  chloride,  FeCl^  and  ferric  chloride,  Fe^Cl^, — 
which  correspond  in  composition  to  the  two  basic  oxides  of  the 
metal. 

Ferrous  Chloride^  ProtocTiloride  of  Iron  (FeCl2=127,  or  FeCl 
= 63*5) ; Sp.  Gr.  anhydrous^  2*528  ; cryst.  1*926.— By  passing  dry 
hydrochloric  acid  gas  over  ignited  metallic  iron,  the  acid  is  de- 
composed, hydrogen  gas  escapes,  chlorine  combines  with  the  iron, 
and  the  white  anhydrous  ferrous  chloride  sublimes  at  a tempera- 
ture at  which  glass  begins  to  soften.  Its  solution  may  be  formed 
by  dissolving  iron  in  hydrochloric  acid  ; the  hot,  saturated  liquid 
deposits  the  salt,  on  cooling,  in  green  crystals,  which  contain 
FeCl^,  4 H^O.  It  is  very  soluble  in  water,  and  is  taken  up  in 
considerable  quantity  by  alcohol.  If  heated  in  the  open  air,  chlo- 
rine escapes  and  peroxide  of  iron  remains. 

Ferrous  chloride  unites  with  chloride  of  ammonium  and  forms 
a double  salt,  from  which  the  iron  may  be  deposited  upon  various 
metallic  articles,  by  boiling  them  in  this  solution  with  scraps  of 
zinc  ; the  zinc  displaces  the  iron,  which  is  deposited  in  a coherent 
lamina  upon  the  other  metals,  in  consequence  of  a voltaic  action. 

(765)  Sesquichloride  or  Ferchloride  of  Iron  (Fe2Cl6=325) ; 
Sp.  Gr.  of  Vapour^  11*39;  Mol.  Yol.  \ | ' |,  (or  Fe2Cl3=162*5). — 
This  compound  sublimes  in  anhydrous  brown  scales  when  dry 
chlorine  gas  is  transmitted  over  iron  heated  to  redness.  The  an- 
hydrous chloride  is  very  deliquescent,  and  hisses  when  thrown  into 
water,  forming  a red  solution.  It  is  also  soluble  both  in  alcohol 
and  etlier.  In  a hydrated  condition  it  may  be  procured  by  eva- 
porating a solution  of  ferrous  chloride  through  which  chlorine  has 
been  passed  to  saturation,  or  by  dissolving  hydrated  peroxide  of 
iron  in  hydrochloric  acid : the  solution,  by  concentration,  yields 
large,  red,  deliquescent  crystals  (Fe^Clg,  6 llaO),  but  the  salt  can- 
not be  rendered  anhydrous  by  evaporation,  as  it  is  decomposed 


BROmDE,  IODIDE,  AND  SULPHATE  OF  lEON. 


521 


into  hydrochloric  acid  and  peroxide  of  iron.  It  also  crystallizes 
in  stellate,  orange-colonred  groups,  with  12  which  are  less 

deliquescent  than  the  other  hydrate.  Perchloride  of  iron  forms 
a double  salt  with  chloride  of  ammonium,  which  crystallizes 
readily  in  cubes,  and  is  known  in  pharmacy  as  the  ammonio-chlo- 
ride  of  iron.  The  composition  of  this  salt  varies  considerably  : 
it  is  of  a ruby-red  colour,  and  seldom  contains  more  than  2 per 
cent,  of  iron.  A double  salt  of  perchloride  of  iron  with  chloride 
of  sodium  and  with  chloride  of  potassium  may  also  be  formed. 

A hydrated  oxychloride  of  iron  is  formed  when  a solution  of 
ferrous  chloride  is  exposed  to  the  air,  or  when  the  perchloride  is 
precipitated  by  a small  quantity  of  caustic  alkali.  It  is  insoluble 
in  water  containing  salts,  but  is  partially  soluble  in  pure  water. 

(766)  The  bromides  of  iron  correspond  in  composition  to  the 
chlorides. 

Ferrous  Iodide^  or  Protoiodide  of  Iron  (Pel2=310,  or  Fel= 
155)  is  formed  by  digesting' iron  wire  or  filings,  in  a closed  vessel, 
with  four  times  their  weight  of  iodine  suspended  in  water ; direct 
combination  with  the  elements  takes  place,  the  iodide  is  dissolved 
and  forms  a pale-green  solution,  which,  by  evaporation  in  vacuo^ 
yields  crystals  containing  Fel2,  4 II2O.  By  a continued  heat  it 
may  be  rendered  anhydrous,  and  in  that  state  is  fusible.  Its  solu- 
tion, if  exposed  to  the  air,  absorbs  oxygen  and  is  decomposed ; 
iodine  is  set  free,  and  a hydrated  oxyiodide  of  iron  falls.  This 
change  is  retarded  by  mixing  the  solution  with  strong  syrup  ; and 
as  the  compound  is  employed  in  medicine,  this  method  is  fre- 
quently adopted  to  preserve  uniformity  in  its  composition.  iSTo 
definite  iodide  is  crystallizable. 

(767)  Ferrous  Sulphate,  Protosulphate  of  Iron^  Copperas^  or 
Green  Vitriol^  (FeSO^ . 7 1120= 152 -f  126,  or  Fe0,S03 . 7 110  = 
76  + 63) ; Sp,  Gr.  anhydrous^  3T38,  cryst.  1*857 : Cou'ip.  cryst.  in 
100  parts ^ FeO,  25*91 ; SO3,  28*77 ; H2O,  45*32. — This  salt  is  pre- 
pared in  a state  of  purity  by  dissolving  1 part  of  pure  iron,  or  1-J 
of  its  protosulphide,  by  the  aid  of  heat,  in  1^  parts  of  oil  of  vitriol 
diluted  with  4 of  water.  On  filtering  the  solution  quickly,  it  de- 
posits beautiful  transparent,  bluish-green,  rhomboidal  crystals  on 
cooling,  with  7 II2O.  They  effloresce  in  a dry  air,  and  form  a 
white  crust,  which  soon  becomes  of  a rusty-brown  colour,  owing 
to  the  absorption  of  oxygen  and  formation  of  a basic  ferric  sul- 
phate. If  crystallized  at  a temperature  of  176°  the  ferrous  sul- 
phate forms  right  rhombic  prisms,  which  contain  only  4 II2O.  It 
may  also  be  obtained  crystallized  with  3 and  with  2 atoms  of  water. 
For  commercial  purposes  sulphate  of  iron  is  formed  by  the  decom- 
position of  iron  pyrites,  or  of  aluminous  schists  containing  ])yrites, 
as  already  described  when  speaking  of  the  manufacture  of  alum 
(667).  The  sulphate  of  iron  thus  obtained  has  a grass-green  col- 
our, owing  to  the  presence  of  ferric  suljdiate.  Sul})hate  of  iron 
is  largely  used  in  combination  with  astringent  vegetable  matters 
as  a black  dye;  ordinary  writing-ink  is  a compound  of  this  kind. 

This  salt  is  insoluble  in  alcohol,  and  requires  twice  its  weight 
of  cold  water  for  its  solution.  Its  solubility  is  greater  at  194° 


522 


PERSULPHATE  OF  IRON. 


tlian  at  212°,  100  parts  of  water  dissolving  3Y0  parts  of  the  crys- 
tals at  191°  and  only  333  at  the  boiling-point.  This  anomaly  is 
probably  dependent  upon  causes  similar  to  those  observed  in  the 
case  of  the  sulphate  and  the  carbonate  of  sodium.  If  exposed  to 
the  air,  the  solution  absorbs  oxygen,  and  a rusty  precipitate  occurs, 
which  is  a basic  ferric  sulphate  composed  of  2 Fe203,SO-3 . 3 H^O, 
while  normal  ferric  sulphate  remains  in  solution.  Owing  to  its 
strong  attraction  for  oxygen,  ferrous  sulphate  is  occasionally  used 
as  a reducing  agent : it  is  thus  employed  to  precipitate  gold  and 
palladium  in  the  metallic  form  from  their  solutions,  and  indigo  is 
by  its  means  brought  into  the  soluble  condition.  If  heated  grad- 
ually, each  atom  of  the  crystallized  sulphate  loses  6 atoms  of  water 
and  forms  a white  powder ; 1 atom  of  water  being  retained  at  all 
temperatures  below  500°.  At  a red  heat  the  sulphate  is  decom- 
posed ; sulphuric  anhydride  is  liberated,  but  one  portion  of  the 
anhydride  yields  part  of  its  oxygen  to  the  iron,  which  is  converted 
into  the  sesquioxide,  whilst  sulphurous  anhydride  escapes  (2  FeSO^ 
=Fe2O3-l-S02  + SO3) ; but  as  in  practice  the  salt  cannot  be  ren- 
dered anhydrous  in  large  quantities,  a little  water  distils  with  the 
sulphuric  anhydride,  which  is  condensed  as  a brown  fuming  liquid, 
the  ‘Aordhausen  Sulphuric  Acid’ (415).  The  residual  sesqui- 
oxide of  iron  is  sold  under  the  name  of  colcothar  (Y5Y). 

The  aqueous  solution  of  ferrous  sulphate  in  common  wdth  that 
of  all  the  ferrous  salts,  absorbs  a large  quantity  of  nitric  oxide ; 
forming  a deep  brown  solution  which  has  a powerful  attraction 
for  oxygen  : if  this  solution  be  heated  in  closed  vessels,  the‘gas  is 
for  the  most  part  expelled  unchanged ; if  heated  in  air,  nitric 
acid  is  formed  in  the  liquid,  and  this  converts  the  iron  into  a fer- 
ric salt. 

With  the  sulphates  of  potassium  and  ammonium,  green  vitriol 
yields  double  salts  precisely  analogous  in  form  and  composition  to 
those  which  are  formed  by  these  sulphates  with  sulphate  of  copper. 
The  formula  of  the  potassium  salt  is  (FeS04,K2S04 . 6 H^O). 

(7 68)  Ferric  8ulj)hate  ; Persulphate  or  Sesquisulphate  of  Iron 
8 80^=400,  or  Fe203,  3 803=200)  is  made  either  by  treat- 
ing brown  hsematite  with  an  excess  of  strong  sulphuric  acid,  allow- 
ing it  to  digest  for  some  time,  and  then  expelling  the  excess  of  acid 
at  a heat  short  of  redness  ; or  by  adding  to  the  solution  of  1 equi- 
valent of  ferrous  sulphate,  half  an  equivalent  of  oil  of  vitriol,  boil- 
ing, and  peroxidizing  the  iron  by  adding  to  the  solution  nitric  acid 
in  small  quantities  as  long  as  any  red  fumes  are  given  off.  A yel- 
lowish-white deliquescent  mass  is  obtained  on  evaporation,  from 
which  tlie  acid  is  expelled  by  a red  heat ; at  a more  moderate  heat 
the  salt  is  rendered  anhydrous  : water  dissolves  it  but  slowly.  It 
is  found  native  in  large  quantities  in  Chili  in  the  form  of  a white 
powder  (Fe'^j  3 SO^  . 9 IT^O).  Several  hydrated  basic  ferric  sul- 
phates may  be  obtained. 

With  sulphate  of  potassium  and  the  sulphates  of  the  other 
alkali-metals  ferric  sulphate  forms  double  salts,  resembling  common 
alum,  in  form  and  composition  as  well  as  in  taste.  The  potassium 
salt  (KFe'^'  2 . 12  II3O)  is  astringent,  very  soluble  in  water, 


FERROUS  NITRATE  AND  CARBONATE. 


523 


but  insoluble  in  alcohol : it  is  very  prone  to  spontaneous  decompo- 
sition, and  becomes  converted  from  a colourless  transparent  crystal 
into  a brown,  gummy,  deliquescent  mass  : this  change  is  also  pro- 
duced by  heating  the  salt  to  a temperature  below  212°.  The  mixed 
solutions  of  the  two  sulphates  should  therefore  be  allowed  to  eva- 
porate spontaneously  during  the  preparation  of  this  salt.  The 
double  salt  with  ammonium  2 80^ . 12  H20, 8]).  gr.  1*Y18) 

is  much  more  permanent,  and  crystallizes  readily  in  beautiful  oc- 
tohedra. 

(769)  Ferrous  Titrate  (Fe  21^^03 . 6 180 -1-108). — This 

salt  may  be  obtained  by  dissolving  protosulphide  of  iron  in  cold 
nitric  acid  diluted  with  4 or  5 times  its  bulk  of  water.  Sulphuret- 
ted hydrogen  is  evolved  in  abundance,  and  on  evaporating  the  so- 
lution in  vacuo  over  oil  of  vitriol,  it  crystallizes  in  pale  green 
rhombs,  which  when  heated  evolve  nitric  oxide,  and  yield  a basic 
ferric  nitrate ; 6 (Fe  2 ISTOg)  = 2 4-  3 Fe^Og,  5 This 

change  sometimes  occurs  in  warm  weather  spontaneously.  The 
l)asic  salt  is  then  freely  soluble  in  water,  and  is  not  decomposed  by 
ebullition.  Ferrous  nitrate  may  also  be  procured  by  decomposing 
a solution  of  ferrous  sulphate  by  an  equivalent  quantity  of  nitrate 
of  barium.  It  cannot  be  obtained  in  a pure  form  by  treating  iron 
with  diluted  nitric  acid  : since  in  that  case  the  metal  is  dissolved 
without  evolution  of  gas,  and  ammonia  is  formed  in  the  liquid : — 

10  HFTOg-hd  Fe=4  (Fe  2 FTOg)  + -f  3 H^O. 

Ferric  Nitrate  (Fe'''  3 HOg,  — When  nitric  acid  of  sp. 

gr.  1'2  or  1‘3  is  digested  upon  metallic  iron,  a violent  action  occurs 
attended  with  the  extrication  of  nitrous  anhydride  and  of  nitric 
oxide  ; the  iron  is  at  the  same  time  converted  into  ferric  nitrate, 
which  is  obtained  with  difficulty  on  evaporation  in  prismatic  hy- 
drated crystals.  An  insoluble  basic  nitrate  is  commonly  formed 
at  the  same  time. 

(770)  Ferrous  Carbonate  or  protocarbonate  of  Iron  (FeOOg  = 
116  ; or  FeO,  002=58) ; Comp,  in  100yj>(2r^  Fe,  48'27,  or  FeO, 
62'07 ; OOg,  37*93. — This  substance  is  found  native  in  immense 
quantities,  forming  a valuable  ore  of  iron.  In  its  less  usual  condi- 
tion, when  crystallized,  it  constitutes  spathic  iron  ore,  and  occurs 
in  yellowish  lenticular  crystals,  the  primary  form  of  which  is  a 
rhombohedron,  isomorphous  with  calcareous  spar.  Tlie  native 
carbonate  very  often  contains  carbonate  of  manganese.  Tlie  clay- 
iron  ore,  from  which  the  greater  part  of  the  English  iron  is  ob- 
tained, is,  as  already  mentioned,  an  impure  carbonate  of  iron. 
Clay  iron-stone,  besides  the  more  usual  form  of  bands  or  seams 
accompanying  the  coal  strata,  occurs  also  in  detaclied  nodules  or 
lumps,  sometimes  of  very  large  size,  imbedded  in  the  clay  of  the 
same  formations.  When  carbonate  of  iron  is  heated  strongly  in 
vessels  from  which  air  is  excluded,  carbonic  anhydride  and  carbonic 
oxide  are  expelled,  and  magnetic  oxide  of  iron  is  left,  the  decom- 
position being  as  follows  : 3 FeOOg=Fe304-t-2  OOg-l-OO.  Car- 
bonate of  iron  is  the  salt  contained  in  most  ferruginous  springs,  in 
which  it  is  held  in  solution  by  free  carbonic  acid ; it  is  rarely  pre- 


524 


OXALATES  AND  PHOSPHATES  OF  IRON. 


sent  in  a larger  quantity  than  1 grain  per  pint.  Mere  exposure 
to  air  causes  its  separation  ; the  acid  escapes,  oxygen  is  absorbed, 
and  hydrated  peroxide  of  iron,  mixed  with  a small  quantity  of  or- 
ganic matter,  subsides,  forming  the  ochry  deposits  so  usual  around 
chalybeate  springs.  The  ferrous  carbonate  may  be  produced  arti- 
ficially by  mixing  a ferrous  salt  with  a carbonate  of  one  of  the 
alkali-metals,  when  it  falls  as  a pale  green  voluminous  hydrate 
which  is  speedily  altered  by  exposure  to  air ; it  absorbs  oxygen, 
rapidly  losing  its  carbonic  acid,  and  is  converted  into  the  red  hy- 
drated sesquioxide ; during  the  process  of  drying  it  is  therefore 
almost  completely  decomposed.  No  stable  ferric  carbonate  exists, 
but  the  acid-carbonate  of  potassium  as  well  as  that  of  sodium  dis- 
solves the  hydrated  peroxide  of  iron  ; the  red  solution  thus  formed 
is  very  slowly  decomposed  by  prolonged  ebullition. 

(771)  Oxalates  of  Iron. — Ferrous  oxalate  (2  FeO^^^,  3 H^O) 

is  occasionally  formed  in  the  brown-coal  strata,  in  yellow  fibrous 
or  granular  masses,  known  as  Humboldtite  or  iron-resin.  It  may 
be  prepared  artificially  by  precipitating  the  solution  of  green  sul- 
phate of  iron  by  oxalate  of  ammonium ; or  by  exposing  a solution 
of  ferric  oxalate  in  oxalic  acid  to  the  sun.  Carbonic  acid  is  then 
evolved,  and  ferrous  oxalate  with  2 is  thrown  down  as  a 

yellow  crystalline  and  nearly  insoluble  powder. 

Ferric  oxalate  is  also  a lemon-yellow  powder,  nearly  insoluble 
in  water,  but  soluble  in  excess  of  oxalic  acid.  It  may  be  obtained 
by  mixing  a slight  excess  of  a ferric  salt  with  one  of  a soluble 
oxalate. 

Ferric  oxalate  forms  several  double  salts  of  the  formula 
(MgFe^''  3 O^O^),  analogous  to  the  blue  double  oxalates  of  chro- 
mium (794).  Double  oxalates  of  iron  with  potassium,  sodium, 
ammonium,  barium,  strontium,  and  calcium  have  been  obtained 
by  digesting  the  acid  oxalates  of  these  metals  upon  hydrated 
oxide  of  iron.  These  double  oxalates  are  all  freely  soluble.  It 
is  owing  to  the  formation  of  the  soluble  potassium  salt  that  acid 
oxalate  of  potassium  (salt  of  sorrel)  is  useful  for  removing  stains 
of  ink  and  oxide  of  iron  from  linen. 

(772)  Phosphates  of  Iron. — Ferrous  phosjohate  (Fe'^IIPO^, 
or  HO,  2 FeO,  PO^)  falls  as  a white  powder  on  adding  triphos- 
phate of  sodium  to  a ferrous  salt ; by  exposure  to  air  it  absorbs 
oxygen,  and  becomes  blue.  A hydrated  blue  phosphate  of  iron  is 
found  native ; it  is  known  as  vivianite.  It  is  probably  a mixture 
of  ferrous  and  ferric  phosphates  (Fe"HP0„  2 Fe'''  PD,),  and 
contains  in  addition  about  30  per  cent,  of  water. 

A ferric  phosphate  (Fe'^'PO,,  2 II^O)  is  obtained  as  a white 
powder  by  decomposing  perciiloride  of  iron  by  an  alkaline  ortho- 
phosphate. Exposure  of  this  salt  to  air  produces  no  change.  It 
is  insoluble  in  acetic  acid,  but  soluble  in  ferric  acetate : phos- 
phoric acid  is  sometimes  precipitated  in  this  form  in  the  course  of 
analysis.  Its  composition  varies  according  as  the  phosphate  of 
sodium  or  the  salt  of  iron  is  in  excess. 

Several  native  silicates  of  iron  are  known,  but  they  are  not 
important.  The  ‘ finery  slag  ’ obtained  in  the  conversion  of  cast 


CHAEACTERS  OF  THE  SALTS  OF  IRON. 


525 


into  wronglit  iron  consists  cliieiiy  of  ferrous  orthosilicate  (Fe^SiO^, 
or  2 FeO,  SiO^).  Oxide  of  iron  rapidly  attacks  clay  crucibles  if 
fused  in  them. 

(773)  Characters  of  the  Salts  of  Iron. — Iron  forms  two 
classes  of  salts,  both  of  which  are  readily  distinguished  from  each 
other  and  from  those  of  other  metals.  The  salts  of  iron  are  not 
poisonous,  unless  administered  in  excessive  quantities ; they  form 
valuable  tonics  and  astringents  when  taken  internally.  The  solu- 
tions both  of  the  ferrous  and  of  the  ferric  salts  have  an  inky, 
astringent  taste. 

1.  Ferrous  Salts ^ or  Salts  of  the  Protoxide. — These  salts, 
when  in  solution,  or  when  crystallized,  have  a pale-green  colour ; 
they  redden  litmus,  but  very  feebly.  With  the  alkalies  a grey 
or  green  precipitate  of  hydrated  protoxide  is  formed  in  their  solu- 
tions: it  passes  quickly  through  various  shades  of  green  into 
brown  by  exposure  to  the  air ; this  change  of  colour  is  due  to  the 
absorption  of  oxygen,  in  consequence  of  which  the  sesquioxide 
is  eventually  produced.  If  the  precipitate  be  produced  by  am- 
monia.^ an  excess  of  this  reagent  redissolves  a part  of  tlie  precipi- 
tate ; and  if  the  solution  contains  chloride  of  ammonium,  the 
whole  of  the  oxide  will  be  redissolved:  this  solution  absorbs 
oxygen  rapidly  from  the  air,  and  a him  of  sesquioxide  of  the 
metal  is  formed  upon  the  surface.  Ferrous  salts  of  the  mineral 
acids  are  not  precipitated  in  slightly  acid  solutions  by  sulphuret- 
ted hydrogen  / but  they  give  a black  precipitate  of  hydrated  sul- 
phide on  adding  a solution  of  sidphide  of  ammonium.  Ferro- 
cyanide  of  potassium  gives  a pale  blue  precipitate,  which,  on  ex- 
posure to  the  air,  deepens  in  tint,  owing  to  the  absorption  of 
oxygen.  Ferricyanide  of  potassium.^  when  added  to  a neutral  or 
acid  solution,  gives  a bright-blue  precipitate,  which  is  one  of  the 
varieties  of  Prussian  blue.  If  a solution  of  a ferrous  salt  be 
boiled  with  nitric  acid^  the  metal  is  completely  converted  into  a 
ferric  salt : the  same  thing  is  effected  by  the  action  of  chlorine 
or  of  bromine,  or  by  boiling  an  acidulated  solution  of  the  salt 
with  a small  quantity  of  chlorate  of  potassium. 

2.  Ferric  Salts.,  or  Persalts,  or  Salts  of  the  Peroxide. — In 
solution  they  have  a yellow  or  reddish-brown  colour.  Ilydrosul- 
phuric  acid  reduces  them  to  the  state  of  ferrous  salts,  whilst  a 
white  deposit  of  sulphur  occurs : for  example,  with  ferric  sulphate 
the  following  reaction  takes  place;  2 (Fe'"^  3 S04)-t-2  Il2S=4Fe" 

-h  2 Il^SO^-hSo.  With  sulphide  of  ammonium  a black  hy- 
drated sesquisulphide  of  iron  is  precipitated.  The  hydrated  alka- 
lies give  a reddish-brown  voluminous  precipitate  of  hydrated  ])er- 
oxide,  insoluble  in  excess  of  alkali.  Sidphocyanide  of  potassium 
in  neutral  or  acid  solutions  gives  an  intense  blood-red  solution  ; 
ferrocyanide  of  potassium^  a bright  blue  precipitate  of  ordinary 
Prussian  blue.  Ferricyanide  of  potassium  occasions  no  precipi- 
tate in  solutions  of  the  ferric  salts,  but  the  liquid  acquires  a green- 
ish hue ; the  ferric  salts  may  thus  be  destinguished  from  the  fer- 
rous salts.  Tincture  of  galls.,  in  neutral  solutions,  yields  a bluish- 
black  inky  precipitate  ; it  is  the  colouring  matter  of  ordinary 


526 


SEPARATION  OF  IRON  FROM  OTHER  METALS. 


writing-ink ; this  test  is  rendered  much  more  delicate  in  its  indica- 
tions by  the  addition  of  water  holding  a little  carbonate  of  cal- 
cium in  solution  in  carbonic  acid.  In  neutral  solutions  the  hen- 
zoates  and  the  succmates  of  the  alkali-metals  give  volnminons  in- 
soluble precipitates  : benzoate  or  succinate  of  ammonium  or  potas- 
sium is  sometimes  employed  to  separate  iron  from  nickel  and 
cobalt,  as  the  benzoates  and  the  succinates  of  these  metals  are 
soluble.  If  a solution  of  a ferric  salt  to  which  an  alkali  has  been 
added  till  it  begins  to  occasion  a permanent  precipitate  be  raised 
to  the  boiling-point,  it  is  completely  decomposed,  and  an  insoluble 
basic  ferric  salt  is  precipitated : this  property  is  often  turned  to 
account  in  the  separation  of  iron  from  cobalt,  nickel,  and  manga- 
nese, which  are  not  precipitated  under  similar  circumstances. 
When  a ferric  salt  in  solution  is  digested  with  a bar  of  zinc  in  a 
flask  provided  with  a tube  for  the  escape  of  the  gas,  the  zinc  be- 
comes dissolved,  hydrogen  is  evolved,  and  the  whole  of  the  iron  is 
precipitated  as  peroxide,  whilst  a salt  of  zinc  is  formed  in  the  liquid. 

Before  the  Uowpipe  both  classes  of  the  salts  of  iron  act  alike : 
with  borax  in  the  reducing  flame  they  give  a green  glass,  which 
becomes  colourless,  or  yellowish  (if  the  iron  be  in  large  quantity) 
when  held  in  the  oxidating  flame. 

(771:)  Estimation  of  Iron.  — In  estimating  the  quantity  of 
iron  for  the  purposes  of  analysis,  it  should  always  be  flrst  con- 
verted into  a ferric  salt,  by  boiling  with  nitric  acid  or  otherwise, 
after  which  it  may  be  precipitated  by  excess  of  ammonia,  and 
then  well  washed  and  ignited : pure  sesquioxide  of  iron  remains, 
consisting  in  100  parts  of  70  of  iron  and  30  of  oxygen.  Iron  is 
thus  readily  separated  from  the  alkalies  and  alkaline  earths.  If 
magnesia  be  present,  it  is  apt  to  be  partially  precipitated  with 
the  oxide  of  iron,  unless  the  solution  contain  a considerable 
quantity  of  chloride  of  ammonium.  In  the  presence  of  tartaric 
acid,  of  sugar,  and  of  various  other  forms  of  organic  matter,  am- 
monia precipitates  the  peroxide  of  iron  very  imperfectly  from  its 
solutions : in  such  a case  sulphide  of  ammonium  must  be  em- 
ployed. The  iron  is  then  thrown  down  completely  as  sulphide ; 
this  precipitate  must  be  redissolved  in  nitric  acid,  and  afterwards 
the  iron  may  be  obtained  as  peroxide  by  adding  an  excess  of  am- 
monia to  the  solution. 

(775)  Separation  of  Iron  from  Aluminum  and  Glucimim. — 
If  alumina  and  glucina  are  contained  in  the  liquid,  they  accom- 
pany the  peroxide  of  iron  when  precipitated  by  ammonia.  When 
these  earths  are  present  tlie  precipitation  should  be  effected  by 
an  excess  of  caustic  potash  instead  of  by  ammonia ; the  precipi- 
tate should  be  gently  warmed  with  the  liquid,  for  the  purpose  of 
dissolving  out  the  earths.  The  solution  is  filtered  from  the  per- 
oxide of  iron,  which  requires  long  washing  with  boiling  water  to 
remove  the  last  traces  of  potash.  The  alumina  and  glucina  are 
obtained  from  the  alkaline  filtrate  by  neutralizing  it  with  hy- 
drochloric acid,  and  then  adding  a slight  excess  of  ammonia ; the 
alumina  and  glucina  are  precipitated  together,  and  must  be  sepa- 
rated in  the  manner  described  in  (677). 


ESTIMATION  OF  IKON  IN  ITS  MIXED  OXIDES. 


527 


(776)  Separation  of  Iron  from  Zinc,  Cadmium,  Cobalt, 
Niclcel,  and  Manganese. — Having  precipitated  the  cadmium  by 
sulphuretted  hydrogen,  and  reconverted  the  iron  into  peroxide  hy 
boiling  the  liquid  with  a small  quantity  of  nitric  acid,  the  solution 
is  to  be  largely  diluted  with  water,  and  carbonate  of  sodium 
added  gradually  to  the  acid  liquid  until  a permanent  precipitate 
is  formed,  though  the  liquid  remains  acid.  The  solution  must  be 
boiled,  and  the  liquid  filtered  from  the  bulky  precipitate  of  the 
basic  ferric  salt:  the  clear  solution  must  then  be  slightly  super- 
saturated with  carbonate  of  sodium,  and  afterwards  feebly  acidu- 
lated with  acetic  acid : on  again  boiling  the  liquid,  the  last  trace 
of  iron  is  thrown  down  in  the  form  of  basic  acetate,  whilst  the 
other  metals  are  retained  in  the  solution : the  precipitated  salt 
of  iron  must  be  redissolved  in  hydrochloric  acid,  and  the  iron 
thrown  down  as  peroxide  by  the  addition  of  ammonia. 

Sometimes  ammonia  in  excess  is  made  use  of  to  separate  iron 
from  these  metals,  which  all  form  soluble  compounds  with  ammo- 
nia, and  which,  it  is  supposed,  will  retain  them  in  solution ; but 
this  method  should  never  be  resorted  to  in  analysis,  because  the 
oxide  of  iron  always  retains  a large  quantity  of  the  other  oxides. 

(777)  Separation  of  Iron  from  Uranium. — The  iron  having 
been  converted  into  peroxide  is  precipitated  by  a large  excess  of 
sesqui carbonate  of  ammonium,  which  retains  most  of  the  ura- 
nium. This  process,  however,  although  usually  adopted,  is  im- 
perfect : for  if  the  quantity  of  iron  be  at  all  large,  a considerable 
proportion  of  uranium  is  precipitated  along  with  it. 

(778)  Estimation  of  Ferrous  Salt  in  a Mixture  of  Ferric  and 
Ferrous  Salts. — It  often  happens  that  the  chemist  has  to  ascer- 
tain the  relative  proportions  of  protoxide  and  sesquioxide  of  iron 
which  a compound  contains.  If  the  compound  of  iron  for  exami- 
nation be  soluble  in  hydrochloric  acid,  the  following  process  by 
Penny  will  be  found  both  easy  in  execution  and  accurate  in  its 
results.  It  is  based  upon  the  power  which  a solution  of  the  an- 
hydro-chromate  (bichromate)  of  potassium  in  excess  of  hydro- 
chloric acid  possesses  of  converting  ferrous  chloride  into  ferric 
chloride,  while  the  chromic  acid  is  reduced  to  the  state  of  chromic 
chloride  : — 

K,erA  + 6 FeCl,+  M HC1=3  Fe,Cl,+er,Cle  + 2 KC1+  711,0. 

In  order  to  carry  this  process  into  effect,  MT  grains  of  pure  anhy- 
dro-chromate  of  potassium  are  introduced  into  an  alkalimeter 
burette  (577),  which  is  to  be  tilled  up  to  0°  with  tepid  water;  the 
mixture  is  to  be  agitated  until  the  salt  is  dissolved.  Each  division 
of  the  instrument  contains  sufficient  of  the  anhydro-chroniate  to 
convert  half  a grain  of  metallic  iron,  present  in  the  form  of  fer- 
rous chloride,  into  sesquichloride.  The  ore  for  experiment  hav- 
ing l)een  reduced  to  an  extremely  fine  powder,  100  grains  of  it 
are  boiled  in  a flask  for  ten  or  fifteen  minutes  vvdth  about  2 ounces 
of  hydrochloric  acid  of  sp.  gr.  ITOO:  about  6 ounces  of  boiling 
distilled  water  are  added,  and  the  mixture  immediately  transferre(l 
to  an  evaporating  basin,  taking  care  to  rinse  out  the  flask  tho- 


528 


ESTIMATION  OF  IRON  IN  ITS  MIXED  OXIDES. 


roughly.  A white  plate  is  then  spotted  over  with  a few  di’ops  of 
a weak  solution  of  ferricyanide  of  potassium,  and  the  anhydro- 
chromate  is  cautiously  added  from  the  alkalimeter  to  the  solution 
of  iron  (which  is  kept  in  continual  agitation),  until  it  assumes  a 
dark-greenish  shade ; as  soon  as  this  begins  to  appear,  it  must  be 
tested  after  each  addition  of  the  anhydro-chromate,  by  taking  out 
a di*op  of  the  solution  on  a glass  rod,  and  adding  it  to  one  of  the 
drops  of  the  ferricyanide.  When  the  last  drop  no  longer  occasions 
a blue  precipitate,  the  operation  is  ended,  and  the  number  of  divi- 
sions of  the  liquid  which  has  been  added,  when  divided  by  two, 
indicates  the  amount  of  metallic  iron  which  exists  in  the  form  of 
a ferrous  compound  in  100  parts  of  the  ore.  The  total  quantity 
of  iron  present  in  the  solution  may  be  ascertained  by  making  a 
second  experiment  on  a fresh  portion  of  the  ore,  and  reducing  the 
metal  whilst  still  in  the  flask  with  the  hydrochloric  acid,  to  the 
state  of  a ferrous  salt : this  is  readily  effected,  either  by  transmit- 
ting a current  of  sulphuretted  hydrogen  and  then  expelling  the 
excess  of  that  gas  by  ebullition ; or  by  boiling  the  concentrated 
solution  vflth  metallic  zinc ; or  by  nearly  neutralizing  the  liquid 
with  carbonate  of  sodium,  and  adding  a solution  of  sulphite  of 
sodium  until  a drop  of  the  liquid  ceases  to  give  a red  colour  when 
mixed  with  a drop  of  a solution  of  sulphocyanide  of  potassium,''^ 
placed  upon  a white  plate  : the  liquid  is  then  boiled,  to  expel  the 
excess  of  sulphurous  acid.  ^ When  the  iron  has  thus  been  reduced 
to  the  state  of  ferrous  salt,  the  whole  quantity  of  the  metal  pre- 
sent may  be  ascertained  by  means  of  the  solution  of  anhydro- 
chromate  of  potassium,  as  before ; the  difference  between  the  two 
results  will  give  the  per-centage  of  metallic  iron  present  in  the 
form  of  ferric  salt. 

Another  excellent  process  for  determining  the  amount  of  a 
ferrous  salt  present  was  contrived  by  Margueritte  (Ann.  de  Chimie.^ 
III.  xviii.  211).  It  consists  in  ascertaining  the  quantity  of  a 
measured  solution  of  permanganate  of  potassium  of  known  strength, 
which  the  cold  acidulated  and  largely  diluted  solution  of  iron  in 
hydrochloric  acid,  can  deoxidize  and  deprive  of  colour,  owing  to 
the  reaction  expressed  in  the  following  equation : — 

2 KWnO,  -h  10  Fe"Cl,  -f  16  HCl  = 2 WnCl,  -f  2 KCl-f 
5 Fe"',Cl,  -h  8 H,e. 

The  strength  of  the  solution  of  permanganate  is  ascertained 
by  dissolving  5 grains  of  clean  iron  wire  in  boiling  hydrochloric 
acid,  diluting  the  solution  largely,  and  ascertaining  the  number  of 
divisions  of  permanganate  measured  from  a burette,  which  it  is 
capable  of  decolorizing. 

The  total  quantity  of  iron  present  in  an  ore  or  other  com- 
pound may  be  ascertained  by  a second  experiment  upon  a fresh 
portion  of  the  ore,  reducing  the  iron  to  the  state  of  a ferrous  salt 

* The  reducing  effect  of  sulphite  of  sodium  on  the  perchloride  of  iron  may  be  ex- 
plained by  the  following  equation,  from  which  it  will  be  seen  that  the  sulphite  is 
converted  into  sulphate  of  sodium  during  the  operation;  Fe'"2Cl6-l-H20-pN’a2S03 
=2  Fe''Cl2  + 2 HCl  + NaiSOi. 


ANALYSIS  OF  CAST  IKON,  STEEL,  AND  BAR  IKON.  529 

oy  means  of  zinc,  or  otherwise,  as  described  when  treating  of 
Penny’s  process. 

(779)  Analysis  of  Cast  Iron^  Steely  and  Bar  Iron. — For  this 
purpose  the  metal  must  be  reduced  to  a fine  state  of  subdivision 
by  means  of  a new  file,  previously  freed  from  oil  by  the  action  of 
a solution  of  potash ; the  fine  particles  detached  are  to  be  sifted 
through  a lawn  sieve.  Some  kinds  of  cast  iron  are  too  hard  to 
admit  of  being  filed;  they  must  be  crushed  in  a small  mortar 
made  of  hard  steel. 

1.  The  proportion  of  carbon  is  ascertained  by  mixing  from  50 
to  100  grains  of  finely-divided  iron  with  about  10  times  its  weight 
of  chromate  of  lead  or  of  oxide  of  copper ; then  placing  it  in  an 
apparatus  similar  to  that  shown  in  fig.  288,  p.  68,  and  burning  the 
iron  in  a very  gentle  current  of  oxygen ; the  carbonic  anhydride 
which  is  formed  is  collected  in  a solution  of  potash  placed  in  Liebig’s 
bulbs.  The  tube  which  contains  the  iron  is  gradually  heated  with 
charcoal,  commencing  at  the  extremity  nearest  the  potash  bulbs, 
and  the  fire  is  slowly  advanced  towards  the  other  end,  until,  when 
the  operation  is  completed,  the  whole  length  of  the  tube  is  red  hot. 
From  the  quantity  of  carbonic  anhydride  thus  obtained,  the  pro- 
portion of  carbon  in  the  iron  maybe  calculated.*  But  it  has  been 
already  explained  that  cast  iron  contains  carbon  partly  in  chemi- 
cal combination,  partly  in  a state  of  mechanical  mixture,  and  it 
is  important  to  determine  the  relative  proportions  of  the  carbon 
which  exist  in  these  different  conditions.  This  may  be  effected 
by  dissolving  the  iron  in  hydrochloric  acid.  In  this  operation  all 
the  carbon  which  was  chemically  ccmibined  with  the  iron  is  sepa- 
rated in  the  form  either  of  a gaseous  compound  of  carbon  and 
hydrogen,  or  as  a liquid  hydrocarbon  ; whilst  the  scales  of  graphite 
mechanically  diffused  through  the  metal  are  not  acted  upon  by  the 
acid,  and  are  left  in  a solid  form  mixed  with  silica.  In  order  to 
ascertain  the  proportion  of  graphite  in  this  residue,  it  is  collected 
on  a small  weighed  filter,  and  washed  with  ether,  to  remove  any 
adhering  liquid  hydrocarbon  ; the  filter  and  its  contents  are  dried 
at  212°,  and  weighed  in  a covered  crucible.  The  residue  is  then 
burned,  and  the  silica  which  remains  is  deducted  from  the  weight 
of  the  precipitate  collected  on  the  filter. 

2.  Nitrogen.— methods  were  employed  by  Boussingault 
for  ascertaining  the  amount  of  nitrogen  : the  first  consisted  in  oxi- 
dizing a known  weight  of  iron  (by  heating  it  to  redness)  in  a cur- 
rent of  steam,  condensing  the  water  after  it  had  passed  over  the  iron, 
and  determining  the  amount  of  ammonia  that  it  contained,  by  a 
method  previously  contrived  by  him  for  ascertaining  its  amount  in 
rain-water  : the  second  consisted  in  converting  a given  weight  of 
iron  into  sulphide,  by  heating  it  wfith  cinnabar,  and  measuring  the 
amount  of  nitrogen  in  the  gaseous  state  by  a method  exactly  ana- 
logous to  that  invented  by  l)umas  for  determining  the  amount  of 

* A less  rapid  but  accurate  plau  consists  in  digesting  the  iron  in  filings  or  in  frag- 
ments with  an  excess  of  normal  chloride  of  copper  (6uClo)  dissolved  in  water ; the 
iron  is  slowly  dissolved,  and  copper  precipitated  in  its  place,  whilst  the  carbon  is  loft 
in  a finely  divided  condition.  The  precipitate  must  bo  collected  on  a filter,  dried,  and 
transferred  to  a tube  in  which  it  is  burned,  as  above  directed. 

34 


530 


CHKOMIUM. 


nitrogen  in  an  organic  body.  For  details,  the  reader  is  referred  to 
the  papers  in  the  ComjyUs  Rendus  (vol.  lii.  pp.  1008  and  1250p 

3,  The  quantity  of  silicon  contained  in  the  iron  is  ascertained 
by  dissolying  the  metal  in  hydrochloric  acid  and  eyaporating  the 
solution  to  dryness,  moistening  with  concentrated  hydrochloric 
acid,  then  dissolying  all  the  soluble  matter  in  water,  and  collect- 
ing the  silica  on  a hlter  : from  this  residue,  after  the  graphite  is 
burned  off,  the  quantity  of  silicon  can  be  estimated,  100  parts  of 
silica  representing  16 ‘66  of  silicon. 

1.  Sul])liui\  P}LOspl\orus^2C[\^^  Arsenic.  — The  most  accurate 
mode  of  estimating  these  substances  consists  in  deflagrating  about 
50  grains  of  the  finely  diyided  iron  with  about  six  times  its  weight 
of  a mixture  of  5 parts  of  pure  nitre,  and  1 part  of  carbonate  of 
potassium,  in  a crucible  of  silyer,  or,  still  better,  of  gold.^  The 
phosphorus,  sulphur,  and  arsenic  are  thus  conyerted  into  phos- 
phoric, sulphuric,  and  arsenic  anhydrides,  which  form  salts  by  their 
action  upon  the  potash ; when  the  fused  mass  is  digested  in 
water  they  are  dissolyed,  whilst  the  peroxide  of  iron  remains  un- 
dissolyed.  The  filtered  solution  is  supersaturated  with  hydro- 
chloric acid,  and  the  sulphuric  acid  is  thrown  down  by  means  of 
chloride  of  barium  ; the  excess  of  barium  is  remoyed  by  adding 
sulphuric  acid,  and  the  arsenic  is  thrown  down  by  a current  of 
sulphuretted  hydi’ogen.  The  liquid,  filtered  from  sulphide  of 
arsenic,  is  now  neutralized  by  ammonia,  and  on  the  addition  of  a 
few  drops  of  solution  of  sulphate  of  magnesium,  the  phosphoric 
acid  is  gradually  separated,  on  standing,  as  the  crystalline  double 
phosphate  of  magnesium  and  ammonium. 

The  sesquioxide  of  iron  is  dissolyed  in  hydrochloric  acid,  and 
a current  of  sulphuretted  hydrogen  is  transmitted,  by  which  copper 
would  be  separated  as  sulphide ; the  filtrate  is  boiled  with  nitric 
acid,  and  the  iron  separated  from  manganese,  cobalt,  or  nickel, 
by  means  of  carbonate  of  sodium  in  the  manner  already  described 
(776). 

§ y.  Chromium:  ■0r=52-5;  or  Cr=26*27.  Sp.  Gr.  6*81. 

(780)  CnROiNnuM  is  a metal  which  is  but  sparingly  distributed 
oyer  the  earth.  Its  most  important  ore  is  the  chrome  ironstone, 
a compound  of  protoxide  of  iron  with  sesquioxide  of  chromium 
(FeO,  -Gr^Og),  which  is  generally  found  massiye  ; but  has  now  and 
then  lieen  met  with  crystallized  in  regular  octohedra  like  the  mag- 
netic oxide  of  iron,  to  which  it  corresponds  in  composition : it  is 
principally  supplied  from  Xorth  America  and  from  Sweden. 
Occasionally  the  metal  occurs  in  a higher  state  of  oxidation,  in 
combination  with  lead,  as  chromate  of  lead  (PbGrO,).  Indeed  it 
was  in  this  beautiful  mineral  that  Yauquelin,  in  the  year  1797, 
first  discoyered  the  existence  of  chromium. 

To  obtain  the  metal,  oxide  of  chromium  is  intimately  mixed, 
in  fine  powder,  with  charcoal,  and  made  up  into  a paste  with  oil ; 

* Any  traces  of  vanadium  or  of  chromium  would  also  be  oxidized,  and  on  digest* 
ing  the  mass  in  water  would  be  dissolved  out  in  the  alkaline  liquid. 


COMPOUNDS  OF  CHEOMIUM  WITH  OXYGEN. 


531 


it  is  then  placed  in  a cnicible  lined  with  charcoal,  and  the  cover 
of  the  crucible  is  luted  on,  after  which  it  is  exposed  for  two  liours 
to  the  heat  of  a good  wind  furnace : an  agglomerated  mass  of 
metallic  appearance  is  thus  obtained.  It  is  not  pure  chromium, 
but  consists  of  a combination  of  carbon  with  the  metal.  Chro- 
mium obtained  by  this  method  is  very  difficult  of  fusion  ; it  gene- 
rally forms  a porous  mass  composed  of  brilliant  grains,  which  are 
hard  enough  to  scratcli  glass.  In  this  state  it  has  a specific 
gravity  of  about  5 ’9,  which  is  no  doubt  lower  than  it  would  be 
after  complete  fusion.  Deville  found,  on  reducing  chromium 
from  pure  sesquioxide  by  means  of  charcoal  from  sugar,  in  quan- 
tity insufficient  for  complete  reduction,  that  the  mass  underwent 
partial  fusion,  but  could  not  be  melted  into  a compact  button 
even  at  a temperature  sufficient  to  fuse  and  volatilize  platinum. 
If  ignited  wfith  the  hydrated  alkalies,  alkaline  carbonates,  or 
nitrates,  chromium  is  rapidly  converted  into  chromic  acid,  which 
furnishes  a chromate  by  action  on  the  alkaline  base.  It  may, 
however,  be  heated  to  redness  in  the  open  air  without  becoming 
oxidized,  and  is  not  acted  on  by  any  acid  except  hydrofluoric  acid, 

Fremy  transmits  the  vapour  of  sodium  over  chromic  chloride, 
which  is  placed  in  a porcelain  tray,  and  heated  to  redness  in  a 
porcelain  tube  : the  chromium  is  obtained  in  brilliant  crystals, 
which  belong  to  the  regular  system  ; they  are  insoluble  in  aqua 
regia.  Wohler  reduces  chromium  from  the  violet  chloride  by 
fusing  it  with  twice  its  weight  of  zinc  under  a flux  of  the  mixed 
chlorides  of  potassium  and  sodium  : nitric  acid  is  employed  to 
dissolve  tlie  zinc,  and  the  chromium  is  left  as  a grey  brilliant 
crystalline  powder  of  sp.  gr.  6'81.  If  chromic  chloride  be  mixed 
with  potassium,  and  heated  in  a covered  crucilile,  another  modi- 
fication of  chromium  may  be  procured  ; after  washing  the  residue 
with  water,  the  metal  remains  in  the  form  of  a dark -grey  powder ; 
which  assumes  a metallic  lustre  under  the  burnisher.  This  pul- 
verulent chromium,  if  heated  in  the  air,  takes  fire  below  redness, 
and  burns  brilliantly  : it  is  oxidized  with  great  violence  by  nitric 
acid,  sometimes  becoming  incandescent  during  the  action  ; and  it 
is  dissolved  by  hydrochloric  acid  and  diluted  sulphuric  acid,  with 
evolution  of  hydrogen. 

Metallic  chromium  has  not  been  applied  in  the  arts,  but  its 
sesquioxide  and  many  of  the  chromates  are  highly  valued  as 
colouring  materials,  both  in  painting  on  porcelain  and  in  calico- 
printing. 

(781)  Compounds  of  Chromium  with  Oxygen. — Chromium 
forms  four  well-marked  oxides  : a protoxide,  OrO,  and  a sesqui- 
oxide, Or^Oa,  both  capable  of  forming  salts  with  acids  ; an  inter- 
mediate oxide  (Ci’0,0ra03),  corresponding  to  the  magnetic  oxide 
of  iron ; and  a stable  anhydride  (OrOg)  which  by  its  action  on 
bases  forms  salts  corresponding  to  the  manganates  and  ferrates. 
It  also  appears  to  be  probable  that  a perchromic  acid  (IlOrOd 
exists ; at  least,  a blue  liquid,  which  is  soluble  in  ether,  is  obtainea 
on  pouring  peroxide  of  hydrogen  into  a solution  of  chromic  acid; 
but  none  of  its  compounds  are  known. 


532 


SESQnOXIDE  OF  CnSOMITM. 


Protoxide  of  Chromium^  or  Chromoxis  Oxide  (OrO  = 68'5, 
or  CrO  = 34‘3). — This  oxide  is  known  only  in  the  hydrated  con- 
dition. It  is  obtained  as  dark-brown  precipitate  on  adding  caustic 
potash  to  a solution  of  the  chromons  chloride ; it  absorbs  oxygen 
with  great  avidity,  and  even  decomposes  water  with  extrication 
of  hyd  rogen,  and  then  becomes  converted  into  the  intermediate 
hydrated  oxide  (C^rOj-Gr^OjjII.O),  which  is  of  the  colour  of 
Spanish  snnff. 

The  protoxide  of  clirominm  forms  a double  sulphate  witli 
sulphate  of  potassium  (Or'K^  2 SO^,  6 H^O),  corresponding  to  the 
double  sulphate  of  iron  and  potassium  both  in  form  and  composi- 
tion. The  crystals  are  of  a fine  blue  colour. 

(782)  Sesquioxide  of  Chromium^  or  Chromic  Oxide  (■0r2O3= 
153,  or  Cr.jOg  ==  76*5)  Sj).  Gr.  cryst.  5*21 : Comp,  in  100  parts^ 
Or,  68*68  ; O,  31*3. — This  oxide  is  obtained  as  a greyish-green 
hydrate,  by  boiling  with  alcohol  a solution  of  anhydro-chromate 
(bichromate)  of  potassium  acidulated  with  sulphuric  acid.  The 
alcohol  deprives  the  chromic  acid  of  half  its  oxygen,  and  the 
liquid  becomes  green  from  the  formation  of  chromic  sulphate.  A 
current  of  sulphurous  acid  may  be  employed  instead  of  alcohol 
in  the  reduction  of  chromic  acid.  On  the  addition  of  ammonia, 
a bulky,  gelatinous,  bluish-green  precipitate  of  the  hydrated  oxide 
is  produced,  which  retains  alkali  with  great  obstinacy  even  when 
boiled  with  water.  In  this  form  it  is  freely  soluble  in  acids,  and 
forms  salts,  the  solutions  of  wliich  are  of  a green  colour;  but  they 
do  not  crystallize.  (See  note  below.) 

Sesquioxide  of  chromium  gives  rise  also  to  another  set  of  solu- 
ble salts,  which  are  of  a violet  colour  and  crystallize  readily.  If 
these  violet -coloured  salts  be  precipitated  by  ammonia,  they  give 
a bluish-green  hydrated  oxide,  which  if  redissolved  in  an  acid 
without  the  application  of  heat,  reproduces  the  violet-coloured 
salts.  This  precipitated  oxide  becomes  green  by  the  action  of 
concentrated  saline  solutions  upon  it.  If  a solution  of  one  of  the 
violet  salts  be  heated  to  the  boiling-point,  or  a little  short  of  it, 
the  salt  at  once  becomes  green. The  hydrated  oxide  from  the 
violet  salts  is  the  metachromic  oxide  of  Fremy  (-Gr^Og,  9 H2O,  when 
dried  in  vacuo).,  and  is  soluble  in  excess  of  ammonia  in  presence 
of  acetic  acid : but  according  to  Siewert,  who  has  lately  exammed 
this  precipitate  with  great  care,  it  is  not  a pure  oxide,  but  a com- 
pound of  the  hydrated  oxide  with  ammonia  and  one  of  the  salts 
of  ammonium.  It  is  soluble  in  excess  of  ammonia  and  acetic 
acid,  owing  to  the  strong  tendency  of  chromic  oxide  and  ammonia 

* This  change  of  colour  from  violet  to  green  has  been  long  known,  and  was  ac- 
counted for  by  Berzehus  upon  the  admission  of  two  distinct  hydrates  of  chromic  ox- 
ide, one  green,  the  other  violet.  But  Siewert  appears  to  have  distinctly  proved  that 
one  form  of  the  oxide,  the  blue  hydrate,  only  exists.  The  green  precipitate  in  every 
instance  is  a compound  of  the  pure  oxide  with  potash  or  soda.  It  is  true  that  the 
violet  solutions  of  the  pure  salts  become  green  by  boiling,  but  this  Siewert  has  traced 
to  the  conversion  of  the  normal  salt  into  two  soluble  s^ts.  each  green,  and  capable 
of  co-existing  in  the  liquid.  One  of  these  salts  contains  excess  of  acid,  the  other 
excess  of  base  {Liebig's  Ann.  cxxvL  86).  Solutions  of  the  green  salts  at  once  become 
blue  or  violet,  if  acidulated  by  the  addition  of  nitric  acid.  The  investigation  of  these 
compounds  is  beset  with  unusual  difficulties. 


SESQnOXIDE  OF  CHKOMITJM. 


533 


to  produce,  in  the  presence  of  acetic  acid,  double  salts,  wliicli  are 
not  susceptible  of  decomposition  by  ammonia.  If  the  original 
precipitate  be  thoroughly  washed  till  all  the  soluble  salts  are  re- 
moved from  it,  and  then  air-dried,  it  is  no  longer  soluble  in  acetic 
acid,  or  in  other  diluted  acids 

The  only  way  to  ensure  the  production  of  a pure  hydrated 
chromic  oxide,  according  to  Siewert,  consists  in  precipitating  a 
soluble  chromic  salt  by  the  addition  of  ammonia,  and  boiling  it 
with  excess  of  tlie  alkali.  A light-blue  precipitate  is  thus  ob- 
tained, which,  when  well  washed  and  dried  in  air  over  oil  of  vit- 
riol, consists  of  (Or^Oa,  7 H^O).  If  dried  in  vacuo,  it  retains  only 
4 IIjO,  and  if  dried  in  a current  of  hydrogen  at  400°  it  retains 
TIjO ; it  then  forms  a blue  powder  with  a greenish  lustre,  and  is 
insoluble  in  boiling  diluted  hydrochloric  acid.  Hydrates  of  pot- 
ash and  soda  precipitate  the  hydrated  sesquioxide,  and  redissolve 
it  if  added  in  excess,  forming  a green  solution,  from  which,  on 
boiling,  the  whole  of  the  sesquioxide  of  chromium  is  separated  as 
a green  hydrate,  which  retains  a portion  of  alkali.  Indeed  potash 
and  soda  have  so  strong  a tendency  to  combine  with  chromic  ox- 
ide that  if  either  of  these  alkalies  be  used  to  precipitate  the  oxide 
from  its  salts,  or  if  salts  of  potash  or  soda  be  present  when  am- 
monia is  employed  as  the  precipitant,  the  green  precipitate  always 
contains  one  of  the  fixed  alkalies.  When  the  hydrated  oxide  is 
heated,  it  parts  with  its  water  below  redness,  and  if  heated  a 
little  beyond  this  point,  it  suddenly  becomes  incandescent,  shrinks 
considerably  in  bulk,  and  is  no  longer  attacked  by  acids. 

Besides  the  soluble  variety  of  the  salts  of  chromium,  an  anhy- 
drous, insoluble  series  is  known,  corresponding,  it  would  seem,  to 
the  dense  and  comparatively  inert  modification  of  the  metal  itself. 

Anhydrous  green  oxide  of  chromium  is  not  decomposed  by 
heat,  and  hence  is  used  as  a green  colour  in  enamel  ])ainting.  It 
is  usually  prepared  for  this  purpose  by  decomposing  basic  mercur- 
ous chromate  by  a red  heat : half  the  oxygen  of  the  anhydride  is 
expelled  along  with  the  oxide  of  mercury.  Chromate  of  ammo- 
nium may  be  employed  instead  of  chromate  of  mercury  with 
equally  good  results.  Another  method  consists  in  strongly  igniting, 
in  a covered  crucible,  an  intimate  mixture  of  4 parts  of  powdered 
anhydro-chromate  of  potassium  and  1 part  of  starch  ; the  carbon- 
ate of  potassium  resulting  from  the  decomposition  is  washed  out, 
and  the  sesquioxide  of  chromium  which  remains,  after  undergo- 
ing a second  calcination,  yields  a beautiful  clear  green  colour. 
There  are  also  a variety  of  otlier  modes  of  obtaining  it.  Sesqui- 
oxide of  chromium  is  the  colouring  ingredient  in  greenstone,  in 
the  emerald,  in  pyrope,  and  in  several  other  minerals.  The^An/: 
colour  used  on  earthenware  is  prepared  by  heating  to  redness  a 
mixture  of  30  parts  of  peroxide  of  tin,  10  of  chalk,  and  1 ])art 
of  chromate  of  potassium;  the  ywoduct  is  then  finely  powdered, 
and  washed  with  weak  hydrochloric  acid ; a beautiful  rose-tint  is 
thus  obtained. 

A beautiful  green  y)igment  known  as  vert  de  Gnvjnet  is  manu- 
factured on  a large  scale  by  calcining  anhydro-chromate  of  potas- 


534: 


CHKOMIC  AGED,  OR  CHKOMIC  ANHYDRIDE. 


sium  with  3 times  its  weight  of  crystallized  boracic  acid : oxy- 
gen and  water  are  expelled,  and  on  washing  the  residue  with 
water  a basic  borate  of  chromium  is  left,  while  boracic  acid  and 
borate  of  potassium  are  dissolved  out. 

(783)  Chrome  iron-stone  (FeO,'0r2O3 ; 8}}.  Gr.  4*5)  is  the 
principal  ore  of  chromium ; it  corresponds  in  composition  to  the 
brown  oxide  of  chromium  and  to  the  magnetic  oxide  of  iron ; 
part  of  the  iron  is,  however,  generally  displaced  by  tlie  isomor- 
phous  metal  magnesium,  and  part  of  the  chromium  by  aluminum. 
Like  magnetic  iron-ore,  chrome  iron-stone  often  crystallizes  in 
octohedra,  which  have  about  the  same  hardness  as  felspar.  Chrome 
iron-stone  is  scarcely  attacked  by  any  of  the  acids.  It  is  infusible 
in  the  furnace,  and  when  heated  absorbs  oxygen  from  the  air ; 
this  oxidation  takes  place  rapidly  when  it  is  powdered  and  mixed 
with  a carbonate  of  one  of  the  alkalies  or  alkaline  earths,  chro- 
mate of  the  base  being  formed.  100  parts  of  this  ore,  if  pure, 
contain  48*27  of  chromium,  and  yield  89*6  of  chromic  acid. 

(784)  Fremy  believes  in  the  existence  of  a series  of  ammo- 
niated  compounds  of  chromium  presenting  some  analogy  with 
those  of  cobalt,  but  other  chemists  have  not  confirmed  his  re- 
sults. If  a solution  of  sal  ammoniac  containing  free  ammonia  be 
digested  on  the  hydrated  oxide  precipitated  by  ammonia  from  one 
of  the  violet  salts  of  chromium,  the  oxide  is  dissolved,  and  a fine 
violet-coloured  solution  is  formed,  owing  to  the  formation  of  a 
double  salt  of  ammonium  and  chromium.  If  the  solution  be 
evaporated  to  dryness,  it  furnishes  a fine  violet  compound,  which 
is  very  soluble  in  water,  has  scarcely  any  alkaline  reaction,  and 
gives  no  precipitate  with  nitrate  of  silver ; the  ordinary  tests  of 
chromium  do  not  show  the  presence  of  the  metal.  . When  the 
solution  is  boiled,  ammonia  is  expelled  and  hydrated  oxide  of 
chromium  is  precipitated. 

(785)  Chromic  Anhydride,  or  Chromic  Acid  (-01*03= 100*5, 
or  CrO3  = 50*3);  Sp.  Gr.  2*676. — There  are  several  modes  of  ob- 
taining this  compound.  1. — The  simplest  consists  in  mixing  4 
measures  of  a cold  saturated  solution  of  anhydro-chromate  of 
potassium  with  5 of  oil  of  vitriol : as  the  liquid  cools,  the  chromic 
anhydride  separates  in  beautiful  crimson  needles  ; for  though  very 
soluble  in  water,  tliis  compound  has  the  peculiarity  of  being  nearly 
insoluble  in  sulphuric  acid  of  sp.  gr.  1*55,  but  is  freely  dissolved 
by  it  either  in  a more  concentrated  or  in  a more  dilute  condition. 
The  crystals  are  allowed  to  dry  upon  a porous  tile,  under  a bell- 
glass.  A good  deal  of  sulphuric  acid,  however,  still  adheres  to 
them ; in  order  to  remove  it,  the  crystals  should  be  dissolved  in 
water,  and  a solution  of  acid-chromate  of  barium  should  be  added 
in  quantity  just  sufficient  to  throw  down  the  whole  of  the  sul- 
phuric acid  as  sulphate  of  barium  : the  solution  may  be  recrystal- 
lized by  evaporation  in  vacuo.  2. — Chromic  anhydride  may  also 
be  prepared  from  the  fiuoride  of  chromium,  by  decomposing  this 
compound  with  water  (790). 

Chromic  anhydride  is  easily  freed  from  water  by  drying  it  at 
a gentle  heat.  While  hot  it  is  black,  but  it  becomes  dark  red  on 


THE  CHROMATES. 


535 


cooling : at  about  400°  it  fuses,  and  if  heated  more  strongly,  be- 
comes vividly  incandescent,  and  is  converted  into  the  sesquioxide 
with  disengagement  of  oxygen.  The  anhydride  deliquesces  when 
exposed  to  the  air.  Its  solution  has  a sour,  metallic  taste,  and  pos- 
sesses considerable  oxidizing  power,  from  the  facility  with  which 
it  is  reduced  to  sesquioxide  of  chromium.  When  heated  with 
hydrochloric  acid,  chlorine  is  evolved  and  chloride  of  chromium  is 
formed  ; 2 -GrO-a-f-  12  HCl=Gr2Cl6+  6 + 3 Clj.  The  anhy- 

dride forms  more  than  one  crystalline  compound  with  sulphuric 
acid ; these  compounds  are  decomposed  by  water. 

(786)  Chromates. — Chromic  acid  forms  3 classes  of  salts — 
basic,  normal,  and  acid.^  The  chromates  of  the  alkali-metals 
are  soluble  in  water ; the  normal  salts  have  the  general  formula 
; they  have  a yellow  colour ; the  acid  salts  are  of  a 
bright  orange ; the  most  important  of  these  salts  are  the  chro- 
mate and  anhydro-chromate  of  potassium,  from  which  the  other 
chromates  are  generally  obtained. 

Anhydro-chromate  of  potassium  (K^O  2 OrOg,  or  K^Gr^O^ 
=295);  or  Bichromate  of  potash  (KO,  2 Cr03=147’5);  Sp.  Gr. 
2*624:  Comp,  in  parts 31*86;  Gi'Gj,  68*14. — This  salt 
crystallizes  in  large  red,  transparent,  anhydrous  four-sided  tables. 
It  fuses  below  redness,  and  as  it  cools  splits  to  pieces  from  the 
inequality  of  its  contraction.  By  heating  the  anhydro-chromate 
to  bright  redness,  normal  chromate  and  green  oxide  of  chromium 
are  formed,  whilst  oxygen  escapes.  It  requires  about  10  times  its 
weight  of  water  at  60°  for  its  solution. 

In  order  to  procure  the  anhydro-chromate  of  potassium,  chrome 
iron-stone  is  heated  to  redness  and  quenched  in  cold  water,  by 
which  means  it  is  rendered  friable,  and  is  then  reduced  to  an 
extremely  fine  powder,  and  heated  to  bright  redness  in  a current 
of  air  in  a reverberatory  furnace  with  a mixture  of  chalk  and 
carbonate  of  potassium,  the  mixture  being  constantly  stirred  to 
hasten  the  oxidation.  When  this  is  complete,  the  product  is 
digested  in  water,  carbonate  of  potassium  being  added,  if  neces- 
sary, to  decompose  any  chromate  of  calcium  which  may  have 
been  formed,  and  the  yellow  solution  is  drawn  ofi*  from  the  in- 
soluble matter ; it  is  then  supersaturated  with  nitric  acid  ; a por- 
tion of  silica  is  thus  precipitated,  and  after  this  has  been  sepa- 
rated, tlie  liquid,  on  evaporation,  yields  crystals  of  anhydro- 
chromate  of  potassium,  which  are  purified  by  recrystallization. 
The  addition  of  chalk  in  the  furnace  favours  the  oxidation  by 
])reserving  the  mass  in  a porous  condition  : if  potash  alone  were 
used,  it  would  fuse,  and  the  chrome  ore  would  fall  to  the  bottom. 

According  to  Schweitzer  several  double  salts  may  be  formed 
by  digesting  anhydro-chromate  of  potassium  with  an  equivalent 
of  some  base,  such  as  lime  or  magnesia.  The  chromate  of  mag- 
nesium and  potassium  crystallizes  in  obli(pie  rhombic  prisms 

* Chromic  acid  is  remarkable  for  the  anhydro-salts  which  it  forms  witli  potash ; 
like  iodic  acid,  it  yields  three  salts  with  this  base:  1,  that  known  as  the  chromato 
( KaO.-erOs) ; 2,  the  bichromate  (K-^O,  2 ^rOa);  and  3,  the  terchromato  of  potash 
(KaO,  3 €r03). 


536 


THE  CHROMATES. 


(K^Mg  2 OrO^ . 2 1120),  and  a salt  of  similar  composition  may  he 
obtained  with  calcium  : but  there  is  no  analogy  between  these 
double  chromates  and  the  magnesian  double  sulphates. 

If  a solution  of  carbonate  of  potassium  be  added  to  the  anhy- 
dro-chromate,  until  it  becomes  of  a pale  yellow  colour,  carbonic 
anhydride  is  expelled,  and  the  normal  or  neutral  chromate  (K^OrO^ 
= 19d-5,  or  KO,Cr()3  = 97'3  ; sp.  gr.  2-682)  is  formed.  This  salt  is 
soluble  in  about  twice  its  weight  of  cold  water,  and  still  more 
freely  so  in  boiling  water  ; it  has  a pure  and  intense  yellow  col- 
our. A very  small  quantity  of  the  salt  suffices  to  impart  a yel- 
low tinge  to  a considerable  volume  of  water.  By  evaporation  of 
its  solution  chromate  of  potassium  may  be  obtained  with  some  diffi- 
culty, in  transparent,  yellow,  anhydrous  prisms,  which  are  isomor- 
phous  with  those  of  sulphate  of  potassium  : at  a red  heat  it  fuses 
without  undergoing  decomposition.  A terchromate  of  potassium 
(KjO,  3 OrOg,  or  KO,  3 CrOg),  also  anhydrous,  was  obtained  by 
Mitscherlich  in  deep  red  crystals,  by  adding  an  excess  of  nitric  acid 
to  a solution  of  the  anhydro-chromate,  and  allowing  it  to  evaporate. 

Chromate  of  sodium  (ISTa^OrO^  . 10  1120=162-5 -f  180,  or 
N’a0,Cr03 . 10  Aq=81-3-f  90)  may  be  obtained  by  a process  sim- 
ilar to  that  employed  in  preparing  chromate  of  potassium  : it  forms 
efflorescent  crystals : an  acid-chromate  of  sodium  may  likewise  be 
formed. 

Chromate  of  calcium  is  soluble,  as  is  also  the  acid-chromate^ 
which  is  formed  in  many  chrome  works  as  a preliminary  stage  in 
the  manufacture  of  the  chromates.  Jacquelain  decomposes  chrome 
ore  by  roasting  it  in  line  powder  intimately  mixed  with  chalk, 
grinds  the  roasted  mass  with  water,  and  adds  sulphuric  acid  till 
the  liquid  has  an  acid  reaction,  in  which  case  acid-chromate  of 
calcium  is  formed,  and  remains  in  solution.  Chromate  of  harium 
(BaOrO^ ; sp.  gr.  3-90)  is  a canary-yellow  insoluble  powder. 
Chromake  of  strontium  is  yellow  and  but  slightly  soluble. 

Chromate  of  lead  (PbCr04=324-5,  or  Pb0,Cr03=162-3  ; 
sp.  gr.  5-653)  forms  the  pigment  called  ‘ chrome  yellow.’  It  is 
obtained  by  precipitating  a somewhat  dilute  solution  of  acetate 
of  lead  by  one  of  chromate  or  of  anhydro-chromate  of  potassium. 
Chromate  of  lead  is  insoluble  in  water  and  in  acids,  but,  like  all 
the  insoluble  salts  of  lead,  it  is  dissolved  by  a large  excess  of  hy- 
drate of  potash  or  of  soda.  When  heated  to  400°  or  500°,  its 
colour  becomes  reddish  brown  ; at  a higher  temperature  it  fuses, 
and  when  heated  still  more  strongly  it  gives  off  about  4 per  cent, 
of  oxygen,  sesquioxide  of  chromium  and  basic  chromate  of  lead 
being  formed;  8 PbOrO,  = 4 (PbOrO„PbO)  + 2 01-303 -f  3 O2. 
Fused  chromate  of  lead  when  reduced  to  powder  is  sometimes 
advantageously  substituted  for  oxide  of  copper  in  the  combustion 
and  analysis  of  organic  substances  very  rich  in  carbon.  A dibasic 
chromate  of  lead  (2  Pb0,0r03 ; sp.  gr.  6-266),  of  a splendid 
scarlet  colour,  may  be  obtained  by  boiling  a solution  of  the  yellow 
chromate  of  lead  with  half  an  equivalent  of  lime,  or  by  adding 
to  a solution  of  nitrate  of  lead  a solution  of  chromate  of  potas- 
sium, with  which  an  additional  equivalent  of  hydrate  of  potash  has 


SULPHIDE  OF  CnEO:MirM CHLORIDES  OF  CHROMim^I.  537 


been  previously  mixed.  It  may  be  obtained  of  a still  more  bril- 
liant colour  by  fusing  one  part  of  the  normal  chromate  of  lead 
with  5 parts  of  nitre ; chromate  of  potassium  and  dibasic  chro- 
mate of  lead  are  formed ; the  salt  of  potassium  may  be  removed 
by  washing.  This  salt  is  used  to  impart  a permanent  orange  to 
calico  ; it  is  easily  fixed  upon  the  fabric  by  dyeing  it  yellow  with 
chromate  of  lead  and  then  boiling  it  with  lime-water,  by  which 
half  the  chromic  acid  is  abstracted  and  the  dibasic  chromate  is 
left  attached  to  the  fibre. 

Basic  mercurous  chromale  (3  IIg20r04,IIg20)  falls  as  an 
orange-coloured  insoluble  precipitate  on  adding  basic  mercurous 
nitrate  to  a soluble  chromate.  Chromate  of  silver  (AggOrO^ ; 
sp.  gr.  5*770)  is  of  a dark-red  colour,  the  tint  of  which  is  deeper 
if  the  solutions  be  mixed  whilst  hot : it  is  crystalline,  and  sparingly 
soluble. 

An  anhydro-chromate  of  silver  is  obtained  in  beautiful  crimson 
tables  by  heating  metallic  silver  with  anhydro-chromate  of  potas- 
sium and  sulphuric  acid,  chrome-alum  being  formed  during  the 
l^rocess : — 

3 Ag2  + 4 KjOr^O,  -f  7 112804= 3 Ag20r20,-f  2 (KOr  2 SOJ-f 
3 1x2804 -f  7 H2O. 

Chromic  acid  is  the  colouring  matter  of  the  ruby. 

Bichromate  of  Chloride  of  Potassium  (KCl,0r03  ? or  K2'^i’^45 
0r02Cl2 ; Sp.  Gr.  2*466). — This  remarkable  compound  may  be 
obtained  crystallized  in  orange-coloured  needles,  by  dissolving  3 
parts  of  anhydro-chromate  of  potassium  and  4 of  hydrochloric 
acid  in  a little  water  at  a gentle  heat,  and  allowing  it  to  cool : a 
large  quantity  of  water  decomposes  the  salt. 

(787)  Sesquisulphide  of  Chromium  (■01*283  = 201). — This  com- 
pound may  be  obtained  in  black  shining  scales,  resembling  plum- 
bago in  appearance,  when  the  vapour  of  bisulphide  of  carbon  is 
transmitted  over  sesquioxide  of  chromium  strongly  heated  in  a 
]>orcelain  tube.  The  attraction  of  chromium  for  sulphur  is  but 
slight.  If  tlie  sulphide  of  ammonium  be  mixed  with  a chromic 
salt,  the  hydrated  sesquioxide  of  the  metal  is  precipitated,  whilst 
sulphuretted  hydrogen  is  evolved. 

(788)  Compounds  of  Chromiuim  with  Chlorine. — Chromium 
forms  two  chlorides,  chromous  chloride,  0rCl2,  and  chromic 
chloride,  OrjClgi  the  latter  is  the  more  important.  It  also  forms 
an  oxychloride  (0rCl2O2),  frequently  termed  chlorochromic  acid. 

Chromous  chloride  (religot’s  protochloride,  0rCl2  = 123*5,  or 
CrCl  = 61*7)  is  obtained  by  heating  the  chromic  chloride  to 
redness  in  a current  of  dry  hydrogen  (carefully  freed  from  every 
trace  of  oxygen)  ; it  is  a white  substance  which  is  readily  dis- 
solved by  water,  forming  a blue  solution  which  rapidly  absorbs 
oxygen,  and  becomes  green  : like  ferrous  chloride,  it  absorbs 
nitric  oxide  quickly  and  becomes  brown. 

Chromic  Chloride^  or  Sesguichloride  of  Chromium  (0r2Cle  = 
318,  or  Cr2Cl3  = 159.) — When  a current  of  dry  chlorine  is  trans- 
mitted over  an  intimate  mixture  of  finely  divided  sesquioxide  of 


538 


CHLOEOCHEOMIC  ACID FLUOEIDE  OF  CHEOMITJM. 


cliromium  and  charcoal,  heated  to  redness  in  a glass  tube,  beau- 
tiful pale  violet-coloured  scales  of  anhydrous  chromic  chloride 
sublime.  When  rubbed  upon  the  skin  they  have  a soapy  feel ; 
they  are  quite  insoluble  in  cold  water,  but  by  boiling  them  with 
water  for  some  time  a green  solution  is  gradually  formed.  Sul- 
phuric and  hydrochloric  acids,  and  even  aqua  regia,  do  not  dissolve 
them.  It  is,  however,  very  remarkable  that  the  change  from  this 
insoluble  to  the  soluble  green  variety  is  effected  in  a few  moments 
with  extrication  of  heat,  by  the  addition  of  a minute  quantity  of 
the  chromous  chloride  to  the  insoluble  chloride  when  it  is  sus- 
pended in  water.  When  the  green  hj^drated  sesquioxide  of  chro- 
mium is  dissolved  in  hydrochloric  acid  a similar  green  solution  is 
formed ; the  liquid  furnishes,  by  spontaneous  evaporation,  green 
crystals,  which  may  be  represented,  according  to  Peligot,  as  con- 
sisting of  (0r202Cl2  4 HCl,  10  H^O) ; for  it  is  singular  that  only 
two-thirds  of  the  chlorine  which  this  solution  contains  is  precipi- 
tated when  it  is  mixed  with  nitrate  of  silver  {^Ann.  de  Chimie^ 
III.  xii.  536,  xiv.  239,  and  xvi.  294).  A soluble  violet  chloride  of 
the  metal  which  contains  the  same  proportion  of  chlorine  may  be 
formed  by  precipitating  the  violet-coloured  sulphate  of  chromium 
by  an  equivalent  quantity  of  chloride  of  barium : nitrate  of  silver 
precipitates  the  whole  of  the  chlorine  from  this  solution. 

Several  oxychlorides  of  chromium  may  be  formed. 

(789)  ChlorochromiG  Acid  (OrChO^);  Sp.  Gr.  of  'oapoui% 
5*52;  of  liquid^  I'Tl ; ALol  ml.  | | | ; Boiling-pt.  250°. — This 
is  a dense  red  liquid,  which  emits  copious  red  fumes  of  a suffocat- 
ing odour ; it  is  immediately  decomposed  by  water  into  chromic 
and  hydrochloric  acids.  When  dropped  into  a strong  solution  of 
ammonia  or  into  alcohol,  it  bursts  into  flame  from  the  intensity  of 
the  reaction.  If  the  vapour  be  passed  through  a tube  of  porce- 
lain heated  to  redness,  beautiful  rhombohedral  crystals  of  sesqui- 
oxide of  chromium  are  formed : these  crystals  are  isomorphous 
with  those  of  corundum ; they  are  hard  enough  to  cut  glass,  and 
are  of  a very  dark  green  colour.  During  their  formation, 
oxygen  and  chlorine  escape,  in  consequence  of  the  following  reac- 
tion ; 4 OrCl^O^  = 2 Or^Og  -f  4 Cl^ 

Chlorochromic  acid  is  analogous  to  the  chloromolybdic,  chloro- 
tungstic,  and  chlorosulphuric  acids  in  composition,  and  in  the 
products  which  it  yields  when  decomposed.  In  order  to  prepare 
it,  10  parts  of  common  salt  are  fused  with  17  of  chromate  of  po- 
tassium ; the  melted  mass,  when  cold,  is  broken  into  fragments, 
and  gently  heated  in  a retort  with  30  parts  of  oil  of  vitriol : the 
chlorochromic  acid  distils  over  readily. 

(790)  Fluoeide  of  Cheomium  (OrF^  = 166*5,  or  CrFg  = 83*3) 
is  obtained  by  distilling  4 parts  of  chromate  of  lead,  3 of  powdered 
fluor-spar,  and  8 of  strong  sulphuric  acid,  in  a platinum  retort ; 
sulphates  of  lead  and  calcium  are  formed,  and  the  fluoride  distils 
as  a deep  red  vapour,  which  by  a low  temperature  is  reduced  to 
a blood-red  liquid  ; PbOrO,  + 3 OaF^  + 4 H^SO,  = PbSO,  -f  3 
OaSO^  -f  4 HgO  -h  OrFa.  Any  other  chromate  may  be  substi- 
tuted for  chromate  of  lead  in  this  operation. 


NITEEDE  AND  SULPHATES  OF  CHEOMIUM. 


539 


Fluoride  of  cliromium  forms  deep-red  fumes  of  chromic  anhy- 
dride the  moment  that  it  comes  into  the  air,  as  it  is  instantly  de- 
composed by  moisture : by  conducting  the  vapour  into  a moistened 
platinum  crucible  the  vessel  becomes  speedily  filled  with  volumi- 
nous crystals  of  chromic  anhydride : hydrofluoric  acid  is  formed 
at  the  same  time,  and  may  be  expelled  from  the  chromic  anhy- 
dride by  a gentle  heat.  The  action  of  water  upon  the  fluoride 
may  be  thus  represented  ; OrF^  -f  3 F[20  = OrOg  -f  6 HF. 

(791)  h^iTEiDE  OF  Cheomium  (-01*3x7,?  ; Schrotter). — If  the 
anhydrous  violet  chloride  of  chromium  be  heated  in  a current  of 
dry  ammoniacal  gas,  chloride  of  ammonium  sublimes,  whilst  the 
chloride  of  chromium  is  decomposed,  emitting  a purple  light,  and 
an  insoluble  chocolate-brown  compound  of  chromium  and  nitro- 
gen is  left.  If  it  be  heated  to  between  300°  and  400°  in  a cur- 
rent of  oxygen,  it  takes  fire  and  burns  wflth  a beautiful  red  light 
into  oxide  of  chromium,  emitting  nitrogen  gas  mixed  with  red 
fumes  of  peroxide  of  nitrogen. 

(792)  Sulphates  of  Cheomium  (Or^  3 SO,  = 393,  or  Cr^Og, 

3 SO3  = 196*5) — There  are  three  varieties  of  this  salt.  One  of 
them  is  a green  soluble  compound,  which  is  freely  dissolved  by 
alcohol,  but  does  not  crystallize.  It  is  view’'ed  by  Siewert  as  a 
mixture  of  a basic  and  an  acid  sulphate  {Liebig'’ s Annal.  cxxvi. 
95).  It  may  be  obtained  by  boiling  hydrated  oxide  of  chromium 
with  sulphuric  acid.  A second  modification,  of  a violet  colour, 
may  be  procured  by  digesting  8 parts  of  the  hydrated  oxide  of 
chromium  dried  at  212°  with  9 parts  of  oil  of  vitriol,  in  a shallow 
vessel  exposed  to  the  air  at  ordinary  temperatures.  The  mixture 
gradually  absorbs  water,  and  becomes  converted  in  two  or  three 
weeks’  time  into  a greenish-blue  mass  of  crystals  : if  these  crystals 
are  dissolved  in  water  they  form  a blue  liquid  from  which  alcohol 
separates  the  salt  in  small  octohedra  containing  15  Ft^O.  This 
modification  forms  with  sulphate  of  potassium,  or  with  sulphate 
of  ammonium,  a beautiful  violet  double  salt  (chrome  alum)  which 
crystallizes  by  spontaneous  evaporation  in  bold  octohedra,  and 
corresponds  in  form  and  composition  to  ordinary  alum,  the 
formula  of  the  potassium-salt  being  (K0r  2 SO,,  12  II2O,  or 
K0,S03  • 3 SO3,  24  IIO),  sp.  gr.  1*826.  The  solution 

of  the  violet  sulphate,  when  boiled,  becomes  green  ; and  if  the 
crystals  of  chrome  alum  be  dissolved  in  water,  and  the  solution 
be  boiled,  the  plum-coloured  liquid  also  becomes  green,  and 
loses  the  power  of  crystallizing  on  cooling.  If  the  violet  sul- 
])hate  be  heated  to  212°  it  melts  in  its  water  of  crystallization, 
loses  10  lljO,  and  becomes  converted  into  the  green  salt ; but  if 
the  temperature  be  raised  to  about  700°,  both  the  green  and 
the  violet  modification  are  rendered  anhydrous,  and  a third 
salt  is  obtained  in  red  crystals,  wliich  are  no  longer  soluble  in 
water,  or  even  in  concentrated  acids,  or  aqua  regia.  If  digested 
for  a long  time  with  water,  however,  it  becomes  converted  into 
the  soluble  form  (Schrotter,  l*oggendo7'ff’s  A^inal.  liii.  513).  The 
composition  of  these  three  suhihates  would  be  represented  as 
follows 


540 


NITRATE  AND  OXALATES  OF  CHROMIUM. 


Red  insoluble  sulphate . 
Green  soluble  sulphate 
Yiolet  soluble  sulphate 


Brl  3 5 H,0 


Or^  3 


Otj  3 SO4  . 15  H2O. 


Several  subsulphates  of  chromium  may  also  be  formed. 

(793)  Ritrate  of  Chromium  (Or  3 blOg)  is  a green  very 
soluble  salt ; when  gently  ignited,  it  loses  its  acid,  and  yields  a 
brown  oxide  of  chromium  (OrO^),  which  is  regarded  as  a chromate 
of  sesquioxide  of  chromium  ; (0r203,0r0-3)  = 3 OrO^. 

(794)  Oxalates  of  Chromium. — Oxalate  of  ammonium  gives 
a green  insoluble  precipitate  when  mixed  with  a solution  of  green 
sesquichloride  of  chromium,  but  if  the  hydrated  sesquioxide  of 
chromium  be  digested  with  oxalic  acid,  a green  soluble  oxalate  is 
formed. 

The  oxalate  of  chromium  forms  two  remarkable  series  of 
double  salts,  viz.,  dark  hlue  salts,  which  form  bluish-green  solu- 
tions in  water,  with  the  general  formula  (M'30r''^  3 OgO^,  or 
3 M0,Cr203,  3 C^Og),  and  garnet-coloured  salts,  which  form  cherry- 
red  solutions  in  water,  of  the  formula  (M'Or^^'  2 O^OJ.  The  hlue 
potassium-salt  (K30r''',  3 O^O^  . 3 HjO)  may  be  obtained  by 
boiling  a solution  of  19  parts  of  the  anhydro -chromate  of  potas- 
sium, 23  of  normal  oxalate  of  potassium,  and  55  of  crystallized 
oxalic  acid : the  chromic  acid  is  reduced  to  the  state  of  sesqui- 
oxide, and  carbonic  anhydride  is  evolved  in  abundance;  K^OiqO, 
-f  2 K^-e^O.-f  7 H2O2O,  z=  6 e02d-7  H2O  + 2 (K3er"'  3 O2O,). 
The  solution  is  evaporated  to  dryness,  redissolved  in  water,  and 
set  aside  to  crystallize.  The  salt  is  deposited  in  large  rhombic, 
prisms  which  appear  to  be  black  by  reflected  light,  and  blue  by 
transmitted  light.  They  appear  greenish  when  powdered,  the 
solution  is  red  by  transmitted  and  green  by  reflected  light : am- 
monia does  not  precipitate  the  oxide  of  chromium  from  the  solu- 
tion ; hydi'ate  of  potash  occasions  no  precipitate  till  the  liquid  is 
boiled.  Corresponding  salts  may  be  obtained  containing  sodium, 
ammonium,  barium,  strontium,  calcium,  and  magnesium  instead 
of  potassium,  but  these  different  salts  vary  in  the  proportion  of 
water  which  they  retain. 

The  red  potassium  salt  (KOr"'  2 O^O^ . 4 H^O,  or  6 H^O)  may 
be  procured  by  adding  55  parts  of  oxalic  acid  to  a boiling  concen- 
trated solution  of  19  parts  of  anhydro-chromate  of  potassium, 
carbonic  anhydride  being  expelled,  owing  to  the  following 
decomposition : — 


It  may  be  obtained  by  spontaneous  evaporation  crystallized  in 
small  rhomboidal  tables,  which  are  dark-red  both  by  reflected 
and  by  transmitted  light : the  salt  requires  about  10  parts  of 
cold  water  for  solution,  but  is  soluble  to  any  extent  in  boiling 
water.  The  concentrated  solution  is  dark -green  or  nearly  black 
by  reflected  light,  but  red  by  transmitted  light.  Hydrate  of 
potash  gives  no  precipitate  in  the  solution  till  raised  to  ebullition  ; 
neither  does  ammonia  cause  any  separation  of  oxide  of  jhromium. 


CnAEACTEKS  OF  THE  COMPOUNDS  OF  CHEOMIUAI. 


541 


An  analo2:oTis  salt  may  be  formed  with  ammonium  (H^NOr'" 

2 OA, 

(795)  ClIARACTEKS  OF  THE  COMPOUNDS  OF  ChEOMIUM  I 

1.  — The  chromous  salts,  or  salts  of  the  protoxide,  are  but  little 
known.  They  absorb  oxygen  rapidly  from  the  air  ; they  are 
sparingly  soluble  in  water,  and  form  either  red  or  bine  solutions, 
which,  like  those  of  the  ferrons  salts,  absorb  nitric  oxide  in  large 
quantity,  and  form  dark-brown  solutions.  With  the  chromous 
salts  hydrate  of  potash  gives  a brown  precipitate  of  hydrated  prot- 
oxide of  chromium  ; ammonia,  a greenish-white  precipitate,  which, 
if  chloride  of  ammonium  be  present,  is  redissolved  by  excess  of 
ammonia,  forming  a blue  liquid  whicli  becomes  red  as  it  absorbs 
oxygen.  With  sidphide  of  potassium  they  give  a black  sulphide  ; 
and  \Yii\\f err  ocyanide  of  potassium  a greenish-yellow  precipitate. 
These  salts  reduce  solutions  of  gold  to  the  metallic  state,  and 
convert  corrosive  sublimate  into  calomel. 

2.  — The  chromic  salts,  or  salts  of  the  sesquioxide,  have  a 

sweetish  astringent  taste,  and  are  poisonous ; their  solutions  red- 
den litmus.  They  are  either  green  or  violet-coloured  ; the  green 
solutions  generally  transmit  a red  light.  With  ammonia  they 
yield  a bulky  gelatinous  precipitate  of  hydrated  sesquioxide  of 
chromium.  Hydrates  of  potash  and  soda  give  a green  precipitate, 
which  is  dissolved  with  a green  colour  in  excess  of  the  cold  alka- 
line solution,  but  is  re-precipitatd  completely  by  boiling  the  liquid, 
carrying  down  alkali  with  it.  The  carbonates  of  the  aTkali-metals 
give  a green  precipitate  which  is  redissolved  by  an  excess  of  the 
alkaline  liquid.  Sulphuretted  gives  no  precipitate.  The 

sulphides  of  the  alhcdine  metals  precipitate  the  green  sesquioxide 
of  chromium,  with  escape  of  sulphuretted  hydrogen.  If  any  of 
these  precipitates  be  fused  with  a mixture  of  nitre  and  carbonate 
of  potassium,  it  yields  a yellow  soluble  chromate  of  potassium. 

3.  — The  Chromades. — Before  the  blowpipe  they  colour  borax 
and  microcosm ic  salt  green.  When  boiled  with  diluted  sulphuric 
acid,  to  which  a little  alcohol  or  sugar  has  been  added,  they  are 
decomposed,  and  the  chromic  acid  is  reduced  to  the  green  oxide 
of  chromium,  which  is  dissolved  by  the  sulphuric  acid,  and  is  pre- 
cipitated with  its  characteristic  colour  on  adding  an  excess  of 
ammonia.  An  alcoholic  tincture  of  guaiacum,  1 of  resin  to  100  of 
spirit,  is  turned  blue  by  a very  minute  trace  of  free  chromic  acid 
(1  millionth  part,  Schiff),  but  the  colour  speedily  disappears  ; an 
excess  of  sulphuric  acid  favours  the  reaction,  which,  thoiigli  exceed- 
ingly  delicate,  is  not  characteristic.  Most  of  the  chromates  are 
strongly  coloured.  Many  of  them  are  insoluble  in  water,  but  they 
are  nearly  all  readily  dissolved  by  diluted  nitric  acid.  Their  solu- 
tions give  a yellow  precipitate  with  salts  of  lead  ^ a red  Ys\\\\nitrate 
of  silver,  and  an  orange  with  basic  mercurous  nitrate : these  ])reci- 
])itates  are  soluble  in  nitric  acid,  but  not  in  acetic  acid.  When 
heated  with  oil  of  vitriol  the  chromates  evolve  oxygen  ; with  hydro- 
chloric acid  they  evolve  chlorine.  In  both  cases  salts  of  the  green 
oxide  of  chromium  are  formed.* 

* Workmen  engaged  in  the  manufacture  of  anhydro-chromate  of  potassium 


542 


MANGANESE. 


(796)  Estimation  of  Chromium^  and  Separation  fiwn  the  Alka- 
lies and  Alkaline  Earths. — Chromium  may  be  most  accurately 
estimated  in  the  form  of  sesquioxicle.  It  may  be  easily  reduced 
to  this  condition,  even  if  it  exist  in  solution  in  the  form  of  a chro- 
mate, by  acidulating  Avith  hydrochloric  acid,  and  transmitting  a 
current  of  sulphuretted  hydrogen  : the  liquid  must  then  be  boiled, 
and  on  the  addition  of  ammonia  to  the  hot  solution  the  oxide  of 
chromium  is  precipitated.  It  is  to  be  well  Avashed,  and  ignited 
in  a covered  platinum  crucible ; 100  parts  of  the  anhydrous  oxide 
contain  68'68  of  chromium.  The  presence  of  acetic  acid  prevents 
the  precipitation  of  chromic  oxide  from  its  solutions  by  the  addi- 
tion of  ammonia,  even  after  long  boiling. 

The  separation  of  chromium  from  the  metals  of  the  earths.^ 
and  from  zinc^  cadmium^  cobalt.^  nickel.,  and  iron  may  be  effected 
by  fusing  the  mineral,  or  the  precipitate  obtained  by  ammonia 
from  its  solution  in  an  acid,  Avith  a mixture  of  carbonate  of 
potassium  and  nitre  ; the  chromium  is  thus  converted  into  a 
soluble  chromate,  from  which  the  chromium  may  be  precipitated 
as  directed  in  the  foregoing  paragraph,  whilst  the  earths  and  the 
other  metals  remain  in  the  insoluble  portion,  either  in  the  form 
of  oxides  or  of  carbonates. 

§ YI.  Manganese:  Mn— 55,  or  Mn=:27'5.  Sp.  Gr.  8*013. 

(797)  The  ores  of  this  metal  are  tolerably  abundant,  and  it 
enters,  in  greater  or  less  quantity,  into  the  composition  of  a vast 
number  of  minerals,  so  that  it  is  Avidely  diffused  throughout  the 
mineral  kingdom.  The  most  important  and  valuable  ore  of  man- 
ganese is  the  black  oxide,  Avhich  occurs  either  massive  or  in  radiated 
crystals. 

Manganese  Avas  first  recognised  as  a distinct  metal  by  Gahn 
in  1774.  It  is  reduced  to  the  metallic  state  with,  difficulty.  The 
best  method  consists  in  mixing  the  carbonate  into  a paste  with 
oil  and  sugar,  and  introducing  it  into  a crucible  lined  Avith  char- 
coal, furnished  with  a cover  luted  on : it  must  at  first  be  heated 
gently,  to  expel  the  volatile  matters,  and  then  ignited  intensely 
for  a couple  of  hours  in  the  heat  of  a forge.  It  may  thus  be  ob- 
tained in  the  form  of  a metallic  globule  Avhich  contains  a variable 
quantity  of  carbon ; the  carbon  may  be  removed  by  fusing  the 
metal  a second  time  in  a porcelain  crucible  with  a little  carbonate 
of  manganese.  A solution  of  chloride  of  manganese  also  yields 
plates  of  the  reduced  metal  wJien  subjected  to  electrolysis. 

Manganese  is  of  a greyish- white  colour,  and  is  brittle,  but 
hard  enough  to  scratch  steel ; it  is  A^ery  feebly  magnetic.  By  ex- 
posure to  the  air,  it  speedily  becomes  oxidated ; it  decomposes 
Avater  sloAAdy  at  ordinary  temperatures,  and  should  be  preserA^ed 
either  in  sealed  tubes  or  under  naphtha. 

are  liable  to  the  gradual  destruction  of  the  nasal  bones,  and  to  the  occurrence 
of  ulceration  of  the  throat,  in  appearance  a good  deal  resembling  that  occasioned  by 
secondary  syphilis.  Small  doses  of  corrosive  sublimate  have  been  found  to  act  as 
an  effectual  remedy  in  such  cases  (Grace  Calvert). 


OXIDES  OF  MANGANESE. 


543 


Manganese  enters  into  combination  with  both  carbon  and 
silicon  when  fused  with  them  ; the  carbide,  when  treated  with 
acids,  leaves  part  of  the  carbon  as  a black  powder : the  compound 
of  manganese  with  silicon  is  decomposed  with  difficulty  even  by 
aqua  regia,  in  which  case  it  leaves  a residue  of  silica. 

Metallic  manganese  is  not  employed  as  such  in  the  arts.  It 
yields  various  alloys,  but  none  of  them  are  of  practical  importance, 
with  the  exception  of  its  combination  with  iron,  which  is  harder 
and  more  elastic  than  iron  alone.  The  chief  uses  of  the  com- 
pounds of  manganese  are  chemical,  the  peroxide  being  extensively 
employed  to  decompose  muriatic  acid  and  furnish  chlorine.  It 
likewise  supplies  the  chemist  with  his  cheapest  source  of  oxygen, 
and  is  employed  as  a colouring  material  in  the  manufacture  of 
glass  and  enamels.  It  is  also  used  as  a flux  in  the  preparation  of 
cast  steel ; and  it  furnishes  a useful  mordant  to  the  calico-printer, 
when  precipitated  in  the  form  of  brown  hydrate  upon  the  fibre. 

(798)  Oxides  of  Manganese. — Manganese  forms  several  com- 
pounds with  oxygen.  The  protoxide,  MnO,  is  a powerful  base  ; 
the  sesquioxide,  Mn^Og,  is  feebly  basic ; the  red  oxide,  a compound 
of  these  two,  Mn0,Mn203,  is  quite  indifferent  to  the  action  of 
acids ; so  also  is  the  deutoxide  or  black  oxide,  MnO-^ : but  the  twm 
higher  oxides  have  well-marked  acid  characters.  The  general 
formula  for  the  salts  of  manganic  acid  is  M'^MnO^,  and  for  those 
of  permanganic  acid  M^MnO^.  Neither  of  these  acid  oxides,  how- 
ever, can  be  obtained  except  in  combination  with  water  or  with  a 
metallic  oxide. 

T\\q protoxide  or  manganous  oxide  (MnO=71,  or  MnO  = 35*5) 
may  be  obtained  easily  by  igniting  carbonate  of  manganese,  or 
any  of  the  higher  oxides  of  the  metal,  in  a current  of  hydrogen  ; 
it  is  of  an  olive-green  colour,  and  unless  it  has  been  strongly 
heated,  absorbs  oxygen  from  the  air ; if  ignited  in  the  air  it  burns, 
and  is  converted  into  a brown  superior  oxide.  It  may  be  ob- 
tained as  a white  hydrate  (Mn0,Il20),  by  decomposing  a salt  of 
manganese  by  any  alkali,  but  it  immediately  begins  to  absorb 
oxygen  from  the  air,  and  turns  brown.  It  is  soluble  in  ammonia, 
especially  if  the  solution  contain  an  ammoniacal  salt.  The  prot- 
oxide, by  its  action  upon  acids,  readily  forms  salts,  which  are  of  a 
pale  rose  colour ; they  are  neutral  to  litmus. 

Sesquioxide  (Mn203=:158,  or  Mn203=79);  Sp.  Gr.  4-82. — 
This  oxide  is  found  in  its  anhydrous  form  in  acute  square-based 
octohedra,  constituting  hraunite  ; it  occurs  naturally  in  a hydrated 
state  in  manganite  (Mn203,Il20;  sqj.  gr.  4*35),  which  is  of  a 
blackish-brown  colour,  and  forms  brilliant  right  rhombic  prismatic 
crystals.  The  sesquioxide  of  manganese  may  be  obtained  as  a 
brown  hydrate,  by  passing  chlorine  through  manganous  carbo- 
nate suspended  in  water,  and  afterwards  removing  tlie  excess  of 
the  carbonate  by  means  of  diluted  nitric  acid.  Sulphuric  acid 
dissolves  it  slowly  if  a portion  of  the  protoxide  lie  present,  and  a 
deep-red  solution  is  formed : hydrochloric  acid  in  the  cold  also 
forms  a soluble  compound  with  it : if  these  solutions  be  heated 
they  are  decomposed,  and  a manganous  salt  is  the  result.  When 


544  BINOXIDEj  DEUTOXIDE,  OE  PEROXIDE  OF  MANOA^IESE. 


ignited,  the  sesqiiioxide  loses  one-eighth  of  its  oxygen,  and  leaves 
the  red  oxide.  The  salts  of  the  sesquioxide  are  isoinorphous  with 
those  of  alumina  and  sesquioxide  of  iron.  It  appears  to  he  the 
sesquioxide  of  manganese  that  imparts  the  violet  colour  to  glass 
to  which  the  black  oxide  has  been  added ; and  the  colour  of  the 
amethyst  is  also  said  to  be  due  to  this  oxide. 

Binoxide^  deutoxide^  or  peroxide  (Mn0,MnO3  = 1^4,  or 
Mn02=43-5) ; Gr.  4-94:  Comp,  in  100  parts^  Mn,  63-22; 
O,  36-78. — This  oxide  is  the  black  manganese  of  commerce  and  the 
pyrolusite  of  mineralogists  ; it  is  found  in  steel-grey  rhombic  prisms. 
Psilomelane  is  a black  stalactitic  or  amorphous  variety  frequently 
mixed  with  one  of  the  lower  oxides  of  the  metal.  Yarvicite 
(Mn^Og,  2 MuO2,H20  ; sp.  gr.  4-53)  is  the  name  given  to  a hard 
lamellated  crystalline  hydrate,  found  by  Phillips  at  Hartshill,  in 
Warwickshire.  Wad  is  also  a hydrated  peroxide  of  manganese, 
with  a variable  amount  of  water ; it  is  in  a less  compact  form 
than  psilomelane,  and  is  of  a brown  colour.  Small  quantities  of 
cobalt  and  of  the  carbonates  and  nitrates  of  the  metals  of  the 
earths  are  frequent  constituents  of  these  ores. 

Binoxide  of  manganese  is  a good  conductor  of  electricity,  and 
is  strongly  electro-negative  in  the  voltaic  circuit.  When  mixed 
with  acids  it  furnishes  a valuable  oxidizing  agent.  When  ignited, 
it  gives  off  one-third  of  its  oxygen,  and  the  red  oxide  is  left ; 3 MnO^ 
^MugO^-f  O2 : if  heated  with  concentrated  sulphuric  acid,  half  its 
oxygen  escapes,  and  manganous  sulphate  is  formed  ; 2 WnO^  -f 
2 112804  = 2 WnS04-|-2  Ti^O-bOg.  With  hydrochloric  acid  cldo- 
rine  is  abundantly  evolved,  and  manganous  chloride  is  left.  Hitric 
acid  has  but  little  effect  upon  it.  Binoxide  of  manganese  is  pro- 
cured in  a hydrated  form  as  a reddish-brown  powder  (Mn02,H20) 
when  manganate  or  permanganate  of  potassium  is  decomposed  by 
an  acid.  \Yhen  the  red  oxide  is  treated  with  nitric  acid,  a black 
hydrate  of  the  peroxide  is  left,  containing  4 Wn02,IT2^-  The 
same  hydrate  is  probably  formed  on  adding  a solution  of  chloride 
of  lime  to  a neutral  solution  of  sulphate  or  chloride  of  manganese. 

(799)  Commercial  Assay  of  Oxide  of  Manganese. — The  com- 
mercial value  of  black  oxide  of  manganese  depends  upon  the  pro- 
portion of  chlorine  which  a given  weight  of  it  wull  liberate  when 
it  is  heated  with  hydrochloric  acid.  This  quantity  of  chlorine 
varies  much  in  different  samples,  and  is  dependent  upon  the  pro- 
portion of  oxygen  which  the  oxide  of  manganese  contains  in  excess 
of  that  which  is  necessary  to  its  existence  as  protoxide.  A conve- 
nient method  of  estimating  this  excess  of  oxygen  is  founded  upon 
the  circumstance  that  the  black  oxide  of  manganese  is  decomposed 
in  the  presence  of  oxalic  acid  and  free  sulphuric  acid  ; manganous 
sulphate  is  formed,  and  all  the  excess  of  oxygen  reacts  upon  the 
oxalic  acid,  and  converts  it  into  carbonic  anhydride,  which  passes 
off  with  effervescence.  If  the  mixture  be  weighed  before  the  de- 
composition is  effected,  and  again  after  it  has  been  completed,  the 
loss  will  indicate  the  amount  of  carbonic  anhydride  ; and  from  this 
the  available  amount  of  oxygen  is  readily  calculated.  The  reaction 
may  be  traced  thus  : MnOg  -f  II2SO4  -f  H2O2O4 = MnS04  4-  2 OO3  -f- 


MANGANIC  ACID. 


545 


2 H,0.  Each  equivalent  of  peroxide  of  manganese  gives  2 equi- 
valents, or  almost  exactly  its  own  weight,  of  carbonic  anhydride. 

The  apparatus  of  Will  and  Fresenins  (fig.  332,  p.  350)  is  well 
adapted  to  the  performance  of  this  experiment : 50  grains  of  the 
oxide  of  manganese  to  be  tested,  are  reduced  to  an  extremely  fine 
powder,  and  mixed  with  75  grains  of  oxalic  acid  ; the  mixture  is 
placed  in  the  fiask  a,  and  about  1|-  ounce  of  water  is  added  : the 
experiment  is  then  proceeded  with  exactly  as  in  the  method  al- 
ready described  for  estimating  carbonic  anhydride  in  a carbonate 
(578).  The  decomposition  of  the  ore  is  known  to  be  complete  as 
soon  as  all  the  black  particles  have  disappeared. 

If  the  sample  of  oxide  of  manganese  contain  a carbonate  of  any 
of  the  earths,  as  may  be  readily  ascertained  by  the  effervescence 
which  will  be  occasioned  on  moistening  a portion  of  the  oxide  with 
diluted  nitric  acid,  it  will  be  necessary  to  remove  this  carbonate. 
This  is  easily  done  by  washing  the  weighed  portion  in  the  fiask 
itself  with  nitric  acid  diluted  with  from  16  to  20  parts  of  water ; 
as  soon  as  the  efiervescence  has  ceased,  the  acid  liquid  must  be 
carefully  poured  off*,  and  the  fiask  filled  up  once  or  twice  with  dis- 
tilled water ; the  oxide  must  be  allowed  to  subside : in  order  to 
retain  any  suspended  particles,  the  washings  may  be  thrown  upon 
a small  filter,  which  is  afterwards  introduced  into  the  fiask,  and 
the  experiment  is  then  proceeded  with  as  usual. 

The  Icecl  Oxide  (Mn304=229,  or  Mn0,Mn203= 114*5) ; Comp, 
in  100  Mn,  72*7  ; O,  27*3. — This  oxide  corresponds  to  the 
black  oxide  of  iron  ; it  is  formed  by  igniting  any  of  the  oxides  of 
manganese  in  the  open  air  : it  occurs  native  in  hausmannite^  {sp. 
gr.  4*72)  either  massive  or  in  four-sided  pyramidal  crystals  of  a 
black  colour.  The  oxide  is  soluble  in  phosphoric  and  in  sulphuric 
acid,  but  does  not  form  definite  salts  with  either  of  them. 

(800)  Manganic  Acid  (H^WnO,  = 121 ; or  IIO,Mn03  = 9 + 
51*5). — When  equal  weights  of  caustic  potash  and  finely  levigated 
peroxide  of  manganese  are  fused  together,  a substance  is  formed, 
which,  when  dissolved  in  a small  quantity  of  water,  has  a green 
colour,  but  which,  when  largely  diluted,  becomes  purple,  and  ulti- 
mately claret-coloured,  whilst  a precipitate  of  hydrated  biuoxide 
of  manganese  is  deposited.  This  substance  has,  owing  to  these 
changes  of  colour,  been  long  known  under  the  name  of  mineral 
chameleon.  The  colouring  material  is  manganate  of  potassium, 
wliich  has  a green  colour  : it  is  an  unstable  compound,  and  readily 
either  parts  witli  oxygen,  or  absorbs  a larger  amount  of  it,  in  the 
latter  case  forming  a red  compound  ; and  hence  these  changes  of 
colour  are  produced. 

Manganic  acid  undergoes  rapid  spontaneous  decomposition 
unless  it  be  in  combination  with  some  powerful  basyl.  A tolerably 
stable  manganate  may  be  procured  by  heating  finely  powdered 
peroxide  of  manganese  with  its  own  weight  of  hydrate  of  potash, 
of  soda,  or  of  baryta.  Becliamp  heats  an  intimate  mixture  of  10 
])arts  of  finely  ])owdered  black  oxide  of  manganese  with  12  of 
hydrate  of  potash,  dries  it  in  an  iron  dish,  and  heats  the  porous 
residue  to  dull  redness  in  an  earthen  retort,  into  the  tubulure  of 
35 


54G 


PERMANGANIC  ACID. 


M^hicli  a green  glass  tube  is  luted ; be  then  transmits  a current 
of  pure  dry  oxygen  as  long  as  it  is  absorbed.  If  the  green  mass 
thus  obtained  be  treated  with  a small  quantity  of  cold  water,  it  is 
partially  dissol^^ed,  forming  a green  solution,  from  which  the 
manganate  of  the  metal  may  be  crystallized  by  evaporating  it  in 
vacuo  over  sulphuric  acid.  These  crystals  are  isomorphous  with 
the  corresponding  sulphates  and  chromates.  Manganate  of  potas- 
sium (K^^nOJ  is  anhydrous,  and  readily  soluble  in  water. 
Manganate  of  sodium  is  prepared  on  a large  scale  by  Mr.  Condy, 
by  heating  a mixture  of  caustic  soda  and  finely  powdered  oxide 
of  manganese,  to  a dull  red  heat  in  shallow  vessels,  for  48  hours  ; 
7 cwt.  of  oxide  of  manganese  are  mixed  with  the  alkali  obtained 
from  1|-  ton  of  soda-ash.  Manganic  acid  has  a very  intense 
colouring  power : this  fact  enables  manganese  in  very  minute 
quantity  to  be  detected  before  the  blowpipe ; the  material  sup- 
posed to  contain  it  is  fused  upon  platinum  foil  with  a little  car- 
bonate of  potassium  or  of  sodium  ; if  any  trace  of  manganese  be 
present,  a green  colour  is  imparted  to  the  fused  mass. 

The  manganates  are  very  unstable ; they  are  decomposed  by 
boiling  their  solutions.  A small  quantity  of  any  free  acid 
changes  the  colour  of  their  solutions  from  green  to  red,  owing  to 
the  formation  of  a permanganate,  and  of  a manganous  salt : thus 
for  instance,  5 K^MnO^  + 4 gives  4 KMnO^  MnSO^ 

+ 3 K2S0'^  -f  4 H.^O.  Organic  matter  also  readily  abstracts  oxy- 
gen from  them ; their  solutions  must  not  even  be  filtered  through 
paper.  In  the  solid  form  they  are  readily  decomposed  by  eleva- 
tion of  temperature,  and  oxygen  is  evolved ; an  excess  of  alkali 
renders  the  salt  more  stable.  Sulphurous  and  hypophosphorous 
acids  readily,  and  phosphorous  acid  more  slowly,  reduce  the  man- 
ganates to  a manganous  salt ; sulpliurous  acid  and  manganate  of 
potassium,  for  example,  produce  the  following  result : — 

K^MnO,  -f-  2 H,S03  = MnSO,  -f  K.SO,  -f-  2 H^O. 

(801)  Permanganic  Acid  (HMnO,,  or  H0,Mn20,  = 120). — 
If  a solution  of  manganate  of  potassium  be  largely  diluted  with 
water,  the  colour  changes  from  green  to  violet ; the  manganic  acid 
passes  to  a higher  state  of  oxidation,  and  permanganate  of  potas- 
sium is  formed. 

This  salt  may  be  prepared  by  mixing  intimately  4 parts  of 
finely  powdered  peroxide  of  manganese  with  3^  parts  of  chlorate 
of  potassium;  5 parts  of  hydrate  of  potash  are  dissolved  in  a 
small  quantity  of  water,  and  added  to  the  mixture,  which  is  dried 
and  reduced  to  powder,  and  then  heated  to  dull  redness  for  an 
hour  in  an  earthen  crucible  (Gregory).  When  cold,  the  mass  is 
treated  with  water,  and  filtered  through  a funnel  plugged  with 
asbestos  ; the  solution,  after  being  neutralized  with  sulphuric  acid, 
on  evaporation  yields  beautiful  red  acicular  crystals  of  perman- 
ganate of  potassium  (KMuG^,  or  K0,Mn20,=158).  If  a solution 
of  manganate,  prepared  by  Bech amp’s  process,  be  decomposed  by 
transmitting  a current  of  carbonic  acid  until  the  green  colour  has 
been  converted  into  red,  very  fine  crystals  of  the  permanganate 


PEEMANG  AN  ATES . 


547 


are  obtained  on  evaporating  tlie  clear  liquid  after  decantation 
from  the  precipitated  oxide  of  manganese.  The  crystals  of 
the  permanganate  are  isomorplions  with  those  of  perchlorate  of 
potassium ; they  require  about  16  parts  of  cold  water  for  solu- 
tion. 

Permanganate  of  potassium  is  in  certain  cases  a useful  oxidiz- 
ing agent : it  may  be  employed  to  detect  the  occurrence  of  sul- 
phurous acid  in  solution  in  sulphuric  or  hydrochloric  acid ; sul- 
phurous acid  quickly  deoxidizes  it,  and  destroys  its  colour  if  pre- 
sent. Neutral  solutions  of  the  sulphides  and  the  pentathionates 
quickly  discharge  the  colour  of  a solution  of  permanganate  of 
potassium,  and  a similar  effect  is  produced  by  acid  solutions  of 
the  sulphites,  hyposulphites,  tetrathionates,  sulphocyanides,  and 
nitrites.  The  trithionates  produce  the  same  effect,  but  more 
slowly.  Acidulated  solutions  of  the  mercurous,  ferrous,  stannous, 
and  antimonious  salts,  and  acid  solutions  of  arsenious  acid,  like- 
wise decolorize  a solution  of  permanganate  rapidly.  A solution 
of  this  salt  constitutes  a test-liquid  which  may  be  Yerj  usefully 
employed  in  many  cases  of  volumetric  analysis,  as  already  exem- 
plified in  the  instance  of  the  ores  of  iron  (778). 

The  jpermanganates  are  much  more  stable  than  the  manga- 
nates  ; their  solutions  may  be  boiled  without  undergoing  decom- 
position. Organic  matter,  however,  combines  with  a part  of  the 
oxygen  contained  in  the  acid,  and  reduces  it  first  to  manganic 
acid  and  then  to  the  bin  oxide  of  the  metal,  which  is  precipitated 
in  flocculi  as  a hydrate  : their  solutions,  therefore,  must  not  be  fil- 
tered through  paper,  but  through  a funnel  loosely  plugged  with 
asbestos.  When  ignited,  oxygen  is  given  off,  and  amanganate  is 
reproduced,  which,  if  the  heat  be  too  great,  is  in  turn  decomposed 
with  a further  extrication  of  oxygen.  Most  of  the  permanganates 
are  freely  soluble  in  water ; the  permanganate  of  silver  is  the 
least  soluble  of  these  salts.  If  concentrated  solutions  of  perman- 
ganate of  potassium  and  nitrate  of  silver  be  mixed  together,  a red 
crystalline  permanganate  of  silver  is  deposited.  It  may  be  em- 
])loyed  for  the  preparation  of  the  other  permanganates ; if  it  be 
levigated  with  water,  and  mixed  with  a solution  of  the  chloride 
of  the  metal  of  which  the  permanganate  is  required,  double  de- 
composition occurs,  and  chloride  of  silver  is  formed,  wliilst  the 
desired  permanganate  is  obtained  in  solution.  In  this  way  the 
j)ennanganate  of  barium  may  be  procured,  and  from  it  the  per- 
manganic acid  may  be  obtained  in  solution,  by  tlie  cautious  addi- 
tion of  diluted  sulphuric  acid,  so  long  as  any  precipitate  is  pro- 
duced : on  evaporation  it  may  be  obtained  as  a brown  partially 
crystalline  mass,  which  is  very  soluble  in  water  : its  solution  is 
decomposed  by  mere  elevation  of  temperature  ; at  a little  beyond 
100°  I.  hydrated  peroxide  of  manganese  is  deposited,  and  oxy- 
gen gas  escapes. 

Condy  has  employed  solutions  of  manganate,  and  of  per- 
manganate of  potassium,  as  disinfecting  agents,  for  which  pur])ose 
they  are  admirably  adapted  ; the  organic  matter  is  rapidly  and 
completely  oxidized  by  their  means,  and  as  the  solutions  have 


518  SULPHIDE  AND  CHLOKIDE  OF  MANGANESE. 

no  coiTosiv^e  action,  solutions  of  these  salts  form  valuable  local 
applications  to  foetid  sores. 

(802)  Protosidphide  of  manganese  (MnSjCrH^O)  is  obtained 
as  a yellowish-red  hydrate,  by  precipitating  a manganous  salt 
by  sulphide  of  ammonium.  The  presence  of  traces  of  iron,  cobalt, 
or  nickel  renders  it  black : it  speedily  becomes  oxidized  by  expo- 
sure to  the  air.  A crystalline  sulphide  may  be  obtained  in  black 
rhombic  prisms,  by  heating  the  hydrated  sesquioxide  in  the  vapour 
of  bisulphide  of  carbon.  A native  sulphide  of  manganese  is 
occasionally  met  with,  as  manganese  hlende^  of  a brownish-black 
or  steel-grey  colour,  and  feeble  metallic  lustre.  The  other  sul- 
phides of  manganese  have  not  been  accurately  examined. 

(803)  Chlokides  of  Manganese. — Two  chlorides  of  this  metal 
may  be  obtained : manganous  chloride,  MnClg,  and  manganic  chlo- 
ride, Mn^Cle. 

Manganous  CJdoride  (MnCl2,4  H20=:126-|- Y2),  or  Protochlo- 
ride of  Manganese  (MnCl,4  Aq=:  63  -f-  36) ; Sp.  Gr.  2-01. — This  sub- 
stance is  obtained  abundantly  as  a waste  product  in  the  prepara- 
tion of  chlorine,  by  acting  on  the  black  oxide  of  the  metal : the 
chlorine  escapes,  and  the  chloride  of  manganese  is  dissolved.*  If 
this  solution  be  evaporated  to  dryness,  redissolved  in  water,  and 
about  one-fourth  of  its  bulk  be  precipitated  by  means  of  carbonate 
of  sodium,  an  impure  carbonate  of  manganese  is  obtained.  If 
this  precipitate,  after  it  has  been  well  washed,  is  boiled  with  the 
remainder  of  the  solution,  the  whole  of  the  iron  will  be  precipitated 
in  the  form  of  peroxide,  while  oxide  of  manganese  takes  its  place, 
and  carbonic  anhydride  is  expelled,  leaving  a solution  of  chloride 
of  manganese  freed  from  all  metallic  impurities  except  cobalt  and 
nickel.  A still  better  process  consists  in  concentrating  a solution 
of  the  crude  chloride  by  evaporation,  to  expel  the  excess  of  acid, 
and  afterwards  diluting  with  water.  A current  of  sulphuretted 
hydrogen  is  transmitted,  by  which  the  iron  is  reduced  to  the  state 
of  ferrous  salt ; the  manganese  may  then  be  obtained  free  from  iron, 
nickel,  and  cobalt  by  suspending  freshly  precipitated  sulphide  of 
manganese  in  water,  and  adding  it  to  the  liquid  as  long  as  the 

* Various  attempts  have  been  made  to  economize  the  vast  quantities  of  chloride 
of  manganese  formed  during  the  manufacture  of  chloride  of  lime.  The  most 
successful  is  one  employed  by  Mr.  Dunlop.  It  consists  in  precipitating  the  manga- 
nese as  carbonate,  and  roasting  the  carbonate  at  a temperature  of  about  600°.  The 
crude  acid  solution  of  the  chloride  is  treated  with  milk  of  lime  in  quantity  suflBcient 
not  only  to  neutralize  the  excess  of  acid,  but  to  precipitate  the  iron  as  sesquiox- 
ide. The  clear  liquid  is  then  pumped  up  into  an  iron  boiler  and  mixed  with  a pro- 
portion of  chalk  just  sufficient  to  precipitate  the  whole  of  the  manganese,  an  excess 
being  carefuUy  avoided.  The  mixture  is  heated  by  the  injection  of  steam,  which  is 
maintained  for  about  24  hours  under  a pressure  of  from  2 to  2^  atmospheres ; under 
these  circumstances  carbonate  of  manganese  is  precipitated,  and  chloride  of  calcium 
formed  in  the  liquid.  The  solution  is  run  off  from  the  precipitate,  and  this  is  well 
washed,  pressed,  and  partially  dried.  In  this  condition  it  is  introduced  in  shallow 
sheet-iron  cases  on  wheels  into  large  vaulted  galleries  of  brickwork  heated  to  about 
600° : through  these  a current  of  air  is  maintained.  The  carbonate  is  gradually  made 
to  pass  from  the  cooler  to  the  hotter  portions  of  these  galleries,  being  from  time  to 
time  sprinkled  with  water.  The  carbonic  anhydride  is  gradually  expelled,  and 
oxygen  absorbed:  so  that  at  the  end  of  48  hours  about  72  per  cent,  of  the  carbonate 
has  been  converted  into  black  oxide.  The  process,  however,  is  expensive. — 
{UofmanrCs  Int.  Exhib.  Jury  Beport,  1862,  p.  36.) 


OTHER  SALTS  OF  MANGANESE. 


549 


fresh  portions  of  sulphide  become  blackened  ; the  manganese  dis- 
places the  other  metals  from  their  solution,  and  they  are  precipi- 
tated as  black  hydrated  sulphides  : for  example,  FeCl,  -f  MnS,a?Il20 
=MnCl2-l-FeS,a?H20.  On  evaporation  the  chloride  of  manganese 
crystallizes  in  a tabular  form  with  4 HjO.  It  is  of  a delicate  pink 
colour  and  slightly  deliquescent ; by  heat  an  anhydrous  chloride 
may  be  procured,  which  is  soluble  in  alcohol ; from  this  solution 
it  crystallizes  with  4 atoms  of  alcohol  (MnCl2,4  ■©2HgO). 

Mamganic  chloride  (Mn2Cl6)  may  be  obtained  in  solution  by 
acting  on  the  sesquioxide  of  manganese  with  cold  hydrochloric 
acid  : it  is  of  a dark  brown  colour : it  must  be  concentrated  by 
evaporation  in  vacuo.  It  is  converted  by  heat  into  2 MnCl2  4-Cl2. 

An  oxychloride  (the  jperchloride^  Mn2Cl,  ? of  Dumas)  is  ob- 
tained by  dissolving  permanganate  of  potassium  in  oil  of  vitriol 
and  adding  fused  chloride  of  sodium,  in  small  portions  at  a time : 
it  is  a greenish-yellow  gas,  which  condenses  at  0°  F.  to  a greenish- 
brown  liquid.  The  fumes  in  a moist  air  assume  a purple  colour 
from  the  formation  of  permanganic  acid : water  decomposes  it 
instantly,  forming  a red  solution  of  permanganic  and  hydro- 
chloric acids.  It  is  probable  that  this  compound  is  an  oxy- 
chloride of  the  metal,  somewhat  analogous  to  chlorochromic 
acid  (789). 

Fluorides  of  manganese,  corresponding  to  each  of  these  chlo- 
rides, have  been  formed. 

(804)  Sulphate  of  Manganese  (MnSO^,  5 II2O  = 151  -f-  90, 
or  Mn0,S03,  ^ Aq=75'5H-45)  is  obtained  for  the  use  of  the  cal- 
ico-printer, by  digesting  the  binoxide  in  diluted  sulphuric  acid, 
in  order  to  remove  the  carbonates,  then  lieating  the  oxide  with 
oil  of  vitriol,  evaporatiog  to  dryness,  and  gently  igniting  the 
residue  to  decompose  the  sulphate  of  iron,  which  does  not  resist 
so  high  a temperature  as  the  sidphate  of  manganese.  On  digest- 
ing the  mass,  after  it  has  become  cool,  in  water,  the  sulphate  of 
manganese  is  dissolved,  and  may  be  obtained  in  crystals  by  eva- 
poration : it  crystallizes  below  42°  with  7 II2O  in  efflorescent 
prisms  ; between  45°  and  68°  with  5 II2O;  and  between  68°  and 
86°  with  4 1120-  (Brandes).  It  forms  a double  salt  with  sulphate 
of  X)otassium  (MnS04,K2S04,6  Ha^)?  which  is  isomorphous  with 
the  corresponding  double  sulphate  of  magnesium. 

The  manganic  sulpliate  cannot  be  obtained  in  crystals,  but  it 
was  obtained  by  Mitscherlich  combined  with  sul])hate  of  ])otas- 
sium  crystallized  in  octohedra  (KMn''^  2 . 12  li„0),  and  cor- 

responding in  form  and  composition  with  common  alum. 

(805)  Carbonate  of  Manganese  (MnCOg  = 115,  or  MnO, 
06)2= 57'5). — The  anhydrous  carbonate  forms  the  native  onanga- 
nese  spar.^  and  frequently  accompanies  spathic  iron  : the  artificial 
carbonate  may  be  obtained  as  a white  hydrate  (2  Mn-0O3,Il2O) 
on  precipitating  the  chloride  by  a carbonate  of  one  of  the  alkalies  : 
it  becomes  brownish  by  drying. 

(806)  Characters  of  the  Salts  of  Manganese. — The  salts 
formed  from  protoxide  are  the  only  salts  of  manganese  of  im- 
])ortance:  they  are  of  a delicate  rose  colour,  and  have  an  astrin- 


550 


TESTS  FOR  MAXGAXESE. 


gent  taste.  'U^itli  tlie  hydrates  of  j)otash  and  soda  their  solutions 
^deld  a white  precipitate  of  hydrated  protoxide,  which  absorbs 
oxygen  rapidly,  and  becomes  brown  by  exposure  to  the  air. 
Ammonia  gives  a similar  precipitate,  which  is  soluble  in  excess 
of  the  ammoniacal  liquid,  especially  when  it  contains  chloride  of 
ammonium ; the  solution  absorbs  oxygen  quickly,  and  deposits  a 
brown  hydrated  protosesquioxide  of  manganese.  The  carbonates 
of  the  alkali-metals  give  a white  precipitate  of  carbonate  of  man- 
ganese, soluble  in  chloride  of  ammonium.  With  sulphide  of  am- 
monium a characteristic  flesh-coloured  hydrated  sulphide  of  man- 
ganese is  formed,  which  is  readily  dissolved  by  hydrochloric  and 
by  nitric  acid ; it  becomes  brown  by  exposure  to  air.  Sulphu- 
retted hydrogen  gives  no  precipitate  in  the  solutions  of  manganese  ; 
but  a neutral  solution  of  acetate  of  manganese  is  partially  preci- 
pitated by  this  gas.  Ferrocyanide  of  potassium  gives  in  neutral 
solutions  a white  precipitate  soluble  in  acids ; in  neutral  solutions 
ferricyanide  of  p)otassium  produces  a brown  precipitate.  Mr. 
Crum  has  pointed  out  an  extremely  delicate  test  of  the  presence 
of  a salt  of  manganese,  provided  that  the  solution  is  free  from 
chlorides ; the  liquid  must  be  mixed  with  diluted  nitric  acid,  and 
a little  peroxide  of  lead  added : on  boiling  the  mixture,  the  red 
colour  of  permanganic  acid  is  produced  by  a trace  of  manganese 
which  is  too  small  to  be  otherwise  recognised.  Before  the  blow- 
pipe^ when  fused  on  platinum  wire  or  foil,  with  a little  carbonate 
of  sodium,  the  compounds  of  manganese  give  a very  characteris- 
tic bluish-green  opaque  bead  : a bead  of  borax  or  of  microcosmic 
salt  becomes  violet  in  the  oxidizing  flame,  if  manganese  be  pres- 
ent ; the  colour  disappears  in  the  reducing  flame. 

(807)  Estimation  of  21anganese^  and  Separation  from  the 
Alkalies, — Manganese  is  generally  estimated  in  analysis  in  the 
form  of  the  red  oxide  of  manganese,  which  contains  T2‘T  per  cent, 
of  the  metal.  For  this  purpose  it  is  precipitated  from  a boiling 
solution  of  its  salts  by  carbonate  of  potassium  or  of  sodium ; the 
precipitated  carbonate  is  well  washed  and  then  heated  to  redness, 
by  which  carbonic  anhydride  is  expelled,  and  the  red  oxide  is 
produced  by  absorption  of  oxygen  from  the  air. 

Separation  of  2fa?iganese  from  the  Alkaline  Earths, — The 
solution  must  be  rendered  nearly  neutral,  and  sulphide  of  am- 
monium added,  which  precipitates  the  manganese  as  sulphide : 
the  sulphide  must  then  be  redissolved  in  hydrochloric  acid,  pre- 
cipitated by  carbonate  of  potassium,  and  the  manganese  estimated, 
after  ignition,  as  red  oxide.  It  is  apt  however  to  retain  some 
portions  of  the  earths  when  thus  separated.  The  oxide  must 
therefore  be  again  redissolved  in  hydrochloric  acid ; chloride  of 
ammonium  must  be  added,  and  then  a mixture  of  ammonia  and 
carbonate  of  ammonium  in  excess,  by  which  the  manganese  will 
be  held  in  solution  ; and  if  strontium,  calcium,  or  barium  be  pres- 
ent, they  will  remain  undissolved  in  the  form  of  carbonates, 
which  must  be  collected  on  a filter,  weighed,  and  deducted  from 
the  weight  of  the  oxide  previously  obtained. 

Separation  from  Zinc,,  Cadmium,  Cobalt,  and  Nickel. — The 


Tm. 


551 


solution  is  mixed  with  acetate  of  potassium  in  excess,  to  convert 
the  metals  into  acetate,  then  sulphuretted  hydrogen  is  transmitted  ; 
the  manganese  remains  in  solution,  whilst  the  other  metals  are 
precipitated  as  sulphides  if  the  solution  is  only  faintly  acid.  If 
cadmium  alone  is  present,  the  addition  of  acetate  of  potassium  is 
unnecessary. 

Separation  from  Iron^  Chromium^  Uramium^  Aluminum^ 
and  Glucinum. — This  is  readily  effected  after  converting  the  iron 
into  a ferric  salt  and  diluting  the  solution  largely  with  water,  by 
digesting  it  upon  finely  levigated  carbonate  of  barium.  Manganese 
alone  remains  in  the  liquid,  the  other  oxides  being  displaced  by 
baryta.  The  excess  of  barium  is  removed  by  sulphuric  acid,  and 
the  manganese  precipitated  by  carbonate  of  sodium. 

Manganese  is  connected  by  isomorphous  relations  with  a great 
number  of  the  elementary  bodies.  Its  protoxide  is  isomorphous 
with  the  oxides  of  the  magnesian  group  : its  sesquioxide  is  isomor- 
plious  with  alumina  and  the  sesquioxides  of  iron  and  chromium. 
The  manganates  are  isomorphous  with  the  sulphates,  and  the  per- 
manganates wdth  the  perchlorates. 


CHAPTEE  XYII. 

GROUP  VI. CERTAIN  METALS  WHICH  FORM  ACIDS  WITH  OXYGEN. 


Metal. 

Symbol. 

Atomic 

weight. 

Atomic 

vol. 

Specific 

heat. 

Fusing- 

pt.F«. 

Specific 

gravity. 

Electric 
conductivity 
at  32«  F. 

j Tiu 

Sn 

118 

16-20 

0-0562 

442 

7-292 

12-36 

) Titanium 

Ti 

50 

i Molybdenum  . . . 

Mo 

96 

10-56 

8-62 

•<  Tungsten 

W 

184 

10-56 

0-0334 

17-60 

! Vanadium 

V 

137 

i Arsenic 

As 

75 

12-96 

0-0814 

5-969 

4-76 

■ -<  Antimony 

Sb 

122 

18-16 

0-0508 

1150 

6-71 

4-65 

1 ( Bismuth 

1 

Bi 

210 

21-34 

0-0308 

507 

9-799 

1-245 

In  this  list  columbium  and  tantalum  are  omitted,  because  so 
little  is  known  of  them.  The  foregoing  list  of  metals  capable  of 
yielding  acids  with  oxygen  is  divisible  into  three  natural  families, 
Avhich  have  little  in  common.  (See  pp.  9 and  292.) 

§ I.  Tin:  Sn^^=118,  or  Sn=59.  Sp.  Gr.  7*292;  Fusiiuj-point^ 

442°. 

(808)  This  beautiful  metal  is  one  of  those  which  have  been 
longest  known  to  man,  as  it  is  mentioned  in  the  Books  of  Moses. 
Till,  however,  is  met  with  in  but  few  localities.  Its  only  ore  of 
importance  is  the  binoxide,  or  tin-stone,  which  occurs  crystallized 
in  prisms  isomorphous  with  those  of  rutile.  It  is  usually  found 


552 


EXTRACTION  OF  METALLIC  TEX. 


in  veins,  running  tlirongli  primitive  rocks  of  poi^iliyry,  granite,  or 
clay-slate,  and  is  generally  mingled  with  the  sulphides  and  arse- 
nides of  copper  and  iron,  and  fi'equently  also  with  wolfram.  Tlie 
most  celebrated  tin  mines  are  those  of  Cornwall,  which  were 
worked  before  the  Roman  invasion  ; they  furnish  annnally  up- 
wards of  6000  tons  of  the  metal.  The  mines  of  Malacca  also 
yield  a very  pure  tin  : the  metal  is  likewise  obtained  to  a smaller 
extent  from  Mexico.  The  tin-veins  in  Cornwall  are  frequently 
associated  with  those  of  copper,  and  they  run  almost  invariably 
east  and  west.  The  tin  ore  is  often  met  with  in  alluvial  soils, 
whither  it  has  been  carried  from  its  original  position  by  the  action 
of  water.  In  this  case  the  ore  occurs  in  detached,  rounded  masses, 
and  is  verv  pure,  constituting  what  is  termed  stream  tin.  The 
position  of  the  veins  is  frequently  traced  by  following  the  stream 
towards  its  source,  np  to  the  point  where  the  ore  ceases  to  be 
found ; a careful  examination  of  the  vicinity  generally  leads  to  the 
discovery  of  the  vein. 

(809)  Extraetion  of  Metallic  Tin. — In  order  to  extract  the 
metal  from  the  ore,  it  is  subjected  to  a series  of  operations,  some 
of  which  are  of  a mechanical  and  others  of  a chemical  character. 
They  may  be  classified  thus  : — 

1. — Stamping  and  washing.^  to  remove  the  earthy  and  lighter 
portions.  2. — Boasting.^  to  decompose  the  pyrites  and  get  rid  of 
the  arsenic  and  sulphur.  3. — Washing^  to  dissolve  out  sulphate 
of  copper,  and  carry  oft"  the  oxide  of  iron.  4.  — Reduction.^  by 
which  the  tin  is  separated  from  the  oxygen  and  the  gangue  or 
earthy  matter.  5.  — Refining,  or  liquation,  and  hoiling  with 
green  wood. 

1.  — The  purer  portions  of  the  ore  are  first  picked  out  by  hand ; 
the  residue,  consisting  chiefiy  of  tin-stone,  with  the  earthy  impu- 
rities of  the  matrix,  mixed  with  arsenical  copper  and  iron  pyrites, 
passes  to  the  stamping  mill,  where  it  is  reduced  to  a coarse  powder. 
This  powder  is  then  huddled  and  washed  (529),  to  remove  the 
lighter  impurities. 

2.  — The  heavier  portion,  however,  still  retains  a considerable  ' 
quantity  of  arsenical  iron  and  copper  pyrites.  The  next  operation 
is  intended  to  get  rid  of  these  substances;  with  this  ^fiew  the 
washed  ore  is  roasted  in  a reverberatory  furnace  until  the  arsenic 
and  a good  deal  of  the  sulphur  are  expelled,  and  the  ore  becomes 
converted  into  yellowish-brown  powder  ; this  process  usually  lasts 
about  twelve  hours.  During  this  roasting,  frequent  stirring  is 
necessary  in  order  to  expose  fresh  surfaces  freely  to  the  air.  By 
this  means  the  iron  pyrites  is  decomposed,  and  is  converted  into 
sulphurous  anhydride  and  peroxide  of  iron  ; the  arsenic  is  expelled 
as  arsenious  anhydride,  and  the  greater  part  of  the  sulphide  of 
copper  is  converted  into  sulphate  of  copper ; this  conversion  is 
completed  by  exposing  the  mass  in  a moistened  state  to  the  air  for 
some  days. 

3.  — The  sulphate  of  copper  is  then  dissolved  out  by  lixiviation  ; 
after  which  the  principal  part  of  the  peroxide  of  iron,  as  it  is  much 
lighter  than  the  oxide  of  tin,  is  got  rid  of  by  washing. 


EXTRACTION  OF  METALLIC  TIN. 


553 


4.  — The  washed  ore  is  now  ready  for  reduction.'^  In  order 
to  attain  this  object  it  is  mixed  with  from  one-tifth  to  one-eighth 
its  weight  of  powdered  anthracite  or  of  charcoal,  and  witli  a small 
proportion  of  lime  to  facilitate  the  fusion  of  the  siliceous  gangne, 
which  still  remains  mingled  with  the  ore.  The  mixtnre  having 
been  rendered  damp,  for  the  purpose  of  preventing  the  finer  par- 
ticles from  being  carried  away  by  the  current  of  air,  is  introduced 
into  the  reducing  furnace.  This  is  a reverberatory  furnace  with 
a low  arch  or  crown.  The  charge  having  been  placed  upon  the 
hearth,  the  doors  are  closed  up  and  the  heat  is  gradually  raised 
for  five  or  six  hours  ; the  binoxide  of  tin  is  thus  reduced  by  the 
carbon,  before  the  temperature  rises  high  enough  to  cause  the 
oxide  to  fuse  with  the  silica,  with  which  it  would  form  an  enamel 
difficult  of  reduction.  Towards  the  end  of  the  operation  the  heat 
is  raised  until  it  becomes  very  intense ; the  slags  are  thus  rendered 
fluid,  and  the  reduced  metal  subsides  to  the  bottom,  and  is 
allowed  to  run  off  into  cast  iron  pans,  from  which  it  is  ladled 
off  into  moulds ; but  the  ingots  thus  obtained  are  by  no  means 
pure. 

5.  — They  are  therefore  next  submitted  to  a process  of  liquation^ 
which  consists  in  heating  the  ingots  to  incipient  fusion,  upon  the 
bed  of  a reverberatory  furnace  : the  purer  tin,  being  the  more  fusi- 
ble portion,  gradually  melts  out  and  leaves  an  alloy,  which  has  a 
higher  melting-point.  This  less  fusible  portion,  when  remelted, 
forms  the  inferior  variety  called  block  tin.  The  tin  which  has  run 
out  of  the  ingots  is  drawn  off*  into  a second  pan  in  which  the 
metal  is  gently  heated,  being  kept  in  a state  of  fusion  by  a fire 
underneath  ; here  it  is  agitated  briskly  by  thrusting  into  the  mass 
stakes  soaked  in  water  ; the  steam  thus  produced,  as  it  bubbles  up 
through  the  molten  metal,  carries  the  dust,  slag,  and  other  me- 
chanical impurities  to  the  surface.  After  this  treatment  has  been 
continued  for  about  three  hours  the  metal  is  allowed  to  remain 
undisturbed  for  a couple  of  hours  ; it  is  then  skimmed,  ladled  out, 
and  cast  into  ingots  for  the  market.  The  portion  contained  in 
the  u])per  half  of  the  pan  is  the  purest,  as  owing  to  the  low  den- 
sity of  tin,  and  its  tendency  to  separate  from  its  alloys,  it  rises  to 
the  surface.  The  finest  quality  of  the  metal  is  frequently  heated 
a second  time  to  a temperature  a little  short  of  its  melting-point ; 
at  this  high  temperature  it  becomes  brittle,  and,  if  allowed  to  fall 
from  a height,  it  breaks  into  irregular  prismatic  fragments,  which 
are  known  as  dropped  or  grain  tin.  The  splitting  of  the  mass 
into  these  fragments  is  a rude  guarantee  of  the  purity  of  the  metal, 
since  impure  tin  does  not  become  brittle  in  this  manner. 

On  the  continent  the  stream  tin  is  frequently  reduced  in  small 
blast  furnaces  termed  by  the  Yyq,wc\\  fourneanx  d manche  ' the  fuel 
used  in  this  case  is  charcoal.  The  tin  which  is  imported  from 

* When  much  wolfram  is  contained  in  the  ore  it  is  sometimes  fused  with  carbo- 
nate of  sodium  before  proceeding  to  the  reduction ; the  tungstic  acid  is  thus  removed 
in  the  form  of  tungstate  of  sodium,  which  is  extracted  by  water,  and  is  sometimes 
employed  in  calico-printing  as  a mordant : it  has  lately  also  been  proposed  to  apply 
it  to  muslin  dresses  to  prevent  them  from  burning  with  flame,  should  they  happen  to 
take  fire  (618). 


554 


PEOPERTIES  USES  OF  TIN. 


Banca  is  almost  chemically  pure.  English  tin  usually  contains 
small  quantities  of  arsenic,  copper,  iron,  and  lead,  and  often  traces 
of  gold. 

When  required  in  a state  of  perfect  purity,  the  metal  may  he 
obtained  by  means  of  voltaic  action.  For  this  purpose  a concen- 
trated solution  of  crude  tin  in  hydrochloric  acid  may  be  placed  in 
a beaker,  and  water  cautiously  poured  in  without  disturbing  the 
dense  solution  below.  If  a bar  of  tin  be  plunged  into  the  liquid, 
beautiful  prismatic  crystals  of  pure  tin  are  gradually  deposited  on 
the  bar  at  the  point  of  junction  between  the  metallic  solution  and 
the  water. 

(810)  Properties. — Tin  is  a white  metal  with  a tinge  of  yel- 
low, and  a high  metallic  lustre.  It  is  rather  soft,  and  is  very 
malleable,  but  is  deficient  in  tenacity.  At  a temperature  of 
about  212°  its  ductility  is  considerable,  and  it  may  then  be  easily 
drawn  into  wire.  In  a laminated  state  it  is  well  known  as  tin- 
foil.  If  a bar  of  tin  be  bent,  it  emits  a creaking  sound,  a pro- 
perty which  it  possesses  in  common  with  cadmium ; if  bent  seve- 
ral times  in  succession  backwards  and  forwards,  it  becomes  sensi- 
bly hot  at  the  point  of  fiexure.  These  effects  depend  upon  a 
mechanical  alteration  of  the  relative  position  of  its  molecules, 
and  their  mutual  friction.  Tin,  when  handled,  communicates  a 
peculiar  odour  to  the  fingers.  It  is  a tolerably  good  conductor 
both  of  heat  and  electricity.  It  fuses  at  442°,  according  to  Crich- 
ton (or  451°,  Person),  but  is  not  sensibly  volatilized  in  the  fur- 
nace. It  may  be  obtained  in  crystals  by  slow  cooling  after  fusion. 
Tin  is  but  slowly  tarnished  by  exposure  to  the  air  and  moisture 
at  ordinary  temperatures,  but  if  heated  to  redness  in  a current  of 
steam,  or  if  exposed  to  the  air  at  a high  temperature,  it  becomes 
rapidly  converted  into  the  binoxide  and  burns  with  a brilliant 
white  light.  Xitric  acid  of  sp.  gr,  1-52  does  not  attack  tin,  but 
if  diluted  to  1*3  it  acts  upon  it  ^fiolently,  and  produces  an  insolu- 
ble hydrated  binoxide  of  the  metal  known  as  metastannic  acid ; 
at  the  same  time,  owing  to  the  decomposition  of  water,  a con- 
siderable quantity  of  ammonia  is  formed,  which  enters  into  com- 
bination with  the  excess  of  nitric  acid.  Strong  hydrochloric  acid, 
when  heated  upon  tin,  dissolves  it  gradually  with  extrication  of 
hydrogen.  Aqua  regia,  if  not  too  concentrated,  dissolves  the 
metal  and  converts  it  into  the  perchloride.  Diluted  sulphuric 
acid  is  without  action  on  the  metal  in  the  cold ; but  if  the  con- 
centrated acid  be  boiled  upon  it,  the  tin  becomes  converted  into 
sulphate  of  the  peroxide,  and  globules  of  sulphur  are  separated, 
while  sulphurous  anhydride  escapes : the  tin  appears  in  this 
case  to  be  dissolved  as  stannous  sulphate,  which  is  oxidized  to 
stannic  sulphate  at  the  expense  of  the  sulphurous  acid,  and  sul- 
phur is  deposited ; Sn  + 2 II^SO^  yielding  Sn'^SO^  -f-  SO,  -f  2 11,0 ; 
and  2 Sn"  SO,  -f  SO,  + 2 H,SO,  furnish  2 (Sn-  2 SO,)  -f  S + 2 H,0. 
The  hydrates  of  potash  and  soda  act  upon  tin  at  high  tempera- 
tures, hydrogen  being  evolved,  whilst  a soluble  metastannate  of 
the  alkali-metal  is  formed.  Tin  combines  readily  with  sulphur, 
phosphorus,  chlorine,  and  bromine,  if  heated  with  them. 


TIN-PLATE PROCESSES  OF  TINNING. 


555 


Owing  to  its  brilliancj,  and  its  power  of  resisting  ordinary 
atmospheric  changes,  tin  is  largely  employed  as  a coating  upon 
other  more  ahnndant  but  more  oxidizable  metals,  to  protect  them 
during  use.  Iron  and  copper  are  especially  adapted  to  the  opera- 
tion of  tinning.  In  India,  tin  is  applied  instead  of  silver  to  steel 
and  iron  articles  by  way  of  ornament ; the  tin  is  melted,  and 
while  still  liquid  is  agitated  in  a box  till  it  has  become  solid ; the 
fine  powder  thus  procured  is  separated,  by  suspension  in  water, 
from  the  coarser  particles,  and  is  made  into  a thin  paste  with 
glue ; it  is  then  applied  in  the  desired  pattern ; when  perfectly 
dry  it  is  burnished,  and  afterwards  varnished;  its  brilliancy  is 
thus  preserved  unchanged. 

(811)  Tin-Plate. — The  ordinary  process  of  tinning  iron  differs 
from  the  foregoing  one,  and  is  far  more  important  in  its  economi- 
cal results.  In  tin-plate  an  actual  alloy  of  the  two  metals  is 
formed  upon  the  surface  of  the  iron,  the  external  surface  being 
pure  tin.  For  the  manufacture  of  tin-plate,  the  best  charcoal  iron 
is  required.  After  the  iron  has-  been  rolled  and  cut  into  sheets 
of  suitable  thickness  and  size,  its  surface  is  made  chemically 
clean.  For  this  purpose  the  sheets  are  immersed  for  four  or  five 
minutes  in  a mixture  of  sulphuric  acid  and  water ; after  which 
the}-  are  raised  to  a red  heat  in  a reverberatory  furnace ; they  are 
then  withdrawn,  allowed  to  cool,  and  hammered  fiat.  In  order 
to  detach  from  them  all  the  scales  of  oxide,  they  are  passed  be- 
tween polished  rollers,  and  as  they  emerge  they  are  plunged  one 
by  one  into  a mixture  of  bran  and  water  which  has  become  sour 
by  exposure  to  the  air ; here  they  remain  for  some  hours,  and  are 
thence  transferred  to  a vessel  containing  a mixture  of  diluted  sul- 
phuric and  hydrochloric  acids ; lastly,  they  are  scoured  with  bran, 
and  plunged  into  pure  water  or  lime-water,  in  which  last,  if  the 
surface  be  clean  on  immersion,  they  may  remain  for  any  length 
of  time  without  rusting : these  preliminary  steps  are  necessary  in 
order  to  secure  a clean  surface,  as  the  tin  will  not  adhere  to  an 
oxidated  or  even  a dusty  plate.  In  some  works,  the  plates,  after 
they  have  been  scoured,  are  further  cleaned  with  hydrochloric 
acid  holding  zinc  in  solution,  and  then  dipped  into  the  melted 
tin  in  the  manner  about  to  be  described. 

The  plates  having  been  prepared  by  either  of  the  foregoing 
processes  are  next  plunged  one  by  one  into  a large  vessel  of  melted 
tallow  free  from  salt,  and  after  remaining  there  for  an  hour  they 
are  immersed  in  the  bath  of  melted  tin,  which  is  preserved  from 
oxidation  by  a stratum  of  grease  three  or  four  inches  thick. 
Here  tliey  remain  for  about  an  hour  and  a half ; they  are  then 
withdrawn  and  allowed  to  drain.  After  this  they  are  plunged 
into  a second  bath  of  pure  tin,  and  the  excess  of  tin  is  removed 
by  again  heating  them  in  a bath  of  tallow : the  tin  melts  and 
runs  down  to  the  lower  edge  of  the  ])late ; when  cool,  this 
thickened  margin  is  finally  reduced  by  dipping  the  edge  of  the 
])late  once  more  into  tin  kept  at  a temperature  much  above  its 
melting-point ; the  heat  quickly  fuses  the  superfluous  metal, 
which  is  then  detached  by  giving  the  plate  a sharp  blow.  Tin- 


556 


ALLOTS  OF  TIX  WITH  LEAD  ATD  COPPER. 


plate  is  sometimes  made  to  exhibit  a beautiful  crystalline  appear- 
ance, known  under  the  term  moiree  metallique.  A mixture  of  2 
parts  of  nitric  acid,  with  2 of  hydrochloric  acid,  is  made  with  4 
of  water : the  tin-plate  is  gently  heated,  and  the  liquid  spread 
eyenly  oyer  with  a sponge  ; the  crystals  gradually  appear.  The 
plate  is  then  plunged  into  water,  dried  quickly,  and  yarnished. 
Different  coloured  yarnishes  are  used  to  yary  the  effects. 

Tinning  of  copper  is  the  same  in  principle,  but  is  a simpler 
operation  than  the  tinning  of  iron : the  surface  of  the  metal  is 
rendered  clean  by  rubbing  it,  while  heated,  with  sal  ammoniac ; 
when  quite  bright  the  copper  is  sprinkled  with  a little  rosin  to 
preyent  oxidation,  and  melted  tin  is  then  poured  on  and  spread 
oyer  the  surface  with  tow  by  the  workman,  who  keeps  the  article 
constantly  at  a high  temperature  ; the  superfluous  tin  is  wiped  off 
with  the  tow.  The  addition  to  the  tin  of  one-fourth  of  its  weight 
of  lead  renders  the  operation  more  easy,  as  the  alloy  is  more  per- 
fectly liquefied.  Pins,  which  are  made  of  brass  wire,  are  tinned 
by  boiling  them  for  a few  minutes  with  a solution  containing  1 
part  of  cream  of  tartar,  2 parts  of  alum,  and  2 of  common  salt  in 
12  parts  of  water,  with  a quantity  of  granulated  tin : in  the 
course  of  a few  minutes  a brilliant,  white,  closely  adhering  coat 
of  tin  is  deposited  upon  the  surface  of  the  pins. 

(812)  The  alloys  of  tin  which  are  employed  in  the  arts  are 
numerous.  Britannia  metal  is  one  which  is  a good  deal  used  for 
making  teapots  and  spoons  of  a low  price ; it  consists  of  equal 
parts  of  brass,  tin,  antimony,  and  bismuth.  Pewter  is  another 
alloy  of  this  description ; both  uf  these  possess  considerable  mal- 
leability, pewter  being  intermediate  in  hardness  between  lead  and 
Britannia  metal.  The  best  pewter  consists  of  4 parts  of  tin,  and 
1 of  lead.  Another  alloy,  which  is  intermediate  in  properties 
between  pewter  and  Britannia  metal,  is  called  Queen’s  metal ; it 
is  used  for  the  manufacture  of  teapots  and  common  spoons.  It 
consists  of  9 parts  of  tin,  1 part  of  antimony,  1 of  bismuth, 
and  1 of  lead.  Plumber’s  solder  is  an  alloy  of  tin  and  lead  which 
is  more  fusible  than  pure  lead : fine  solder  consists  of  2 parts  tin 
and  1 of  lead ; common  solder  of  equal  parts  of  lead  and  tin ; and 
coarse  solder  is  composed  of  2 of  lead  to  1 of  tin.  Lead  and  tin 
may  be  melted  together  in  all  proportions,  and  notwithstanding 
their  difference  in  density,  they  do  not  separate  when  the  fused 
mixture  is  allowed  to  cool  slowly  (^latthiessen).  The  same  is 
true  also  of  the  alloy  of  tin  and  zinc ; if  the  two  metals  be  fused 
together  in  equal  proportions,  the  result  forms  a hard,  white  alloy 
nearly  as  tough  as  brass. 

Tin  forms  seyeral  important  alloys  with  copper.  Speculum 
metal^  used  for  the  mirrors  of  reflecting  telescopes,  consists  of  1 
part  tin  and  2 copper,  or  (Ou^Sn) : it  is  of  a steel-white  colour, 
extremely  hard,  brittle,  and  susceptible  of  a high  polish.  The 
proportions  of  the  constituents  of  speculum  metal  recommended 
by  different  authorities  yary,  and  sometimes  a small  quantity  of 
arsenic  is  added  to  the  alloy.  Bell  metal  consists  of  about  78  of 
copper  and  22  of  tin,  or  (OugSn) ; sometimes  a mixtm’e  of  zinc 


AMALGAM  OF  TIN  AND  MERCURY. 


55T 


and  lead  is  substituted  for  a part  of  the  tin.  Gnn  metal  contains 
only  9 or  10  per  cent,  of  tin.  Bronze  contains  less  tin  than  bell- 
metal,  with  usually  an  addition  of  3 or  4 per  cent,  of  zinc.  The 
bronze  used  for  coin  consists  of  95  parts  of  copper,  4 of  tin,  and  1 
of  zinc.  Bronze  admits  of  a peculiar  kind  of  tempering.  If  it  be 
annealed,  and  allowed  to  cool  slowly,  it  becomes  hard,  brittle,  and 
elastic ; but  if  cooled  suddenly,  it  may  be  hammered,  and  worked 
at  the  lathe ; this  property  is  taken  advantage  of  in  the  manufacture 
of  articles  with  this  alloy ; they  are  wrought  in  the  soft  state,  and 
are  afterwards  hardened  by  annealing.  The  effect  of  sudden 
cooling  upon  bronze  is  therefore  just  the  reverse  of  that  which  is 
produced  by  it  upon  steel.  These  alloys  of  copper  and  tin  are 
much  harder  than  copper  itself,  and  considerably  more  fusible. 
The  melting-point  of  copper,  according  to  Daniell,  is  1996° ; but 
an  alloy  of  tin  and  copper  containing  6*6  per  cent,  of  tin,  fused 
at  1690°;  and  1 with  12’3  per  cent,  of  tin,  at  1534°  F.  These 
alloys  have  a specific  gravity  greater  than  the  mean  of  that  of  the 
metals  wliich  enter  into  their  composition.  They  resist  oxidation 
in  the  air  more  completely  than  copper. 

An  inconvenience  in  the  use  of  the  alloys  of  copper  and  tin 
arises  from  the  circumstance,  that,  when  melted,  the  two  metals, 
owing  to  their  difference  in  density,  have  a tendency  to  separate 
from  each  other,  even  after  they  have  been  well  incorporated ; the 
tin  accumulates  in  the  upper  portions  of  the  melted  mass,  where 
it  forms  a more  fusible  alloy.  It  is  therefore  very  difiicult  in  large 
castings  to  obtain  a mass  of  metal  the  composition  of  which  is 
uniform  throughout. 

The  amalgam  of  tin  and  mercnry  is  employed  for  the  silver- 
ing of  mirrors.  In  order  to  apply  it  to  the  glass,  a slieet  of  tin- 
foil  is  spread  evenly  upon  a smooth  slab  of  stone,  which  forms  the 
top  of  a table  carefully  levelled,  and  surrounded  by  a groove,  for 
the  reception  of  the  superfluous  mercury.  Clean  mercury  is 
poured  upon  the  tin-foil,  and  spread  uniformly  over  it  with  a roll 
of  flannel ; more  mercury  is  then  poured  on  till  it  forms  a fluid 
layer  of  the  thickness  of  about  half-a-crown  ; the  surface  is  cleared 
of  impurities  by  passing  a linen  cloth  lightly  over  it ; the  plate 
of  glass  is  carefully  dried,  and  its  edge  being  made  to  dip  below 
the  surface  of  the  mercury,  is  pushed  forward  cautiously  ; all 
bubbles  of  air  are  thus  excluded  as  it  glides  over  and  adheres  to 
the  surface  of  the  amalgam.  The  plate  is  then  covered  with 
flannel,  weights  are  placed  upon  the  glass,  and  the  stone  is  gently 
inclined  so  as  to  allow  the  excess  of  mercury  to  drain  off;  at  the 
end  of  24  hours  it  is  placed  upon  a wooden  table,  the  inclination 
of  which  is  increased  from  day  to  day  until  the  miri*or  assumes  a 
vertical  position ; in  about  a month  it  is  sufficiently  drained  to 
allow  the  mirror  to  be  framed.  The  amalgam  usually  contains 
abour  4 parts  of  tin  to  1 part  of  mercury. 

Several  of  the  compounds  of  tin  are  employed  in  the  arts. 
The  binoxide  is  used  to  some  extent  in  the  preparation  of  enamels, 
and  both  the  chlorides  of  tin  are  substances  of  great  importance 
to  the  dyer  and  the  calico-printer. 


55S 


OXIDES  OF  TIX. 


(SI 3)  Oxides  of  Tix. — '^ith  oxygen,  tin  forms  t^vo  principal 
compounds,  the  protoxide  and  the  hinoxide,  besides  some  interme- 
diate oxides  of  minor  importance. 

Stanjious  oxide  ot protoxide  of  tin  (SnO  = 13d,  or  SnO  = 
67)  is  obtained  as  a white  hydrate  (2  Sn0,H20),  by  pouring  a so- 
lution of  stannous  chloride  into  one  of  carbonate  of  sodium  or  of 
potassium  in  excess  ; the  carbonic  anhydride  escapes  with  efferves- 
cence. When  moist,  this  hydrate  absorbs  oxygen  from  the  air, 
but  not  when  dry.  By  ignition  in  closed  vessels  filled  with 
nitrogen  or  with  carbonic  anhydride  it  becomes  anhydrous.  The 
anhydrous  protoxide  may  also  be  obtained  by  decomposing 
stannous  oxalate  by  heat  in  closed  vessels.  If  heated  in  the  open 
air  it  glows,  and  is  converted  into  the  hinoxide.  If  the  hydrated 
oxide  be  boiled  with  a solution  of  potash  in  excess,  it  is  dissolved, 
and  in  a few  days  metallic  tin  is  separated,  peroxide  of  the  metal 
remaining  in  solution.  If  boiled  with  a weak  solution  of  potash, 
in  quantity  insufficient  to  dissolve  the  oxide,  it  becomes  anhydrous, 
and  is  converted  into  a mass  of  black  crystalline  needles;  these 
needles  when  heated  decrepitate  powerfully,  increase  in  bulk,  and 
are  converted  into  an  olive-brown  powder.  By  evaporating  down 
a solution  of  sal  ammoniac  containing  hydrated  oxide  of  tin  in 
suspension  imtil  the  sal  ammoniac  begins  to  crystallize,  the  oxide 
of  tin  becomes  anhydrous  and  assumes  a brilliant  scarlet  colour, 
which,  however,  by  friction  disappears,  and  becomes  brown.  The 
hydrated  oxide  is  readily  dissolved  by  acids,  but  the  anhydrous 
oxide  is  more  slowly  acted  upon  by  them. 

(Sid)  Binoxide  of  Tin  — 150,  or  SnO^  = 75);  Sp.  Gr. 

6‘95 ; Comp,  in  100  parts,  Sn,  78*66;  O,  21*31:. — This  oxide 
occurs  native  in  the  anhydrous  form  as  tin-stone,  and  constitutes 
the  only  ore  of  tin  that  is  worked.  It  is  met  with  crystalhzed  in 
square  prisms,  which  are  hard  enough  to  scratch  glass ; they  have 
usually  a bro^vn  colour,  owing  to  the  presence  of  peroxide  of  iron 
or  of  manganese.  It  is  insoluble  in  acids,  but  if  heated  with  an 
alkali,  it  enters  into  combination  with  it,  and  forms  a soluble 
compound. 

In  its  hydrated  condition  binoxide  of  tin  has  the  characters  of 
an  acid,  and  forms  two  remarkable  varieties,  which  have  been 
termed  respectively  metastannic  and  stannic  acids  (Fremy,  Ann. 
de  Chimie,  III.  xviii.  393).  Like  the  metaphosphonc  and  phos- 
phoric acids,  they  require  each  a different  amount  of  base  for 
saturation,  the  stannic  acid  combining  with  the  greatest  propor- 
tion of  base. 

2Letastannic  Acid  (H^Sn^Oj^ . 4 II„0)  is  readily  procured  by 
treating  metallic  tin  with  nitric  acid;  violent  action,  attended 
with  extrication  of  nitrous  fumes,  occurs,  and  the  tin  is  converted 
into  a white,  crystalline,  insoluble  mass,  which  is  hydrated  meta- 
stannic acid ; after  washing  it  with  cold  water,  the  acid,  when 
dried  in  air,  consists  of  Sn^Oj,  10  II^O  (Fremy).  In  this  state  it 
reddens  litmus-paper ; when  dried  at  212°  it  loses  half  its  water, 
and  by  ignition  becomes  anhydrous,  and  of  a pale  buff  colour  ; in 
this  form  it  possesses  the  properties  of  the  native  oxide,  and  con- 


STANNIC  ACID STANNATES. 


559 


stitntes  the  putty  powder  employed  for  polishing  plate  ; it  is  also 
largely  used  for  giving  whiteness  and  opacity  to  enamels. 

In  its  hydrated  condition,  metastannic  acid  is  insoluble  in 
nitric  acid ; concentrated  snlphnric  acid,  when  heated  with  it,  dis- 
solves it  freely  and  forms  a compound  solnhle  both  in  water  and 
in  alcohol ; by  boiling  the  solution  it  is  decomposed,  and  the  two 
acids  are  separated.  Hydrochloric  acid  combines  with  it,  but 
does  not  dissolve  it ; the  compound  is  soluble  in  pure  water,  but 
is  reprecipitated  on  the  addition  of  acid  in  excess,  or  on  boiling  the 
solution.  Metastannic  acid  is  freely  soluble  in  solutions  of  potash 
and  of  soda,  as  well  as  in  solutions  of  their  carbonates,  but  it  is  not 
dissolved  by  ammonia,  unless  recently  precipitated  from  a cold 
solution  of  its  salts  by  the  addition  of  an  acid  ; the  precipitate  is 
not  soluble  in  ammonia  after  it  has  been  boiled.  The  metastan- 
nates  are  not  crystallizable,  and  are  precipitated  by  adding  caustic 
potash  to  their  aqueous  solution  ; the  granular  precipitate  may  be 
drained  upon  a tile,  and  dried  at  260° ; their  normal  formula  is 
M'^SiigOj,  with  usually  4 ; or  (M'0,Sn^50jo,  4 HO).  The  potas- 

sium salt  has  a strongly  alkaline  reaction  ; it  consists  of  (K^Sn^O^j, 
4 H2O).  The  metastannates  of  the  alkalies  can  only  exist  in  the 
hydrated  condition ; if  strongly  heated  they  are  decomposed  and 
become  insoluble  ; when  the  residue,  after  ignition,  is  treated  with 
water,  metastannic  acid  is  left,  whilst  the  alkali  is  dissolved. 
Metastannic  acid  may  be  recognised  by  the  beautiful  golden-yel- 
low colour  which  it  yields  -when  its  hydrate  is  moistened  with 
protochloride  of  tin,  owing  to  the  formation  of  metastannate  of 
tin  (Sn,Sn50u  4 H^O).  The  only  metastannates  which  are  solu- 
ble are  those  of  potassium  and  sodium ; they  are  precipitated  in 
the  gelatinous  state  from  their  solutions  by  the  addition  of  almost 
any  of  the  neutral  salts  of  sodium,  potassium,  or  ammonium. 

(815)  Stannic  Acid  (H^SnOg  or  H0,Sn02). — This  variety  of 
the  hydrated  oxide  of  tin  may  be  procured  by  precipitating  a 
solution  of  tetrachloride  of  tin  by  ammonia,  or  still  better  by  add- 
ing to  the  solution  of  the  tetrachloride  a quantity  of  an  insoluble 
carbonate,  such  as  chalk  or  carbonate  of  barium,  insufRcient  for 
its  entire  decomposition ; it  is  thus  separated  as  a gelatinous  pre- 
cipitate, which  may  be  readily  washed  clean  : when  dried  in  vactio^ 
the  composition  of  the  hydrate  is  (H^SnOg).  In  this  state  it  is 
freely  soluble  in  hydrochloric  acid,  with  which  it  reproduces  tetra- 
chloride  of  tin ; it  is  also  soluble  even  in  diluted  sulpliuric  acid, 
but  the  stannic  acid  is  separated  on  boiling.  Hitric  acid  dissolves 
it  freely.  Stannic  acid  is  soluble  in  the  cold  in  solutions  of  potash 
and  of  soda,  but  not  in  ammonia ; by  a lieat  of  284°  it  is  con- 
verted into  metastannic  acid.  In  combination  with  tlie  alkalies 
it  foians  compounds  which  crystallize  readily,  especially  from  solu- 
tions which  contain  an  excess  of  alkali.  The  general  formula  is 
M'gSnOg,  or  M0,Sn02. 

The  soluble  stannates  have  a powerfully  alkaline  reaction ; 
they  absorb  carbonic  acid  from  the  air  when  in  solution,  and  are 
precipitated  by  solutions  of  most  of  the  salts  of  potassium,  sodium, 
and  ammonium. 


560 


SULPHIDES  OF  TDI. 


Stannate  of  potussium  (K2Sn03,4  H^O)  is  easily  prepared  by 
beating  any  form  of  peroxide  of  tin  with  excess  of  caustic  potash  ; 
on  dissohdng  and  evaporating  the  product,  transparent  oblique 
rhombic  prisms  are  formed.  When  heated  to  redness,  the  stan- 
nate of  potassium  may  be  rendered  anhydrous.  StannaU  of 
sodiiun  (]S’a2Sn03,4H2^)  maybe  prepared  in  the  same  way  as  the 
stannate  of  potassium.  It  crystallizes  with  facility  in  six-sided 
tables,  when  a solution  saturated  at  about  100°  F.  is  heated  to  the 
boiling-point,  as  it  is  more  soluble  in  cold  than  in  hot  water. 
This  s'tannate  is  now  largely  prepared  as  a mordant  for  the  use  of 
the  dyer  and  calico-printer.  It  forms  the  basis  of  what  is  tech- 
nically known  as  tin-prepare  liquor.  Copper  is  quickly  tinned  by 
a solution  of  this  salt. 

Sesquioxide  of  tin or  stannate  of  tin  as  it  is  often  called 
(Sn30-3,  or  SnOjSnO^),  may  be  prepared  as  a slimy  grey  hydrate, 
soluble  in  ammonia,  by  boiling  pure  hydi’ated  sesquioxide  of  iron 
with  a solution  of  stannous  chloride ; ferrous  chloride  remains  in 
solution,  2 SnCL  + Fe^Og  = 2 FeCl^  -1-  SnOjSnOg.  It  is  soluble  in  hy- 
drochloric acid  and  also  in  ammonia,  which  latter  reaction  seems  to 
indicate  that  it  is  really  a distinct  oxide  ; the  hydrochloric  solution 
gives  a purple  precipitate  with  salts  of  gold. 

(816)  The  SULPHIDES  of  tlx  are  three  in  number, — the  proto- 
sulphide, the  bisulphide,  and  the  sesquisulphide  : the  latter  is  un- 
important. 

The  P rotosidpJiide  (SnS=150,  or  SnS  = T5)  may  be  procured 
by  fusing  the  metal  with  sulphur,  when  it  forms  a bluish-grey 
crystalline  mass,  easily  dissolved  by  melted  tin ; it  may  also  be 
obtained  by  passing  sulphuretted  hydrogen  through  a stannous 
salt  in  solution,  when  it  falls  as  a chocolate-brown  hydrate.  It  is 
soluble  in  solution  of  bisulphide  of  ammonium,  and  in  the  sul- 
pliides  of  the  alkaline  metals,  if  they  contain  an  excess  of  sulphur. 
Protosulphide  of  tin  combines  with  the  sulphides  of  the  electro- 
negative metals,  such  as  arsenic  and  antimony.  Hydrochloric 
acid  dissolves  it  with  extrication  of  sulphuretted  hydi*ogen. 

The  SesquisvdpMde  (Sn^Sg)  may  be  prepared  by  mixing  the 
protosulphide  with  one-third'  of  its  weight  of  sulphur,  and  heating 
to  dull  redness ; it  is  only  partially  soluble  in  hydrochloric  acid. 

The  Bisulphide  of  tin  (SnS2=lS2,  or  SnS2=91)  is  known  as 
mosaic  gold  / it  forms  a beautiful  yellow  flaky  compound,  which 
is  obtained  by  prepanng  an  amalgam  of  12  parts  of  tin  and  6 of 
mercury  : this  is  reduced  to  powder  and  mixed  with  7 parts  of 
sublimed  sulphur  and  6 of  sal  ammoniac.  This  mixture  is  in- 
troduced into  a flask  with  a long  neck,  and  is  heated  gently  so 
long  as  any  smell  of  sulphuretted  hydrogen  is  perceptible ; the 
temperature  is  then  raised  to  low  redness  ; calomel  and  cinnabar 
are  sublimed,  and  a scaly  mass  of  bisulphide  of  tin  remains.  If 
the  heat  be  pushed  too  far,  part  of  the  sulphur  is  exjielled,  and 
the  operation  fails  : the  sal  ammoniac  appears  by  its  volatilization 
to  moderate  the  heat  produced  during  the  sulphuration  of  the  tin, 
which  would  otherwise  rise  so  high  as  to  decompose  the  bisul- 
phide, and  mechanically  preserves  the  requisite  flaky  structm-e  of 


STANNOUS  CHLOEIDE,  OE  PEOTOCnLOEIDE  OF  TIN.  561 

tlie  compound.  Bisulphide  of  tin  is  used  in  the  arts  to  imitate 
bronze.  Aqua  regia  is  the  only  acid  that  decomposes  it,  but  it  is 
readily  soluble  in  the  alkalies.  A hydrated  bisulphide  of  tin,  of 
a dingy  yellow,  is  produced  by  passing  sulphuretted  hydrogen 
through  a solution  of  one  of  the  stannic  salts.  This  hydrate  is 
readily  dissolved  by  hydrosulphate  of  ammonium,  evolving  sul- 
phuretted hydrogen  : it  is  also  soluble  in  the  alkalies,  and  in  hot 
hydrochloric  acid.  With  sulphide  of  sodium  it  forms  a salt  which 
may  be  obtained  in  yellow  crystals,  consisting  of  2 I^a2S,SnS2 . 12 

H,e. 

The  bisulphide  fuses  when  chlorine  is  passed  over  it ; 6 atoms 
of  the  gas  are  absorbed,  without  the  aid  of  heat,  by  each  atom  of 
bisulphide,  and  a yellow  crystalline  compound  is  obtained  which 
may  be  considered  as  a combination  of  1 atom  of  tetrachloride  of 
tin  with  2 atoms  of  tetrachloride  of  sulphur,  SnCl^,  2 SCI,. 

(817)  Chloetdes  of  Tin. — Tin  forms  with  chlorine  two  com- 
jiounds,  SnClj,  and  SnCl„  formerly  termed  the  chloride  and  bi- 
chloride of  the  metal,  but  they  are  now  better  distinguished  as 
stannous^  and  stannic  chloride. 

Stannous  chloride  (SnCl2=189),  or  protochloride  of  tin  (SnCl 
=:91:'5). — The  hydrate  of  this  salt  may  be  obtained  by  dissolving 
tin  in  hydrochloric  acid.  This  solution  is  usually  effected  on  the 
large  scale  in  copper  vessels,  since  the  voltaic  opposition  of  the 
two  metals  favours  the  solution  of  the  tin  : on  evaporating  the 
liquid  till  it  crystallizes,  prismatic  needles  are  formed  (SnCl^,  2 
HjO;  sp.  gr.  2*759) ; by  a heat  of  212°  it  may  be  rendered  anhy- 
drous, but  it  generally  loses  a portion  of  hydrochloric  acid  at  the 
same  time.  Stannous  chloride  is  decomposed  if  mixed  with  a 
large  quantity  of  water,  hydrochloric  acid  remains  in  solution, 
and  a white  hydrated  oxycldoride  (SnCl2,SnO,  2 Ha^),  subsides. 
When  exposed  to  the  air  in  crystals  or  in  solution,  stannous  chlo- 
ride absorbs  oxygen  and  forms  a mixture  of  perchloride  and  oxy- 
chloride of  tin.  Stannous  chloride  has  a strong  attraction  both 
for  chlorine  and  for  oxygen ; it  therefore  acts  as  a powerful  re- 
ducing agent.  Thus  it  deoxidizes  completely  the  salts  of  mercury, 
of  silver,  and  of  gold.  Advantage  is  sometimes  taken  of  this 
circumstance  in  the  analytical  determination  of  the  quantity  of 
mercury,  since  all  the  salts  of  mercury,  when  boiled  with  the 
stannous  chloride,  are  decomposed,  and  yield  their  mercury  in  a 
metallic  form.  Sulphurous  acid  is  likewise  deprived  by  it  of  its 
oxygen,  ])roducing  a yellow  precipitate  of  bisulphide  of  tin  when 
mixed  with  a solution  of  the  salt.  Stannous  chloride  reduces  tlie 
metallic  acids  in  tlie  salts  of  chromic,  tungstic,  molybdic,  arsenic, 
antimonic,  and  manganic  acids  to  a lower  state  of  oxidation  ; it 
also  converts  the  ferric  into  ferrous  salts,  and  the  cupric  into 
cupreous  salts.  Stannous  chloride  is  extensively  employed  as  a 
mordant  by  the  dyer  and  calico-printer,  under  the  name  of 
salts  of  tin.,  and  they  also  use  it  for  deoxidizing  indigo  and  the 
jieroxides  of  iron  and  manganese.*  It  forms  double  chlorides 

* The  proportion  of  stannous  chloride  available  for  this  purpose  in  any  commer- 
cial sample  may  be  determined  by  Penny’s  method: — A solution  of  a weighed  quan- 
36 


562 


CHAEACTEES  OF  THE  SALTS  OF  TIX. 


with  many  of  the  chlorides  of  the  metals  of  the  alkalies  and  al- 
kaline earths  ; these  double  salts  are  capable  of  crystallization. 

The  anhvdrons  stannous  chloride,  or  hiitter  of  tin^  may  be 
procured  by  distilling  a mixture  of  equal  weights  of  tin  tilings  and 
corrosive  sublimate;  HgCl^  + Sn^SnCl^  + Hg  : it  remains  behind 
as  a grey  brilliant  mass  with  a vitreous  fracture  ; at  a full  red 
heat  it  may  be  distilled.  On  passing  a current  of  chlorine  over 
it,  heat  and  light  are  evolved,  and  the  tetrachloride  of  tin  is 
formed. 

(818)  Stannic  chloride^  or  Tetrachloride  of  Tin  (SnC1,=260) ; 
S}J.  Gr.  of  vapour^  9’2  ; of  liquid^  2-36T  at  32°  ; Mol.  Yol.  | | I ; 
Boiling pt.  239°. 5 ; (k  Bichloride  of  Tin  (SnCl2=130). — This  com- 
pound may  be  prepared  either  by  passing  dry  chlorine  over  melted 
tin,  or  by  mixing  4 parts  of  corrosive  sublimate  with  1 part  of  tin 
tilings : on  the  application  of  heat  a colourless  liquid  distils  ; 2 
HgCla  + Sn  yielding  SnCl4-}-2  Hg.  It  emits  dense  white  fumes 
when  exposed  to  the  air : when  mixed  with  water,  intense  heat  is 
evolved,  and  a hydrate  is  formed ; this  compound  crystallizes  in 
rhombohedra  (SnCl^,  5 1120 ; Tewy)  when  it  is  allowed  to  form 
spontaneously,  by  attracting  moisture  from  the  air ; in  vacuo  it 
loses  3 ITO  : but  though  freely  soluble  in  a small  quantity  of 
water,  copious  dilution  causes  the  precipitation  of  hydrated  stannic 
acid,  and  hydrochloric  acid  is  set  free.  Tetrachloride  of  tin  is 
readily  soluble  in  water  acidulated  with  hydi’ochloric  acid.  TThen 
its  aqueous  solution  is  mixed  with  a solution  of  the  sulphate  of 
one  of  the  alkali-metals,  hydrated  binoxide  of  tin  is  precipitated ; 
SnCl^-f  4 1120  + 1:  ]Sra2S04  becoming  Sn02,  2 TI2O  + 4 XaCl  + 
4 XaliSO^,  acid  sulphate  of  the  alkaline  metal  remaining  in  solu- 
tion. 

Tetrachloride  of  tin  forms  numerous  double  salts  with  the 
soluble  chlorides ; the  compound  with  chloride  of  potassium  crys- 
tallizes in  anhydrous  octohedra,  2 KCl,SnCl^ ; a similar  constitution 
holds  in  the  corresponding  ammoniacal  salt  (2  II^IICl,SitCl^), 
which  is  the  pinTz  salt  of  the  dyer.  An  impure  tetrachloride  of 
tin  is  largely  used  by  the  dyers  under  the  name  of  nitromiiriate 
of  tin,  or  composition  ; it  is  generally  prepared  by  dissolving  tin 
at  a gentle  heat  in  a mixture  of  nitric  acid  and  sal  ammoniac. 

The  other  salts  of  tin  are  unimportant.  Stannic  sulphate  is 
soluble  in  water  strongly  acidulated  by  sulphuric  acid,  but  is  pre- 
cipitated to  a large  extent  on  copious  dilution  with  water. 

(819)  Chaeacters  of  the  Salts  of  Tlx. — Tin  forms  two  series 
of  salts,  the  salts  formed  from  the  protoxide  and  the  salts  formed 
from  the  binoxide : the  tetrachloride  of  tin  is  the  only  salt  of  the 
latter  class  that  has  been  minutely  examined. 

1. — The  stannous  salts,  or  protosalts  of  tin,  are  nearly  colour- 
less ; with  the  exception  of  the  chloride,  they  are  not  often  pre- 
pared ; they  haA^e  a powerfully  astringent  taste ; when  in  solution 

tity  of  stannous  chloride  in  hydrochloric  acid  is  taken,  and  a standard  solution  of 
anhydro-chr ornate  of  potassium  is  added  until  a drop  of  the  hquid  when  mixed  with 
acetate  of  lead  gives  a yellow  precipitate,  showing  that  the  chromic  acid  is  no  longer 
reduced:  3 SnCl2 -h Kj^raO: -f  1-i  HC1=3  SnCl4-f-2  KCl-l-^raCle+t  HjO. 


TESTS  FOE  TIN" ESTI^klATION  OF  TIN. 


663 


they  absorb  oxygen  rapidly  from  the  air ; when  largely  diluted 
with  water  the  solution  becomes  milky,  but  it  is  rendered  clear  by 
a small  excess  of  hydrochloric  acid.  The  hydrates  of  the  fixed 
cdJcalies  produce  a white  precipitate  of  liydrated  protoxide  of  tin, 
which  is  soluble  in  excess  of  the  alkali,  but  on  boiling,  part  of  the 
oxide  is  deposited  as  a black  crystalline  powder.  Ammonia 
a white  hydrated  oxide  of  tin,  but  the  precipitate  is  not  redissolved 
by  an  excess  of  ammonia.  The  carhonates  of  the  alhali-metals 
give  a similar  precipitate,  whilst  carbonic  anhydride  escapes  with 
effervescence.  A very  characteristic  reaction  is  the  production, 
with  sidpJmretted  hydrogen^  of  a chocolate  brown  precipitate  of 
hydrated  protosulphide  of  tin.  With  sidjoliide  of  ammonium^  a 
similar  precipitate  is  formed,  which  is  soluble  in  excess  of  the  pre- 
cipitant and  in  the  sulphides  of  the  alkaline  metals.  With  a 
dilute  solution  of  chloride  of  gold^  they  give,  if  used  in  excess,  a 
brown  precipitate  of  reduced  gold  ; in  smaller  quantity,  they  yield 
a beatiful  purple  precipitate,  the  purple  of  Cassius.  Ferrocyanide 
of  jpotassium  gives  a white  precipitate,  soluble  in  hydrochloric 
acid. 

2.  — The  stannic  salts'^  are  found  to  give  with  the  caustic 
alkalies  a white  precipitate,  soluble  in  excess  of  the  alkalies,  and 
this  solution  yields  no  precipitate  when  it  is  boiled.  Carbonates 
of  the  alkali-metals  give  a white  hydrated  binoxide  with  escape  of 
carbonic  anhydride  : the  precipitate  is  insoluble  in  excess  of  the 
alkaline  salt.  Suljphuretted  hydrogen  and  sidyghide  of  ammonium 
both  produce  a dirty  yellow  precipitate  of  hydrated  bisulphide  of 
tin,  which  is  soluble  in  excess  of  the  precipitant,  as  well  as  in  the 
sulphides  of  the  alkaline  metals,  and  in  the  caustic  alkalies. 

All  the  compounds  of  tin  before  the  blowjpipe^  in  the  reducing 
flame  on  charcoal,  give  with  carbonate  of  sodium  white  malleable 
globules  of  the  reduced  metal. 

(820)  Estimation  of  Tin^  and  Separation  from,  the  foregoing 
Metals. — Tin  is  estimated  in  the  form  of  the  anhydrous  binoxide ; 
100  parts  of  which  contain  78*66  of  the  metal. 

The  separation  of  tin  from  all  the  metals  hitherto  described, 
with  the  exception  of  cadmium,  is  effected  by  means  of  sulphur- 
etted hydrogen,  which  precipitates  none  of  tliese  metals  from  their 
solutions  in  the  mineral  acids.  The  mixed  sulphides  of  tin  and 
cadmium  may  be  at  once  evaporated  to  dryness  with  nitric  acid  : 
on  treating  the  residue  with  water,  nitrate  of  cadmium  will  be 
dissolved,  and  the  insoluble  oxide  of  tin  will  remain.  The  sul- 
phide of  cadmium  is  also  easily  separated  from  the  suljihides  of 
tin  by  bisulphide  of  ammonium,  which  dissolves  the  sul])hides  of 
tin  and  leaves  the  sulphide  of  cadmium.  Both  the  sulphides  of  tin, 
by  ignition  in  a current  of  air,  are  gradually  converted  into  the 
binoxide  of  tin:  this  change  maybe  accelerated  by  moistening 
them  with  nitric  acid. 

Tin  may  also  be  separated  from  all  metals  with  tlie  exception 
of  antimony,  arsenic  (and  lead  if  sulphuric  acid  be  present),  by 
evaporating  the  solution  nearly  to  dryness  with  nitric  acid,  and 

♦ The  presence  of  tartaric  add  in  some  cases  interferes  with  these  reactions. 


564 


TITAXIOr. 


washino^  tlie  residue  with  water  strongly  acidulated  with  nitric 
acid.  The  tin  remains  as  raetastannic  acid,  and  by  ignition  fur> 
nishes  the  anhydrous  binoxide. 

§ II.  Titaxium:  Ti=:50,  or  Ti=25. 

(821)  Tit.axium  is  a comparatively  rare  metal,  which  presents 
considerable  analogy  with  tin.  It  was  discovered  by  Gregor  as  a 
constituent  of  menaccanite  in  the  year  1791.  Its  principal  ores 
are  titaniferous  iron,  and  rutile,  anatase,  and  brookite,  which  are 
three  different  forms  of  titanic  anhydride,  coloured  by  variable 
quantities  of  the  oxides  of  iron,  manganese,  and  chromium. 
When  titanic  anhydride  is  intensely  heated  with  charcoal,  it  is 
reduced,  but  is  not  fused.  A remarkable  compound  of  the  metal 
is  frequently  found,  in  the  form  of  copper-coloured  cubic  crystals, 
adhering  to  the  slags  of  the  AV elsh  and  other  iron  furnaces.  These 
crystals  are  hard  enough  to  scratch  agate ; they  have  a specific 
gravity  of  5 '3.  Xo  acid,  except  a mixture  of  nitric  and  hydro- 
fluoric acids,  has  any  action  upon  them,  but  they  are  oxidized  by 
fusion  with  nitre,  or  by  ignition  in  a current  of  oxygen : they  are 
volatile  at  an  extremely  high  temperature.  These  crystals  were 
supposed  by  Wollaston  to  be  metallic  titanium,  but  AVbhler 
showed  that  they  consist  of  a combination  of  cyanide  with  nitride 
of  titanium ; they  contain  18  per  cent,  of  nitrogen,  and  4 of  car- 
bon, having  a formula  (TiCy,  3 TigA^).  Another  nitride  of  the 
metal  (TigX^),  also  formerly  mistaken  for  metallic  titanium,  is 
procured  in  copper-coloured  scales  by  igniting  the  ammonio-chlo- 
ride  of  titanium  (4  H3X,TiCl4)  in  closed  vessels,  in  a current  of 
ammonia.*  If  a current  of  dry  ammoniacal  gas  be  transmitted 
over  powdered  titanic  anhydride,  heated  to  redness  in  a porcelain 
tube,  a violet-coloured  nitride  of  titanium  (TiX2)  is  formed.  So 
strong,  indeed,  is  the  attraction  of  titanium  for  nitrogen  at  a high 
temperature,  that  if  a mixture  of  titanic  anhydride  and  charcoal, 
both  in  a minute  state  of  division,  be  heated  to  whiteness,  and 
submitted  to  a current  of  nitrogen,  the  whole  of  the  nitrogen  is 
rapidly  absorbed,  whilst  carbonic  oxide  escapes,  and  copper- 
coloured  crystals,  having  the  same  composition  as  those  obtained 
from  the  blast-furnace,  are  formed  (Deville  and  AYohler). 

Pure  titanium  may  be  obtained  by  decomposing  the  double 
fluoride  of  titanium  and  potassium,  with  potassium  in  a tube  filled 
with  pure  hydrogen,  and  throngh  which  a current  of  pure  hydro- 
gen is  maintained.  It  then  forms  a grey,  amorphous  powder, 
which  burns  in  air  with  scintillation,  and  deflagrates  in  oxygen 
with  dazzling  brilliancy.  It  may  also  be  obtained  in  prismatic 
crystals  by  heating  sodium  in  the  vapour  of  tetrachloride  of 
titanium.  The  metal  is  soluble  in  hydrochloric  acid  witli  evolu- 
tion of  hydrogen,  forming  a colourless  solution,  from  which  am- 
monia precipitates  a black  hydrated  protoxide. 

* The  ammonio-chloride  of  columbium  yields  a similar  nitride  when  treated  in  like 
manner : the  same  remark  applies  also  to  molybdenum. 


OXIDES  OF  TITANIUM TITANIC  ACID. 


565 


(822)  Three  oxides  of  titanium  probably  exist — the  protoxide, 
the  sesqiiioxide,  and  the  binoxide,  or  titanic  anhydride. 

The  protoxide  (TiO=66,  or  TiO  = 33)  has  not  been  obtained 
in  a pure  state.  It  appears  to  be  formed  when  titanic  anhydride 
is  heated  in  a crucible  lined  with  charcoal : but  where  the  anhy- 
dride is  actually  in  contact  with  the  charcoal,  a film  of  metallic 
titanium,  mixed  with  a portion  of  nitride,  is  obtained.  The  prot- 
oxide is  a black  powder  nearly  insoluble  in  acids,  and  is  gradu- 
ally oxidized  by  exposure  to  a high  temperature  in  air,  or  by 
fusion  with  nitre. 

If  a solution  of  titanic  acid  in  hydrochloric  acid  be  digested 
with  zinc,  a purple,  hydrated  sesquioxide  (Ti^Og,  x II20-),  or  titan- 
ate  of  titanium  (Ti0,Ti02)  is  deposited,  which  absorbs  oxygen 
from  the  air  witli  great  rapidity,  becoming  white  from  the  forma- 
tion of  titanic  acid.  Hydrochloric  acid  dissolves  it  sparingly,  and 
forms  a blue  solution. 

Titanic  Anhydride  (Ti02=:82,  or  TiO^^Il). — This  com- 
pound occurs  in  menaccanite  and  iserine  as  titanate  of  iron  ; but 
more  'commonly  it  is  met  with  in  the  uncombined  condition,  con- 
stituting the  principal  ore  of  the  metal.  It  is  found  native  under 
three  distinct  crystalline  forms,  each  of  which  has  a difierent 
specific  gravity.  Of  these,  the  densest  and  most  abundant  is 
rutile  (sp.  gr.  4*25) ; it  occurs  in  long  striated  prisms  or  needles  of 
a brown  colour,  isomorphous  with  those  of  tin-stone.  The  second 
variety,  hrookite  (sp.  gr.  4'13),  is  found  in  right  rhombic  prisms, 
sometimes  opacpie,  at  others  transparent,  and  of  a pale  brown  ; 
whilst  the  third  variety,  anatase  (sp.  gr.  3*9),  is  found  in  Dau- 
phiny,  in  acute  octohedra  which  are  semi-transparent,  and  of  a 
yellowish- brown  or  blue  colour.  Corresponding  differences  are 
observed  in  the  titanic  anhydride  artificially  prepared  in  the  labo- 
ratory. Ebelmen  obtained  needle-shaped  transparent  yellow  crys- 
tals of  rutile  of  sp.  gr.  4*283  by  prolonged  heating  in  a porcelain 
kiln,  of  a mixture  of  1 part  of  powdered  titanic  anhydride  and  5 
parts  microcosrnic  salt.  Like  the  binoxide  of  tin,  it  may,  when 
hydrated,  be  obtained  in  two  isomeric  forms  possessed  of  difierent 
properties.  In  fact,  the  existence  of  two  dissimilar  modifications 
is  a very  usual  occurrence  in  the  case  of  metallic  oxides  possessed 
of  feeble  acid  powers. 

Pure  titanic  anhydride  may  be  obtained  by  reducing  rutile,  or 
titanic  iron-sand  to  a fine  powder,  and  fusing  it  with  thrice  its 
weight  of  carbonate  of  potassium.  On  treating  the  mass  with 
hot  water,  an  impure  acid  titanate  of  potassium  remains.  It  is 
dissolved  in  hydrochloric  acid,  next  mixed  with  an  excess  of  am- 
monia, and  the  precipitate  is  digested  in  sulphide  of  ammonium, 
by  which  the  tin,  iron,  and  manganese  are  converted  into  sul- 
phides, whilst  the  titanic  acid  remains  unchanged  : a solution  of 
sulphurous  acid  then  dissolves  the  sulphides,  and  a i)ure  wliite 
hydrate  of  titanic  acid  is  left.  The  water  may  be  expelled  by 
heat,  and  by  long-continued  ignition  the  colour  of  the  compound 
deepens,  its  specific  gravity  increasing  till  it  ac(pnres  a density 
ecpial  to  that  of  rutile.  In  this  state  it  is  insoluble  either  in  solu- 


566 


CHAKACTEPwS  OF  THE  COMPOUNDS  OF  TITANIUM. 


tions  of  the  alkalies,  or  in  acids,  except  hydi’ofliioric  acid  and 
boiling  oil  of  vitriol.  This  anhydidde  may,  however,  be  brought 
into  solution  by  heating  it  with  a fixed  alkaline  carbonate,  and 
dissolving  the  residue  with  cold  hydrochloric  acid ; the  titanic 
acid  may  be  precipitated  by  means  of  carbonate  of  ammonium : 
it  then  forms  a white  gelatinous  hydrate,  which  dries  into  a semi- 
transparent mass  capable  of  reddening  litmus.  The  liquid  long 
remains  turbid ; it  cannot  be  rendered  clear  by  filtration,  unless 
an  excess  of  some  ammoniacal  salt  be  present.  Hych’ated  titanic 
acid  is  insoluble  in  solutions  of  the  caustic  alkalies,  but  it  yields 
definite  salts  with  them.  When  fused  with  hydrate  of  potash  it 
forms  a transparent  yellowish  glass.  The  hydrate  of  titanic  acid 
is  soluble  in  diluted  liydi’ochloric  acid  ; it  is  also  dissolved  by  sul- 
phuric acid,  and  forms  a definite  sulphate  (TiO2,S0'3),  which  may 
be  evaporated  to  dryness  at  a low  temperature  without  under- 
going decomposition.  Both  these  acid  solutions  when  diluted  are 
decomposed  by  prolonged  boiling,  and  the  insoluble  variety  of 
titanic  acid  is  precipitated.  When  the  soluble  hydrate  is  heated, 
it  loses  water  and  becomes  converted  into  the  anhydride.  This 
compound  becomes  yellow  on  ignition,  but  recovers  its  whiteness 
on  cooling.  When  fused  with  acid  sulphate  of  potassium,  titanic 
anhydride  is  dissolved,  and  may  be  obtained  in  solution  by  add- 
ing water ; it  may  thus  be  distinguished  and  separated  from  silica, 
which  is  not  rendered  soluble  by  this  means. 

(S23)  A Bisuljphide  of  titanium  (BiSJ  may  be  obtained  in 
green  scales  ; it  is  not  soluble  in  the  sulphides  of  the  alkaline  metals. 

Tetrachloride  of  titanium^  BiCl^=192  ; Sp.  Gr.  of  vapour^ 
6’836,  of  liquich  1'761  at  32°  ; i}Lol.  Yol.  j ^ | ; Boiling-pt.  277°  : 
or  Bichloride^  (TiCl^  = 96). — This  is  a fuming  volatile  liquid, 
resembling  the  tetrachloride  of  tin.  It  may  be  obtained  by  de- 
composing pime  titanic  anhydride,  intimately  mixed  with  char- 
coal, and  heated  to  redness  in  a porcelain  tube,  by  means  of  a 
current  of  dry  chlorine  gas.  It  is  a colourless  liquid,  which  com- 
bines with  a small  quantity  of  water  to  form  a crystallizable  com- 
pound. A large  quantity  of  water  produces  its  decomposition, 
hydrated  titanic  acid  being  separated.  Deville  obtained  square 
prisms  of  metallic  titanium  by  decomposing  the  vapour  of  the 
tetrachloride  with  sodium. 

(S2I)  Charactees  of  the  Compounds  of  TirANiuM. — 1. — The 
salts  corresponding  to  the  protoxide  are  but  little  known ; with  the 
carbonates  of  the  aUcali-raetals  they  give  a blue  precipitate,  which 
becomes  first  brown  and  ultimately  green. 

2. — The  titanates  of  the  alkali-metals  are  of  a yellowish  white 
colour : the  normal  salts  are  insoluble  in  cold  water ; hot  water 
removes  the  alkali,  while  most  of  the  titanic  acid  remains  undis- 
solved. Cold  hydrochloric  acid  dissolves  them,  forming  a solu- 
tion which,  when  boiled,  becomes  turbid  from  deposition  of 
titanic  acid:  ammonia,  when  added  to  this  solution,  produces  a 
white  precipitate.  Infusion  of  galls  produces  an  orange-coloured 
precipitate  in  the  acid  solution  of  the  titanates ; a precipitate  of 
similar  colour  is  produced  by  ferrocyanide  of  potassium.  In  the 


COLUMBIUM TANTALUif MOLYBDENUM. 


567 


reducing  flame  of  the  tlowjpipe  the  titanates  give  with  microcosmic 
salt  a beautiful  purple  or  bluish  glass,  which  becomes  colourless 
in  the  oxidizing  flame.  This  reaction  distinguishes  the  titanates 
from  the  tantalates. 

(825)  Estimation  of  Titanium. — Titanium  is  always  estimated 
in  the  form  of  titanic  anhydride.  Its  solution  in  cold  hydrochloric 
acid  is  not  precipitated  by  sulphuretted  hydrogen,  a circumstance 
which  may  be  taken  advantage  of  in  separating  it  from  tin  and 
cadmium,  both  of  which  are  thrown  down  from  the  acid  as  in- 
soluble sulphides.  The  solution  is  next  mixed  with  tartaric  acid, 
and  supersaturated  with  sulphide  of  ammonium : iron,  nickel, 
cobalt,  manganese,  and  zinc  are  thus  separated  in  the  form  of 
sulphides.  The  solution  is  afterwards  evaporated  to  dryness,  and 
the  tartaric  acid  is  burned  ofi*;  titanic  anhydride  is  left,  mixed 
with  the  salts  of  the  earths  and  alkalies  contained  in  the  mixture  ; 
the  residue  is  fused  wnth  hydrate  of  potash,  redissolved  in  the 
cold  with  hydrochloric  acid,  and  on  boiling  the  liquid,  to  which  a 
little  diluted  sulphuric  acid  has  been  added,  the  titanic  acid  is 
precipitated,  collected,  and  converted  into  the  anhydride  by  igni- 
tion. This  process,  however,  does  not  yield  very  accurate  results ; 
indeed  the  exact  determination  of  the  quantity  of  titanium  in  its 
compounds  is  a matter  of  considerable  difficulty. 

§ III.  CoLUMBiuM — Tantalum. 

(826)  Columbium,  or  ISTiobium  (5Ib=97'5)  w^as  discovered  in 
the  year  1801  by  Hatchett,  who  found  it  in  a black  mineral  from 
Massachusetts,  termed  columbite.  In  the  following  year  Eke- 
berg  obtained  a new  metal,  which  he  termed  tantalum  (Ta= 137*5), 
from  the  tantalite  and  yttro-tantalite  of  Sweden. 

These  two  metals  were  asserted  by  Wollaston  to  be  identical — 
an  opinion  generally  received  until  Rose  showed  that  the 
American  mineral  contained  a metallic  acid  difterent  from  that 
furnished  by  tantalite : this  acid  he  termed  the  niohio  (HbO^) ; 
and  its  metallic  constituent,  niobium^  is  the  columbium  of 
Hatchett.  Rose  at  the  same  time  stated  that  associated  with 
this  was  a second  metallic  acid,  which  he  termed  pelopic^  but 
this  he  has  since  ascertained  to  be  a compound  of  the  metal  which 
he  called  niobium. 

Columbium  and  tantalum  have  been  but  incompletely  studied  ; 
they  are  too  rare  to  need  a detailed  description  here : they  have  a 
considerable  analogy  with  silicon, — tantalic  anhydride,  according 
to  Rose,  having  the  formula  TaO^. 

Hermann  supposed  the  yttro-tantalite  of  Siberia  to  contain  a 
new  metal,  analogous  to  columbium,  to  which  he  gave  the  name 
oi  Ihnenium  ^ but  he  has  since  proved  the  so-called  ilnienic  acid 
to  be  a mixture  of  the  tantalic  and  columbic  anhydrides. 

§ ly.  Molybdenum:  Mo =96,  or  Mo =48.  Sp.  Gr.  from 
8*615  to  8*636. 

(827)  The  principal  ore  of  molybdenum  is  the  bisulphide,  a 


568 


OXIDES  OF  MOLYBDENUM. 


mineral  which  occurs  chiefly  in  Bohemia  and  in  Sweden,  in 
appearance  much  resemblino^  plumbago,  and  hence  its  name,  from 
lj.oXvl35aiva,  ‘‘  a mass  of  lead."”  Molybdenum  is  also  occasionally 
found  oxidized,  in  combination  with  lead,  as  molybdate  of  lead. 
The  metal  may  be  obtained  by  roasting  the  pure  native  sulphide  in  a 
free  current  of  air ; the  sulphur  passes  off  as  sulpliurous  anhydride, 
wliilst  the  molybdenum  also  combines  with  oxygen,  and  remains 
behind  in  the  form  of  molybdic  anhydride.  If  this  be  mixed 
into  a paste  with  oil  and  charcoal,  and  exposed  to  the  heat  of  a 
smith’s  forge,  in  a crucible  lined  with  charcoal,  it  is  reduced  to 
the  metallic  state.  In  this  form  molybdenum  is  white,  brittle, 
and  very  difficult  of  fusion.  The  anhydride  may  also  be  reduced 
by  heating  it  to  redness  in  a porcelain  tube  in  a current  of 
hydrogen  : when  the  pulverulent  metal  is  heated  in  the  open 
air  it  is  gradually  oxidized,  and  Anally  converted  into  molybdic 
anhydride.  It  is  readily  oxidized  by  nitric  acid ; if  the  metal  be 
in  excess,  a soluble  nitrate  of  the  binoxide  is  obtained ; if  the 
acid  predominate,  the  oxidation  proceeds  further,  and  molybdic 
acid  is  formed : aqua  regia  produces  similar  results.  Molybdenum 
is  also  oxidized  when  fused  with  nitre,  and  molybdate  of  potassium 
is  produced. 

(828)  Oxides  of  Molybdenum. — Molybdenum  forms  three 
oxides ; the  protoxide  (MoO),  and  the  binoxide  (MoO^)  are  both 
possessed  of  basic  characters  : the  third  (MoOg)  reacts  energetically 
upon  bases,  and  yields  w^ell  characterized  salts. 

The  protoxide  (MoO=112,  or  MoO =56)  is  precipitated  from 
the  solution  of  a molybdate  in  hydrochloric  acid  which  has  been 
reduced  by  means  of  a bar  of  zinc,  on  adding  ammonia  in  excess  ; 
it  is  thus  thrown  down  as  a black  hydrate  which  absorbs  oxygen 
from  the  air : it  is  soluble  in  a solution  of  carbonate  of  ammonium, 
but  not  in  those  of  the  fixed  alkalies  or  their  carbonates.  It  may 
also  be  obtained  in  the  anhydrous  form,  by  digesting  molybdic 
anhydride  with  ziuc  and  hydrochloric  acid. 

The  hinoxide  (Mo0-2=i2S,  or  MoOg^dl)  may  be  prepared  by 
igniting  a mixture  of  2 parts  of  molybdate  of  sodium  and  1 part 
of  sal  ammoniac,  and  digesting  the  mass  in  a solution  of  potash, 
to  remove  any  undecomposed  molybdic  acid.  The  residue  when 
w’ell  washed,  is  the  pure  anhydrous  oxide,  which  has  been  re- 
duced from  molyddic  acid  by  the  hydrogen  of  the  ammonia. 
It  is  of  a dark  brown  colour,  but  it  becomes  purple  if  exposed  to 
solar  light ; it  is  nearly  insoluble  in  acids.  The  hydrated  binoxide 
may  be  obtained  by  digesting  molybdic  anhydride  mixed  with 
copper  filings,  in  hydrochloric  acid ; an  excess  of  ammonia  preci- 
pitates the  oxide  of  a rusty-brown  colour,  whilst  the  copper  is 
retained  in  solution.  Hydrated  binoxide  of  molybdenum  is  soluble 
in  pure  water,  but  is  precipitated  by  the  addition  of  any  salt. 
The  solution  gelatinizes  on  keeping.  The  salts  which  this  oxide 
forms  with  acids  are  of  a reddish-brown  colour,  or,  if  anhydrous, 
are  nearly  black. 

If  a solution  of  tetrachloride  of  molybdenum  (MoCl,)  be  added, 
ffi'op  by  drop,  to  a concentrated  solution  of  the  acid-molybdate  of 


MOLTBDIC  ACID MOLYBDATES. 


569 


ammonium,  a deep  blue  precipitate  of  molybdate  of  molybdenum 
(Mo02,4  M0O3)  is  formed.  This  compound  is  soluble  in  water, 
but  is  precipitated  by  the  addition  of  any  saline  body.  The  addi- 
tion of  a small  quantity  of  a stannous  salt  to  a soluble  molybdate 
reduces  the  molybdic  acid,  and  produces  this  beautiful  blue  com- 
pound, which  may  serve  as  a test  of  the  presence  of  molybdic 
acid : care  must  be  taken  not  to  add  the  tin  salt  in  excess. 
Another  molybdate  of  the  binoxide  of  molybdenum  (MoO^j 
2 M0O3)  has  a green  colour. 

(829)  Molybdic  Anhydride  (Mo03=144,  or  Mo03=:72) : Com- 
position in  jparts^  k£o,  66.6;  O,  33*4. — This  compound  is  ob- 
tained in  the  form  of  an  impure  anhydride  by  roasting  the  sul- 
phide of  molybdenum  at  a low  red  heat ; it  remains  behind  as  a 
dirty  yellow  powder;  caustic  ammonia  dissolves  the  anhydride, 
leaving  oxide  of  iron  and  other  impurities.  The  ammoniacal 
solution  crystallizes  on  evaporation,  and  by  a low  red  heat  the 
ammonia  is  expelled,  leaving  the  anhydride  behind,  of  a pale  buff 
colour.  The  anhydride  reddens  moistened  litmus-paper,  and  is 
sparingly  soluble  in  water,  forming  a yellow  solution.  At  a red 
heat  it  fuses  to  a straw-coloured  glass  of  sp.  gr.  3 ‘49 : it  under- 
goes volatilization  in  open  vessels,  and  is  deposited  on  cool  sur- 
faces in  brilliant  transparent  needles.  'No  definite  hydrate  of 
molybdic  acid  is  known.  When  precipitated  from  its  salts  by 
the  addition  of  an  acid,  it  may  be  redissolved,  if  the  acid  be  added 
in  excess:  with  concentrated  sulphuric  acid  it  forms  a yellow 
solution.  It  is  also  freely  soluble  in  a solution  of  cream  of  tartar. 
Molybdic  acid  forms  well  characterized  salts,  both  normal  and  acid. 
Those  of  the  alkalies  are  soluble.  Hormal  molybdate  of  ammonium 
crystallizes  in  colourless  square  prisms.  An  acid  molybdate  of 
ammonium  [(H4br)JIg  5 MoOJ,  crystallizes  readily  in  six-sided 
prisms.  Various  anhydro-molybdates  of  the  alkalies  have  been 
formed,  which  contain  as  many  as  3,  4,  and  even  5 equivalents 
of  the  anhydride  to  1 of  fixed  base.  Molybdate  of  lead  (PbMoO^) 
occurs  native  in  crystals  of  a yellow  colour ; it  is  soluble  in 
nitric  acid,  and  in  solution  of  caustic  potash  if  the  alkali  be  in 
large  excess. 

A solution  of  molybdate  of  ammonium  may  be  advantageously 
employed  in  certain  cases  to  detect  the  presence  of  very  small 
quantities  of  phosphoric  acid  in  solution.  The  solution  suspected 
to  contain  the  phosphate  must  be  acidulated  with  nitric  acid,  and 
the  molybdate  then  added.  The  liquid  becomes  yellow,  and  on 
boiling,  deposits  a yellow  crystalline  precipitate,  consisting  of  mo- 
lybdic and  phosphoric  acids  in  combination  with  ammonia.  Ac- 
cording to  Sonnenschein  it  contains  6-747  per  cent,  of  ammonia, 
and  about  3 per  cent,  of  Arsenic  acid  forms  a similar 

compound  with  molybdate  of  ammonium  when  the  solutions  are 
boiled. 

Sonnenschein  takes  advantage  of  the  insolubility  of  the  ])hos- 
phoric  compound  to  detect  small  quantities  of  ammonia  by  its 
means.  In  order  to  prepare  the  test  solution,  he  first  procures 
the  yellow  precipitate,  by  adding  molybdate  of  ammonium  to  an 


5T0 


CHAEACTEE3  OF  THE  SALTS  OF  MOLYBDENUM. 


acidulated  solution  of  phosphate  of  sodium,  ignites  the  precipitate 
to  expel  the  ammonia,  adds  nitric  acid  to  the  residue,  in  order 
completely  to  reoxidize  any  reduced  molyhdic  acid,  evaporates  to 
dryness,  and  expels  the  nitric  acid  by  ignition.  A solution  of  car- 
bonate of  sodium  is  employed  to  dissolve  the  remaining  mixture 
of  phosphoric  and  molybdic  acids,  and  the  solution  is  supersatu- 
rated with  hydrochloric  acid.  This  liquid,  it  is  stated,  will  easily 
detect  the  presence  of  1 part  of  sal  ammoniac  in  10,000  of  water. 
Salts  of  sodium  are  not  affected  by  it,  but  strong  solutions  of  the 
salts  of  potassium  yield  a similar  yellow  precipitate. 

(830)  Sulphides  of  Molybdenum. — Three  sulphides  of  mo- 
lybdenum are  known,  MoS^,  M0S3,  and  MoS^ : the  last  two  are 
sulphur-anhydrides. 

Bisulphide  of  Molybdenum  (MoS^— 160,  or  MoS2=80 ; Sp.  Gr. 
4’6) : Comp,  in  iOO  parts^  Mo,  60  ; S,  40. — This  sulphide  is  the 
principal  ore  of  the  metal : it  is  a soft  solid  of  a leaden-grey  colour 
and  metallic  lustre.  The  bisulphide  may  also  be  formed  artificially 
by  heating  molybdic  anhydride  in  the  vapour  of  sulphur.  It  is 
unchanged  by  heat  in  closed  vessels,  but  if  roasted  in  the  open 
air,  sulphurous  anhydride  is  formed  and  is  volatilized,  while  mo- 
lybdic anhydride  remains.  Hitric  acid  decomposes  it,  and  con- 
verts the  metal  into  molybdic  acid ; oil  of  vitriol  also  decomposes 
it  when  boiled  upon  it,  forming  a blue  solution,  whilst  sulphurous 
anhydride  escapes. 

The  ter  sulphide  (MoS3=192,  or  MoS3=:96)  is  precipitated  by 
transmitting  sulphuretted  hydrogen  through  a solution  of  a mo- 
lybdate, and  adding  hydrochloric  acid,  it  is  of  a dark-brown 
colour,  and  forms  sulphur  salts  with  the  sulphides  of  the  alkaline 
metals.  The  potassium  salt  crystallizes  in  magnificent  iridescent 
crystals  (K2M0S4,  or  KS,  M0S3).  The  tetrasulphide  of  molybdenum 
also  combines  readily  with  the  sulphides  of  the  alkaline  metals. 

K molybdous  chloride  (MoCl2=167),  or  protochloride  of  mo- 
lybdenumX^lsd^\—%?>''i))  is  obtained  by  dissolving  the  protoxide  in 
hydrochloric  acid.  A tetrachloride  (MoCl^)  is  procured  by  heat- 
ing the  metal  in  a current  of  dry  chlorine : it  forms  a red  vapour, 
which  sublimes  in  deliquescent  fusible  crystals,  in  appearance  re- 
sembling those  of  iodine.  It  may  also  be  obtained  in  solution  by 
dissolving  the  binoxide  in  hydrochloric  acid. 

A cldoromolybdic  acid  sublimes  in  yellowish  scales  when  the 
binoxide  is  heated  in  a current  of  chlorine.  It  is  soluble  both  in 
w- ater  and  in  alcohol,  and  consists  of  (MoCle,2  M0O3),  or  (MoO^Cl^). 
Similar  compounds  may  be  formed  with  many  acidifiable  metals, 
such,  for  example,  as  tungsten,  chromium,  and  vanadium. 

(831)  Characters  of  the  Salts  of  Molybdenum  : — 

1. — Little  is  known  of  the  molybdous  salts ^ or  salts  correspond- 
ing to  the  protoxide.  They  yield  a dark-brown  precipitate  with 
the  hydrates  of  the  alkalies  and  their  carbonates  / the  precipitate 
is  soluble  in  excess  of  carbonate  of  ammonium,  and  is  deposited 
again  on  boiling  the  liquid  ; sulphuretted  hydrogen  slowly  pro- 
duces a brown  precipitate  of  hydrated  sulphide  which  is  soluble 
in  sulphide  of  ammonium. 


Tins:GSTEN. 


571 


2.  — The  salts  corresponding  to  the  hinoxide  have  a dark  colour, 
and  a metallic  astringent  taste.  Infusion  of  galls  produces  with 
them  a brownish-yellow  solution ; fen'ocyanide  of  potassium  gives 
a dark-brown  precipitate ; ammonia  a rusty-brown  precipitate  of 
the  binoxide, 

3.  — The  molybdates  yield  characteristic  reactions  with  zinc, 
tin,  and  copper.  With  zinc  in  dilute  acid  solutions,  the  liquid 
becomes  first  blue,  then  green,  and  finally  black,  after  which  the 
addition  of  ammonia  produces  a deposit  of  hydrated  protoxide  of 
molybdenum.  The  addition  of  a small  quantity  of  stannous  cldo- 
ride  in  solution  to  a liquid  containing  a molybdate,  produces  a 
beautiful  blue  molybdate  of  molybdenum  (Mo02,4  MoOg),  but  care 
must  be  taken  not  to  have  the  tin  salt  in  excess,  or  the  precipitate 
becomes  of  a dull  green.  Copper  filings  in  similar  solutions  re- 
duce the  molybdic  acid  to  the  binoxide,  which  is  precipitated  as  a 
brown  hydrate  by  ammonia.  Befare  the  blowpipe^  the  compounds 
of  molybdenum  yield,  in  the  oxidating  flame,  a colourless  bead 
with  borax,  and  with  microcosmic  salt ; in  the  reducing  flame  they 
give  a brownish-red  bead  wfith  borax,  and  a green  one  with  mi- 
crocosmic salt. 

Molybdenum  is  usually  estimated  in  the  form  of  the  bisulphide, 
of  which  100  parts  contain  60  of  the  metal. 

§ Y.  Tungsten:  W=184,  or  W==92.  Sp.  Gr.  17*6. 

(832)  Tungsten  is  a metal  found  in  small  quantities,  in  the 
mineral  known  as  Scheelite^  or  tungstate  of  calcium  (OaW O^),  or 
else  in  wolfram^  as  a tungstate  of  iron  and  manganese  (MnWO^, 
3 FeWOJ.  It  is  easily  obtained  from  the  tungstate  of  calcium, 
by  digesting  the  powdered  mineral  in  hydrochloric  acid,  which 
combines  with  and  dissolves  the  calcium,  but  leaves  the  insoluble 
tungstic  acid  behind  : from  this  compound  the  metal  itself  is  pro- 
cured, by  heating  it  to  bright  redness  in  a current  of  hydrogen 
gas.  It  is  thus  left  of  a dark-grey  colour,  but  it  assumes  a me- 
tallic lustre  under  the  burnisher.  If  tungstic  anhydride  be  made 
into  a paste  with  oil,  and  heated  intensely  in  a crucible  lined  with 
charcoal,  for  some  hours,  tungsten  is  obtained  as  a heavy,  iron- 
grey  metal,  which  is  very  hard,  and  difiicult  of  fusion.  It  may 
l)e  heated  in  the  air  whilst  in  the  compact  state  without  sensible 
change,  but  in  the  pulverulent  form  it  burns  easily  into  tungstic 
anhydride.  Aqua  regia  and  nitric  acid  convert  it  into  tungstic 
acid,  and  the  same  change  is  produced  by  heating  it  in  contact 
with  the  alkalies  or  with  nitre.  Pulverulent  tungsten  is  also  ox- 
idized and  dissolved  by  boiling  it  in  a solution  of  tlie  caustic  alka- 
lies or  of  their  carbonates.  When  tungsten  is  alloyed  in  tlie  pro- 
portion of  9 or  10  parts  with  90  of  steel,  it  yields  a metallic  mass 
of  extraordinary  hardness. 

(833)  Oxides  of  Tungsten. — Two  of  these  are  known,  viz.,  a 
binoxide,  which  does  not  form  salts  with  acids,  and  an  acid  terox- 
ide.  Wbliler  attributes  to  an  intermediate  blue  oxide  tlie  compo- 
sition (we2,wo3). 


572 


TUNGSTIC  ANHTDEIDE. 


The  hinoxide  (WO^)  is  obtained  as  a brown  powder  by  heating 
tungstic  acid  to  low  redness  in  a stream  of  hydrogen ; or  in  cop- 
per-coloured scales,  by  adding  tungstic  anhydride  to  dilute  hydro- 
chloric acid  in  which  some  pieces  of  zinc  have  been  placed.  In 
the  latter  form  it  attracts  oxygen  rapidly  from  the  air,  and  is  dis- 
solved by  a solution  of  caustic  potash,  with  evolution  of  hydrogen 
and  formation  of  tungstate  of  potassium.  Wohler  obtains  the 
binoxide  from  wolfram  by  fusing  1 part  of  this  mineral  with  2 
parts  of  carbonate  of  potassium : the  melted  mass  is  treated  with 
boiling  water,  filtered,  and  mixed  with  a solution  of  1-|-  part  of 
chloride  of  ammonium.  The  solution  is  then  evaporated  to  dry- 
ness, and  the  residue  ignited ; upon  treating  the  mass  with  boiling 
water,  the  oxide  of  tungsten  remains  as  a heavy  black  powder, 
which  must  be  washed,  first  with  a weak  solution  of  potash,  and 
afterwards  with  water.  In  this  operation  the  hydrogen  of  the 
ammoniacal  salt  partially  reduces  the  tungstic  acid  of  the  mineral. 

With  soda,  the  oxide  of  tungsten  forms  a remarkable  com- 
pound of  a yellow  colour  and  metallic  lustre,  containing,  according 
to  Wright,  (IIa^O,WG^,  2 WO3).  It  crystallizes  in  cubes,  and 
is  not  acted  upon  by  any  acid,  or  mixture  of  acids,  except  the 
hydrofluoric  ; the  solutions  of  the  caustic  alkalies  are  equally 
without  effect  upon  it : if  heated  in  the  air  it  is  decomposed  and 
partially  converted  into  tungstate  of  sodium.  It  is  best  obtained 
by  fusing  tin  with  an  excess  of  the  acid  tungstate  of  sodium  : in 
order  to  remove  the  un  decomposed  tungstate  of  sodium  and  free 
tungstic  acid,  the  residue  is  treated  in  succession  with  concentrated 
solution  of  potash,  water,  and  hydrochloric  acid ; finally  it  is 
washed  with  water.  Corresponding  compounds  with  potassium 
and  lithium  have  also  been  obtained. 

Tungstic  anhydride^  WO-3=232;  often  tungstic  acid  ; 

(WO^— 11^)'^  Sp.Gr.  6T2  : Comp,  in  100  parts  79*32  ; O,  20*68. 
— Laurent  considered  that  there  were  not  fewer  than  six  modifi- 
cations of  this  acid,  each  of  which  formed  a distinct  class  of  salts  ; 
but  the  subsequent  researches  of  Riche  {Ann.  de  Chimie.^  III.  1.  5), 
confirmed  by  those  of  Scheibler,  appear  to  have  shown  that  there 
are  but  two  modifications  in  addition  to  the  anhydilde.  These 
two  different  acids  he  terms  the  tungstic  (H^WOj,  and  the  meta- 
tungstic  acid  (H^W^Ojg).  De  Marignac  continues  to  apply  the 
designation  of  par atung states  to  a class  of  salts  of  the  form  of 
(5  MO,  12  WO3,  2^-f-l  HO),  or  (M,H,  3 W^O^^H^O),  though  he 
has  not  isolated  any  specific  modification  of  acid  from  them. 

Tungstic  anhydride  may  be  obtained  from  tungstate  of  cal- 
cium by  the  process  already  described,  or  by  decomposing  wol- 
fram wdth  aqua  regia,  evaporating  to  dryness,  and  dissolving  the 
liberated  tungstic  acid  in  ammonia ; tlie  tungstate  of  ammonium 
is  purified  by  crystallization,  and  when  heated  in  open  vessels 
loses  ammonia  and  water,  and  is  converted  into  pure  tungstic 
anhydride.  This  compound  is  a straw-yellow,  tasteless,  insoluble 
powder,  which  assumes  a deeper  orange  tint  when  heated,  the 
colour  fading  again  as  the  temperature  falls.  In  this  form  it  is 
insoluble  in  acids,  but  is  readily  soluble  in  alkaline  solutions  ; and 


TUNGSTATES. 


573 


when  heated  with  solutions  of  the  alkaline  carbonates,  it  decom- 
poses them  with  effervescence. 

Hydrated  tungstic  acid  (H^WO,,  or  HOjWOg)  is  obtained  in 
the  form  of  a yellow  powder  by  adding  hydrochloric  acid  in 
excess  to  a boiling  solution  of  the  anhydride  in  any  of  the  alka- 
lies. The  modification  of  acid  thus  obtained  forms  two  classes 
of  salts,  one  of  which  is  normal,  the  other  acid  in  composition. 
Even  the  normal  salts  all  redden  litmus  faintly.*  When  mixed  in 
the  cold  with  an  excess  of  hydrochloric  acid,  they  are  decomposed, 
and  a white  sparingly  soluble  hydrate  of  tungstic  acid  (H^ W G^, 
lIjO)  is  deposited. 

The  following  table  contains  the  formulse  of  a few  of  the 
tungstates,  and  shows  their  complex  character  : — 


Normal  tungstates 
Paratungstates  . . . 
Metatungstates. . . 


M0,W03 

5 MO,  12  W03,2ri  + 1 HO 
MO,  4 W03,n  HO 


or  M2W04 
M5H,  3 W207,wH20 

M2,  W4O1  sjtoHqO 


Tungstate  of  potassium K0,W03,H0 

“ sodium NaO.WOs,  2 HO 

Paratungstate  of  potassium 5 KO,  12  WO3,  11  HO 

“ sodium 5NaO,  12  WO3,  21  HOf 

“ ammonium. . ..5  H4NO,  12  WO3,  H HO 

“ ditto  (hot) 5H4NO,  12  WO3,  5 HO 

“ potassium)  ..4KO,NaO,  12  WOs, 

“ & sodium  ) 15  HO 

Acid  tungstate  of  sodium 3 NaO,  7 WOs.  16  HO 

Metatungstate  of  potassium. . . . KO,  4 'WO3,  5HO 
Metatungstate  and  nitrate  ) . .3  H4NO,  8 WO3  NO5, 
of  ammonium \ 4 HO 


K2W04,H20 
Na2W04,  2 H2O 
K5H,  3 W2O7,  5 H2O 
Nar,H,  3 W2O7,  13  HoO 
(H4N)5H,  3 W207,  5 H20 
(H4N)5H,  3 W207,  2 020 

K4NaH,  3 W207,  7 020 

NacHf,  7 W04,  12  H20 
K2W4013  5 020 
(040)2, W4013,  H4NN03, 
2 020 


Tungstate  of  potassium  is  obtained  by  heating  a strong  solu- 
tion of  carbonate  of  potassium  to  nearly  its  boiling  point,  and  add- 
ing tungstic  anhydride  so  long  as  it  produces  an  effervescence : 
long  slender,  anhydrous  deliquescent  needles  of  the  tungstate  are 
deposited  from  the  solution  as  it  cools  : if  redissolved,  and  allowed 
to  recrystallize  by  spontaneous  evaporation  over  oil  of  vitriol, 
at  a temperature  not  exceeding  50°,  large  limpid  prisms  (K^WO,, 
II^O)  are  formed ; this  salt  is  soluble  in  about  half  its  weight  of 


* Scheiblor  (JoMrri. /iir  Pra^^.  Chemie,  Ixxxiii.  273)  attributes  to  the  tungstates 
formube  much  more  complicated  than  those  given  by  Riche  ; and  He  Marignac  {Ann. 
de  Chimie,  III.  Ixix.  5)  gives  others  for  certain  compounds  yet  more  complicated  than 
those  of  Scheibler,  though  the  analyses  of  De  Marignac  agree  almost  exactly  with 
Scheibler’s. 

The  complexity  of  these  formulae  has  led  Persoz  to  attempt  to  simplify  them  by 
altering  the  number  assumed  as  the  atomic  weight  of  tungsten  {Ann.  de  Chimie,  IV. 
i.  93).  He  calls  the  atomic  weight  of  tungsten,  153-3,  and  if  we  take  for  this  new 
weight  the  symbol  Tu,  the  formula  for  the  anhydride  will  be  TuOo,  or  Tu20r,.  But 
if  Regnault’s  determination  of  the  specific  heat  of  tungsten  be  correct,  it  is  not 
probable  that  this  number  represents  that  of  the  atomic  weight ; and  indeed  the 
formulae  which  Persoz  proposes,  when  reduced,  as  needful,  for  the  larger  atomic  weight 
of  oxygen,  are  not  less  complicated  than  those  for  which  he  attempts  to  substitute 
them.  I have,  with  one  or  two  exceptions,  adopted  the  formulm  of  De  Marignac  as 
being  the  most  symmetrical,  and  therefore  the  most  probable,  whilst  they  correspond 
quite  as  closely  with  the  experimental  results  as  any. 

Since  this  sheet  was  in  type,  a paper  has  appeared  by  Graham  {Proceed.  Roy.  Soc. 
xiii.  355),  on  the  soluble  colloids  of  the  tungstic,  molybdic,  and  other  metallic  acids, 
which  throws  some  further  light  upon  their  anomalies. 

f De  Marignac  adopts  the  formula  with  28  HO. 


574 


TUNGSTATES — ^IVIETATUNGSTIC  ACID. 


cold  water.  When  pure  it  is  not  decomposed  by  the  addition  of 
a solution  of  the  acid-carbonate  of  sodium,  but  if  silica  be  present, 
a precipitate  is  occasioned  by  this  test.  Acid-tungstate  of  jgotas- 
siuin  may  be  obtained  as  (K2W2O,)  by  fusing  an  ecpiivalent  of  the 
foregoing  salt  with  one  of  the  tungstic  anhydride,  or  by  adding  a 
second  equivalent  of  tungstic  anhydride  to  a hot  solution  of  an 
equivalent  of  the  normal  salt,  when  it  crystallizes  in  hydrated 
plates  with  A sparingly  soluble  jparatungstate  (K^H  3 

W^O,,  5 H^O)  is  obtained  by  transmitting  a current  of  carbonic 
anhydride  through  a solution  of  the  normal  tungstate : it  is  de- 
posited in  pearly  scales.  The  normal  tungstate  of  sodium  (I^a^ 
W0-^,2  HjO)  crystallizes  readily  in  rhqmboidal  plates.  Thej?<7.r<i^ 
tungstate  of  De  Marignac  (ISTa^H,  3 13  HjO)  may  also  be 

obtained  crystallized  in  large  efflorescent  oblique  prisms.  This 
salt  becomes  modified  by  long  boiling  of  its  solution,  which  then 
on  evaporation  deposits  long  8-sided  prisms  of  an  acid  salt 
Hg,  7 W0-^,  17  HjO).  Anotlier  acid  salt  containing  only  12  instead 
of  17  H20-,  is  also  known  ; and  if  either  of  these  salts  be  fused 
at  a full  red  heat,  an  insoluble  salt  (IS^a^O,  4 WBg)  is  left  on  treat- 
ing the  mass  with  water.  Paratungstate  of  amm^onium  is  easily 
obtained  by  digesting  the  anhydride  in  excess  of  ammonia  : it  is 
a sparingly  soluble  salt  which  at  ordinary  temperatures  crystal- 
lizes in  two  distinct  forms,  either  in  delicate  needles  or  in  thin 
brilliant  plates,  with  the  formula  3 5 H^O].  If 

crystallized  at  a little  below  the  boiling-point,  it  is  deposited  in 
hard  brilliant  rhomboidal  needles  which  contain  2 instead  of  5 II2O. 
A tungstate  of  tungsten  (W0^,WO3),  of  a splendid  blue  colour, 
somewhat  analogous  to  the  molybdate  of  molybdenum,  may  be 
obtained  by  a partial  reduction  of  tungstic  acid,  either  by  hydro- 
gen gas,  or  by  strongly  igniting  the  tungstate  of  ammonium  in 
closed  vessels,  or  by  digesting  tungstic  anhydride  with  zinc  and 
hydrochloric  or  sulphuric  acid. 

• The  most  important  native  ore  of  tungsten  is  wolfram^  which 
occurs  in  hard  prismatic  crystals  of  a dark  brown  colour : it  is 
regarded  as  a mixture,  in  variable  proportions,  of  ferrous  and 
manganous  tungstates.  Its  specific  gravity  is  very  high,  being 
about  7*3.  It  was  this  circumstance  that  gave  rise  to  the  name 
tungsten^  the  term  being  a combination  of  two  Swedish  words, 
implying  “heavy  stone.”  This  mineral  is  decomposed  when 
boiled  with  hydi'ochloric  acid,  or  with  aqua  regia,  the  tungstic 
acid  remaining  undissolved.  It  is  also  readily  decomposed  by 
fusion  with  nitre  or  with  carbonate  of  sodium,  and  a soluble 
tungstate  of  the  alkaline  metal  is  formed. 

ALetatungstic  Acid  or  II0,W40i2). — The  salts  of 

this  acid  colour  litmus  of  a wine-red,  and  crystallize  generally 
with  facility.  They  pass  readily  when  in  solution  into  the  salts 
of  tungstic  acid;  the  change  is  gradual  in  neutral  solutions  at 
ordinary  temperatures,  more  rapid  in  boiling  liquids,  or  on 
the  addition  of  a powerful  acid,  and  the  conversion  is  instan- 
taneous if  the  hot  liquid  is  mixed  with  a caustic  alkali  or  alkaline 
carbonate  in  excess.  The  metatungstates  are  always  prepared  by 


SULPHIDES  AHD  PHOSPHIDES  OF  THHGSTEH. 


575 


the  action  of  hydrated  tungstic  acid  upon  the  tungstates.  If  the 
white  liydrated  acid  (H2W04,H20),  obtained  by  the  action  of 
hydrocldoric  acid  in  the  cold  upon  the  soluble  tungstates,  be 
neutralized  by  bases,  it  furnishes  salts  which  are  identical  with 
the  ordinary  tungstates ; but  if  one  of  the  soluble  normal  tung- 
states, such  as  the  tungstate  of  potassium,  be  boiled  with  the 
white  hydrate  of  the  acid  in  the  proportion  of  an  atom  of  each 
until  the  solution  no  longer  becomes  turbid  on  the  addition  of  an 
acid,  a new  salt,  the  metatungstate  of  jpotassium  (K2W40j3,  8 H2O) 
is  formed,  and  is  deposited  in  square  based  octohedra ; a second 
salt  containing  only  4 H2O  crystallizes  in  delicate  needles,  after 
adding  alcohol  to  a strong  solution  of  the  first  salt.  A metatung- 
state of  sodium  with  10  H20-  crystallized  in  brilliant  octohedra 
may  be  obtained  by  operating  as  for  the  first  potash  salt.  Meta- 
tungstate of  ammonium  [(H4N)2,  8 H2O]  crystallizes  in 

brilliant  fusible  octohedra.  The  metatungstates,  when  mixed  with 
nitric  acid,  do  not  at  once  yield  a precipitate  of  the  metallic  acid. 

Metatungstate  of  harium  (BaW^O^g,  9 HgO)  may  be  obtained  in 
crystals  with  a fatty  lustre,  by  mixing  a warm  concentrated 
solution  of  metatungstate  of  ammonium  with  an  equivalent  quan- 
tity of  one  of  chloride  of  barium ; and  by  decomposing  metatung- 
state of  barium  with  its  exact  equivalent  of  diluted  sulphuric  acid, 
a solution  of  the  metatungstic  acid  is  obtained. 

De  Marignac  has  found  that  when  acid  tungstate  of  potassium 
is  boiled  with  gelatinous  silica,  the  liquid  becomes  alkaline,  silica 
is  dissolved,  and  a new  salt,  a silico-tung state  is  formed.  The 
acid  is  unstable,  but  it  may  be  obtained  crystallized  at  ordinary 
temperatures  in  square  tables  (4  H20,Si02,  12  WO3, 29  HgO) ; or 
in  cubo-octohedra,  which  contain  18  HgO,  by  evaporation  at 
a rather  high  temperature.  Two  other  silicated  tungstic  acids 
appear  to  exist : each  of  the  three  forms  is  soluble  in  alcohol ; with 
the  alkali-metals  they  form  very  soluble  salts. 

(834)  Sulphides  of  Tungsten. — There  are  two  sulphides  of 
this  metal,  the  bisulphide  and  the  tersulphide. 

The  bisulphide  (WSg)  was  obtained  by  Biche  in  a pure  form 
by  heating,  in  a covered  clay  crucible,  an  intimate  mixture  of 
equal  parts  of  acid  tungstate  of  potassium  and  sulphur.  After 
fusion  at  a very  high  temperature  for  half  an  hour,  the  mass 
is  poured  out,  powdered,  and  washed  with  boiling  water.  The 
bisulphide  is  left  in  the  form  of  bluish-black  slender  crystals, 
wliich  feel  unctuous  to  the  touch,  and  stain  paper  or  the  skin  like 
I'dumbago ; it  admits  of  being  consolidated  by  pressure,  and  might, 
probably,  be  used  in  the  manufacture  of  drawing-pencils. 

The  tersulphide  (WS3)  may  be  obtained  by  dissolving  tungstic 
anhydride  in  a solution  of  sulphide  of  potassium,  and  ])recipitat- 
ing  by  the  addition  of  an  acid  : it  is  sliglitly  soluble  in  pure  water. 

The  tersulphide  is  a strong  sulphur  acid ; with  sul])hide  of 
potassium  it  forms  an  orange-yellow  crystallizable  compound. 
These  sulpho-salts  may  be  formed  by  heating  the  tungstates  of 
the  alkali-metals  with  an  excess  of  suljihur. 

Phosphides  of  Tungsten. — Phosphorus  enters  into  combina- 


576 


CHAEACTEKS  OF  THE  SALTS  OF  TUNGSTEN. 


tion  with  tungsten,  when  its  vapour  is  passed  over  the  metal  in  a 
finely-divided  state,  and  heated  to  redness  in  a glass  tube ; a dull, 
dark  grey  powder  (W3P4),  difficult  of  oxidation,  is  thus  formed. 
Another  compound  (W^P)  is  formed  in  beautiful  crystalline  groups 
like  geodes,  by  reducing  a mixture  of  2 atoms  of  phosphoric  and 
1 atom  of  tungstic  anhydride,  at  a very  high  temperature,  in  a 
crucible  lined  with  charcoal : brilliant  six-sided  steel-grey  prisms, 
of  sp.  gr.  5 ’207,  are  thus  obtained.  It  is  a good  conductor  of 
electricity.  It  is  oxidized  with  difficulty  when  heated,  and  is 
not  attacked  by  acids. 

Both  the  CHLORIDES  of  this  metal  (WCl^,  or  WCI2),  and 
(WClg,  or  W CI3),  are  volatile : they  are  decomposed  by  water  into 
hydrochloric  acid  and  the  corresponding  oxide  of  tungsten.  The 
hexachloride  is  formed  by  passing  pure  and  dry  chlorine  over 
heated  metallic  tungsten  ; it  fuses  at  362°,  and  is  of  a bronze 
colour,  but  by  exposure  to  the  air  quickly  acquires  a violet  hue, 
owing  to  its  partial  decomposition  by  the  absorption  of  moisture. 

The  oxychloride  (WO^Cl^)  may  be  obtained  in  yellow  volatile 
crystalline  scales,  by  passing  dry  chlorine  over  either  the  binoxide 
of  tungsten  or  tungstic  anhydride  when  heated  to  redness.  It  is 
sometimes  termed  chlorotungstic  acid.  The  red  volatile  compound, 
formerly  supposed  to  be  a perchloride,  is,  according  to  Riche,  an 
oxychloride  of  the  form  (WOCl,). 

Tetrachloride  of  tungsten  (WCl^)  absorbs  ammonia,  and  by  a 
gentle  heat,  the  whole  of  the  chlorine  is  expelled  in  the  form  of  sal 
ammoniac,  leaving  a black  powder  consisting  of  2 WI72,WIl4K2. 
When  this  powder  is  heated  in  the  air  it  burns,  evolving  ammonia 
and  leaving  a residue  of  tungstic  anhydride  (W older) : it  is  not 
soluble  in  acids. 

(835)  Characters  of  the  Salts  of  Tungsten. — The  com- 
pounds of  this  metal  are  not  poisonous.  No  salts  corresponding 
to  binoxide  of  tungsten  are  known. 

The  tungstates  in  solution  are  colourless.  They  are  not  pre- 
cipitated either  by  sulphuretted  hydrogen  or  by  hydrosulphate  of 
ammonium.  K har  of  tin^  placed  in  their  acidulated  solution  in 
a vessel  from  which  air  is  excluded,  produces  a deep  violet- 
coloured  liquid,  owing  to  the  reduction  of  the  acid  to  a lower 
degree  of  oxidation.  Zinc,  stannous  chloride,  and  other  reducing 
agents,  in  the  presence  of  acids,  produce  a like  result.  The  addi- 
tion of  any  stronger  acid  to  a boiling  solution  of  the  tungstates 
causes  the  separation  of  a yellow  precipitate  of  tungstic  acid  which 
is  soluble  in  phosphoric  and  in  tartaric  acid.  They  yield  before 
the  blowpipe.,  with  borax,  a colourless  transparent  glass,  which 
becomes  yellow  in  the  reducing  flame,  and  blood-red  on  cooling. 
With  microcosmic  salt  (621)  they  give  a beautiful  blue  in  the 
reducing  flame,  which  becomes  yellow  or  colourless  in  the  oxi- 
dating flame;  the  addition  of  a little  metallic  tin  to  the  bead 
favours  the  production  of  the  blue  colour. 

Tungsten  is  always  estimated  in  the  form  of  tungstic  anhy- 
dride, 100  grains  of  which  contain  79*32  of  the  metal. 


VANADIOr. 


577 


§ YL  YANADiin^i:  Y=3l37,  or  Y=:6S‘4:6. 

(836)  Vanadium  is  one  of  those  rare  metals  at  present 
known  only  as  chemical  curiosities : it  \ras  discovered  in  1830, 
by  Sefstrdm,  in  a Swedish  iron  ore  from  Taberg,  wdiich  yielded 
bar  iron  remarkable  for  its  malleability ; but  its  most  abundant 
ore  is  the  vanadiate  of  lead,  which  has  been  found  at  Zimapan  in 
Mexico,  at  Wanlockhead  in  Scotland,  and  more  recently  in  Chili ; 
lately  Wohler  has  found  vanadium  accompanying  some  of  tlie 
ores  of  uranium  and  iron.  It  is  best  obtained  by  reducing 
vanadic  acid  in  a covered  porcelain  crucible,  by  means  of  potas- 
sium : the  reduction  takes  place  wuth  vivid  incandescence ; the 
potash  is  dissolved  by  water,  and  vanadium  is  deposited  as  a 
brilliant  metallic  powder.  It  is  readily  dissolved  by  nitric  acid 
and  by  aqua  regia,  forming  a line  blue  solution  ; but  it  is  not 
acted  upon  even  by  boiling  sulphuric,  hydrochloric,  or  hydro- 
fluoric acid ; when  heated  with  the  caustic  alkalies  in  closed 
vessels,  it  undergoes  no  change.  By  passing  a current  of  dry 
ammonia  over  heated  chloride  of  vanadium,  a nitride  of  the  metal 
is  obtained  in  a coherent  form  with  a steel-white  lustre;  it  is 
brittle  and  very  infusible. 

(837)  Oxides  of  Vanadium. — This  metal  forms  three  distinct 
compounds  with  oxygen,  VO ; VO^ ; and  VO3.  The  protoxide 
(VO=153)  is  obtained  from  vanadic  anhydride,  by  reducing  it, 
by  means  of  a stream  of  hydrogen,  or  by  charcoal : it  is  a black, 
crystalline,  brittle  mass,  resembling  graphite  in  appearance,  and 
like  it,  conducts  electricity.  It  does  not  combine  either  with 
acids  or  with  bases.  If  heated  in  air  for  some  time  it  absorbs 
oxygen,  forming  the  hinoxide  (V02  = 169),  as  a black  anhydrous 
powder,  wdiich  forms  salts  with  acids ; they  have  a blue  colour, 
and  wdien  mixed  wdth  the  hydrates  of  the  alkalies  furnish  a grey 
hydrate  of  the  binoxide ; in  this  form  it  rapidly  absorbs  oxygen, 
and  becomes  first  brown  and  then  green.  Binoxide  of  vanadium 
appears  also  to  possess  feebly  acid  properties,  for  it  combines 
wdth  bases. 

Vanadic  anhydride  (V03=185  ; sp.  gr.  3*49)  is  of  a browmish- 
red  colour ; at  a red  heat  it  fuses  without  further  change,  and 
crystallizes  on  cooling,  becoming  incandescent  from  evolution  of 
latent  heat  in  the  act  of  solidification.  It  is  sparingly  soluble  in 
w^ater,  to  wdiich  it  communicates  a yellow  tint : the  solution  is 
powerfully  acid  and  reddens  litmus  strongly.  It  forms  both  nor- 
mal and  acid  salts : the  normal  salts  wdien  first  prepared  are 
yellow,  but  in  a few  hours  they  spontaneously  become  wdiite. 
The  most  important  of  these  salts  is  the  vanadiate  of  ammnnium 
(II,]Ni)3VO„  from  which  the  acid  itself  is  usually  obtained.  Vana- 
diate of  ammonium  is  procured  by  putting  pieces  of  sal  ammo- 
niac into  a crude  solution  of  vanadiate  of  potassium  (such  as  is 
prepared  by  the  deflagration  of  the  slag  obtained  from  the  iron 
ore  of  Taberg,  with  nitre,  after  the  excess  of  alkali  has  been 
neutralized  with  hydrochloric  acid) : the  vanadiate  of  ammonium 
being  insoluble  in  a saturated  solution  of  chloride  of  ammonium 
37 


578 


AESENICUM. 


is  gradually  deposited  in  small  crystalline  grains.  Cold  water 
dissolves  it  sparingly,  but  it  is  much  more  soluble  in  hot  water : 
when  heated  in  the  open  air  the  ammonia  is  expelled,  and  pure 
vanadic  anhydride  is  left.  The  acid  vanadiaU  of  ammonium 
yields  crystals  of  an  orange  colour.  If  mixed  with  tincture  of 
galls,  th|Jp  salts  give  a deep  blackx  liquid,  which  preserves  its 
blackness  even  when  much  diluted  : it  forms  a very  permanent 
writing  ink,  since  it  is  not  destroyed  either  by  acids,  which  turn 
it  blue,  or  by  alkalies,  or  by  chlorine. 

Yanadic  acid  appears  to  combine  in  different  proportions  with 
the  inferior  oxides  of  the  metal,  forming  compounds  which  are 
either  of  a green  or  a purple  colour.  It  also  combines  with  many 
acids  in  dehnite  proportions,  such  as  the  compound  (YOg,  3 SOgj : 
several  of  these  compounds  crystallize  with  facility. 

The  attraction  of  vanadium  for  sulphur  is  but  small.  It  com- 
bines with  it  in  two  proportions,  YSj  and  YS3. 

A Tetrachloride  of  vanadium  (YCl^),  corresponding  to  the 
binoxide,  may  be  formed ; it  is  of  a blue  colour;  and  a hexachlo- 
ride  (YClg : sp.  gr.  of  vapour^  GTl ; of  liquid^  l'  76-I;  Boiling-pt. 
260°)  which  is  a yellow,  fuming,  volatile  liquid,  is  obtained  by 
heating  a mixture  of  vanadic  anhydride  and  charcoal  in  a current 
of  chlorine.  Bromides,  iodides,  fluorides,  and  cyanides  of  vana- 
dium have  also  been  formed. 

(838)  CuAKACTERS  OF  THE  COMPOUNDS  OF  YaXADIUM. 1.  The 

salts  corresponding  to  the  Mnoxide  of  vanadium  yield  blue  solu- 
tions, which  give  a black  colour  with  tincture  of  galls^  and  a grey 
precipitate  with  the  hydrated  alhalies^  becoming  red  by  exposure 
to  the  air.  Ferrocijanide  of  potassium  gives  a yellow  precipitate, 
which  becomes  green  when  exposed  to  the  air.  The  sulphides  of 
the  alkaline  metals  give  a brownish-black  precipitate,  readily  solu- 
ble in  excess,  and  forming  a magnificent  purple  liquid. 

2. — The  vanadiates^  when  treated  with  sulphuretted  hydro- 
gen, or  when  boiled  with  sulphuric  acid  and  either  alcohol  or 
sugar,  give  a beautiful  blue  solution,  a reaction  that  distinguishes 
them  from  the  chromates,  which  under  these  circumstances  fur- 
nish a green  liquid.  Before  the  blowpipe  with  borax  in  the  re- 
ducing flame,  compounds  containing  vanadium  give  a green  glass, 
which  becomes  yellow  in  the  oxidating  flame. 

§ YII.  Aksenicttm:  As'"=T5.  Theoretic  Sp.  Gr.  of  vap>our^ 
10T67 ; Observed^  10*6 ; of  solid.,  from  5'TO  to  5‘959. 
Atomic  Yol.  -I-  or  □ ; Molecular  Yol.  As^  | | 

(839)  AKSENiCDxr,  or  arsenic.,  in  various  states  of  combination, 
was  known  to  mankind  before  the  Christian  era.  This  element 
presents  many  analogies  with  phosphorus,  and  with  nitrogen : it 
is  considered  by  several  French  writers  to  belong  to  the  non- 
metalhc  elements.  It,  however,  conducts  electricity  with  facility, 
and  possesses  a high  metallic  lustre.  Arsenic  generally  presents 

* Four  atoms  of  arsenic  enter  into  the  formation  of  one  molecule  of  its  vapour, 
corresponding  in  this  respect  with  phosphorus. 


METALLIC  AKSENIC. 


579 


itself  in  the  form  of  an  alloy  with  some  other  metal,  especially 
with  iron,  or  with  cobalt,  nickel,  copper,  or  tin.  It  is  found  occa- 
sionally in  the  native  state,  and  it  sometimes  occurs  united  wdth 
oxygen  and  certain  metals,  constituting  arseniates,  such  as  those 
of  iron,  copper,  and  lead.  More  rarely  it  occurs  united  with  sul- 
phur, either  as  the  red  bisulphide  (realgar),  or  as  orpiment,  the 
yellow  tersulphide. 

The  greater  part  of  the  arsenic  of  commerce  is  prepared 
from  mispickel  (FeAsS),  an  arsenical  sulphide  of  iron,  furnished 
abundantly  by  the  Silesian  mines  ; and  from  the  arsenides  of 
nickel  and  cobalt,  which  yield  arsenious  anhydride  as  a secondary 
product  in  the  ordinary  process  of  working  these  ores.  The  sepa- 
ration of  the  arsenic  is  effected  by  roasting  the  mineral  in  a man- 
ner similar  to  that  employed  for  driving  off  sulphur ; but  the  ar- 
senious anhydride  which  is  produced,  being  less  volatile,  more 
valuable,  and  more  deleterious,  is  condensed  in  large  chambers, 
through  which  the  flues  from  the  furnaces  pass.  The  emptying 
of  these  chambers,  which  is  performed  about  once  in  six  weeks, 
is  an  operation  attended  with  danger  to  the  workmen,  from  the 
poisonous  and  irritating  nature  of  the  flnely-powdered  arsenious 
anhydride.  In  order  in  some  degree  to  protect  the  men  wdiilst 
thus  engaged,  they  are  cased  in  leather,  with  glazed  apertures  for 
the  eyes,  and  are  made  to  cover  their  mouths  and  nostrils  with 
damp  cloths,  which  arrest  most  of  the  acrid  particles.  Much  of 
the  anhydride  obtained  from  these  chambers  is  in  the  form  of  a 
fine  powder ; it  is  still  very  impure,  and  it  is  therefore  again  sub- 
limed in  iron  pots,  the  upper  part  of  which  is  kept  moderately 
cool ; here  it  is  condensed  into  a transparent,  half-fused,  vitreous 
mass.  The  lower  portions  only  of  this  sublimate  are  pure,  and 
. these  are  sold  as  white  arsenic ; the  upper  are  either  resublimed, 
or  are  employed  for  the  purpose  of  furnishing  metallic  arsenic. 
In  order  to  obtain  the  metal,  the  sublimed  anhydride  is  powdered, 
mixed  wdth  charcoal,  or  with  twice  its  weight  of  black  flux,  and 
lieated  in  an  earthen  crucible,  upon  the  top  of  which  a second 
inverted  crucible  is  luted,  and  screened  from  the  Are  by  means  of 
a perforated  iron  plate.  The  reduced  metal  is  condensed  in  the 
upper  crucible. 

Properties. — Metallic  arsenic,  or  arseniciim^  has  a brilliant, 
dark  steel-grey  lustre ; it  is  very  brittle,  and  is  easily  reduced  to 
powder.  When  heated  to  356°  in  closed  vessels,  it  begins  to 
volatilize  without  fusing,  and  crystallizes  indistinctly,  as  it  is  con- 
densed, in  rhombohedra,  which  are  isomorphous  with  those  of 
antimony.  Its  vapour  is  colourless,  and  possesses  a powerful, 
oppressive,  alliaceous  odour.  The  metal  may  be  exposed  to  a dry 
air  without  undergoing  change : when  exposed  in  a moist  state  to 
the  air  it  is  slowly  oxidized,  and  a substance  known  fly -powder 
is  formed ; it  is  probably  a mixture  of  arsenious  anhydride  and 
metallic  arsenic,  though  it  is  regarded  by  some  chemists  as  a sub- 
oxide. If  the  metal  be  heated  in  open  vessels  it  absorbs  oxygen, 
burns  with  a lurid  bluish  flame,  and  is  converted  into  arsenious 
anhydride,  which  is  condensed  as  a white,  mealy  powder,  upon 


580 


OXIDES  OF  ARSENIC. 


cool  bodies  in  the  neiglibourliood.  When  thrown  in  fine  powder 
into  chlorine  gas  it  talves  fire  spontaneously,  and  is  converted  into 
chloride  of  arsenic.  Bromine,  iodine,  and  sulphur  also  combine 
readily  with  arsenicum  wlien  aided  by  a gentle  heat.  Mtric  acid 
easily'  oxidizes  the  metal,  and  converts  it  into  arsenic  acid : if 
deflagrated  with  nitre,  it  is  converted  into  arseniate  of  potassium. 
Hydrochloric  acid  exerts  but  little  action  on  the  metal,  but  if  this 
acid  be  mixed  with  nitric  acid,  or  with  chlorate  of  potassium,  the 
metal  is  rapidly  converted  into  arsenic  acid. 

A small  quantity  of  arsenic  is  added  to  lead  to  facilitate  its 
assuming  the  gloluilar  form  in  the  manufacture  of  shot.  In  the 
form  of  arsenious  anhydride  it  is  extensively  used  in  the  prepara- 
tion of  green  and  yellow  pigments  ; it  is  likewise  employed  to 
])revent  smut  in  grain,  but  the  practice  is  to  be  reprobated ; it  is 
also  used  in  the  manufacture  of  flint  glass  as  an  oxidizing  agent, 
for  converting  the  protoxide  of  iron  into  peroxide,  in  order  to  get 
rid  of  the  green  tinge  which  protoxide  of  iron  communicates  to 
the  vitreous  mass.  Its  employment  as  a poison  for  vermin  has 
often  been  made  a pretext  for  procuring  it  for  criminal  purposes. 

Oxides  of  Arsenic. — These  are  two  in  number;  arsenious 
anhydride,  AS2O3,  and  arsenic  anhydride,  As^O^ ; both  have  acid 
properties,  no  basic  oxide  being  known. 

(840)  Arsenious  Acid^  qt  Arsenious  Anhydride  (As203i=198, 
or  AsOg  = 99) ; 8p.  Gr.  of  raj)our^  13-85 : Composition  in  100 
paHs^  As,  75-15 ; O,  24-25.  Moleeular  Yol.  (As203)2=|  | — 

This  compound  is  the  white  arsenic  of  the  shops.  It  is  prepared 
upon  the  large  scale  during  the  roasting  of  arsenical  ores  in  the 
manner  already  described.  In  exists  in  two  modifications,  a vitre- 
ous and  a crystalline  form.  When  purified  by  resublimation  and 
freshly  obtained,  it  is  in  semi-transparent,  vitreous,  lamellated 
masses ; but  by  exposure  to  the  air,  it  gradually  becomes  opaque, 
and  of  a yellowish-white  colour.  Tliis  change  advances  slowly, 
from  the  exterior  towards  the  interior,  so  that  the  mass  is  often 
opaque  at  the  surface  whilst  it  remains  transparent  in  the  centre. 
Both  varieties  of  arsenious  anhydride  are  freely  soluble  in  hot 
liydrochloric  acid ; wlien  this  solution  is  boiled,  a portion  of  the 
arsenic  is  volatilized  in  the  form  of  terchloride ; as  the  liquid 
cools  the  excess  crystallizes  in  transparent  anhydrous  octohedra, 
consisting  of  uncombined  arsenious  anhydride ; but  when  the  trans- 
parent variety  has  been  employed,  the  formation  of  each  crystal 
is  marked  by  the  emission  of  a flash  of  light  which  is  perceptible 
in  a darkened  room.  The  opaque  variety  exhibits  no  such  phe- 
nomenon in  crystallizing  from  its  solution.  A hot  solution  of  am- 
monia also  dissolves  white  arsenic  freely,  and  deposits  it  in  anhy- 
drous octohedra  of  the  uncombined  anhydride  on  cooling,  mixed 
with  prismatic  crystals  of  arsenite  of  ammonium,  Il4l4,As02 
(Bloxam ; Journ.  Chem.  Soc.  1862,  297).  Guibourt  found  the 
opaque  variety  to  have  a specific  gravity  of  3-699  ; it  is  less  dense 
than  the  transparent  form,  the  speciflc  gravity  of  which  he  states 

* The  molecular  volume  of  this  body  is  anomalous,  the  density  of  its  vapour 
being  double  of  that  which  might  from  analogy  have  been  expected. 


AJISENITES. 


581 


to  be  3*7385.  The  two  varieties  also  differ  in  their  solubility : 
according  to  Bussy,  water  dissolves  much  less  of  the  opaque  than 
of  the  transparent  anhydride.  A cold  saturated  solution  of  tlie 
vitreous  variety  gradually  deposits  its  excess  of  anhydride  in  the 
opaque  form,  and  retains  between  2 and  3 per  cent,  in  solution ; 
the  liquid  reddens  litmus.  Mere  giinding  to  a fine  powder  con- 
verts the  transparent  into  the  opaque  variety,  and  reduces  its  solu- 
bility. Heat,  however,  gradually  reconverts  the  opaque  into  the 
vitreous  modification,  so  that  long-continued  boiling  renders  the 
opaque  as  soluble  as  the  vitreous  form.  It  is  therefore  difficult  to 
state  the  precise  degree  of  solubility  of  either  form  of  the  com- 
pound, because  the  two  varieties  are  liable  to  be  formed  in  vary- 
ing proportion  in  the  course  of  an  experiment.  The  largest  pro- 
portion which  water  will  dissolve  at  the  boiling-point  is  between 
11  and  12  per  cent.  Both  nitric  acid  and  aqua  regia  dissolve  the 
anhydride,  and  convert  it  into  arsenic  acid. 

Arsenious  anhydride,  when  heated  to  380°,  softens  and  is  sub- 
limed without  fusing,  being  condensed  in  transparent  octohedra 
upon  warm  surfaces,  but  it  occasionally  forms  long  prismatic 
needles,  isomorphous  with  tliose  of  oxide  of  antimony.  Its  vapour 
is  without  odour ; it  is  colourless,  and  contains  1 volume  of  vapour 
of  arsenic  and  3 volumes  of  oxygen,  condensed  into  1 volume. 

Arsenites. — Arsenious  acid  is  soluble  in  solutions  of  the  alka- 
lies and  of  their  carbonates : with  potassium  and  sodium  it  forms 
soluble  compounds  which  do  not  crystallize.  Its  acid  properties 
are  feebly  marked,  but  it  appears  to  be  tribasic,  the  most  usual 
formula  of  its  salts  being  M'gAsO^,  or  3 M0,As03  (Bloxam). 
Arsenite  of  potassium  has  been  used  medicinally  for  many  years 
under  the  name  of  Folder’s  solution.  The  arsenites  of  the  met- 
als of  the  earths  (particularly  arsenite  of  calcium)  are  nearly  in- 
soluble in  water,  but  are  readily  dissolved  by  acids.  Arsenite  of 
copper  (-GuIIAsOa)  is,  in  a commercial  point  of  view,  the  most 
important  of  these  salts ; it  is  of  a delicate  and  beautiful  green 
colour,  constituting  the  pigment  sold  under  the  name  of  Sclieelds 
green.  It  is  prepared  by  dissolving  1 part  of  arsenious  anhydride 
and  3 parts  of  carbonate  of  potassium  in  14  of  water,  and  adding 
the  liquid  to  a boiling  solution  of  3 parts  of  sulphate  of  copper  in 
40  of  water  : the  shade  of  green  may  be  varied  by  altering  the 
proportion  of  arsenious  anhydride.  This  compound  is  a danger- 
ous poison.  It  is  soluble  in  acids  and  in  ammonia.  When  heated 
it  is  partially  decomposed,  and  arsenious  anhydride  sublimes.  The 
Schweinfurt  green.^  which  is  also  used  largely  as  a pigment,  is  a 
double  salt  of  arsenite  and  acetate  of  copper  (3  -GuAs^O^,  Gu 
2 GJIgGj),  made  by  mixing  equal  parts  of  arsenious  anhydride  and 
acetate  of  copper,  in  solution  at  a boiling  temperature,  adding  an 
equal  bulk  of  cold  water,  and  allowing  the  mixture  to  stand  for 
some  days.  Arsenite  of  siher  (AggAsOg)  is  of  a canary -yellow 
colour ; it  is  obtained  by  tlie  addition  of  a solution  of  nitrate  of 
silver  to  one  of  arsenite  of  potassium.  If  a slip  of  bright  co])])er 
foil  be  introduced  into  a solution  of  arsenious  acid  in  hydrochloric 
acid,  a grey  film  of  reduced  arsenic  is  deposited  on  the  copper ; if 


582 


ABSENIC  ANHYDKIDE. 


zinc  be  substituted  for  copper,  arseniuretted  hydrogen  is  evolved 
(84:5,  846).  Arsenious  acid  in  solution  may  readily  be  converted 
into  arsenic  acid  by  acidulating  the  liquid  with  hydrochloric  acid, 
warming  it,  and  gradually  adding  chlorate  of  potassium  in  small 
quantities.  Arsenious  acid  is  indeed  a powerful  reducing  agent ; 
its  solution  in  hydrochloric  acid  reduces  terchloride  of  gold ; it 
bleaches  permanganate  of  potassium,  and  reduces  anhydro-chro- 
mate  of  potassium  to  a sesquisalt  of  chromium. 

If  a solution  of  arsenious  acid  in  carbonate  of  sodium  be 
mixed  with  a little  starch,  and  a solution  of  iodine  or  of  chlorine 
be  added  till  the  starch  turns  blue,  the  arsenious  is  converted  into 
arsenic  acid  ; this  reaction  forms  the  basis  of  a volumetric  process 
for  the  determination  of  iodine  and  chlorine  in  solution. 

If  a minute  fragment  of  arsenious  anhydride  be  heated  with  a 
similar  portion  of  acetate  of  sodium  in  a small  test-tube,  the  char- 
acteristic and  peculiarly  offensive  odour  of  kakodyl  is  perceived. 

(841)  Arsenic  Anhydride  (As^O^  = 230),  or  Arsenic  Add 
(AsO^  = 115) : Comjp.  in  100  jparts^  x\.s,  65*22  ; O,  34*78. — This 
compound  is  obtained  by  treating  arsenious  anhydride  with  nitric 
acid  in  slight  excess,  and  then  boiling  down  to  dryness  in  a plati- 
num vessel.  A white,  somewhat  deliquescent  mass  of  arsenic 
anhydride  remains:  by  slow  evaporation  of  its  solution  arsenic 
acid  may  be  obtained  in  hydrated  crystals.^  Ho  attempts  to  pro- 
cure the  dibasic  and  monobasic  forms  of  arsenic  acid  have  hither- 
to been  successful : indeed  I find  that  it  forms  but  a single  stable 
hydrate,  the  so-called  dihydrate  (II^As^O,,  or  2 H0,As05),  and 
this  is  obtained  whether  the  solution  be  evaporated  over  sulphuric 
acid  at  the  ordinary  temperature,  or  in  the  open  air  at  any  tem- 
perature not  exceeding  300°  : in  this  way  hard  brilliant  prisms  of 
the  dihydrate  are  procured ; at  a temperature  of  500°  these  be- 
come anhydrous,  and  finally,  if  the  mass  be  suddenly  heated  to 
redness,  it  fuses,  and  becomes  decomposed  into  arsenious  anhydride 
and  oxygen.  If  a current  of  sulphurous  acid  be  transmitted 
through  a solution  of  arsenic  acid  it  is  slowly  reduced  to  the  state 
of  arsenious  acid,  whilst  sulphuric  acid  is  formed,  II3 AsO^  -f  HgSOg 
becoming  HgAsOg  + II^SO^.  Arsenic  acid  has  recently  been  em- 
ploj^ed  in  calico-printing  to  some  extent  as  a substitute  for  tartaric 
and  phosphoric  acids,  but  its  employment  is  dangerous  if  the 

* E.  Kopp  {Ann.  de  Chimie,  III  .xlviii.  106)  found,  when  operating  on  a large  scale, 
that  if  a concentrated  solution  of  the  acid  was  stirred  briskly  at  a temperature  not 
exceeding  59°,  a semi-liquid  mass  was  often  obtained,  filled  with  elongated  prisms  or 
rhomboidal  plates  (2  H3As04,H20) : they  are  extremely  deliquescent ; when  heated 
to  212°  they  become  liquid,  lose  water,  and  gradually  deposit  a white  creamy  mass, 
consisting  of  small  needles,  which,  when  dried  by  pressure  between  folds  of  filtering- 
paper,  were  found  to  consist  of  the  hydrate  (H3ASO4).  In  order  to  obtain  the  hy- 
drate (H4As207),  Kopp  evaporated  at  a temperature  ranging  between  284°  and  366° ; 
if  a very  concentrated  solution  of  this  so-called  hydrate  be  kept  for  some  time  at 
392°,  and  then  be  gradually  raised  to  403°  the  liquid  suddenly  boils  up,  becomes  pas- 
ty, and  is  converted  into  a pearly  mass  of  dazzling  whiteness,  consisting  of  the  mono- 
hydrate, which  it  is  difficult  to  obtain  free  from  the  anhydride.  At  a temperature 
below  redness  it  becomes  anhydrous ; all  these  difterent  forms  when  dissolved  in 
water  reproduce  a hquid  like  the  original  solution.  In  preparing  arsenic  acid,  Kopp 
employs  606  lb.  of  nitric  acid,  sp.  gr.  1'35,  to  800  lb.  of  arsenious  anhydride,  and  by 
adding  the  nitric  acid  gradually,  no  application  of  artificial  heat  is  necessary. 


ARSENIATES — SELPHIDES  OF  ARSENIC. 


583 


waste  products  are  allowed  to  run  into  the  streams.  Its  chief 
consumption  is  in  the  preparation  of  magenta  dye  from  aniline. 

Arseniates. — The  arsenic  is  a powerful  tribasic  acid,  expelling 
the  volatile  acids  from  their  combinations,  and  decomposing  the 
carbonates  with  effervescence.  The  salts  of  this  acid  have  the 
general  formula  M'gAsO^,  and  of  the  three  atoms  of  its  basic 
hydrogen,  1,  2,  or  3,  may  consist  of  a metal.  It  forms  a series  of 
soluble  crystallizable  salts  with  the  alkali-metals,  which  present 
considerable  interest,  as  they  are  isomorphous  with  the  tribasic 
jihosphates.  Arseniate  of  sodium  is  a manufactured  product  of 
considerable  importance.  It  is  best  obtained  by  saturating  arsen- 
ious  anhydride  with  crude  soda-ash,  and  deflagrating  the  dry 
residue  in  a reverberatory  furnace  with  a suitable  proportion  of 
nitrate  of  sodium.  By  adding  caustic  soda  in  excess  to  arsenic 
acid,  an  efflorescent  salt  (HagAsO^,  12  H^O)  may  be  obtained  on 
evaporation,  crystallized  in  prismatic  needles.  If  to  a hot  solu- 
tion of  arsenic  acid,  carbonate  of  sodium  be  added  till  efferves- 
cence ceases,  the  salt  which  is  obtained  on  evaporation  (hfaJIAsO^, 
12  H^O)  corresponds  in  form  and  composition  to  the  rhombic 
phosphate  of  sodium,  though  more  usually  it  crystallizes  with 
7 ; and  by  adding  to  a solution  of  this  compound  a quantity 

of  arsenic  acid  equal  to  that  which  it  contains,  a deliquescent  salt 
(NaIl2As04,Il20)  is  procured,  which  crystallizes  with  difficulty. 
The  corresponding  potassium-salt  crystallizes  in  bold  brilliant 
octohedral  crystals  (KII^AsO^) : it  is  readily  prepared  by  defla- 
grating equal  parts  of  arsenious  anhydride  and  nitre,  then  dis- 
solving the  residue  in  water,  and  allowing  it  to  crystallize.  All 
these  salts  may  be  rendered  anhydrous  by  heat,  but  when  redis- 
solved, they  recover  their  basic  w^ater.  An  arseniate  of  magnesium 
and  ammonium  (H^NMgAsO^,  6 H^O)  may  be  procured  in  the 
form  of  prismatic  crystals  isomorphous  with  the  corresponding 
phosphate,  by  mixing  a solution  of  sulphate  of  magnesium  con- 
taining an  excess  of  ammonia  with  a neutral  or  ammoniacal 
solution  of  an  arseniate  of  one  of  the  alkali-metals : it  is  some- 
times used  as  a precipitant  for  arsenic  acid ; it  is  very  sparingly 
soluble  in  weak  ammoniacal  solutions : when  dried  at  212°  it  loses 
11  Aq,  and  the  dried  salt  contains  60*52  parts  of  arsenic  anhydride. 
A brick-red  tribasic  arseniate  of  silver  (AggAsO^)  is  precipitated 
when  any  arseniate  in  solution  is  mixed  with  a solution  of  nitrate 
of  silver  : it  is  readily  soluble  in  excess  either  of  nitric  acid  or  of 
ammonia,  and  is  characteristic  as  a test  of  arsenic  acid.  Tlie  ar- 
seniate of  copper  (-GuIIAsO^)  is  of  a pale  greenish-blue  colour : 
the  arseniates  of  calcium  and  lead  are  white ; whilst  ferric  and 
uranic  salts  give  yellowish  white  arseniates : all  these  are  readily 
soluble  in  excess  of  diluted  nitric  acid. 

(842)  Sulphides  of  Arsenic. — Arsenicum  and  sulphur  may  be 
melted  together  in  all  proportions  ; but  they  form  several  well- 
deflned  compounds:  of  these,  the  most  im])ortant  ai’e  realgar, 
ASgSg ; orpiment,  AsgSg ; and  the  pentasulphide,  or  sulpharseiiic 
anhydride,  As.,Sg. 

lieaUjwr  (ASgS^  =214,  or  Bisulphide  of  arsenic^  AsS^  = 107) ; 


584 


SULPHroES  OF  AESEXIC. 


Sp.  Gr.  3*356. — This  substance  is  occasionally  found  native  in 
ruby-red  prismatic  crystals  ; it  may  be  prepared  artificially,  by 
heating  together  9 parts  of  arsenicum  and  4 of  sulphur,  or  198 
parts  of  arsenious  anhydride  with  112  of  sulphur ; 2 As^Og  -f-  T 
S = 2 AS2S2  -f  3 SOj.  When  heated  in  closed  vessels,  realgar 
melts,  and  afterwards  is  sublimed  without  decomposition.  The 
sublimed  mass  is  hard,  brittle,  transparent,  and  of  a beautiful 
red  colour.  Realgar  is  insoluble  in  water : it  is  readily  attacked 
by  nitric  acid  and  by  aqua  regia,  but  not  by  hydrochloric  acid  ; 
sulphide  of  potassium  dissolves  it  and  forms  a double  sulphide. 
Caustic  potash  decomposes  it,  leawng  a bromi  subsulphide  of 
arsenic  (As^.S)  undissolved.  Realgar  is  one  of  the  ingredients  of 
■lohiU  Indian  jirepYhioh  is  often  used  as  a signal  light : it  is  com- 
posed of  a mixture  of  7 parts  of  sulphur,  2 of  realgar,  and  24  of  nitre. 

Sulpharsenious  anhydride^  or  Orpiment  (As2S3=246,  or  AsS3  = 
123);  Sp.  Gr.  3*48:  Comp,  in  100 parts^  As,  60*98;  S,  39*02. — 
Orpiment  is  occasionally  found  native  in  crystals  which  have  the 
same  form  as  those  of  realgar — wz.,  the  oblique  rhombic  prism: 
these  crystals  are  flexible  ; they  have  a yellow  colour  and  a bril- 
liant lustre.  It  may  be  prepared  artificially  by  transmitting  a 
current  of  sulphuretted  hydrogen  through  a solution  of  arsenious 
acid,  or  of  any  of  the  arsenites,  in  hydrochloric  acid ; it  then  falls 
as  a brilliant  yellow  amorphous  powder.  If  the  solution  be  very 
dilute,  part  of  the  sulphide  is  retained  in  solution,  forming  a 
yellow  liquid ; by  exposure  to  the  air  the  excess  of  sulphuretted 
hydrogen  escapes,  and  the  sulphide  is  gradually  and  completely 
deposited. 

Orpiment  is  insoluble  in  water  and  in  dilute  acids,  but  it  is 
decomposed  by  nitric  acid  and  by  aqua  regia.  It  fuses  easily, 
and  when  heated  in  air  burns  with  a pale  blue  flame.  In  closed 
vessels  it  may  be  sublimed  without  undergoing  decomposition. 
Ammonia  and  the  fixed  alkalies  dissolve  it,  and  form  colourless 
solutions  containing  an  alkaline  arsenite  and  sulpharsenite.  The 
ammoniacal  solution  is  sometimes  used  for  dyeing  yellow,  since  by 
exposure  to  air  the  ammonia  evaporates,  leaving  the  yellow  sul- 
phide firmly  adherent  to  the  fibre.  Orj)iment  is  also  soluble  in 
solution  of  sesquicarbonate  of  ammonium.  This  sulphide  of  arsenic 
is  a feeble  sulphur-acid,  so  that  sulphide  of  ammonium  and  the 
sulphides  of  the  alkaline  metals  in  solution  dissolve  it  easily,  and 
form  double  sulphides,  which  are  decomposed  on  the  addition  of 
an  acid.  Orpiment  is  the  colouring  ingredient  in  the  pigment 
called  King's  yellow.^  which  is  a mixture  of  arsenious  anhydride 
with  this  sulphide. 

Sulpharsenic  anhydride  (As3S3=310,  or  AsS3=155):  Comp, 
in  100  parts As,  48*39 ; S,  51*61. — P entasulphide  of  arsenic^  as  it 
is  sometimes  called,  corresponds  in  composition  to  arsenic  anhy- 
dride. When  a stream  of  sulphuretted  hydrogen  is  transmitted 
through  a solution  of  arsenic  acid,  a yellow  precipitate,  resembling 
orpiment  in  appearance,  and  consisting  of  a mixture  of  orpiment 
and  sulphur,  is  very  gradually  separated  (Rose),  But  by  decom- 
posing a dilute  aqueous  solution  of  the  sulphosalt  by  the 


COMPOUNDS  OF  ARSENIC  WITH  SULPHUR  AND  WITH  HYDROGEN.  585 

addition  of  an  acid,  a bright  yellow  precipitate  of  is  obtained. 
Upon  the  application  of  heat,  the  pentasnlphide  fuses  into  a dark 
liquid,  and  forms  a reddish-yellow  glassy  substance  as  it  cools; 
it  may  be  sublimed  in  closed  vessels.  It  is  soluble  in  the  caustic 
alkalies,  decomposes  the  carbonates  with  effervescence  if  boiled  with 
their  solutions,  and  forms  crystallizable  compounds  with  the 
sulphides  of  the  metals  of  the  alkalies  and  alkaline  earths.  The 
sodium  sulphur-salt  may  be  procured  by  saturating  a solution  of 
10  parts  of  soda  (reckoned  as  Ua^O)  with  sulphuretted  hydrogen, 
adding  an  equal  quantity  of  soda,  and  then  dissolving  26  parts  of 
orpiment  and  7 of  sulphur  in  the  liquid  by  the  aid  of  heat ; on 
evaporation,  the  sodium-salt  is  obtained  in  pale  yellow  crystals. 
The  sulphur-salt  of  ]3otassium  (2  K2S,As2S5)  may  be  made  by 
transmitting  sulphuretted  hydrogen  through  the  solution  of  the 
dibasic  arseniate  of  potassium.  tVhen  an  aqueous  solution  of  this 
sulphur-salt  of  arsenic  is  mixed  with  alcohol,  it  undergoes  decompo- 
sition, and  by  evaporating  the  alcoholic  solution,  after  separating 
the  insoluble  portion  by  filtration,  a still  higher  sulphide  (AsSg) 
was  obtained  by  Berzelius,  in  brilliant  yellow  crystalline  scales. 

(843)  Compounds  of  Arsenic  with  Hydrogen. — Arsenic 
forms  two  combinations  with  hydrogen ; one  of  these  is  solid  at 
ordinary  temperatures,  and  of  a chestnut-brown  colour ; it  is 
obtained  by  employing  a plate  of  arsenicum  as  the  platinode 
during  the  voltaic  decomposition  of  acidulated  water ; its  composi- 
tion has  not  been  accurately  determined.  The  other  is  a gaseous 
body  (HgAs)  of  considerable  importance ; it  corresponds  in  com- 
position to  the  gaseous  phosphuretted  hydrogen. 

Terhydride  of  arsenic  Aseniuretted  Tiyd/rogen  (H3As=78) ; 
Theoretic  Sp.  Gr.  2-645,  Observed^  2'695 ; Mol.  vol.  | | |. — This 
remarkable  gaseous  compound  is  an  exceedingly  poisonous  body ; 
it  is  colourless,  and  has  a foetid  alliaceous  odour  ; it  is  sparingly 
soluble  in  water,  and  possesses  neither  acid  nor  alkaline  qualities. 
It  consists  of  1 volume  of  arsenical  vapour  and  6 volumes  of 
hydrogen  condensed  into  4 volumes. 

The  composition  of  the  gas  may  be  thus  represented — 


Arsenic 

As 

By  weig:ht. 
= 75  or  96T5 

By  volume 

1 or  0-25 

Sp.  Gr. 
2-5417 

Hydrogen 

Ha 

= 3 

3-85 

6 1-5  = 

0-1036 

AsHa 

= 78 

100-00 

4 1-0  = 

2-6453 

By  a temperature  of  —40°  it  is  reducible  to  a limpid  colour- 
less liquid,  which  remains  liquid  at  —166°  F.  Arseniuretted 
hydrogen  is  inflammable,  and  burns  with  a bluish-white  flame, 
whicli  deposits  arsenicum  upon  cold  bodies  introduced  within  it, 
and  arsenious  anhydride  upon  those  held  above.  It  is  also 
decomposed  when  caused  to  pass  througli  tubes  heated  to  a 
temperature  a little  short  of  redness,  arsenicum  being  deposited 
as  a steel-grey  crust,  whilst  hydrogen  gas  escapes : if  a current 
of  dry  sulphuretted  hydrogen  be  transmitted  over  the  heated 
crust  a yellow  sublimate  of  sulphide  of  arsenic  is  formed,  which 
is  not  acted  on  by  a current  of  dry  hydrochloric  acid  gas.  These 


5S6 


CHAKACTEES  OF  THE  COMPOTJXDS  OF  AE3EXIC. 


reactions  distinguisli  the  arsenical  from  the  antimonial  crust, 
which  bj  similar  treatment  gives  a dark  orange-coloimed  sulphide 
decomposable  by  a current  of  dry  hydrochloric  acid  gas.  Chlorine 
decomposes  arseniuretted  hydrogen  with  flame,  forming  hydro- 
chloric acid,  and  causing  the  deposition  of  a solid  brown  hydidde 
of  arsenic.  Concentrated  nitric  acid  also  absorbs  the  gas  com- 
pletely, whilst  arsenic  acid  is  formed.  This  gas  is  entirely  ab- 
sorbed by  a solution  of  sulphate  of  copper,  sulphuric  acid  being 
liberated,  whilst  arsenide  of  copper  is  precipitated.  Xitrate  of 
silver  is  also  decomposed  by  arseniuretted  hydrogen.  Solution 
of  corrosive  sublimate  likewise  dissolves  it  completely,  a com- 
pound of  calomel  and  arsenide  of  mercmy  being  formed.  It  is 
also  largely  absorbed  by  oil  of  turpentine,  with  which  it  forms  a 
crystalline  compound. 

Pure  arseniuretted  hydi’ogen  may  be  prepared  by  decompos- 
ing with  sulphuric  acid  diluted  with  three  parts  of  water,  an 
arsenide  of  zinc,  obtained  by  heating  equal  weights  of  powdered 
arsenicum  and  granulated  zinc  in  an  earthen  retort;  the  fused 
mass  is  removed  by  breaking  the  retort,  and  is  subsequently 
powdered.  The  greatest  care  is  required  not  to  inhale  any 
portion  of  this  deadly  gas. 

(84d)  TERCHLOEroE  OF  Aesexic  (AsClg  = 181‘5):  8p.  Gr  of 
vaj^our^  6 ‘3  ; of  liquid  at  32°,  2*205 ; Boiling-pt.  270°.  Molecular 
vol.  I I ]. — Only  one  compound  of  arsenic  with  chlorine  is 
known.  It  is  produced  either  by  the  combustion  of  the  metal  in 
chlorine,  or  by  distilling  a mixture  of  one  part  of  arsenicum  and 
6 parts  of  corrosive  sublimate,  or  still  more  easily  by  heating 
arsenious  anhych’ide  in  a current  of  dry  chlorine  gas : it  condenses 
as  a heavy,  colourless,  oily-looking  liquid,  which  remains  liquid  at 
— 20°  ; it  fumes  when  exposed  to  the  air,  and  is  immediately  de- 
composed by  water  into  arsenious  and  hydrochloric  acids. 

Teeiodide  of  Aesextc  (Asig  = 456 ; Sp.  Gr.  4*39)  may  be  pre- 
pared by  subliming  a mixture  of  3 parts  of  iodine  and  1 part  of 
the  metal  in  a flask ; it  forms  brick-red  brilliant  flakes.  It  may 
also  be  obtained  by  digesting  3 parts  of  powdered  arsenicum  and 
10  of  iodine  in  100  of  water ; on  evaporation  the  clear  liquid 
}nelds  red  hydi’ated  crystals,  which  become  anhydrous  when 
heated  to  their  fusing-point : it  is  soluble  in  alcohol. 

A terhromide  may  be  formed  by  analogous  means  ; it  is  a crys- 
talline sohd  at  all  temperatures  below  68°,  of  sp.  gr.  3*66  ; it  boils 
at  428°. 

The  terfluoride  may  be  prepared  by  distilling  5 pails  of  fluor- 
spar, mixed  with  4 of  arsenious  anhydride  and  10  of  concentrated 
sulphuric  acid.  It  is  a fuming  colourless  liquid,  which  rapidly 
corrodes  glass,  and  is  decomposed  by  water. 

(845)  Chaeactees  of  the  Compounds  of  Arsenic. — Arsenicum 
forms,  with  most  of  the  metals,  alloys  which  are  generally  brittle 
and  easily  fusible.  The  compounds  of  this  metal  are  all  highly 
poisonous the  substance  which  has  the  best  claim  to  be  consid- 

* For  a singular  statement  respecting  the  arsenic  eaters  of  Styria,  the  reader  is 
referred  to  a paper  by  Mr,  Heisch,  in  the  Pharmaceutical  JourruU  for  May,  1860,  p.  556. 


CHAKACTEES  OF  THE  COMPOUNDS  OF  AESENIC. 


58T 


ered  as  an  antidote  to  it,  is  the  freshly-precipitated  hydrated  ses- 
quioxide  of  iron,  which  should  he  suspended  in  water,  and  given 
freely,  as  early  as  possible  after  the  poison  has  been  swallowed. 
It  is  only  applicable  when  arsenic  or  arsenions  acids  have  been 
taken  nncombined  with  bases,  as  it  forms  an  insoluble  arseniate 
of  iron  ; the  arsenions  acid  being  partially  oxidized  by  the  excess 
of  hydrated  peroxide,  which  is  thereby  reduced  to  the  form  of 
protoxide  of  iron.  Calcined  magnesia  may  be  used  if  the  oxide 
of  iron  be  not  at  hand.  In  cases  of  arsenical  poisoning,  putrefac- 
tion of  the  body  after  death  is  retarded  in  a remarkable  degree  ; 
indeed,  in  several  instances  where  the  body  has  been  disinterred 
several  months  after  death,  it  has  been  found  to  have  been 
sufficiently  preserved  from  decay,  to  allow  many  of  the  principal 
viscera  to  be  distinguished.  In  these  cases  it  has  not  unfrequently 
happened,  that  yellow  patches  of  sulphide  of  arsenic  have  been 
observed  in  various  parts  of  the  alimentary  canal,  although  it  has 
been  ascertained  that  the  poison  had  been  swallowed  in  the  form 
of  white  arsenic.  These  patches  of  orpiment  are  occasioned  by 
the  disengagement  of  sulphuretted  hydrogen  from  the  decompo- 
sition of  the  tissues,  by  which  the  arsenious  anhydride  becomes 
partially  converted  into  the  sulphide  of  the  metal. 

Arsenic  can  be  identified  in  quantities  so  minute  as  to  be  in- 
appreciable by  the  balance.  In  minerals  which  contain  it,  its 
presence  is  revealed  by  the  peculiar  garlic  odour  which  it  emits 
when  a fragment  is  heated  in  the  reducing  fiame  with  carbonate 
of  sodium  on  charcoal,  before  the  hlowjpijpe.  When  in  solution, 
the  compounds  of  arsenic  may  be  detected  by  transmitting 
through  the  solution,  acidulated  with  hydrochloric  acid,  a stream 
of  sulphuretted  hydrogen  for  six  hours  ; a yellow  precipitate  is  thus 
produced  which  must  be  further  examined  as  follows : the  liquid 
must  be  exposed  to  a temperature  of  about  100°  F.,  in  a shallow 
vessel  for  six  hours,  to  allow  the  gas  to  escape,  and  the  precipi- 
tate to  subside  completely  ; the  clear  liquid  must  be  decanted,  and 
the  precipitate  collected  on  a small  filter.  A few  drops  of  ammo- 
nia will  dissolve  it,  and  on  evaporating  this  solution  in  a watch- 
glass,  by  means  of  a water-bath,  the  sulphide  of  arsenic  will  be 
left.  This  substance  is  then  subjected  to  the  process  oi  reduction, 
by  mixing  it  with  three  times  its  bulk  of  black  fiux,*  or  with  a 
mixture  of  one  part  of  cyanide  of  potassium  and  3 parts  of  car- 
bonate of  sodium,  previously  well  dried,  and  introducing  it  into 
a glass  tube  of  the  diameter  of  a common  quill,  care  being  taken 
not  to  soil  the  sides  of  the  tube.  The  mixture  is  heated  strongly 
by  the  blowpipe,  and  the  arsenic  is  condensed  as  a brilliant  mir- 
ror-like ring  of  steel-grey  lustre  in  the  upper  part  of  the  tube. 
The  reaction  which  occurs  when  black  flux  is  used,  may  be  repre- 
sented as  follows : 2 As^Sg  -f  6 K^OOg  -f  6 O = As^  -f  G 
6 OO  -1-  G OOg. 

Sulphide  of  cadmium  gives  a yellow  precipitate  with  sulphur- 
etted hydrogen,  but  it  is  insoluble  in  ammonia:  stannic  salts  also 

* A mixture  of  carbonate  of  potassium  and  charcoal  obtained  by  deflagrating 
equal  weights  of  cream  of  tartar  and  nitre  in  a red-hot  earthen  crucible. 


58S  TESTS  FOE  AESENIC  IN  CASES  OF  POISONING  BY  IT. 

give  a yellow  precipitate  with  sulphuretted  hydrogen,  but  no 
metallic  sublimate  when  they  are  submitted  to  the  process  of  re- 
duction. 

In  addition  to  the  preceding  tests,  arsenious  acid  may  be 
readily  detected  in  a neutral  solution,  by  the  production  of  a yel- 
low precipitate  with  the  ammonia-nitrate  of  silver.  This  re- 
agent is  prepared  by  adding  ammonia  to  a solution  of  nitrate  of 
silver  in  very  slight  excess,  so  as  nearly,  but  not  entirely,  to  redis- 
solve the  precipitate  of  oxide  of  silver  which  is  at  first  formed : 
the  clear  liquid  is  decanted  for  use.  The  yellow  precipitate  is  an 
arsenite  of  silver,  which  is  freely  soluble  both  in  ammonia  and  in 
nitric  acid.  As,  however,  the  tribasic  phosphates  give  a yellow 
precipitate  with  ammonia-nitrate  of  silver,  and  this  precipitate 
also  is  soluble  both  in  nitric  acid  and  ammonia,  a second  test 
should  be  tried — viz.,  the  ammonia-sulphate  of  copper.^  which  is 
prepared  from  a solution  of  sulphate  of  copper,  by  the  addition 
of  ammonia,  with  the  same  precautions  as  those  prescribed  for 
the  preparation  of  the  silver  test.  In  neutral  solutions  contain- 
ing arsenious  acid,  this  copper  test  occasions  a green  precipitate 
consisting  of  arsenite  of  copper : it  is  soluble  both  in  ammonia 
and  in  acids.  The  arsenites  of  silver  and  copper  are  formed  im- 
mediately that  the  tests  are  added;  the  sulphide  of  arsenic  does 
not  appear  at  first  if  the  metal  be  present  as  arsenic  acid,  as  the 
compounds  of  arsenic  acid  are  decomposed  by  hydrosulphuric  acid 
more  slowly  than  those  of  any  other  metal  which  is  precipitable 
by  this  reagent. 

(846)  Search  for  Arsenic  in  Organic  Mixtures.  — In  the 
greater  number  of  cases,  however,  where  the  search  for  arsenic 
becomes  important,  it  is  mixed  with  articles  of  diet,  with  the  con- 
tents of  the  stomach,  or  with  other  matters  of  organic  origin, 
which  render  preliminary  measures  needful  in  order  to  get  rid  of 
them.  If  the  substance  be  in  the  liquid  form,  any  sediment  w^hich 
it  may  contain  must  be  examined  for  solid  particles  of  undissolved 
arsenious  anhydride,  which  are  frequently  found,  and  to  which 
the  preceding  tests  are  readily  applied.  If  any  solid  particles  of 
arsenious  anhydride  be  found,  their  reduction  is  easily  effected  by 
drawing  off  a tube  to  the  thickness  of  a crowquill,  sealing  one 
end,  dropping  in  the  suspected  fragment,  adding  a minute  quan- 
tity of  dried  carbonate  of  sodium,  and  then  a few  small  fragments 
of  charcoal ; upon  ignition,  the  metal  is  sublimed,  and  may  be 
recognised  by  the  steel-grey  ring  which  it  forms  in  tlie  cool  por- 
tion of  the  tube. 

If  no  solid  particles  of  the  anhydride  be  visible,  the  liquid  is 
boiled  and  filtered,  and  divided  into  three  portions,  one  of  which 
is  set  aside  in  case  of  accident. 

A second  portion  is  submitted  to  ReinscWs  test  / it  is  for  this 
purpose  acidulated  with  about  of  its  bulk  of  pure  hydrochloric 
acid,  and  boiled  with  bright  slips  of  pure  electrotype  copper  foil 
for  half  an  hour.*  If  any  arsenical  compound  be  present,  the 

* Dilute  solutions  of  arsenious  acid  in  hydrochloric  acid  may  be  evaporated  below 
212°  without  loss  of  chloride  of  arsenic,  but  if  the  mixture  be  distilled  to  dryness  in 


reinsch’s  and  marsh’s  tests  for  arsenic. 


589 


metal  will  be  reduced  upon  the  surface  of  the  copper  foil.  The 
copper  is  then  withdrawn  from  the  liquid,  washed,  dried  at  212°, 
and  introduced  into  a narrow  glass  tube  (of  about  the  diameter 
of  a quill),  which  is  then  drawn  out  to  a capillary  neck,  taking 
care  not  to  heat  the  copper  foil  in  this  operation.  The  tube  is 
shown  in  fig.  317.  The  foil,  and  the  portion  of  the  tube  which 
contains  it,  are  then  heated 

nearly  to  redness ; the  ar-  Fig.  347. 

senic  combines  with  oxy- 
gen derived  from  the  air 
in  the  tube,  and  it  conden- 
ses in  beautiful  transparent 
octohedra  of  arsenious  anhydride  on  the  contracted  cool  part  of 
the  tube.  The  same  experiment  must  be  first  tried  with  the  cop- 
per and  hydrochloric  acid  employed  alone,  in  order  to^  ascertain 
their  purity,  before  employing  them  as  tests.  The  presence  of 
nitrates  or  of  chlorates  interferes  with  the  application  of  Reinsch’s 
test,  as  the  copper  foil  becomes  dissolved  when  boiled  with  the 
acidulated  solution  under  these  circumstances.  If,  however,  the 
liquid  be  first  acidulated  with  an  excess  of  hydrochloric  acid, 
and  be  evaporated  by  a gentle  heat  on  a water-bath,  the  residue 
may  be  subjected  to  Reinsch’s  process  as  usual.  A slip  of  metallic 
copper  occasions  precipitates  in  many  metallic  solutions  when 
acidulated  with  hydrochloric  acid  and  boiled  with  them : such, 
for  example,  as  antimony,  bismuth,  tin,  silver,  mercury,  lead,  and 
cadmium : cadmium  is  not  precipitable  from  a strongly  acid  solu- 
tion. Of  these  precipitates  mercury  is  the  only  one  which,  like 
arsenic,  is  volatilized  by  heat  in  the  metallic  form,  but  the  subli- 
mate, when  viewed  with  the  microscope,  is  seen,  if  mercurial,  to 
consist  of  globules,  and  is  thus  easily  distinguished  from  arsenic. 
Moreover  the  arsenical  crust  by  resublimation  is  converted  into 
arsenious  anhydride,  whilst  no  such  change  takes  place  with  mer- 
cury. Antimony  becomes  oxidized,  and  sublimes  with  difficulty 
in  needles,  not  in  octohedra,  and  may  be  identified  in  the  manner 
described  at  p.  602. 

The  third  portion  of  the  liquid  is  subjected  to  MarsNs  test: 
the  application  of  this  test  depends  upon  the  formation  of  arse- 
niuretted  hydrogen,  and  the  subsequent  deposition  of  arsenicum 
from  it  by  suitable  application  of  heat : — A wide-mouthed  ffask, 
fig.  348,  of  about  6 oz.  capacity,  is  charged  with  a little  pure  gra- 
nulated zinc ; through  the  cork  a tube  funnel  is  passed  to  within 
an  inch  of  the  bottom  ; a bulb  tube,  bent  to  a right  angle,  passes 
just  through  the  cork,  the  outer  horizontal  tube  <?,  being  loosely 
filled  with  chloride  of  calcium  to  arrest  any  particles  of  fluid 
which  might  be  carried  up  by  the  effervescence  ; it  is  prolonged  by 
fitting  into  it  with  a cork,  a piece  of  German  tube,  free  fi’om 
lead  and  drawn  out  to  a capillary  termination.  Some  distilled 


a retort,  the  chloride  passes  over  in  the  last  portions,  and  may  thus  be  separated 
from  most  other  metals : the  distillate  may  then  be  submitted  to  Rcinsch’s  or  Marsh’s 
test.  This  furnishes  an  excellent  method  of  procedure  in  many  cases.  See  a paper 
by  Dr.  Taylor,  iu  Guy's  llosp.  Reports^  vol.  vi. 


590 


marsh’s  test  for  arsenic. 


water  is  next  introduced  by  the  funnel,  and  a little  pure  sulphuric 
acid  added  to  cause  a steady  evolution  of  hydrogen.  When  all 
the  atmospheric  air  is  expelled,  the  flame  of  a spirit-lamp  is  placed 
under  the  point  where  the  capillary  contraction  commences : if 


riG.  348. 


after  ten  minutes,  the  temperature  of  the  glass  being  at  a red 
heat,  no  indications  of  any  metallic  deposit  show  themselves,  the 
materials  used  are  sufliciently  pure.  Whilst  the  heat  is  still  main- 
tained, the  suspected  liquid  is  to  be  poured  through  the  funnel 
into  the  bottle ; if  arsenic  be  present,  immediate  voltaic  de- 
composition ensues,  part  of  tlie  arsenic  combines  with  the  nascent 
hydrogen ; arseniuretted  hydrogen  is  formed,  and  the  gas  is  de- 
composed as  it  passes  through  the  heated  tube,  the  metal  being 
deposited  in  the  form  of  a steel-grey  ring  just  beyond  the  spot 
Avhere  the  heat  is  applied.  If,  instead  of  heating  the  capillary 
tube,  the  gas  be  kindled  as  it  escapes,  it  will  be  found  to  burn  with 
the  peculiar  flame  of  arsenic  if  the  quantity  be  at  all  considerable, 
and  if  a piece  of  cold  white  porcelain,  such  as  a crucible  lid,  be  in- 
troduced into  the  burning  jet,  the  more  combustible  hydrogen  is 
burned,  and  brown  or  grey  mirror-like  spots  of  reduced  arsenic 
may  be  obtained  upon  the  cold  plate.  Tartar-emetic,  if  present, 
would,  however,  produce  antimoniuretted  hydrogen,  which,  by  its 
decomposition,  would  give  rise  to  appearances  in  the  tube  and  on 
the  porcelain  resembling  those  of  arsenic.  The  antimonial  spots 
immediately  disappear  when  a drop  of  sulphide  of  ammonium,  in 
which  a little  sulphur  is  dissolved,  is  added,  and  the  solution,  by 
its  spontaneous  evaporation,  leaves  the  orange- coloured  sulphide 
of  antimony ; but  the  arsenical  crusts  are  scarcely  acted  on  by  the 
sulphide  of  ammonium  (Dr.  Guy).  The  chief  practical  difficulty 
in  the  use  of  Marsh’s  test,  arises  from  the  inconvenient  way  in 
which  liquids  containing  organic  matter  frequently  froth  up  dur- 
ing the  operation.  The  best  method  of  preventing  this  consists 
in  first  heating  the  suspected  liquid  with  about  a tenth  of  its  bulk 
of  hydrochloric  acid,  and  adding  a small  quantity  of  chlorate  of 
potassium : the  organic  matter  is  tlius  destroyed,  and  after  the 


SEARCH  FOK  ARSENIC  IN  SUSPECTED  POISONING. 


591 


liquid  has  become  cool,  it  may  be  safely  added  to  the  zinc  and 
sulphuric  acid  in  the  apparatus. 

The  process  by  sulphuretted  hydrogen  and  subsequent  reduc- 
tion is  extremely  delicate,  and  open  to  no  objection  except  the 
length  of  time  required.  Marsh’s  test  is  one  of  extraordinary 
delicacy,  and  the  results  are  easily  and  quickly  attained  : Reinsch’s 
test  is  also  easy  of  application,  and  is  extremely  delicate  ; but 
they  act  very  slowly  when  the  arsenic  is  in  the  form  of  arsenic 
acid.  The  arsenical  crusts  deposited  in  the  glass  tube  are  readily 
sublimed  by  a gentle  heat,  and  may  be  converted  into  arsenious 
anhydride,  which  forms  brilliant  minute  octohedml  crystals,  and 
these  again  may  be  subjected  to  the  test  of  the  ammonia-nitrate 
of  silver. 

Although  it  may  not  be  possible  to  detect  arsenic  in  the  fluids 
submitted  to  examination,  it  not  unfrequently  happens  that  the 
coats  of  the  stomach,  and  sometimes  the  liver,  will  yet  contain 
the  poison  in  sufficient  quantity  to  render  its  identification  prac- 
ticable. The  best  mode  of  proceeding  in  this  case  consists  in 
cutting  up  the  organ  into  shreds,  heating  it  on  a water-bath  witli 
a fourth  of  its  weight  of  hydrochloric  acid,  the  mixture  being 
diluted  with  water  till  it  becomes  of  the  consistency  of  a thin 
paste.  It  may  then  be  subjected  to  Reinsch’s  process,  or  it  is  fit 
for  trial  in  Marsh’s  apparatus.  Fresenius  andYoiiBabo  {Liebig'’ s 
Ann.  xlix.  287)  prefer  to  add  to  the  original  mixture  of  hydro- 
chloric acid  and  organic  matter,  small  portions  of  chlorate  of 
potassium  from  time  to  time  until  a homogeneous  yellow  liquid 
is  obtained ; when  cold  it  is  filtered  through  linen,  the  residue 
well  washed,  and  the  clear  liquid  is  concentrated  by  evaporation 
by  a heat  not  exceeding  that  of  the  water-bath.  In  this  case  it  is 
necessary  subsequently  to  reduce  the  arsenic  acid  in  the  liquid  to 
arsenious  acid  by  means  of  a current  of  sulphurous  acid  gas. 
They  then  heat  gently  to  expel  the  excess  of  sulphurous  acid, 
precipitate  the  arsenic  by  sulphuretted  hydrogen,  collect  the  pre- 
cipitate on  a small  filter,  ’wash,  dissolve  out  the  sulphide  of  arsenic 
with  ammonia,  evaporate  the  solution  on  a watch-glass,  and 
reduce  the  sulphide  by  mixing  it  wdth  about  12  times  its 
weight  of  a mixture  of  3 parts  of  dried  carbonate  of  sodium  and  1 
of  cyanide  of  potassium,  and  heating  it  in  a very  slow  current  of 
dried  carbonic  anhydride,  as  shown  in  fig.  3-19,  in  whicli  a repre- 
sents a flask  containing  fragments  of  marble  from  which  the  car- 
bonic anliydride  is  disengaged  by  the  addition  of  hydrochloric 
acid  : b contains  oil  of  vitriol  in  order  to  dry  the  issuing  gas ; the 
arsenical  mixture  is  placed  in  the  bend  of  the  tube  c,  and  the  metal- 
lic crust  sublimed  into  the  contracted  part  of  the  tube  at  d.  Tin's 
process  is  tedious  and  complicated,  and  not  superior  to  Reinscli’s 
if  the  latter  be  conducted  with  due  care.  A very  delicate  mode 
of  detecting  the  presence  of  arsenic  is  afforded  by  the  action  of 
the  voltaic  current,  which  may  be  applied  without  difficulty  by 
adopting  the  precautions  recommended  by  Bloxam  {Q,  J.  Cheia. 
Soc.  xiii.  12).  The  galvanic  process  has  the  advantage  of  being 
applicable  to  the  detection  of  various  other  metallic  poisons  if 


592 


ESTIMATION  OF  ARSENIC ANTIMONY. 


arsenic  be  absent,  as  nothing  is  introduced  which  interferes  with 
their  identification  subsequently  by  appropriate  tests. 

(8-17)  Estimation  of  Arsenic.  — It  is  not  easy  to  ascertain 
accm-ately,  by  analysis,  the  quan  ty  of  arsenic  present  in  a com- 


Fig  349. 


pound:  but  the  following  is  the  plan  generally  adopted: — The 
metal  is  precipitated  in  the  form  of  a sulphide : the  precipitate 
collected  on  a weighed  filter,  dried  at  212°,  and  weighed  : a given 
weight  of  the  sulphide  is  then  oxidized  by  means  of  nitric  acid 
(sp.  gr.  1‘51) ; and  when  it  is  completely  dissolved,  the  sulphur  is 
precipitated  as  sulphate  of  barium.  From  the  weight  of  this  pre- 
cipitate the  quantity  of  sulphur  is  calculated,  and  deducted  from 
the  total  amount  of  sulphide  of  arsenic  ; the  difference  gives  the 
amount  of  the  metal.  The  sulphide  is  apt  to  contain  a variable 
quantity  of  free  sulphur,  and  hence  this  .method  becomes  neces 
sary.  Before  it  can  be  adopted,  the  absence  of  all  other  metals  in 
the  sulphide  must,  of  course,  be  ascertained.  The  arsenic  acid 
in  the  solution  may  further  be  precipitated  as  arseniate  of  mag- 
nesium and  ammonium,  by  neutralizing  with  ammonia,  and 
adding  a solution  of  sulphate  of  magnesium  containing  chloride  of 
ammonium  and  ammonia  in  excess : 100  parts  of  this  precipitate 
dried  at  212°  [2  (II^XMgAs04),Il20]  represent  39TT  of  metallic 
arsenic. 

(818)  Separation  of  Arsenic  from  other  21etals. — By  means 
of  sulphuretted  hydrogen  and  the  subsequent  solution  of  the  sul- 
phide in  sulphide  of  ammonium,  arsenic  is  easily  separated  from 
all  the  foregoing  metals  with  the  exception  of  those  which  form 
soluble  compounds  with  the  sulphides  of  the  alkaline  metals.  A 
solution  of  sesquicarbonate  of  ammonium  (free  from  uncombined 
ammonia),  when  digested  on  the  mixed  hydrated  sulphides  of  ar- 
senic and  antimony,  dissolves  the  arsenical  sulphide  only,  and 
leaves  it  on  evaporation. 

§YIII.  Antbiony:  Sb'"=122.  Sp.  Gr.  (S-IU. 

(819)  Antimony  is  a tolerably  abundant  substance,  and  is 


PUKiriCATION  OF  ANTIMONY. 


593 


always  extracted  from  its  sulphide,  though  it  is  frequently  found 
alloyed  Avith  other  metals,  and  is  sometimes  met  with  in  the  native 
state. 

The  sulphide  of  antimony  usually  occurs  in  a matrix  of  quartz, 
sulphate  of  barium,  and  limestone.  The  crude  antimony  of  com- 
merce is  merely  the  sulphide  freed  from  the  greater  part  of  its 
earthy  impurities.  This  purification  is  efiected  by  placing  the 
ore  upon  the  bed  of  a reverberatory  furnace,  covered  with  char- 
coal-powder. The  sulphide  melts,  the  earthy  impurities  fioat,  and 
the  fluid  portion  is  drawn  oif  into  an  iron  basin,  and  is  afterwards 
cast  into  loaves  or  cakes.  If  it  he  desired  to  extract  the  metal, 
the  sulphide  thus  purified  is  reduced  to  a coarse  powder,  and  again 
placed  upon  the  bed  of  a reverberatory  furnace  : the  temperature 
may  be  gradually  raised  to  dull  redness,  but  must  be  moderated 
to  prevent  the  mass  from  entering  into  fusion : in  about  12  hours 
fumes  cease  to  rise,  most  of  the  sulphur  is  expelled,  and  a red 
mixture  of  the  oxide  and  sulphide  of  antimony  remains.  During 
this  process  copious  vapours  of  sulphurous  and  arsenious  anliy- 
drides  are  given  off,  accompanied  by  a considerable  portion  of 
oxide  of  antimony.  It  is  stated  that  nearly  20  per  cent,  of  the 
metal  is  lost  during  this  operation.  The  roasted  mass  is  now 
mixed  with  about  one-sixth  of  its  wmight  of  powdered  charcoal, 
made  into  a paste  Avith  a strong  solution  of  carbonate  of  sodium, 
and  heated  in  crucibles  to  bright  redness  ; the  metal  collects  at  the 
bottom  ; aboA^e  it  is  a scoria,  consisting  chiefly  of  a double  sul- 
phide of  sodium  and  antimony.  This  scoria  is  knoAAm  in  the  arts 
as  the  crocus  of  antimony.  The  metal  is  remelted  with  the  scoria, 
and  is  then  nt  for  sale.  100  parts  of  sulphide  yield  about  44 
parts  of  metallic  antimony,  so  that  in  the  Avhole  process  about 
three-sevenths  of  the  antimony  are  lost. 

On  the  small  scale  the  metal  is  most  easily  procured  by  taking 

4 parts  of  the  poAA^dered  sulphide,  3 of  crude  tartar,  and  1|-  of 
nitre,  mixing  them  intimately,  and  throwing  the  powder  in  small 
portions  at  a time  into  a crucible  kept  at  a bright  red  heat.  The 
quantity  of  nitre  employed  is  insufficient  to  oxidize  both  the  sul- 
phur and  the  metal,  and  the  sulphur  being  the  more  combustible 
element  of  the  tAvo  is  the  first  to  undergo  oxidation,  whilst  the 
metal  melts  and  collects  at  the  bottom,  beneath  the  slag  of  sul- 
phate of  potassium.  Commercial  antimony  commonly  contains 
arsenic,  iron,  and  often  small  quantities  of  copper  and  lead. 

In  order  to  obtain  antimony  free  from  arsenic,  Wohler  mixes 
intimately  4 parts  of  finely-powdered  commercial  antimony  Avith 

5 of  nitrate  of  sodium,  and  2 of  anhydrous  carbonate  of  sodium. 
The  mixture  is  heated  to  redness  in  a Hessian  crucible,  and  the 
antimony  burns  quietly  at  the  expense  of  the  oxygen  of  the  ni- 
trate. After  the  deflagration  is  complete,  the  crucible  is  covered, 
and  the  mass  is  kept  for  half  an  hour  at  a temperature  sufficient 
to  soften  but  not  to  fuse  it,  from  time  to  time  pressing  it  doAAui 
Avith  an  iron  spatula.  It  is  removed  from  the  crucible  by  means 
of  a spatula,  Avhilst  still  in  a pasty  condition,  tlien  pulverized  and 
throAvn  into  boiling  Avater : the  solution  contains  the  arseniate  of 

38 


594 


ALLOYS  OF  ANTIMONY. 


sodinm,  whilst  the  greater  part  of  the  antimoniate  of  sodium  re 
mains  undissolved,  and  is  well  washed  with  boiling  water.  From 
this  antimoniate  of  sodium  the  metal  is  extracted  by  melting  it 
with  half  its  weight  of  crude  tartar.  The  product  thus  obtained 
is  an  alloy  of  antimony  with  potassium  : it  is  broken  into  small 
pieces  and  thrown  into  water  ; a copious  disengagement  of  hydro- 
gen takes  place,  the  potassium  is  oxidized  and  dissolved,  and  the 
alloy  falls  to  powder.  It  still  retains  iron,  and  sometimes  lead. 
One-third  of  the  mass  is  converted  into  oxide  by  means  of  nitric 
acid ; this  oxide  is  well  washed  with  water,  dried,  and  then  incor- 
porated with  the  powdered  metal ; the  mass  is  again  melted  in  a 
covered  crucible,  and  pure  antimony  is  obtained  beneath  a layer 
of  fused  oxide,  which  retains  the  oxides  of  iron  and  lead. 

(850)  Properties. — Antimony  was  well  known  to  the  alche- 
mists. It  is  a brilliant  bluish- white  metal,  of  a flaky,  crystalline 
texture,  and  so  brittle  that  it  may  readily  be  reduced  to  powder. 
It  fuses  a little  above  a red  heat,  and  by  slow  cooling  may  be  ob- 
tained in  rhombohedral  crystals,  which,  according  to  Mitscherlich, 
are  isomorphous  with  those  of  arsenicum  ; but  absolutely  pure 
antimony  crystallizes  with  difficulty  (Cooke ; Matthiessen).  The 
commercial  cakes  of  the  metal  exhibit  upon  their  upper  surface  a 
beautiful  penniform  crystalline  structure.  At  a bright  red  heat 
it  is  volatilized  slowly  : the  operation  is  facilitated  by  transmitting 
a current  of  hydrogen  over  it.  Antimony  is  inferior  to  most  of 
the  metals  as  a conductor  of  heat  and  of  electricity.  When  ex- 
posed to  either  a moist  or  a dry  air,  at  ordinary  temperatures,  it 
undergoes  no  change,  but  if  heated  it  burns  brilliantly,  emitting 
copious  white  fumes  which  consist  chiefly  of  antimonic  oxide. 
Powdered  antimony  takes  Are  spontaneously  when  thrown  into 
chlorine  gas  ; bromine  and  iodine  likewise  enter  into  combination 
with  the  metal  with  great  evolution  of  heat  when  they  are  brought 
into  contact  with  it  at  ordinary  temperatures.  It  is  also  oxidized 
by  nitric  acid  and  by  boiling  sulphuric  acid.  Aqua  regia  dis- 
solves it  readily.  When  flnely  powdered,  it  is  dissolved  by  strong 
hydrochloric  acid  by  the  aid  of  heat,  with  evolution  of  hydrogen. 
Metallic  antimony,  when  in  flne  powder,  is  readily  dissolved  by 
digestion  with  a solution  of  one  of  the  higher  sulphides  of  potas- 
sium, whilst  the  lead,  iron,  copper,  bismuth,  or  silver,  which  it 
may  contain  is  left  undissolved.  Small  quantities  of  arsenicum 
and  of  tin,  if  present,  enter  into  solution  with  the  antimony. 

Alloys. — This  metal  is  not  used  alone  in  the  arts,  but  it  enters 
into  the  composition  of  several  valuable  alloys.  Type  metal  is  one 
of  these ; ordinary  type  is  composed  of  3 or  4 parts  of  lead,  and  1 
part  of  antimony : but  the  alloy  which  is  now  employed  in  the 
best  description  of  type  contains  2 parts  of  lead,  1 of  tin,  and  1 of 
antimony.  Music  type  contains  tin ; and  the  common  white 
metal  used  for  teapots,  under  the  name  of  Britannia  metal^  con- 
sists of  equal  parts  of  brass,  antimony,  tin,  bismuth,  and  lead. 
The  value  of  the  antimony  in  these  alloys  depends  upon  the  hard- 
ness which  it  communicates  to  the  compounds,  without  rendering 
them  inconveniently  brittle,  and  to  the  expansion  which  it  confers 


ALLOYS  OF  ANTIMONY. 


595 


Upon  them  in  the  act  of  solidification,  so  valuable  in  the  case  of 
type  metal.  Equal  parts  of  antimony  and  lead,  however,  produce 
a brittle  alloy.  The  compounds  of  antimony  with  zinc  and  with 
tin  are  hard,  white,  and  brittle.  A mixture  of  12  parts  of  tin, 
1 part  of  antimony,  and  a small  quantity  of  copper,  furnishes  a 
ductile  alloy,  forming  a superior  kind  of  pewter.  If  lead  be  sub- 
stituted for  copper  in  this  alloy  it  is  rendered  brittle.  Antimony 
also  combines  readily  with  copper,  furnishing  a hard  alloy  which 
takes  a good  polish,  but  which  becomes  paler  and  more  brittle  in 
proportion  as  the  quantity  of  antimony  is  increased.  If  7 parts 
of  powdered  antimony  and  3 of  iron  filings  be  exposed  in  a covered 
crucible  to  a very  high  temperature,  a brittle  alloy  is  formed  suf- 
ficiently hard  to  emit  sparks  when  filed. 

With  zinc,  antimony  unites  to  form  two  definite  alloys,  which 
may  be  prepared  by  fusing  the  two  metals  together  in  the  proper 
proportions.  They  may  be  crystallized  by  a method  similar  to 
that  adopted  in  the  case  of  sulphur  by  fusion  (407).  One  of 
these  (Sb^Zng)  crystallizes  in  long  acicular  prisms,  which  belong 
to  the  oblique  prismatic  system ; it  decomposes  water  rapidly  at 
212°  with  evolution  of  hydrogen.  The  other  alloy  (SbZn)  crys- 
tallizes in  broad  plates  which  twin  together  on  an  octohedral 
face.* 

In  combination  with  acid  tartrate  of  potassium,  oxide  of  anti- 
mony forms  a powerful  and  valuable  medicine.  The  oxide,  when 
ground  up  with  linseed  oil,  furnishes  a pigment  wdiich  is  emplojmd 
to  some  extent  as  a substitute  for  white  lead  : it  is  much  less  in- 
jurious to  the  health  of  those  who  use  it  than  pigments  wdiich 
contain  lead. 

Mr.  Gore  {Phil.  Trans.  1858,  p.  185)  has  described  a re- 
markable modification  of  antimony  which  may  be  procured  by 
electrolytic  action,  in  the  following  manner : Dissolve  1 part  of 
tartar-emetic  in  4 parts  of  the  solution  obtained  by  dissolving  sul- 
phide of  antimony  nearly  to  saturation  in  hydrochloric  acid,  and 
subject  the  solution  to  the  action  of  two  or  three  cells  of  Smee’s 
battery,  using  a plate  of  antimony  for  the  positive  and  a copper 

* J.  P.  Cooke,  who  has  studied  these  alloys  minutely,  finds  that  in  each  case  the 
crystalline  form  of  the  alloy  is  preserved,  although  the  proportions  of  the  two  metals 
may  vary  within  cousiderable  limits ; thus,  the  form  of  needles  (which  would  require, 
if  in  atomic  proportion,  Sb2Zn3,  a per-centage  of  55'7  of  antimony),  is  still  preserved, 
though  the  antimony  may  fall  as  low  as  ssdl  or  may  rise  as  high  as  57’24;  whilst 
the  form  of  plates  is  observed  without  any  variation  in  the  angular  measurements, 
although  the  quantity  of  antimony  may  fall  as  low  as  64’57  or  may  rise  as  high  as 
79-42,  though  65-07  would  represent  the  true  atomic  proportion  (SbZn).  It  is  true 
both  the  forms  belong  to  the  same  crystalline  system,  but  they  do  not  appear  to  be 
derivable  one  from  the  other.  Mr.  Cooke  suggests  that  these  observations  may  throw 
an  important  light  upon  the  cause  of  the  hitherto  unexplained  variation  in  composition 
occasionally  observed  in  minerals  of  the  same  crystalline  form,  the  components  of 
which  are  not  isomorphous  : and  he  proposes  the  term  Allomerism  to  designate  such 
variation  in  the  proportions  of  the  constituents  of  the  crystalline  compound  without 
any  essential  change  in  the  crystalline  form,  the  varying  constituents  not  being  iso- 
morphous with  each  other. 

Matthiessen  and  Von  Bose,  in  their  researches  upon  the  alloys  of  tin  and  gold, 
have  found  that  those  containing  from  27-4  to  43  per  cent,  of  gold  all  crystallize  in 
the  same  form,  the  largest  and  best  defined  cryst^s  containing  about  41  percent,  of 
gold  (AuSn2  = 45-9  per  cent,  of  gold). 


596 


OXIDES  OF  AXTIMOXY AXTIMOXIC  ACID. 


wire  for  the  negative  electrode.  A metallic  deposit  having  the 
colour  and  lustre  of  highly-polished  steel,  with  a peculiar  mammih 
lated  surface  and  an  amorphous  structure,  is  formed.  Its  specific 
gravity  is  about  6 ’55.  The  metal  thus  deposited  retains  5 or 
6 per  cent,  of  terchloride  of  antimony,  and  if  suddenly  struck 
sharply  or  lieated,  it  undergoes  a rapid  molecular  change  attended 
with  a rise  of  temperature  amounting  sometimes  to  450°,  accom- 
panied by  the  disengagement  of  abundant  fumes  of  terchloride  of 
antimony.  The  heat  evolved  is  sufticient  to  boil  water  or  even 
to  fuse  small  pieces  of  tin.  After  this  change  has  occurred  the 
metal  is  found  to  retain  its  cohesion  and  its  metallic  aspect,  but 
it  becomes  grey,  and  acquires  a granular  fracture  and  an  in- 
creased density.  A corresponding  substance  may  be  obtained  if 
terbromide  be  substituted  for  terchloride  of  antimony ; the  de- 
posited metal  in  this  case  retaining  the  bromide  of  antimony. 

(851)  Oxides  of  Antimony. — Antimony  forms  three  well- 
marked  oxides : the  first  is  the  most  important,  as  it  constitutes 
the  basis  of  the  antimonial  salts  employed  in  medicine.  The  ox- 
ides have  the  following  composition  : — 

Oxygen.  Antimony. 

Antimonic  oxide SbQOa  = 16*44  + 83*56 

Antimonic  anhydride Sb205  = 24*69  + 75*31 

Antimoniate  of  antimony....  Sb203,  Sb205=  20*78  + 79*22 

Antimonic  Oxide  or  Sesqnioxide  of  Antimony  (Sb^Og  = 292, 
or,  as  it  is  often  called,  ter  oxide  ^ SbOg^ldB). — In  the  anhydrous 
state  this  oxide  is  found  crystallized  in  prisms  in  a rare  mineral 
called  white  antimony  ore^  of  specific  gravity  5 ’56.  The  anhy- 
drous oxide  is  best  procured  by  boiling  powdered  metallic  anti- 
mony to  dryness  in  an  iron  ladle,  with  excess  of  strong  sulphuric 
acid ; an  insoluble  sulphate  is  formed,  and  sulphurous  anhydride 
is  disengaged.  To  remove  the  sulphuric  acid,  the  residue  is 
treated  with  carbonate  of  sodium  and  is  well  washed : the  greyish- 
white  insoluble  powder  whicli  remains  is  the  oxide.  When  heated 
it  assumes  a yellow  colour,  but  recovers  its  whiteness  on  cooling. 
When  heated  in  closed  vessels  it  may  be  melted ; at  a high  tem- 
perature it  may  be  volatilized,  and  the  vapour  may  be  condensed 
in  brilliant  crystalline  needles  isomorphous  with  the  unusual  form 
of  arsenious  anhydride.  Occasionally  it  crystallizes  in  octohedra, 
like  the  common  variety  of  arsenious  anhydride.  In  the  open 
air  it  burns  like  tinder,  and  is  converted  into  the  so-called  anti- 
monious  acid.  Hydrochloric  and  tartaric  acids  dissolve  it  freely. 
Hitric  acid  converts  it  into  one  of  the  higher  oxides  of  antimony. 
With  sulphuric  acid  it  forms  an  insoluble  sulphate,  though  its  basic 
properties  are  but  feeble.  In  the  hydrated  state  it  may  be  ob- 
tained by  pouring  a solution  of  terchloride  of  antimony  into  an 
excess  of  a solution  of  carbonate  of  sodium.  In  this  form  it  is 
readily  soluble  in  solutions  of  caustic  potash  and  soda ; but  the 
simple  ebullition  or  evaporation  of  the  liquid  causes  a separation 
of  oxide  of  antimony  in  prismatic  crystals. 

(852)  Antimonic  Anhydride  (Sb^O^  = 324),  or  Antimonic 
Acid  (SbOa=162). — Tiiis  compound  may  be  obtained  by  oxidizing 


A^iTTmONIATES. 


r)97 

the  metal  with  nitric  acid,  and  expelling  the  excess  of  nitric  acid 
by  a heat  below  redness.  It  is  of  a pale  yellow  colour,  is  tasteless 
and  insoluble  in  water.  A strong  heat  expels  one-fifth  of  its 
oxygen,  and  converts  it  into  the  antimoniate  of  antimony  (Sb204, 
or  Sb03,Sb05),  which  is  a white  powder,  formerly  termed  anti- 
monious  acid^  but  which  possesses  no  acid  characters  ; for  if  treat- 
ed with  acid  tartrate  of  potassium  it  is  decomposed,  tartrate  of 
antimony  and  potassium  {tartar-emetic)  being  formed,  wdiilst  anti- 
monic  anhydride  is  left. 

Antimoniates. — Antimonic  acid  forms  definite  compounds  with 
the  metals  of  alkalies  : a boiling  solution  of  caustic  potash  dis- 
solves it,  and  on  the  addition  of  an  acid,  the  liquid  deposits  hy- 
drated antimonic  acid  in  the  form  of  white  powder  (Sb^O^,  4 H^O), 
which  reddens  litmus,  and  is  freely  soluble  in  cold  solutions  of 
the  alkalies,  and  in  hydrochloric  acid.  The  hydrated  acid  may 
also  be  obtained  by  treating  metallic  antimony  with  nitric  acid, 
or  by  decomposing  the  pentachloride  of  antimony  with  water. 
Fremy  states  that  antimonic  acid  may,  like  binoxide  of  tin,  be 
obtained  in  two  modifications,  each  of  which  combines  wdth  dif- 
ferent amounts  of  base,  and  forms  a distinct  class  of  salts : to  one 
of  these  modifications  he  gives  the  name  of  antimonic  acid  / its 
normal  salt  with  potassium  has  the  formula  (K^Sb^Og,  5 H^O,  or 
KO,SbOg,  5 HO) : the  other  modification  he  terms  metantimonic 
acid.  To  the  normal  potassium  salt  of  the  latter  acid,  he  assigns 
the  formula  (2  K0,Sb05,  or  K^Sb^O,). 

According  to  Fremy,  antimonic  acid  is  monobasic,  but  it  is 
capable  of  forming  both  normal  and  acid  salts.  Normal  anti- 
moniate of  jpotass%um  may  be  procured  by  heating  1 part  of  me- 
tallic antimony  wdth  4 parts  of  nitre  in  an  earthen  crucible.  The 
w'hite  mass  so  obtained  is  pow^dered,  and  w^ashed  wdth  w^arm  w^ater, 
to  remove  the  excess  of  potash  and  nitrite  of  potassium.  The 
residue  must  be  boiled  in  water  for  an  hour  or  twm ; the  insoluble 
anhydrous  antimoniate  is  thus  converted  into  a soluble  hydrated 
modification  consisting  of  K2Sb20g,  5 H„0.  The  insoluble  residue 
now  consists  chiefly  of  acid-antimoniate  of  potassium.  The  nor- 
mal salt  possesses  the  property  of  freely  dissolving  the  acid-anti- 
moniate,  which  is  precipitated  when  such  a solution  is  mixed  with 
any  neutral  salt  of  one  of  the  alkalies.  The  normal  antimoniate 
does  not  crystallize,  but  forms  a gummy  mass  which  has  an  alka- 
line reaction  ; it  is  readily  decomposed  by  acids,  including  the  car- 
bonic, whilst  the  acid-antimoniate  is  deposited.  When  heated  to 
320°  it  loses  2 out  of  its  5 atoms  of  water,  and  becomes  insoluble 
in  cold  water. 

Acid-antimoniate  of  potassium,  (K^Sb^Oji),  or  biamtimoniate 
of  potash  (KO,  2 SbOg),  is  obtained  by  transmitting  a current  of 
carbonic  anhydride  through  a solution  of  the  normal  antimoniate. 
It  is  soluble  in  a hot  solution  of  the  normal  antimoniate,  and  is 
deposited  in  crystals  as  the  liquid  cools. 

If  antimonic  anhydride  be  heated  wdth  oxide  of  lead  it  com- 
bines with  it  and  yields  a yellow  com])Ound,  which  is  used  as  a 
pigment  under  the  name  of  Naples  yellow. 


598  METANTEMONIC  ACID AA^TIMONIUDETTED  HYDEOGEN. 

(853)  Metantimonic  Acid  (H^SbaO^,  or  2 HO,  SbO^). — Tliis 
compound  derives  its  principal  interest  from  the  circumstance  of 
its  yielding  a soluble  compound  with  potassium,  which  may  be 
employed  as  a test  for  sodium.  The  acid-metantimoniate  of 
potassium^  KJI^Sb^O,,  6 H^O,  or  Mmetcmtimoniate  of  'potash 
(K0,TI0,Sb05,  6 Aq)  is  the  salt  which  is  used  for  this  purpose. 
In  preparing  this  compound,  antimoniate  of  potassium  is  first 
formed  by  deflagrating  antimony  with  nitre,  washing  and  boiling 
the  residue  in  the  manner  already  described,  so  as  to  bring  the 
A^dlole  of  the  normal  antimoniate  into  solution : the  liquid  thus 
obtained  is  filtered,  and  evaporated  to  a syrupy  consistence  in  a 
silver  dish ; fragments  of  hydrate  of  potash  are  then  added,  and 
the  evaporation  is  continued  until  a drop  of  the  liquid  placed 
upon  a cold  slip  of  glass  begins  to  crystallize ; it  is  then  allowed 
to  cool,  and  the  alkaline  supernatant  liquid  is  poured  off  the 
crystals,  which  are  allowed  to  drain  upon  a porous  tile.  When 
the  salt  is  required  as  a test  for  salts  of  sodium,  30  or  40  grains 
of  this  residue  are  to  be  washed  quickly  with  about  twice  their 
weight  of  cold  water,  and  allowed  to  subside ; this  washing  is  to 
be  repeated  two  or  three  times,  in  order  to  remove  traces  of 
adhering  potash ; lastly,  a little  cold  water  is  to  be  digested  for 
a few  minutes  upon  the  residue,  and  the  filtered  liquid  may  be 
used  to  ascertain  the  presence  of  sodium.  The  presence  of 
hydrate  of  potash  impairs  the  delicacy  of  the  reaction.  One  great 
inconvenience  which  attends  the  use  of  this  reagent  is  the  cir- 
cumstance, that  if  the  solution  be  kept  for  a few  days,  the  salt 
passes  spontaneously  into  the  normal  antimoniate,  and  this  salt 
does  not  precipitate  the  compounds  of  sodium ; both  salts  contain 
exactly  the  same  amount  of  acid  and  of  base  (K2H2Sb20,= 
K2Sb206,H20-),  the  difference  in  properties  being  due  to  differ- 
ence in  the  molecular  constitution  of  the  two  salts.  If  the 
solution  of  acid  metantimoniate  be  boiled,  its  conversion  into 
normal  antimoniate  is  effected  in  a few  minutes.  The  acid 
metantimoniate  of  sodhim  (Ha^H^Sb^O,,  6 H^O)  is  an  ins*^luble 
salt,  which  crystallizes  in  octohedra. 

(854)  Antimoniuretted  Hydrogen  (ITgSb  ?) — The  composition 
of  this  gas  is  not  known  with  certainty,  for  at  present  it  has 
never  been  obtained  free  from  hydrogen.  It  is  inferred,  however, 
to  contain  3 atoms  of  hydrogen  to  one  atom  of  the  metal,  because, 
when  transmitted  through  a solution  of  nitrate  of  silver,  a pre- 
cipitate of  antimonide  of  silver  is  formed,  consisting  of  AggSb  ; 
3 AgHOg-fllgSb  becoming  3 HHOg-t- AggSb.  Antimoniuretted 
hydrogen  is  formed  by  dissolving  an  alloy  of  zinc  and  antimony 
in  diluted  sulphuric  acid.  When  any  salt  of  antimony  is  poured 
into  a mixture  of  zinc  and  sulphuric  acid  which  is  disengaging 
hydrogen,  the  antirnonial  salt  becomes  decomposed ; one  portion 
of  the  antimony  is  deposited  in  the  form  of  a black  powder  upon 
the  surface  of  the  zinc,  whilst  another  portion  combines  with  the 
hydrogen,  and  assumes  the  gaseous  state.  It  forms  a colourless 
gas  which  is  without  any  marked  odour.  When  burned,  it  de- 
posits white  fumes  of  oxide  of  antimony,  and  if  transmitted 


SULPHIDES  OF  AlITIMONY. 


599 


tliroHgli  a glass  tube,  lieated  to  low  redness,  the  gas  is  decom- 
posed, and  the  antimony  forms  a brilliant  metallic  crust  upon  the 
heated  portion  of  the  tube. 

(855)  Sulphides  of  Antimony. — Two  compounds  of  anti- 
mony with  sulphur  are  known ; the  ordinary  sulphide  (Sb2S3), 
and  the  sulphantimonic  anhydride,  or  antimonic  sulphide  (Sb^S^), 
corresponding  to  the  antimonic  oxide  and  to  antimonic  anhydride. 
They  are  usually  regarded  as  sulphur-acids,  since  they  combine 
with  the  sulphides  of  the  alkaline  metals,  and  form  definite  salts. 

Sesquisulphide  of  Antimony^  Sb2S3=340  (often  called  the  ter- 
siilphide^  SbS3==170) ; Sj>.  Gr.  4-626 : Comp,  in  100 parts.,  Sb, 71-76  ; 
S,  28-24. — This  substance  constitutes  the  only  ore  from  which  the 
metal  is  obtained.  The  native  sulphide,  or  grey  antimony  ore^  is 
usually  found  in  granite  or  slate  rocks,  and  generally  contains 
lead  and  arsenic,  besides  a variable  amount  of  pyrites.  It  occurs 
crystallized  in  four-sided  prisms,  striated  transversely ; it  has  a 
bluish-black  colour,  and  a strong  metallic  lustre.  It  is  friable, 
and  melts  below  a red  heat,  crystallizing  as  it  cools.  It  may  be 
distilled  unchanged  in  closed  vessels,  at  a very  high  temperature, 
but  by  roasting  in  the  open  air  it  is  converted  into  a fusible  mix- 
ture of  oxide  and  sulphide  of  antimony.  This  oxysulphide,  after 
it  has  been  fused,  constitutes  the  commercial  glass  of  antimony^ 
which  contains  about  8 parts  of  the  oxide  of  antimony  to  1 part 
of  sulphide.  If  the  oxide  be  in  excess,  the  glass  is  transparent,  and 
of  a fine  red  colour : the  greater  the  proportion  of  the  sulphide,  the 
darker  is  the  tint.  The  glass  attacks  the  silica  of  the  crucible  in 
wdiich  the  fusion  is  performed,  and  dissolves  a considerable  portion 
of  it.  A native  oxysidphide  of  antimony  (Sb^Og,  2 Sb2S3,  known  as 
red  antimony  ore)  occurs  crystallized  in  oblique  rhombic  prisms. 

Sulphide  of  antimony  may  be  obtained  in  crystals  by  melting 
together,  at  a red  heat,  a mixture  of  sulphur  and  oxide  of  anti- 
mony ; sulphurous  anhydride  escapes,  and  the  sulphide  is  formed : 
2 Sb203  -f  9 S becoming  2 Sb2S3  -f  3 SO^. 

Attempts  have  been  recently  made,  with  some  success,  to  in- 
troduce the  artificial  sulphide  as  a red  pigment,  under  the  name  of 
antimony  vermilion.  The  colour  is  prepared  by  pouring  a crude 
solution  of  chloride  of  antimony  in  hydrochloric  acid  into  a dilute 
solution  of  hyposulphite  of  calcium,  which  is  maintained  in  excess; 
on  heating  the  liquid  to  140°,  it  becomes  turbid,  and  deposits  a 
precipitate  which  is  at  first  yellow  and  ultimately  a bright  orange 
red.  The  anhydrous  sulphide  may  also  be  obtained  of  a beauti- 
ful orange  colour,  by  transmitting  sulphuretted  hydrogen  through 
a solution  of  any  salt  of  the  metal ; on  being  heated  in  closed 
vessels,  it  assumes  a dark  metallic  appearance,  resend)! iug  that  of 
the  native  sulphide.  If  heated  in  a current  of  hydrogen  gas,  the 
sulphur  is  removed  and.metallic  antimony  is  left.  The  sidphide, 
whether  artificial  or  native,  is  dissolved  by  hot  hydrochloric  acid, 
and  furnishes  a convenient  source  of  pure  sulphuretted  hydrogen, 
provided  that  the  gas  be  washed,  to  free  it  from  traces  of  anti- 
mony and  hydrochloric  acid  which  it  is  apt  to  retain  in  sus- 
pension. 


600 


PEE3ULPHIDE  AXD  CHLOKIDES  OF  ANTIMOXY. 


Sesqiiisiilpliide  of  antimony  is  readily  soluble  in  solutions  of 
the  sulphides  of  tlie  alkaline  metals,  and  forms  colourless  com- 
pounds wliicli  have  been  regarded  as  double  sulphides,  or  sulph- 
antimonites  / a hot  solution  of  the  alkaline  sulphide  can  dissolve 
much  more  of  the  sulphide  of  antimony  than  it  can  retain  when 
cold  ; on  the  addition  of  an  acid,  the  sulphide  of  the  alkaline  metal 
is  decomposed,  and  the  sulphide  of  antimony  is  reprecipitated. 
If  sulphide  of  antimony  in  fine  powder  be  boiled  with  a solution 
of  carbonate  of  potassium,  or  of  caustic  potash,  it  is  dissolved  ; the 
filtered  liquid  on  cooling  deposits  a reddish-brown  substance, 
known  as  leer  tries  mineral.  This  substance  is  not  a definite  com- 
pound, but  is  a variable  mixture  of  sulphide  and  oxide  of  anti- 
mony, the  latter  being  combined  with  a small  portion  of  the  alkali. 
The  action  of  carbonate  of  potassium  on  the  sulphide  may  be  repre- 
sented as  follows : — 

6 K^-GOg-f  3 SbgSg  + S KHOOg-f  3 Sb2Sg,Sb203. 

In  this  mixture  of  SbgSg  and  SbgOg,  H.  Rose  found  crystals  of 
oxide  of  antimony,  which  were  visible  by  the  aid  of  the  micro- 
scope. Acid  tartrate  of  potassium,  or  diluted  hydrochloric  acid, 
dissolves  out  the  oxide,  leaving  the  sulphide.  If  to  the  liquid, 
after  deposition  of  the  kermes,  hydrochloric  acid  be  added,  effer- 
vescence takes  place,  with  escape  of  sulphuretted  hydrogen,  owin^ 
to  the  decomposition  of  sulphide  of  potassium,  and  the  excess  of 
sulphide  of  antimony  which  it  retained  is  precipitated  as  the  golden 
sulphide  of  antimony.  This  sulphide  contains  a larger  proportion 
of  sulphur  than  the  sesquisulphide,  from  the  gradual  oxidation  of 
the  antimony  in  the  solution  before  the  precipitation  is  effected. 

Persulphide  of  Antimony  (Sb2Sg=I:0I:,  or  SbSg=202  : Comp, 
in  parts ^ Sb,  GOA;  S,  39*6),  or  sulphantimonic  acid.^  as  this 

compound  is  often  termed,  may  be  obtained  by  transmitting  a 
current  of  sulphuretted  hydrogen  through  an  acid  solution  of 
pentachloride  of  antimony.  It  forms  an  orange-yellow  precipi- 
tate, which  is  anhydrous,  but  is  remarkable  for  the  facility  with 
which  it  combines  with  the  sulphides  of  the  alkaline  metals.  The 
tri basic  sulphantimoniate  of  sodium  (iN^agSbS^  . 9 HgO),  or 
Schlippe’s  salt,  crystallizes  in  large  and  very  brilliant  transparent 
tetrahedra.  It  may  be  obtained  in  various  ways  : the  easiest  plan 
consists  in  thoroughly  mixing  18  parts  of  finely-powdered  sesqui- 
sulphide of  antimony,  12  of  dried  carbonate  of  sodium,  13  of 
quicklime,  and  3|-  of  sulphur ; the  mixture  is  ground  up  with 
water,  and  placed  in  a well-closed  bottle,  which  is  completely  filled 
with  water  ; it  is  allowed  to  digest,  with  frequent  agitation,  for 
21  hours  ; the  clear  liquid  is  filtered  off,  and  allowed  to  evaporate 
spontaneously  in  a closed  vessel  over  sulphuric  acid.  This  salt 
when  mixed  with  an  acid  deposits  pure  persulphide  of  antimony. 

(856)  Chlokides  of  Antmoxy.  — Antimony  has  a powerful 
attraction  for  chlorine.  It  forms  two  chlorides,  SbClg  and  SbClg : 
they  correspond  in  composition  with  the  oxides  and  sulphides. 

Terchloride  of  Antimony  (SbClg  ==228-5) ; Sp.  Gr.  of  Vapour.^ 
8-1  ; Fasing-pt.  162°  ; 2Lol.  Yol.  | | | ; Boiling-pt.  433°;  Kopp. 


TERCHLOEIDE  AND  OTHER  SALTS  OF  ANTIMONY. 


601 


— This  substance,  from  its  ready  fusibility,  was  formerly  known 
under  the  name  of  hitUer  of  antimony.  It  may  be  obtained  in 
the  anhydrous  form  by  distilling  an  intimate  mixture  of  8 parts 
of  corrosive  sublimate  with  3 of  powdered  metallic  antimony ; 
calomel,  terchloride  of  antimony,  and  an  amalgam  of  antimony 
are  formed  ; 2 Sb  + 2 HgCl^^  SbClg  + SbHg  + HgCl.  Terchlorid’e 
of  antimony  may  be  more  cheaply  prepared  by  mixing  sulphate  of 
antimony  with  twice  its  weight  of  chloride  of  sodium,  and  then 
distilling  the  mixture.  It  may  also  be  obtained  by  distilling  the 
residue  left  on  dissolving  sesquisulphide  of  antimony  in  hydro- 
chloric acid.  The  terchloride  of  antimony  is  a volatile,  fusible, 
crystal! izable  compound,  which  is  deliquescent,  and  powerfully 
corrosive  in  its  action  on  animal  tissues  ; it  is  soluble  in  hydro- 
chloric acid,  and  in  a small  quantity  of  water  : but  if  thrown  into 
a large  mass  of  water  an  insoluble  oxychloride  (SbCl3,Sb20g)  falls, 
which  gradually  assumes  a compact  crystalline  form  ; and  on  dilut- 
ing a hot  solution  of  terchloride  of  antimony  in  hydrochloric  acid 
with  hot  water,  it  deposits,  on  cooling,  brilliant  needles,  which 
may  be  represented  as  (2  SbClg,  5 Sb^Og)  ; it  was  formerly  called 
powder  of  algaroth.  By  heat,  the  chloride  is  sublimed,  leaving 
the  oxide.  Terchloride  of  antimony  is  used  for  bronzing  gun- 
barrels,  in  order  to  prevent  them  from  rusting. 

Perchloride  or  pentacKloride  of  antimony  (SbClj,= 299*5)  is 
prepared  by  exposing  powdered  antimony,  gently  heated  in  a retort, 
to  a current  of  dry  chlorine  in  excess.  It  forms  a volatile,  colour- 
less liquid,  which  emits  dense,  suffocating  white  fumes  when  ex- 
posed to  the  air.  With  a small  quantity  of  water  it  forms  white 
deliquescent  crystals  ; but  it  is  decomposed  by  a large  quantity  of 
water,  and  metantimonic  acid,  which  retains  a little  hydrochloric 
acid,  is  deposited:  2 SbCl^  -k7  Il20=II,Sb20,-h  10  HCl.  Dry 
perchloride  of  antimony  absorbs  sulphuretted  hydrogen,  and  forms 
with  it  a white  crystalline  fusible  solid  (SbClgS),  which  corresponds 
in  composition  to  the  chlorosulphide  of  phosphorus.  Both  the 
chlorides  of  antimony  form  definite  compounds  with  ammonia. 
The  Y>erchloride  of  antimony  is  sometimes  used  as  a chlorinating 
agent,  since  it  readily  parts  with  a portion  of  its  chlorine  to  many 
compounds  of  organic  origin  which  contain  hydrogen. 

The  terhromtde  of  antimony  is  a colourless  crystalline  solid. 
The  teriodide  is  a solid  of  a red  colour.  Tartar-emetic^  2 [K(SbO) 
OJI^OjHgO,  is  an  important  salt  of  antimony,  which  is  used  in 
medicine ; it  will  be  described  hereafter  with  the  other  tartrates. 

(857)  Characters  of  the  Compounds  of  Antimony. — Ac- 
cording to  Peligot  {Ann.  de  CUimie^  III.  xx.  297)  oxide  of  anti- 
mony, by  its  reaction  with  acids,  forms  salts  which  contain  1,  2, 
or  4 equivalents  of  a monobasic  acid  radicle.  Most  of  them  when 
largely  diluted  with  water  become  milky  from  the  deposition  of  a 
basic  salt  of  sparing  solubility;  but  this  milkiness  disapjiears  on 
the  addition  of  tartaric  acid,  or  of  acid  tartrate  of  potassium.  They 
are  all  of  them  colourless,  and  when  taken  internally  in  large 
doses,  produce  poisonous  effects.  Infusion  of  cinchona  bark  yields 
a copious  insoluble  precipitate  with  antimonial  salts,  and  it  has 


602 


ESTIMATIOX  OF  A^^TIMONT. 


been  recommended  to  adminster  this  medicine  in  cases  of  poison- 
ing with  antimony : it  is  not,  however,  to  be  relied  on. 

Except  when  tartaric  acid  is  present,  the  caustic  alkalies  give, 
with  antimonial  salts,  a white  precipitate  soluble  in  excess  of  the 
alkali ; ammonia  and  the  carbonates  of  the  alkalies^  a white  preci- 
pitate nearly  insoluble  in  excess.  But  the  characteristic  reaction 
of  these  salts  when  in  solution  is  the  formation  of  an  orange- 
coloured  precipitate  of  sesqnisnlphide  of  antimony,  when  their 
solutions,  acidulated  with  hydrochloric  acid,  are  acted  on  by  sul 
jphuretted  h ydrogen  ; this  precipitate  is  soluble  in  sulphide  of  am- 
monium. In  detecting  antimony  for  medico-legal  purposes,  anti- 
moniiiretted  hydrogen  is  first  prepared,  and  subsequently  decom- 
posed by  heat.  In  order  to  effect  this,  the  suspected  liquid,  alter 
boiling  with  hydrochloric  acid  and  a little  chlorate  of  potassimn, 
is  filtered  and  introduced  into  Marsh’s  apparatus  ; the  experiment 
is  then  proceeded  with  as  directed  for  arsenic  (81:6).  A more 
delicate  method  is  the  following : — The  suspected  solution  is  aci- 
dulated with  hydrochloric  acid,  and  boiled  with  a slip  of  bright 
copper  foil,  which  becomes  coated  with  a violet-coloured  film  of 
reduced  antimony  : wlien  heated,  the  antimony  gradually  becomes 
oxidized,  and  at  a high  temperature  the  oxide  is  volatilized,  con- 
densing in  needles,  not,  like  arsenic,  in  octohedra ; but  the  metal 
may  be  identified  by  heating  the  slip  in  a tube  with  a solu- 
tion of  pure  hydrate  of  potash,  exposing  the  surface  of  the  metal 
freely  to  the  air ; the  antimony  is  gradually  oxidized  and  dissolved. 
The  solution  should  next  be  somewhat  diluted,  submitted  to  the 
action  of  sulphuretted  hydrogen,  filtered  from  any  sulphide  of 
copper  or  lead,  and  then  on  the  addition  of  hydrochloric  acid  in 
slight  excess  the  antimony  is  precipitated  as  sulphide  in  charac- 
teristic orange  fiocculi.  This  precipitate  may  be  dissolved  in 
hydrochloric  acid,  and  will  then  give  a crust  of  metallic  antimony 
if  introduced  into  Marsh’s  apparatus. 

(858)  Estimation  of  Antimony. — In  determining  the  quantity 
of  this  metal,  the  solution  is  first  acidulated  with  a mixture  of 
hydrochloric  and  tartaric  acids,  then  subjected  to  a current  of  sul- 
phuretted hydrogen,  and  exposed  for  a few  hours  in  an  open, 
shallow  dish,  at  a temperature  not  exceeding  100°  F. : the  excess 
of  sulphm’etted  hydrogen  is  thus  got  rid  of,  and  the  whole  of  the 
antimony  is  separated  as  sulphide,  but  the  weight  of  the  dried 
precipitated  sulphide  of  antimony  cannot  be  relied  upon  as  fur- 
nishing a correct  datum  for  estimating  the  metal,  because  it  is 
liable  to  contain  a variable  excess  of  uncombined  sulphur.  It 
must  therefore  be  dried  at  212°,  and  weighed ; a certain  propor- 
tion of  it  is  then  dissolved  in  hot  aqua  regia,  after  which  the 
solution  is  mixed  with  a little  tartaric  acid ; and  the  sulphur, 
which  has  by  this  means  been  converted  into  sulphuric  acid,  is 
precipitated  by  the  addition  of  chloride  of  barium : the  sulphur 
is  calculated  from  the  weight  of  the  sulphate  of  barium  obtained, 
and  deducted  from  the  weight  of  sulphide  of  antimony  employed  ; 
the  difierence  is  estimated  as  antimony.  According  to  Bunsen, 
the  sulphide  may  be  converted  into  the  so-called  antimonious  acid 


BISMUTH. 


603 


(Sb204),  in  wliicli  form  it  may  be  weighed,  by  proceeding  as  fol- 
lows : — Place  the  sulphide  in  a counterpoised  porcelain  capsule, 
with  a concave  cover,  moisten  it  with  red  concentrated  nitric  acid, 
aud  evaporate  to  dryness  by  the  aid  of  a water-bath  : the  white 
mass  of  sulphate  of  antimony,  which  is  left,  is  converted  by  igni- 
tion into  antimonious  acid,  100  parts  of  which  correspond  to  79 "22 
of  the  metal.  The  oxidation  of  the  sulphide  of  antimony  may 
also  be  elfected  by  mixing  it  intimately  with  40  or  50  times  its 
weight  of  red  oxide  of  mercury,  and  simply  igniting  the  mixture 
in  a covered  crucible  until  it  ceases  to  lose  weight ; sulphurous 
anhydride  and  metallic  mercury  are  expelled,  and  antimonious 
acid  is  left  as  before.  If  the  precipitate  contain  a large  excess  of 
sulphur,  it  may  be  digested  with  bisulphide  of  carbon  before 
proceeding  to  the  oxidation.  Antimony  may  be  separated,  by 
means  of  sulphuretted  hydrogen,  from  all  the  metals  previously 
described,  with  the  exception  of  cadmium,  tin,  tungsten,  molyb- 
denum, and  arsenic.  Sulphide  of  cadmium  is  not  soluble  in 
sulphide  of  ammonium,  whilst  that  of  antimony  is  soluble ; this 
liquid  may  therefore  be  employed  to  separate  these  metals. 

(859)  In  order  to  sejparate ' ai'senic  from  antimony^  the  mixed 
sulphides  are  digested  in  a solution  of  sesquicarbonate  of  ammo- 
nium containing  no  free  ammonia : this  solvent  takes  up  the  sul- 
phide of  arsenic,  and  dissolves  very  little  sulphide  of  antimony. 

Tlie  separation  of  antimony  f i'om  tin  in  a metallic  alloy  may 
be  effected  with  tolerable  accuracy,  by  dissolving  the  alloy  in 
hydrochloric  acid,  which  is  to  be  mixed  with  a small  proportion 
of  nitric  acid,  in  order  to  prevent  loss  of  antimony  as  antimoniu- 
retted  liydrogen.  The  two  metals  are  then  precipitated  together 
by  means  of  metallic  zinc,  and  the  pulverulent  metals  are  dried 
at  212°  and  weighed.  This  precipitate  is  redissolved  in  weak 
aqua  regia,  and  is  digested  at  a gentle  heat  upon  a bar  of  tin, 
which  throws  down  antimony  only.  The  precipitated  metal  is 
collected,  washed,  dried,  and  weighed. 

§ IX.  Bismuth:  Bi"'=:210.  8p.  Gr.  9*799.  Fusing-pt,  507°. 

(860)  Bismuth  is  not 
an  abundant  metal:  it 
occurs  generally  in  the 
native  state  in  quartz 
rock,  and  is  extracted 
from  its  matrix  by  sim- 
ple fusion,  the  mineral 
being  usually  heated 
in  iron  tubes,  which 
are  placed  across  tlie 
furnace  in  an  inclined 
position  ; the  ore  is  in- 
troduced at  the  upper 
end,  and  the  melted 
metal  is  drawn  off  into  iron  basins  below,  by  opening  a plugged 


60^ 


PROPERTIES  AND  USES  OF  BISMUTH. 


aperture  at  intervals.  Fig,  350  shows  a section  of  the  furnace  used 
at  Schneeherg  in  this  operation,  where  the  bismuth  is  extracted 
from  an  ore  rich  in  cobalt.  Occasionally  it  is  found  as  an  oxide,  or 
as  a sulphide,  and  sometimes  it  is  met  with  combined  with  tellu- 
rium. It  generally  contains  silver,  which  may  he  extracted  by 
cupellation.  Its  mines  occur  for  the  most  part  in  Saxony, 
Transylvania,  and  Bohemia.  Commercial  bismuth  is  never  pure  : 
it  is  apt  to  contain  a little  sulphur  and  arsenic,  which  may  he 
got  rid  of  by  fusing  the  metal  with  about  one-tenth  of  its  weight 
of  nitre ; hut  it  still  retains  silver,  lead,  and  iron.  It  may  be 
obtained  free  from  these  impurities  by  solution  in  nitric  acid : the 
acid  liquid  when  saturated  with  the  metal  is  allowed  to  become 
clear,  and  is  poured  into  a large  bulk  of  water.  A sparingly 
soluble  basic  nitrate  of  bismuth  is  thus  precipitated ; it  is  washed, 
dried,  and  reduced  in  a crucible  by  ignition  with  one-tenth  of  its 
weight  of  charcoal : pure  bismuth  collects  at  the  bottom. 

Properties. — Bismuth  is  a hard,  brittle  metal,  of  a reddish- 
white  colour ; it  fuses  at  507°,  according  to  Budberg,  or  513°  to 
Person,  and  it  expands  considerably  at  the  moment  of  congela- 
tion ; when  pure  it  may  be  obtained  by  slow  cooling  after  fusion 
(72)  crystallized  in  large  cubes,*  which  are  frequently  hollow. 
Marchand  and  Scheerer  found  that  the  density  of  bismuth  was 
diminished  by  powerful  compression,  probably  owing  to  the  for- 
mation of  minute  internal  fissures ; they  thus  reduced  it  from 
9*799  to  9*556.  Bismuth  is  slightly  volatile  when  strongly  heated. 
It  is  hut  little  altered  by  exposure  to  the  air  at  ordinary  tempera- 
tures, but  is  rapidly  oxidized  if  exposed  to  the  air  at  a red  heat ; 
if  thrown  in  powder  into  chlorine  it  takes  fire : it  also  unites  easily 
with  bromine,  with  iodine,  and  with  sulphur.  Hydrochloric  acid 
has  little  action  on  it.  Boiling  sulphuric  acid  oxidizes  it  with 
evolution  of  sulphurous  anhydride  ; hut  its  proper  solvent  is  nitric 
acid,  which  oxidizes  and  dissolves  it  rapidly. 

Uses. — The  applications  of  bismuth  are  hut  limited ; it  is 
occasionally  employed  instead  of  lead  in  cupellation ; some  of  its 
compounds  are  used  as  pigments,  and  the  basic  nitrate  is  em- 
ployed medicinally.  Its  most  remarkable  alloy  is  that  known  as 
fusible  metal.  This  is  composed  of  2 parts  of  bismuth,  1 of  lead, 
and  1 of  tin,  or  2 atoms  of  bismuth,  1 of  lead,  and  2 of  tin.  The 
mixture  fuses  at  a little  below  212°,  and  passes  through  a pasty 
condition  previous  to  complete  fusion.  It  dilates  in  an  anomalous 
manner,  when  exposed  to  heat ; according  to  Erman  it  expands 
regularly  fi’om  32°  to  95°,  then  contracts  gradually  to  131°,  at 
which  point  it  occupies  a less  bulk  than  it  did  at  32° ; it  then  ex- 
pands rapidly  till  it  reaches  176°,  and  from  that  point  till  it  melts 
its  expansion  is  uniform.  This  faculty  of  expanding  as  it  cools, 
while  still  in  the  soft  state,  renders  the  alloy  very  valuable  to  the 
die  sinker,  who  employs  it  to  test  the  perfection  of  his  die, — 
every  line  being  faithfully  reproduced  on  taking  a cast.  The 

* The  crystals  of  bismuth,  however,  belong  to  the  rhombohedral  system,  as  they 
are  not  true  cubes,  but  rhombohedra,  the  angles  of  which  are  within  2®  20'  of  right 
angles. 


OXIDES  AND  SULPHIDE  OF  BISMUTH. 


605 


addition  of  cadmium  to  this  alloy,  depresses  its  fusing-point  still 
further  (716). 

Bismuth  increases  the  fusibility  of  those  metals  with  which  it 
is  alloyed,  to  a remarkable  extent. 

(861)  Oxides  of  Bismuth. — Bismuth  forms  two  principal  oxides, 
a hismuthic  oxide  (Bi^Og)  and  an  acid  oxide,  hismuthie  anhy- 
dride (BigOg) ; besides  these  there  is  a compound  oxide  (BigO^), 
formed  by  the  union  of  the  two  preceding  combinations.  A bis- 
muthous  oxide  (BiO)  of  a velvet-black  colour  may  also  be  obtained 
(Schneider)  by  treating  equivalent  quantities  of  terchloride  of 
bismuth  and  stannous  chloride  with  an  excess  of  caustic  potash, 
filtering,  and  drying  in  a current  of  carbonic  anhydride ; it  burns 
into  tlie  bismuthic  oxide  when  heated  in  the  air. 

Bismuthio  Oxide^  BigOg  = 468,  or  teroxide  of  loismuth^  BiOg 
— 234;  S]).  Gr.  8-211 : Com]),  m parts ^ Bi,  89-74;  O,  10-26. 

— This  compound  may  be  obtained  in  the  anhydrous  form  by 
heatins:  the  nitrate  or  the  basic  nitrate  of  the  metal  to  low  red- 
ness. It  is  a yellow,  insoluble  powder,  which  fuses  at  a red  heat, 
and  is  easily  reduced  to  the  metallic  state  by  heating  it  with  char- 
coal. A white  hydrate  of  this  oxide  (BiHOg)  may  also  be  pro- 
cured by  precipitating  a salt  of  bismuth  by  an  excess  of  ammonia. 

Bismuthic  anhydride  (BigO^  = 500),  or  peroxide  of  bismuth 
(BiOg  = 250),  may  be  procured  by  digesting  the  w^ashed  hydrated 
bismuthic  oxide  in  a concentrated  solution  of  potash,  and  trans- 
mitting chlorine  gas.  A blood-red  solution  of  bismuthate  of 
potassium  is  thus  obtained,  and  a red  precipitate  is  formed,  which 
is  to  be  well  w^ashed,  and  then  digested  in  cold  nitric  acid  to 
remove  the  oxide  of  bismuth  with  which  it  is  always  mixed.  A 
red  powder  is  thus  left,  which  is  bismuthic  acid  (ITBiOg) ; by  a 
heat  of  270°  it  is  rendered  anhydrous,  and  assumes  a brown 
colour.  At  a somewhat  higher  temperature  it  loses  oxygen,  and 
becomes  converted  into  the  intermediate  oxide,  or  bismuthate  of 
bismuth.  According  to  Arppe,  more  than  one  of  these  interme- 
diate oxides  may  be  formed.  Bismuthic  acid  forms  salts  with  the 
alkaline  metals,  but  these  compounds  are  decomposed  by  mere 
washing  with  water.  The  acid  is  decomposed  by  concentrated 
sulphuric  acid  at  ordinary  temperatures,  and  by  nitric  acid  if  the 
temperature  be  raised,  oxygen  being  expelled  and  a salt  corre- 
sponding to  bismuthic  oxide  formed. 

(862)  Bismuthic  Sulphide,  or  Sulphide  of  Bismuth  (BigSg  = 
516,  or  BiSg  = 258)  occurs  native  as  bismuth  glance  in  delicate 
needles,  and  in  crystals  isomorphous  with  those  of  native  sul- 
phide of  antimony.  It  may  be  formed  artificially  by  fusing  the 
metal  with  sulphur : a fusible  dark  grey  compound,  with  a feebly 
metallic  lustre,  is  thus  obtained ; in  closed  vessels  it  is  decom- 
posed into  a subsulphide,  and  into  free  sulphur,  which  distils ; in 
the  open  air  sulphurous  anhydride  escapes,  and  bismuthic  oxide 
remains.  When  solutions  of  bismuth  are  treated  with  sul- 
])huretted  hydrogen,  a black  precipitate  of  the  sulphide  of  the 
metal  is  formed.  Sulphide  of  bismuth  is  dissolved  by  the  metal 
in  all  proportions,  a circumstance  which  affords  an  easy  method 


606 


CHARACTERS  OF  THE  SALTS  OF  BISMUTH. 


of  obtaining  it  in  crystals,  since  tlie  sulphide  crystallizes  at  a 
temperature  at  which  the  metal  still  remains  fluid. 

(863)  Terchloride  of  Bismhih  (BiClj  ==  316*5  ; Sp.  Gr.  4*56) 
may  be  obtained  by  heating  bismuth  in  chlorine,  or  by  mixing 
the  metal  in  flue  powder  with  twice  its  weight  of  corrosive 
sublimate,  and  distilling.  It  is  a very  fusible,  volatile,  deli- 
quescent compound  ; but  is  decomposed  by  a large  quantity  of 
water  into  free  hydrochloric  acid,  and  oxychloride  of  bismuth 
[2  (BiClg,  Bi^Og)  . II2O],  known  under  the  name  of  pearl  white. 
This  compound  is  insoluble  in  tartaric  acid,  in  solution  of  potash, 
and  in  sulphide  of  ammonium,  characters  which  distinguish  it 
from  the  corresponding  compound  of  antimony. 

Teriodide  of  Bismuth  (Bilg ; Sp.  Gr.  5*652)  is  obtained  by  heat- 
ing in  closed  vessels  6 parts  of  bismuth  with  11  of  iodine ; it  sublimes 
in  six-sided,  brilliant  plates.  It  is  readily  fusible,  a dark  brown 
colour,  and  is  insoluble  in  water ; but  it  forms  soluble  compounds 
with  hydrochloric  acid,  and  with  iodide  of  potassium. 

(864)  Nitrate  of  Bismuth  (Bi  3 HOg,  5 H^O,  or  BiOg,  3 

10  110=396-1-90);  Sp.  Gr.  2*376. — This  salt  is  the  only  other 
soluble  compound  of  bismuth  of  any  importance,  and  is  easily 
procured  by  dissolving  the  metal  in  nitric  acid : it  may  be  crystal- 
lized from  the  acid  solution  in  large  transparent  prisms.  If  the 
solution,  not  too  strongly  acid,  be  largely  diluted  with  water,  an 
acid  salt  remains  in  the  liquid,  and  a subnitrate  falls  (2  Bi^IO^, 
HgO),  called  by  the  old  writers  magistery  of  bismuth : another 
basic  nitrate  (Bi20g,IIN0g)  is  also  known. 

(865)  Characters  of  the  Salts  of  Bismuth. — Bismuth  when 
in  solution  presents  characters  less  marked  than  many  metals. 
Its  salts  are  colourless  unless  the  acid  be  coloured ; they  are  poi- 
sonous in  large  doses ; its  solutions  have  an  acid  reaction  ; when 
diluted  they  become  milky,  owing  to  the  formation  of  sparingly 
soluble  basic  salts,  unless  a large  excess  of  acid  be  present.  Iron.^ 
zinc^  copper^  and  tin  throw  down  bismuth  from  its  solutions  in  the 
metallic  state.  The  hydrated  alkalies  give  a white  precipitate 
of  the  hydrated  oxide,  which  is  insoluble  in  excess  of  the  precipi- 
tant, and  becomes  yellow  by  boiling  it  with  the  liquid.  Solutions 
of  the  carbonates.^  phosphates.^  tartrates^  and  ferrocyanides  give 
white  precipitates  with  its  salts.  Phosphate  of  bismuth  is  insoluble 
in  diluted  nitric  and  acetic  acids,  and  it  has  in  consequence  been 
proposed  by  Chancel  as  a convenient  form  in  which  phosphoric 
acid  may  be  precipitated  from  acid  solutions  (448).  This  phos- 
phate is,  however,  largely  soluble  in  hydrochloric  acid,  whilst  if 
sulphuric  acid  is  present  the  precipitate  generally  becomes  con- 
taminated with  basic  sulphate  of  bismuth.  Sulphuretted  hydrogen 
throws  down  a black  sulphide  of  bismuth,  which  is  insoluble  in 
sulphide  of  ammonium.  Chromate  of  potassium  gives  a yellow 
precipitate  of  chromate  of  bismuth,  which  is  insoluble  in  caustic 
potash,  but  freely  soluble  in  diluted  nitric  acid ; it  is  thus  dis- 
tinguished from  chromate  of  lead.  Before  the  blowpipe  its  salts 
are  easily  reduced  on  charcoal,  and  yield  a brittle  bead  of  bismuth, 
around  which  the  yellow  oxide  is  deposited. 


COPPER. 


607 


(866)  Estimation  of  Bismuth. — Bisnmtli  is  estimated  in  the 
form  of  bismnthic  oxide,  100  parts  of  which  correspond  to  89-Tlr 
of  the  metal.  Carbonate  of  ammonium  is  its  best  precipitant, 
but  the  solution  must  not  contain  any  chloride  or  hydrochloric 
acid,  as  an  oxychloride  of  bismuth  would  in  that  case  be  precipi- 
tated, and  a portion  of  the  bismuth  would  be  volatilized  with  the 
chlorine  on  ignition ; the  metal  must  in  such  a case  be  precipi- 
tated in  the  form  of  sulphide.  It  may  be  separated  from  the 
alkalies,  from  titanium,  and  from  all  the  metals  of  the  first 
four  groups  (with  the  exception  of  cadmium),  by  means  of  sul- 
phuretted hydrogen  ; the  solution  having  been  first  acidulated 
with  acetic  acid.  From  tin,  and  from  the  metals  of  the  fifth 
group,  it  may  be  separated  by  digesting  the  mixed  sulphides  (ob- 
tained by  transmitting  sulphuretted  hydrogen  through  the  liquid) 
in  sulphide  of  ammonium,  which  leaves  the  sulphide  of  bismuth, 
and  dissolves  the  other  sulphides.  The  sulphide  must  be  dis- 
solved in  nitric  acid,  and  precipitated  by  carbonate  of  ammonium, 
which  after  standing  for  a few  hours  tlirows  down  the  whole  of 
the  bismuth  in  the  form  of  carbonate : it  must  be  ignited  in  a 
porcelain  crucible ; carbonic  anhydride  is  thus  expelled,  and  bis- 
muthic  oxide  remains. 

Bismuth  may  be  separated  from  cadmium  by  the  addition  of 
ammonia  in  excess  to  the  solution  of  the  sulphides  in  nitric  acid ; 
the  cadmium  is  retained  in  solution,  whilst  the  bismuth  is  pre- 
cipitated. 


CHAPTEK  XYIII. 


GROUP  VII. COPPER,  LEAD,  AND  THALLIUM. 


Metals. 

Sym- 

bol. 

Atomic 

weight. 

Atomic 

YOl. 

Specific 

heat. 

Fusing- 
point  F“. 

Specific 

gravity. 

Electric 
conductivity 
32°  F. 

Copper 

•Ou 

63-5 

710 

0-0951 

1996 

8-952 

99-95 

Lead 

Pb 

207-0 

18-24 

0-0314 

617 

11-36 

8-32 

Thallium  . . . 

T1 

204  0 

17-20 

0-0325 

561 

11-862 

9-16 

These  metals  have  no  close  chemical  relationship.  Thallium 
is  a monad,  and  resembles  silver  in  its  specific  heat,  but  is  more 
like  lead  in  physical  properties  and  in  its  compounds. 

§ I.  Copper:  Ou"=63-5,  or  Cu=31-7.  Sf.  Gr.  from 
8’921  to  8'952 : Fusing-jpt.  1996°. 

(867)  The  ORES  of  copper  are  numerous.  The  metal  is  fre- 
quently found  native,  crystallized  in  cubes,  octohedra,  or  dendritic 
crystals;  or  else  in  masses,  as  in  the  North  American  and  Siberian 


608 


COPPER  SMELTING. 


mines.  In  the  neighbourhood  of  Lake  Superior  there  is  a vein  of 
massive  native  copper,  associated  with  silver ; this  vein  is  in  many 
parts  two  feet  in  thickness.  The  most  common  ore  of  copper, 
however,  is  the  copper  pyrites,  or  double  sulphide  of  copper  and 
iron  (■0U2S,Fe2S3),  which  occurs  in  the  primitive  rocks,  and  espe- 
cially in  the  hillas^  or  clay-slate.  More  rarely  the  pure  subsulphide 
of  copper  (Ou^S)  is  found  in  the  mines  of  Cornwall  and  of  the 
Ural  Mountains.  Other  less  abundant  ores  are  the  blue  and 
green  carbonates,  and  the  red  and  black  oxides  of  copper. 

The  Cornish  mines  furnish  more  than  a third  of  the  copper 
which  is  smelted  in  Great  Britain,  but  considerable  supplies  of  ore 
are  received  from  Chili,  Cuba,  and  South  Australia.  The  most 
important  seat  of  the  copper  smelting  is  Swansea,  which  sends 
forth  annually  from  18,000  to  20,000  tons  of  the  refined  metal. 
Uorth  America  and  Saxony  supply  the  larger  portion  of  the 
remainder.  The  Australian  ore  consists  chiefiy  of  the  green  and 
blue  carbonate  in  a siliceous  matrix ; these  ores  contain  from  25 
to  35  per  cent,  of  copper.  Cuba  furnishes  both  the  oxides  and 
the  sulphides  of  the  metal.  Many  of  the  ores  from  Chili  are 
valuable  on  account  of  the  large  proportion  of  silver  which  they 
contain.  The  Cornish  copper  pyrites  usually  occurs  (mixed  with 
small  quantities  of  oxide  of  tin  and  arsenical  pyrites)  in  a matrix 
of  quartz,  fiuor-spar,  and  clay. 

(868)  Extraction. — The  main  object  in  the  treatment  of  such 
an  ore  as  the  Cornish,  is  to  oxidize  and  remove  the  sulphur  and 
arsenic  in  the  form  of  sulphurous  and  arsenious  anhydrides,  and 
to  get  rid  of  the  quartz  and  oxide  of  iron  in  the  form  of  a fusible 
slag,  composed  of  silicate  of  iron  combined  with  other  earthy 
impurities,  leaving  metallic  copper  free  from  admixture. 

After  the  ore  has  been  raised  from  the  mine  it  is  sorted ; the 
purest  portions  are  broken  into  small  pieces  of  the  size  of  a hazel- 
nut, and  the  earthy  portions  are  crushed  and  sifted,  as  in  washing 
tin  ore.  The  English  ore  is  usually  so  mixed  that  it  may  contain 
an  average  of  8-|-  per  cent,  of  copper. 

The  theory  of  copper  smelting  as  practised  at  Swansea,  like 
that  of  many  other  operations  in  the  arts,  is  simple,  though  the 
working  details  have  the  appearance  of  being  complicated.'^  The 
principal  processes  may,  however,  be  enumerated  as  follows : — 

1.  Calcining  the  ore. 

2.  Melting  and  granulating  for  coarse  metal. 

3.  Calcination  of  the  coarse  metal. 

4.  Melting  for  fine  metal. 

* The  apparent  complication  of  the  process  arises  from  one  of  its  great  practical 
merits — viz.,  from  the  circumstance  that  it  admits  of  being  modified  to  suit  almost 
every  variety  of  ore,  and  these  modifications  necessarily  tend  to  increase  its  com- 
plexity. Le  Play  enumerates  six  principal  varieties  of  ores  as  being  wrought  by  this 
method. — 1.  Pyritous  ores,  containing  from  3 to  15  per  cent,  of  copper.  2.  Richer 
ores  of  the  same  kind,  yielding  from  15  to  25  per  cent,  of  copper.  3.  Siliceous 
oxides  of  copper,  yielding  from  12  to  20  per  cent,  of  metal.  4.  Oxides  and  carbonates 
with  subsulphide  of  copper,  in  a siliceous  matrix.  5.  Very  pure  siliceous  sulphides 
of  copper  and  iron,  yielding  from  10  to  15  per  cent,  of  copper;  and  6.  Pure  sulphides 
and  oxides  of  copper  containing  from  60  to  80  per  cent,  of  the  metal. 


CALCINING  THE  ORE. 


609 


5.  Hoasting  of  tlie  fine  metal. 

6.  Eefining  and  toughening. 

We  shall  make  a few  remarks  upon  each  of  these  processes  in 
succession. 

(869)  1.  Calcining  the  Ore. — The  calcination  is  conducted  in 
large  reverberatory  furnaces,  upon  quantities  of  about  3 tons  at  a 
time ; the  heat  is  moderate,  so  as  to  avoid  fusing  the  mass,  which 
is  spread  evenly  over  the  fioor  of  the  furnace,  and  stirred  at  inter- 
vals of  2 hours;  this  roasting  is  continued  for  12  hours,  at  the 
end  of  which  time  the  mass  is  converted  into  a black  powder  con- 
taining sulphide  of  copper,  oxide  and  undecomposed  sulphide  of 
iron,  and  earthy  impurities.  Oxygen  has  a stronger  attraction  for 
iron  than  for  copper,  but  the  attraction-  of  sulphur  for  copper  is 
greater  than  for  iron ; and  the  effect  of  the  roasting  is  seen  in  the 
production  of  oxide  of  iron  and  sulphurous  anhydride,  whilst  the 
sulphide  of  copper  remains  unacted  upon.  During  this  and  the 
subsequent  processes,  abundant  white  deleterious  fumes  are  given 
off;  containing  arsenious,  sulphurous,  sulphuric,  and  hydrofluoric 
acids,  and  a certain  portion  of  metallic  arsenic.  These  fumes  hang 
like  a dense  canopy  over  the  smelting  works  and  their  vicinity : 
the  cloud  of  copper  smoke.^  as  it  is  called,  may  be  discerned  at  the 
distance  of  many  miles. 

The  calcining  furnace  employed  in  Wales  is  shown  in  section 
in  fig.  351,  and  a plan  of  the  hearth  is  exhibited  in  fig.  352.  a is 
the  fireplace  : J,  the  bridge  ; c c,  the  hearth  or  roasting  bed  ; cZ,  d 
are  apertures  in  the  floor,  through  which,  by  withdrawing  an  iron 
slide,  the  charge  can  be  allowed  to  pass  into  the  cub.^  oi*  vault,  e, 
when  the  roasting  is  complete  ; /*,/*  are  the  flues ; y is  an  opening 
for  the  admission  of  air  to  the  hearth ; ii,  h are  the  hoppers  for 
charging  the  furnace,  and  a platform  over  which  the  barrows  of 
ore  are  conveyed  to  the  hoppers. 

Fig.  351. 


The  fuel  used  in  roasting  the  ore  is  cliiefly  antliracite,  a coal 
which,  under  ordinary  management,  yields  no  flame.  Flame, 
however,  is  absolutely  necessary  to  the  proper  roasting  of  the 
copper  ore  ; experience  has  taught  the  co})per  smelter  to  obtain 
this  desideratum  by  limiting  the  supply  of  air  to  the  fuel  in  the 
39 


610 


MELTHTG  FOR  COARSE  METAL. 


fire-grate,  thns  causing  the  carbonic  anhydride  which  is  formed 
at  the  lower  part  of  t&  fire  to  be  converted  into  carbonic  oxide. 
By  a nice  adjustment  of  the  supply  of  air  through  the  other 
apertures  of  the  furnace  being  closed,  the  carbonic  oxide  is 
gradually  burned  as  it  plays  over  the  ore  upon  the  hearth,  g g ; 
the  maximum  of  heat  is  thus  obtained  at  the  minimum  cost  of 


Fig.  352. 


fuel,  the  carbonic  oxide  being  completely  burned  before  it  reaches 
the  flue.  An  admirable  analysis  of  this  operation  is  given  by  Le 
Play  in  his  elaborate  memoir  on  the  Welsh  method  of  copper 
smelting  {Ann.  des  Mines^  lY.  xiii.  128).* 

(870)  2.  Melting  for  Coarse  Metal. — The  roasted  ore  is  now 
subjected  to  fusion  in  the  ore  furnaee  with  certain  proportions  of 
slag,  the  produce  of  a subsequent  operation,  of  siliceous  ore  free 
from  sulphur,  and  of  fluor-spar  if  necessary  ; by  this  means  the 
charge  is  converted  into  a fusible  slag,  consisting  chiefly  of  silicate 
of  iron,  and  into  sulphides  of  copper  and  of  iron,  which  sink 
through  the  slag,  and  form  what  is  termed  a matt.  This  fusion 
occupies  about  5 hours,  each  charge  containing  about  1^  ton  of 
roasted  ore.  The  matt  thus  procured  contains  about  33  per  cent, 
of  copper;  it  is  run  off  while  liquid  into  water,  by  which  it 
is  granulated.  The  product  goes  by  the  name  of  Goarse  metal. 
The  slag  which  floats  above  the  matt  is  raked  out  of  the  furnace 
at  a separate  aperture.  It  ought  to  contain  no  appreciable  quan- 
tity of  copper. 

3.  Caleination  of  the  Coarse  Metal. — The  granulated  metal  is 

* The  heat  emitted  during  the  combustion  of  anthracite  is  very  intense,  so  that 
it  causes  a rapid  oxidation  of  the  fire-bars  of  the  furnace.  This  fuel  has  also  the 
inconvenience  of  splitting  into  small  fragments,  which  choke  the  air-ways  between 
the  bars,  if  the  heat  be  suddenly  applied.  The  copper  smelter  overcomes  these 
difficulties  by  employing  a grate  consisting  only  of  a few  bars,  which  do  not 
come  into  contact  with  the  fuel  itself,  but  only  serve  as  a support  for  the  clinker 
produced  during  the  combustion  of  the  coal.  A bed  of  clinkers,  12  or  16  inches 
thick,  rests  upon  the  fire-bars,  and  above  this  the  fuel  is  burned ; from  time  to  time 
the  fireman  removes  portions  of  the  clinker  as  it  accumulates. 


COPPER  SMELTING BLISTERED  COPPER REFINING. 


611 


again  roasted  for  24  hours,  during  which  operation  a large  pro- 
{)ortion  of  the  sulphide  of  iron  is  converted  into  oxide. 

4.  Melting  for  Fine  Metal. — A second  fusion  is  performed 
upon  this  calcined  matt  with  the  addition  of  a portion  of  copper 
ore  known  to  be  rich  in  oxide  of  copper  and  in  silica,  and  to  con- 
tain but  little  iron  pj^rites.  By  this  means  the  oxide  of  iron 
is  removed  in  the  form  of  a fresh  slag  of  silicate  of  iron,  and  the 
oxygen  contained  in  the  freshly  added  oxide  of  copper  completes 
the  oxidation  of  any  portion  of  sulphide  of  iron  still  remaining ; 
the  oxide  of  copper  and  the  whole  of  the  sulphide  of  this  metal 
being  reduced  to  the  state  of  suhsulphide  of  copper  (-Gu^S)  or  fine 
metal.  The  slags  from  this  process,  and  all  the  subsequent  ones 
are  preserved.  This  matt  contains  about  80  per  cent,  of  copper.  It 
is  cast  into  pigs.  If  a very  pure  metal  be  required,  the  roasting 
is  carried  a little  further ; a portion  of  the  metal  is  thus  reduced  : 
this  portion  contains  the  greater  part  of  the  foreign  metals,  which 
give  up  their  sulphur  more  readily  than  the  copper ; the  reduced 
metal  from  its  greater  density,  sinks  to  the  bottom  ; the  upper  parts 
of  the  pigs  are  subsequently  detached  from  the  lower  portions,  and 
the  metal  extracted  from  the  upper  portions  of  tlie  ingots  is 
known  in  the  market  as  lest  selected  cojpjper. 

5.  Roasting  for  Blistered  Cojpjper. — The  fine  metal  or  subsul- 
phide is  now  to  be  freed  from  the  sulphur  which  has  hitherto 
been  useful  by  forming  a fusible  compound  with  the  copper,  thus 
facilitating  its  separation  from  the  impurities  by  wdiich  it  was 
accompanied.  With  this  view  the  pigs  of  fine  metal  are  next 
subjected  for  several  hours,  upon  the  bed  of  a reverberatory,  to  a 
heat  just  short  of  that  required  to  fuse  them  ; the  metal  by  this 
means  becomes  oxidized  at  the  surface,  and  a part  of  the  sulphur 
which  it  still  retains  is  also  oxidized;  at  last  it  is  fused  : a remark- 
able reaction  then  begins  to  take  place.  When  oxide  of  copper 
and  subsulphide  of  copper  are  heated  together,  they  decompose  each 
other ; sulphurous  anhydride  and  metallic  copper  are  liberated  ; 
OiqS  -f-  2 GuO  = SG^  + 4 Gu.  It  is  not  desirable  that  the  tem- 
perature should  be  too  strongly  raised,  as  the  oxide  of  copper 
would  then  combine  with  the  silica  still  present  in  the  mass,  and 
would  cease  to  exert  its  oxidizing  infiuence.  After  the  charge 
has  become  liquid,  the  temperature  of  the  furnace  is  allowed  to 
fall ; the  melted  mass  solidifies  upon  its  surface,  and  an  appear- 
ance of  violent  ebullition  is  produced  from  the  formation  of  sul- 
phurous anhydride,  and  its  efforts  to  escape  from  the  tenacious 
mixture  : when  this  ceases,  the  desulphuration  is  complete.  The 
heat  is  now  rendered  very  intense,  the  copper  melts  and  sinks  to 
the  bottom,  and  separates  completely  from  the  slag,  which  con- 
sists chiefly  of  silicate  of  copper  ; the  reduced  metal  is  then  run 
off  into  sand  moulds.  The  ingots  thus  obtained,  ])eing  full  of 
bubbles,  are  iQvmad  pimple  or  hlistered  copper. 

(871)  6.  Refining  vre  Toughening. — The  blistered  copper  now 
undergoes  the  concluding  operation  of  refining.  From  7 to  8 tons 
of  the  metal  are  placed  in  a reverberatory  furnace  and  ke])t  in  a 
melted  state  for  upwards  of  20  hours,  in  order  to  oxidate  the  last 


612 


KEEXEL  EOASTIXG. 


traces  of  foreign  metals  : during  this  process  a large  quantity  of 
oxide  of  copper  is  formed  ; part  of  this  oxide  is  absorbed  by  the 
melted  metal,  and  the  copper,  if  examined  at  this  stage,  is  found 
to  be  of  a dull  red  colour,  coarse  grained  and  brittle.  To  reduce 
this  oxide,  the  slags  are  skimmed  off,  and  the  surface  is  covered 
with  a few  shovelfuls  of  anthracite  or  of  charcoal ; the  metal  is 
then  subjected  to  the  process  of  poling^  in  wliich  the  trunk  of  a 
young  tree  is  thrust  into  the  molten  metal.  The  inflammable 
gases  disengaged  from  the  green  wood  as  it  chars,  produce  a 
powerful  agitation  of  the  whole  mass,  and  in  about  20  minutes  the 
poling  is  linished.  The  reducing  influence  of  the  combustible 
gases  lias  in  the  mean  time  been  brought  to  bear  upon  every  por- 
tion of  the  melted  metal.  In  this  way  the  oxide  diffused  through 
the  mass  is  deprived  of  oxygen.  If  the  poling  be  carried  too  far, 
the  copper  again  becomes  brittle,  and  is  said  to  be  overpoled.  This 
defect  may  be  remedied  by  exposing  the  surface  of  the  melted 
metal  to  a current  of  air.  If  too  little  poling  be  used,  the  metal 
is  still  brittle,  and  it  is  then  said  to  be  underpoled.  The  progress 
of  the  poling,  therefore,  requires  careful  watching  : the  refiner 
tests  the  metal  from  time  to  time  by  dipping  a small  test-ladle 
into  the  melted  mass  ; a sample  of  copper  is  thus  removed,  and 
cooled  suddenly  by  immersion  in  water  : the  grain  of  the  copper 
is  judged  of  by  cutting  the  hammered  button  partially  through 
with  a chisel  or  shears,  and  then  bending  it  by  placing  it  in  a 
vice.  If  properly  refined,  the  broken  surface  will  display  a fibrous 
structure  with  a beautiful  silky  lustre.  If  underpoled,  the  fracture 
will  be  granular,  with  a number  of  red  points.  If  overpoled,  the 
fibres  become  coarser,  and  the  fracture  has  a strong  metallic 
lustre,  but  the  silky  appearance  is  wanting.  When,  upon  testing, 
the  copper  appears  to  be  fine  grained,  fibrous,  and  silky,  of  good 
colour,  and  malleable,  it  is  either  ladled  out  and  cast  into  ingots, 
or  it  is  cooled  suddenly  at  the  surface,  by  allowing  water  to  run 
upon  it ; in  the  latter  case  rose  copper  is  produced,  and  successive 
films  are  made  and  removed  till  all  the  metal  is  consumed.  There 
appears  to  be  no  doubt  that  the  brittleness  of  undei-poled  copper 
is  due  to  the  presence  of  red  oxide  of  copper  in  the  metal,  and  Mr. 
Vivian  has  suggested  that  overpoled  copper  may  be  defective  from 
the  presence  of  a little  carbon.  Percy,  however,  was  unsuccess- 
ful in  the  attempt  to  discover  carbon  in  overpoled  specimens.  An 
interesting  paper  by  Abel  on  the  non-metallic  impurities  of  refined 
copper  will  be  found  in  the  Journ.  Chein.  Soc.  186-1,  p.  161. 

The  slags  from  the  various  operations  are  carefully  remelted, 
and  the  copper  which  is  extracted  from  them  is  termed  hlach  cop- 
per ; it  is  run  into  pigs,  which  are  subsequently  refined. 

The  presence  of  a small  quantity  of  tin  in  the  refined  copper 
is  considered  to  be  advantageous,  as  the  toughness  and  tenacity 
of  the  metal  are  thereby  increased.  Antimony  is  singularly  in- 
jurious ; so  small  a quantity  as  10  ounces  in  the  ton  renders  cop- 
per unfit  for  making  brass  that  is  required  for  rolling  ; and  minute 
traces  of  nickel  and  of  bismuth  are  also  said  greatly  to  injure  the 
tenacity  of  the  metal. 


COMMERCIAL  COPPER ITS  PROPERTIES. 


613 


(872)  Kernel  roasting. — cupriferous  iron  pyrites,  con- 
taining from  2 to  3 per  cent,  of  copper,  is  broken  into  lumps  of 
about  the  size  of  the  fist,  and  subjected  to  a very  gradual  roasting, 
a large  portion  of  the  copper  becomes  concentrated  in  the  middle 
of  the  lump,  and  a nucleus  of  sulphide  of  copper  and  iron  is  form- 
ed. This  nucleus  or  Tcernel.^  is  surrounded  by  a more  or  less  porous 
shell,  com^^osed  mainly  of  peroxide  of  iron,  which  may  be  detach- 
ed from  the  nucleus  by  a blow.  Upon  these  observations  a method 
of  roasting  copper  ore  has  been  founded,  to  which  the  name  of 
'kernel  roasting  has  been  given.  This  roasting  is  conducted  in  the 
Venetian  Alps,  at  Agordo,  in  kilns,  and  at  Mulbach  in  enormous 
heaps  in  the  open  air.  These  heaps  are  in  the  form  of  a truncated 
square  pyramid,  the  base  of  which  is  about  30  feet  square  (406). 
The  roasting  is  a very  slow  operation,  requiring  from  5 to  6 months 
for  its  completion.  Spring  and  autumn  are  the  most  favourable 
seasons  in  which  to  commence  it.  Sulphur  distils  off*  to  the  ex- 
tent of  0‘2  per  cent,  of  the  ore  ; the  kernels  constitute  from  13  to 
14  per  cent,  of  the  roasted  mass,  and  they  contain  about  5 per  cent, 
of  metallic  copper.  The  cause  of  this  concentration  of  copper  in  the 
interior  of  the  mass  is  entirely  unexplained.  The  shells,  which 
retain  a small  proportion  of  sulphate  of  copper,  are  washed  to  ex- 
tract this  as  far  as  practicable,  and  the  roasted  ore  is  then  subjected 
to  processes  not  essentially  difi'ering  from  those  already  described. 
(Percy,  Metallurgy.^  i.  439.) 

In  many  copper  mines  the  water  which  is  pumped  up  is  im- 
pregnated with  sulphate  of  copper  derived  from  the  oxidation  of 
the  sulphide  by  exposure  to  the  air : the  copper  is  easily  separated 
in  the  metallic  form,  by  collecting  the  water  in  tanks  containing 
scrap-iron : the  iron  unites  with  the  oxygen  and  the  acid,  whilst 
the  copper  is  set  at  liberty:  ■GuSO^  + Pe^PeSO.  + Ou. 

When  the  ore  consists  of  the  oxides  and  carbonates  of  copper, 
it  is  easily  reduced  to  the  metallic  state  by  simple  fusion  with  coke 
or  charcoal,  oxide  of  iron  and  lime  being  added  in  quantity  suf- 
ficient to  form  a fusible  slag  with  the  silica  which  usually  accom- 
panies these  ores ; the  copper  is  rendered  tough  by  a process 
analogous  to  that  of  poling. 

The  copper  of  commerce  is  often  very  nearly  pure.  It  contains 
minute  quantities  of  arsenic,  of  iron,  of  lead,  and  sometimes  of  tin 
and  silver.  Abel  has  detected  traces  of  selenium  in  some  speci- 
mens, and  of  sulphur  in  others.  Copper  may  be  readily  obtained 
in  a state  of  perfect  purity,  by  decomposing  a solution  of  ])ure 
sulphate  of  copper  by  means  of  the  voltaic  battery : it  is  then 
deposited  in  coherent  plates  upon  the  negative  electrode. 

(873)  Properties. — Copper  is  one  of  the  metals  which  has  been 
longest  known  to  man : before  the  art  of  working  iron  was 
understood,  it  was  in  extensive  use,  either  alone  or  alloyed  with 
tin,  for  many  of  the  purposes  to  which  iron  is  now  a])plied.  It 
is  of  a well-known  red  colour,  and  has  a peculiar,  disagreeable 
odour  and  taste  when  moistened  and  rubbed.  It  is  rather  a hard 
metal,  very  tenacious,  ductile,  and  malleable ; after  it  had  been 
melted  beneath  a layer  of  common  salt,  to  exclude  atmospheric 


614 


USES  OF  COPPEK. 


air,  pure  copper  was  found  by  Sclieerer  and  Marcliand  to  have  a 
sp.  gr.  of  8'921  : the  density  was  increased  by  hammering,  and 
when  drawn  into  fine  wire  it  was  obtained  as  high  as  8*952  : 
Daniell  estimated  its  fusing-point  at  1996°  F.  When  heated  to 
a temperature  approaching  its  melting-point  it  becomes  so  brittle 
that  it  may  be  reduced  to  powder,  and  an  ingot  may  be  broken 
by  a blow  from  a hammer.  If  exposed  to  a very  intense  heat, 
copper  is  capable  of  volatilization,  but  it  is  usually  considered  to 
be  fixed  in  the  fire.  By  slow  voltaic  action  it  may  be  obtained 
crystallized  in  cubes  and  octohedra,  and  is  sometimes  found  native 
in  these  forms.  It  ranks  amongst  the  best  conductors  of  heat 
and  electricity.  If  heated  to  redness  in  the  open  air,  copper 
combines  with  oxygen  rapidly,  a layer  of  oxide  is  formed  upon 
the  surface,  and  as  the  oxide  contracts  more  slowly  than  the 
metal  beneath,  it  scales  ofi‘  if  suddenly  cooled,  leaving  a bright, 
clean,  metallic  surface.  Copper  is  not  oxidized  when  heated  to 
redness  in  a current  of  steam.  Exposure  to  a moist  air  at  ordi- 
nary temperatures  has  no  efiect  upon  copper ; neither  has  pure 
water ; but  in  sea  water,  or  in  solutions  of  the  chlorides,  it  is 

fradually  corroded  with  the  formation  of  an  oxychloride  of  copper. 

'inely  divided  copper  becomes  ignited  when  touched  with  a glow- 
ing coal,  and  burns  like  tinder,  being  converted  into  the  black 
oxide.  Chlorine  attacks  the  metal,  which  when  in  the  form  of 
leaf  takes  fire  in  the  gas  spontaneously.  Xitric  acid  oxidizes  and 
dissolves  the  metal  with  rapidity.  Oil  of  \fitriol  does  not  act 
upon  it  in  the  cold,  but  if  heated  with  it,  the  acid  is  decomposed, 
sulphurous  anhydride  being  evolved  and  oxide  of  copper  formed, 
which  reacts  upon  the  excess  of  acid  to  form  the  sulphate  (410). 
Hydrochloric  acid  with  access  of  air  dissolves  it : but  if  air  be 
ex'cluded,  it  has  no  such  efiect  at  ordinary  temperatures ; though 
if  boiled  upon  the  finely-divided  metal,  it  dissolves  it  very  slowly, 
and  hydrogen  is  evolved  (Odling).  Copper  also  decomposes  hydro- 
chloric acid  gas  when  heated  in  it  to  redness,  cupreous  chloride 
being  formed  and  hydrogen  separated.  The  fixed  alkalies  have 
little  action  on  copper,  but  ammonia  gradually  dissolves  the  metal  if 
the  air  has  access  to  it,  slow  oxidation  taking  place  Before  the  oxy- 
hydrogen  blow-pipe  it  burns  with  a green  fiame,  and  if  introduced 
into  a flame  of  gas  or  of  alcohol  it  communicates  to  it  a green  colour. 

Uses. — The  applications  of  copper  in  the  arts  are  very  nume- 
rous. Independently  of  its  use  in  coinage,  vast  quantities  of  it 
are  annually  consumed  in  the  sheathing  of  ships*  and  in  the 
manufacture  of  boilers,  and  of  various  utensils  for  domestic  pur- 
poses. It  also  forms  the  basis  of  a number  of  valuable  alloys  in 
extensive  use : with  zinc  it  furnishes  the  different  varieties  of 
brass ; and  with  different  proportions  of  tin  it  forms  bronze,  bell- 
metal,  gun-metal,  and  speculum-metal  (812);  whilst  its  oxides 
and  salts  are  largely  employed  as  pigments,  and  yield  articles  of 
some  importance  in  the  materia  medica. 

* Percy’s  experiments  appear  to  show  that  the  presence  of  a small  quantity  of 
phosphorus  in  the  copper  has  some  effect  in  protecting  the  metal  from  the  corrosive 
action  of  sea  water. 


BRASS. 


615 


An  alloy  of  copper  and  silicon  containing  12  per  cent,  of  the 
latter  may  be  obtained  by  fusing  together  3 parts  of  silicotluoride 
of  potassium,  1 part  of  sodium  and  1 of  copper  turnings  : it  is 
hard,  brittle,  and  white,  like  bismuth.  Another  alloy  may  be 
obtained  by  prolonged  heating  of  a mixture  of  sand,  charcoal,  and 
copper : wdien  it  contains  4’8  per  cent,  of  silicon  it  is  of  a fine 
bronze  colour.  It  is  as  fusible  as  bronze,  very  ductile,  and  yields 
a wire  a little  softer  than  iron,  but  quite  as  tenacious : it  may  be 
worked  well  at  the  lathe. 

(874)  Brass. — The  combination  of  zinc  with  copper  has  a 
well-known  yellow  colour,  the  tint  of  which  becomes  paler  in 
proportion  as  the  quantity  of  zinc  is  increased.  A curious  ob- 
servation upon  this  point  was  made  by  Mr.  D.  Forbes,  who  found 
that  a brittle  crystalline  alloy  of  a silver-white  colour  may  be 
formed,  containing  53'49  per  cent,  of  zinc,  and  consisting  of  7 
equivalents  of  copper  and  8 of  zinc  ; but  if  the  quantity  of  zinc 
were  either  increased  or  diminished,  the  alloy  had  the  usual 
yellow  colour  of  brass.  The  specific  gravity  of  brass  is  greater 
than  the  mean  of  that  of  the  metals  which  form  it.  Ordinary 
brass  has  a sp.  gr.  of  8 '29  ; it  contains  about  64  per  cent,  of  copper, 
being  nearly  -Gu^Zn.  Brass  which  contains  25  per  cent,  of  zinc 
melts  at  1750°  (Daniell),  and  a larger  proportion  of  zinc  increases 
its  fusibility.  By  exposure  to  a long-sustained  high  temperature 
in  closed  vessels,  the  whole  of  the  zinc  may  be  expelled,  and  it 
is  not  possible  to  fuse  the  alloy  without  losing  a portion  of  the 
zinc.  The  alloys  of  zinc  and  copper  are  malleable  when  cold,  but 
are  generally  brittle  when  hot.  An  alloy  largely  used  under  the 
name  of  Muntz  metal ^ or  yellow  metal for  the  sheathing  of  ships, 
may  be  rolled  whilst  hot ; it  contains  2 equivalents  of  zinc  to  3 
of  copper,  or  60  per  cent,  of  copper.  The  addition  of  about  2 
per  cent,  of  lead  to  brass  improves  its  quality  if  it  is  to  be  used 
at  the  lathe  ; it  diminishes  its  toughness,  and  prevents  it  from 
hanging  to  the  tool  and  clogging  the  file ; but  if  intended  for 
wire,  the  presence  of  lead  must  be  avoided.  A very  small  pro- 
portion of  tin,  even  if  it  does  not  amount  to  1 part  in  200,  greatly 
increases  the  hardness  of  the  alloy.  The  ordinary  hard  solder  for 
brass  is  an  alloy  consisting  of  2 parts  of  brass  and  1 of  zinc.  Brass 
is  usually  made  by  melting  granulated  copper  in  crucibles  with 
rather  more  than  half  its  weight  of  zinc : formerly  a mixture  of 
calamine  and  charcoal  was  substituted  wholly  or  partially  for 
metallic  zinc.  At  Swansea,  the  Muntz  metal  is  prepared  by 
melting  the  two  metals  in  a reverberatory  furnace,  which  enables 
a large  quantity  of  the  alloy  to  be  prepared  with  ra})idity : but 
the  process  is  attended  wdtli  a considerable  waste  of  zinc. 

Gredge’s  and  Aich’s  alloys  consist  of  a mixture  of  cop})er,  zinc, 
and  iron,  which  can  be  forged,  cast,  rolled,  or  drawn  into  wire  ; 
100  parts  of  the  best  description  of  Gedge’s  alloy  contain — cop})er 
60  parts,  zinc  38'2,  and  iron  1'8  part.  It  is  very  hard,  and 
appears  to  be  well  adapted  to  the  sheathing  of  shi})s.  It  accjuires 
great  stiffiiess  and  elasticity  if  worked  cold,  but  may  be  softened 
by  annealing.  Another  alloy  of  a similar  kind,  termed  sterro- 


616 


OXIDES  OF  COPPER. 


metal^  consists  of  copper  55 -Oi,  zinc  42'36,  iron  1*77,  and  tin 
0‘83  parts. 

(875)  Oxides  of  Copper. — There  are  two  salifiable  oxides 
of  copper,  both  of  which  are  found  in  the  native  state ; viz., 
the  red  oxide  or  siiboxide  (On^O),  and  the  black  oxide  (OnO), 
which  is  the  basis  of  the  ordinary  salts  of  the  metal.  Eose  has 
lately  pointed  out  the  existence  of  a still  lower  oxide,  which  he 
terms  a qtcadrantoxide  ■0n4O-,,'rH2O),  which  is  only  known  as  a 
green  hydrate  of  extreme  oxidability,  obtained  by  digesting  a 
salt  of  copper  in  closed  vessels  for  21:  hours  with  an  excess  of 
stannous  chloride  dissolved  in  a large  excess  of  caustic  potash. 
Some  indications  have  been  obtained  of  the  existence  of  a still 
higher  oxide  than  -GuO,  probably  Gu^Oj,. 

Suboxide  of  Copqm^  or  Cujoreous  Oxide  (Gu,0  = 11:3,  or  Cu^O 
= 71*5  ; Sp.  Gr.  5*75 ; Comp,  in  100  parts.,  Gai,  88*8  ; G,  11*2). 
— This  compound  occurs  native,  crystallized  either  in  the  octo- 
hedron,  or  in  some  of  its  derived  forms,  or  else  in  capillary  crystals 
or  in  lamellar  masses.  There  are  various  ways  of  obtainin;^  this 
oxide  artificially ; one  of  the  best  consists  in  boiling  the  dibasic 
acetate  of  copper  with  sugar ; the  oxide  of  copper  contained  in 
the  salt  is  thus  deprived  of  half  its  oxygen,  and  the  red  oxide  is 
deposited  in  small  octohedra.  It  may  also  be  procured  by  ignit- 
ing 5 parts  of  powdered  black  oxide  of  copper  with  4 parts  of 
copper  filings,  in  a covered  crucible.  The  red  oxide  fuses  at  a 
full  red  heat.  By  decomposing  cupreous  chloride  with  hydrate 
of  potash  it  is  obtained  as  an  orange-yellow  hydrate  (4  Gu^O,  II2G  ; 
Mitscherlich).  In  this  condition  it  is  readily  attacked  by  acids. 
A cupreous  sulphate  as  well  as  carbonate  and  acetate  appear  to 
exist.  The  cupreous  salts  are  unstable,  and  absorb  oxygen  readily. 
Some  of  its  double  salts  are  more  stable  : a sulphite  of  copper  and 
potassium  (Gu^SGg,  2 K2SG3 ; Muspratt)  may  be  obtained  as  a yel- 
low insoluble  precipitate,  by  mixing  solutions  of  normal  or  of 
acid-sulphite  of  potassium  with  cupric  sulphate ; in  this  case,  the 
cupric  salt  is  reduced  to  the  state  of  cupreous  salt  by  the  sul- 
phite. 

Bed  oxide  of  copper  is  soluble  to  some  extent  in  metallic 
copper,  which  it  renders,  in  technical  terms,  dry.,  or  brittle. 
Abel  found  as  much  as  4*6  of  the  suboxide  in  a specimen  of  very 
dry  copper  which  he  examined.* 

* Abel  has  contrived  a method  of  determining  the  amount  of  oxide  in  the  metal, 
founded  upon  the  fact  that  suboxide  of  copper  decomposes  the  neutral  nitrate  of 
silver,  furnishing  an  insoluble  basic  nitrate  of  copper,  ■GU.2O  + 2 AgN03  = 2 Ag-f -tru 
2NO?,-GuO.  This  basic  salt  is  soluble  in  dilute  sulphuric  acid  ; -Gu  2 NO3,  GuO  + 
2 H2S04  = 2 HXO3  + H2O  + 2 GUSG4.  The  plan  consists  in  digesting  500  or  600 
grains  of  the  copper  for  trial  in  a solution  of  400  grains  of  neutral  nitrate  of  silver 
in  the  cold,  for  three  or  four  hours.  The  uudissolved  portion  of  copper  is  removed, 
washed  into  the  solution  of  silver,  dried,  and  weighed.  The  mixture  of  precipitated 
silver  and  insoluble  basic  nitrate  of  copper  is  separated  by  decantation  from  the  solu- 
tion, then  washed,  and  digested  for  half-an-hour  with  a known  quantity  of  standard 
sulphuric  acid,  being  frequently  agitated  with  it.  It  is  filtered,  and  the  washings 
neutralized  by  carbonate  of  soda.  The  proportion  of  acid  neutralized  by  the  basic 
nitrate  of  copper  fiarnishes  the  means  of  estimating  the  quantity  of  suboxide  of 
copper;  80  grains  of  SO3  being  equivalent  to  16  grains  of  oxygen  in  the  sample,  or 
to  143  of  suboxide  of  copper. 


BLACK  OXIDE  OF  COPPER. 


617 


The  anhydrous  suboxide  is  resolved  by  most  of  the  stronger 
acids  into  a cupric  salt,  and  into  metallic  copper,  l^^’itric  acid 
converts  it  into  cupric  nitrate : hydrochloric  acid  converts  it  into 
the  cupreous  chloride,  which  is  soluble  in  the  excess  of  the  acid. 
Hydrated  cupreous  oxide  is  soluble  in  a solution  of  ammonia, 
forming  with  it  a colourless  liquid.  This  solution  is  an  extremely 
delicate  test  of  the  presence  of  oxygen  in  a gaseous  mixture ; a 
mere  trace  of  oxygen  causes  it  to  assume  a blue  tint  from  the 
formation  of  the  black  oxide  of  copper,  which  when  dissolved  in 
a solution  of  ammonia  has  an  intense  blue  colour.  The  principal 
employment  of  'suboxide  of  copper  is  in  the  manufacture  of 
stained  glass,  to  which  it  imparts  a beautiful  ruby  or  purple 
colour. 

(876)  Cujpric  oxide^  or  hlaclc  oxide  of  copper  (OuO=79*5  or, 
CuO=39-7);  Sp.  Gr.  6*5:  Comp,  in  100  parts^  Hu,  79*85;  O, 
20*15. — This  oxide  is  a compound  of  considerable  importance  to 
the  chemist.  It  is  employed  largely  as  a means  of  furnishing 
oxygen  to  organic  substances  in  the  regulated  combustion  by 
means  of  which  their  composition  is  determined.  The  best  pro- 
cess for  obtaining  the  black  oxide  of  copper  consists  in  dissolving 
copper  in  pure  nitric  acid,  and  decomposing  the  resulting  nitrate 
in  an  earthen  crucible,  by  the  application  of  a red  heat:  the 
water  and  the  nitric  acid  are  thus  expelled,  and  the  black  oxide 
remains  in  a state  of  purity : the  heat  should  be  long  continued, 
but  not  too  violent ; otherwise  the  oxide  sinters  together  and 
concretes  into  hard  ixiasses,  which  are  pulverized  with  difficulty. 
A very  pure  oxide  is  also  furnished  by  the  decomposition  of  the 
carbonate  by  heat;  or  still  more  simply  by  heating  a plate  of 
copper  to  redness  in  a brisk  current  of  air,  and  suddenly  quench- 
ing it  in  water,  in  which  case  the  oxide  separates  in  black  scales. 
It  may  be  obtained  as  a hydrate  of  a light  blue  colour  (Hu0,Il20), 
from  any  of  its  salts,  by  the  addition  of  a slight  excess  of  hydrate 
of  potash,  washing  quickly  with  cold  water,  and  drying  at  ordi- 
nary temperatures  : when  boiled  with  water  it  becomes  black  and 
anhydrous.  This  hydrate  is  soluble  in  an  excess  of  a solution 
of  ammonia,  forming  a liquid  with  a splendid  blue  colour  ; if  slips 
of  metallic  copper  be  introduced  into  a bottle  which  is  tilled  with 
this  liquid,  and  closed  so  as  completely  to  exclude  the  air,  a por- 
tion of  the  metal  equal  to  that  already  in  solution  is  dissolved, 
the  metal  deriving  oxygen  from  the  oxide  already  in  solution, 
both  portions  being  thus  reduced  to  the  state  of  cupreous  oxide ; 
Ou  -f  HuO^Ou^O ; the  colour  gradually  disappears,  since  cupreous 
oxide  produces  a colourless  solution  with  ammonia ; but  tlie 
moment  that  air  is  admitted,  the  blue  colour  is  reproduced. 
Black  oxide  of  copper  is  soluble  in  oils  and  fats,  so  that  greasy 
matters  boiled  in  a copper  saucepan  which  is  not  kept  bright  are 
liable  to  become  impregnated  with  the  metal.  Oxide  of  cop])er 
combines  with  glass,  and  gives  it  a beautiful  green  colour.  The 
oxide  is  hygroscopic,  particularly  if  in  a finely  divided  state,  and 
it  absorbs  water  rapidly  from  the  air.  Its  oxygen  cannot  be 
expelled  from  it  by  mere  exposure  to  heat,  but  if  the  oxide  be 


618 


HYDRIDE,  NITRIDE,  AND  SULPHIDES  OF  COPPER. 


plunged  into  an  atmosphere  of  hydrogen  while  warm,  it  is  decom- 
posed with  evolution  of  light  and  heat,  while  water  is  formed. 
Illack  oxide  of  copper  is  soluble  in  most  of  the  acids,  and  com- 
bines with  them  to  form  salts  which  have  a green  or  a blue 
colour.  When  fused  with  hydrate  of  potash  or  of  soda,  the  oxide 
of  copper  combines  with  the  alkali,  forming  a greenish-blue  mass, 
which  is  decomposed  by  the  addition  of  water. 

Thenard  obtained  a combination  of  peroxide  of  hydrogen  with 
oxide  of  copper ; it  was  of  a yellowish-brown  colom’,  and  when 
moist  quickly  underwent  decomposition  at  ordinary  temperatures. 

(877)  Hydride  of  Copper  (OuH,  or  Cu^H).— This  substance 
was  obtained  by  Wurtz,  as  a brown  hydrate,  when  hypophos- 
phorous  acid  was  mixed  with  a solution  of  sulphate  of  copper,  and 
heated  to  nearly  ldO°.  It  is  very  unstable  : when  dry,  it  is  sud- 
denly resolved  at  158°  F.,  into  hydrogen  gas  and  finely  divided 
metallic  copper.  It  takes  fire  spontaneously  in  gaseous  chlorine. 
Hydrochloric  acid  forms  with  it  cupreous  chloride,  attended  with 
a brisk  disengagement  of  hydrogen.  This  disengagement  of  hydro- 
gen gas  is  remarkable ; Brodie  explains  it  by  supposing  that  the 
hydrogen  of  the  hydride  and  that  in  the  acid  are  in  opposite  elec- 
trical or  polar  conditions,  in  consequence  of  which  they  unite  at 
the  moment  of  liberation  and  form  hydride  of  hydrogen^  or  hydi'o- 
gen  gas  ; thus  HuH  + HCl^-GuCl  + HH. 

(878)  Nitride  of  copper  (OugX)  is  obtained  by  transmitting  a 
current  of  dry  ammoniacal  gas  over  finely  powdered  black  oxide 
of  copper  heated  to  480°  ; water  and  nitrogen  gas  are  evolved,  and 
the  nitride  is  left  as  a dark-green  powder,  which  when  heated  to 
about  590°  explodes  feebly,  emitting  a red  light ; strong  acids  de- 
compose it  with  evolution  of  nitrogen  gas. 

(879)  Sulphides  of  Copper. — These  are  three  in  number: 
OugS ; OuS ; and  OuS^. 

Subsulphide  of  copper^  or  cupreous  sulphide  (■0UgS=159,  or 
Cu2S==79'5  ; sp.  gr.  5 '735 — 5 '977),  is  a soft  mineral  of  a dark-grey 
colour,  occasionally  found  native  in  masses,  but  more  often  in  six- 
sided  prisms.  It  is  easily  fused  by  heat  in  closed  vessels  ; nitric 
acid  and  aqua  regia  decompose  it  readily,  but  hydrochloric  acid 
does  not  dissolve  it.  It  may  be  formed  by  melting  together 
3 parts  of  sulphur  and  8 of  copper ; vivid  incandescence  occurs  at 
the  moment  of  combination.  It  forms  ^^fine  metal  of  the  copper 
smelter. 

Cupric  sulphide^  or  sxdphide  of  copper  (■GuS=95'5,  or  CuS= 
47' 7)  may  be  procured  by  the  direct  union  of  its  constituents  ; it 
is  also  occasionally  found  native  {sp.  gr.  3 '85)  in  flexible  plates  of 
a blue  colour.  It  may  likewise  be  obtained  in  the  form  of  a dark- 
brown  hydrate,  by  decomposing  any  of  the  salts  of  copper  by  a 
stream  of  sulphuretted  hydi’ogen ; this  hydrate  is  quickly  oxidized 
by  exposure  to  the  air,  becoming  converted  into  sulphate  of  cop- 
per, and  it  is  dissolved  easily  by  nitric  acid  and  by  aqua  regia. 
Sulphide  of  copper  is  insoluble  in  a solution  of  sulphide  of  potas- 
sium, but  it  is  soluble  in  one  of  bisulphide  of  ammonium. 

The  copper  pyrites  {sp.  gr.  4'3)  or  ordinary  ore  of  copper,  con- 


PHOSPHIDE  OF  COPPEK. 


619 


sists  of  a double  sulphide  of  copper  and  iron  OuFeS^,  or  Cu^S, 
Fe^Sg.  It  is  of  a yellow  colour,  and  has  a brassy  lustre : it  is 
sometimes  found  crystallized  in  tetrahedra,  but  it  usually  occurs 
in  amorphous  masses,  wdth  a conch  oidal  granular  fracture,  and  is 
less  hard  than  iron  pyrites.  The  variety  called  variegated  or 
peacock  ore  contains  a larger  proportion  of  sulphide  of  copper. 
These  compounds  are  rapidly  oxidized  and  dissolved  by  nitric  acid 
or  by  aqua  regia,  but  not  by  hydrochloric  acid. 

All  the  sulphides  of  copper  are  decomposed  by  roasting  them 
in  air ; if  the  temperature  be  high,  sulphurous  anhydride  escapes, 
and  oxide  of  copper  remains  behind ; at  a lower  temperature,  sul- 
phate of  copper  is  formed. 

Sulphide  of  copper  forms  likewise  a natural  combination  with 
sulphides  of  lead,  silver,  antimony,  and  arsenic,  constituting  grey 
copper  ore,  or  .*  this  mineral  is  essentially  a quadribasic 

sulphantimonite  and  sulpharsenite  of  copper  and  iron ; it  varies 
considerably  in  the  relative  proportions  of  its  constituents,  and 
often  contains  zinc,  lead,  silver,  and  mercury.  It  crystallizes  in 
forms  derived  from  the  regular  tetrahedron,  and  in  composition  it 
corresponds  to  the  general  formula  (4  MS,  4 M^S, 
wdiich  M represents  the  electro-positive  metals,  M^S  being  usually 
subsulphide  of  copper  or  subsulphide  of  silver : whilst  N indicates 
the  electro-negative  metals,  arsenic  or  antimony.  The  principal 
varieties  of  the  ore  are : — I.  Tennamiite  (FeS,  3 OuS, As^Sg . 4 Ou^S, 
ASjSj ; sp.  gr.  4*375),  a sulpharsenite  of  copper  and  iron,  of  a 
leaden-grey  colour ; the  copper  in  this  ore  amounts  to  about  48 
jier  cent.  2.  Light-grey  copper  ore  {sp.  gr.  4*5  to  4*7),  a mixture 
of  sulpharsenite  and  sulphantimonite  of  zinc,  iron,  copper,  and 
silver:  colour,  steel-grey.  3.  Dark-grey  copper  ore  {sp.  gr.  4*7 
to  4*9)  contains  little  or  no  arsenic ; it  is  of  an  iron-black  colour. 
This  variety  and  the  one  preceding  it  contain  from  35  to  40  per 
cent,  of  copper.  4.  Sil/cer  fahlerz  (sp.  gr.  about  5*0),  is  a dark- 
grey  copper  ore,  rich  in  silver.  The  silver  varies  in  this  ore  from 
13  to  30  per  cent.,  and  the  copper  from  14  to  25  per  cent. 

1l\\q pentasulphide  of  copper  (OuS,)  was  obtained  by  Berzelius 
in  the  form  of  a blackish-brown  precipitate,  by  decomposing  a salt 
of  copper  with  a pentasulphide  of  one  of  the  metals  of  the  alka- 
lies. It  undergoes  no  change  by  washing  when  exposed  to  tlie  air, 
but  it  is  completely  soluble  in  a solution  of  carbonate  of  potassium. 

A native  selenide  of  copper  is  found  in  combination  with  sele- 
nide  of  silver.  It  occurs  in  masses  of  a leaden-grey  colour,  and 
is  very  rare,  having  hitherto  been  found  only  in  Sweden  : selenide 
of  copper  may  be  formed  artificially  by  precipitating  the  sulphate 
of  copper  by  seleniuretted  hydrogen. 

(880)  Phosphide  of  copper  (OugF^  ?). — This  compound  is  easily 
obtained  by  boiling  pliosphorus  in  a solution  of  sulpliate  of  copper  ; 
the  liquid  speedily  becomes  decolorized,  and  a black  phosphide  of 
copper,  with  a semi-metallic  lustre,  is  formed.  It  is  not  soluble 
in  hydrochloric  acid,  but  if  thrown  into  a solution  of  cyanide  of 
potassium  is  rapidly  decomposed  without  the  a})plication  of  heat, 
bubbles  of  self-lighting  phosphuretted  hydrogen  being  disengaged. 


620 


CHLORIDES  OF  COPPER. 


Abel  prepares  phosphide  of  copper  by  transmitting  the  vapour  of 
phosphorus  over  finely  divided  copper  heated  in  a tube  ; he  find^ 
that  this  phosphide  when  mixed  with  chlorate  of  potassium  and 
gunpowder  furnishes  a powder  of  sufficient  conducting  power  for 
electricity,  and  at  the  same  time  possessed  of  the  recpiisite  in- 
flammability to  enable  it  to  be  employed  with  great  advantage 
as  a detonating  fuse  for  firing  ordnance  by  magneto-electric  cur- 
rents. 

(881)  Chlorides  of  Copper. — Copper  forms  two  chlorides, 
OuCl,  and  OiiCl,. 

Suhchloride  of  co])per^  or  cupreous  chloride  (Ou2Cl2  = 198,  or 
Cu^Cl^OO  ; sp.  gr.  3 '3 76)  is  obtained  by  distilling  copper  filings 
with  twice  their  weight  of  corrosive  sublimate ; or  by  dissolving 
4 parts  of  finely  divided  copper  and  5 of  the  black  oxide  in  hydro- 
chloric acid ; or  by  boiling  cupric  chloride  with  sugar ; or  by 
digesting  cupric  chloride  in  closed  vessels  with  metallic  copper : 
the  last  is  a slow  process,  but  part  of  the  cupreous  chloride  is  then 
deposited  in  transparent  tetrahedra.  Cupreous  chloride  is  a white 
compound,  which  fuses  easily  into  a yellowish  mass.  It  is  inso- 
luble in  water,  but  soluble  to  some  extent  in  strong  hydrochloric 
acid,  witli  which  it  forms  a pale-brown  solution,  which  deposits 
most  of  the  subchloride  on  dilution.  The  solution  of  cupreous 
chloride  in  hydrochloric  acid  absorbs  carbonic  oxide  gas  with 
facility  : a compound  crystallizing  in  pearly  scales  (4-0U2Cl2,3  OO-, 
7 HjO  ? ; Berthelot)  may  thus  be  obtained  ; it  is  insoluble  in 
water,  which  however  decomposes  it,  setting  subchloride  of  copper 
at  liberty  : it  is  also  quickly  decomposed  by  exposure  to  the  air. 
Cupreous  ehloride  is  soluble  in  a boiling  solution  of  chloride  of 
potassium  ; and  if  the  liquid  be  allowed  to  cool  excluded  from  the 
air,  octohedral  crystals,  composed  of  (4  KC1,-0U2C1„),  are  deposited. 
When  the  solution  in  hydrochloric  acid  is  exposed  to  the  air,  it 
absorbs  oxygen  rapidly,  and  a pale  bluish-green  insoluble  oxychlo- 
ride of  copper  (OuCl^,  3 -GuO,  4 H^O)  is  deposited.  This  oxy- 
chloride is  used  in  the  arts  as  a pigment,  under  the  name  of 
Brunswick  green.  It  is  best  procured  by  exposing  copper  clip- 
pings to  the  action  of  hydrochloric  acid,  or  to  a solution  of  sal 
ammoniac  in  the  open  air.  It  occurs  native  in  the  form  of  a green 
sand  (sp.  gr.  4*4),  composed  of  small  rhombic  prisms,  which  is 
found  at  Atacama  in  Peru ; it  has  hence  been  called  atacamite. 
Sometimes  it  is  also  found  massive.  Other  oxychlorides  of  copper 
of  less  importance  may  also  be  formed.  When  finely  divided 
copper  is  boiled  in  a solution  of  sal  ammoniac,  ammoniacal  gas  is 
expelled,  and  a salt  is  formed  which  is  gradually  deposited  in  white 
rhombic  dodecahedra,  (IlgGuX^)'^!!'^!^ : it  may  be  regarded  as 
subchloride  of  copper  in  which  the  second  atom  of  copper  has  been 
displaced  by  cuprodiammoniuni  A solution  of  this 

salt,  when  exposed  to  the  air,  deposits  blue  crystals  consisting  of 
[(HgGu]N’2)'-0u'Cl2,  (IIg0ulN’2)"Cl2,Il20],  and  the  mother-liquor  on 
further  exposure  yields  cubic  crystals  of  the  salt  (HeOuX^Cb, 
2 H,NC1). 

(882)  Chloride  of  copper.^  or  cupric  chloride  (OuClj^  134-5,  or 


BROMroES  AXD  IODIDES  OF  COPPER. 


621 


CnCl=6T'2;  sjp.  gr.  3-054)  may  be  obtained  by  the  spontaneous 
combustion  of  copper  in  chlorine,  but  it  is  more  advantageously 
prepared  by  dissolving  the  oxide  or  the  carbonate  in  hydrochloric 
acid,  when  on  evaporation  it  crystallizes  in  green  needles,  with 
the  formula  (OuCl^,  2 H2O)  of  sp.  gr.  2-534.  A concentrated  solu- 
tion of  chloride  of  copper  is  of  a green  colour,  but  it  becomes  blue 
on  dilution,  and  when  the  salt  is  anhydrous  it  is  liver-coloured. 
When  heated  it  fuses,  and  at  a red  heat  half  its  chlorine  is  expelled, 
and  cupreous  chloride  remains.  It  forms  double  chlorides  with 
the  chlorides  of  jiotassium  and  ammonium.  Cupric  chloride  is  deli- 
quescent, and  very  soluble  in  alcohol.  This  solution  burns  with 
a splendid  green  flame.  (See  Fig.  80,  'No.  5 ; Part  I.,  p.  144.) 

A double  chloride  of  copper  and  ammonium  (2  Il4NCl,OuCl2. 
2 II2O)  is  obtained  in  blue  square-based  octohedra,  by  mixing  hot 
concentrated  solutions  of  the  two  salts  in  the  proportion  of  one 
equivalent  of  each.  Another  double  chloride  (H4lICl,-0uCl2 . 
2 II2O)  is  obtained  in  flne  bluish-green  crystals,  by  evaporating 
a solution  of  1 equivalent  of  sal  ammoniac  and  2 equivalents  of 
chloride  of  copper. 

Anhydrous  chloride  of  copper  absorbs  ammonia  rapidly,  and 
forms  a blue  powder  (-0uCl2,6  HgISr ; Pose),  which  by  a heat  of 
300°  loses  4 equivalents  of  ammonia,  and  becomes  green  (OuCl^, 
2 HgP  ; Kane).  Graham  and  Kane  regard  this  latter  compound 
as  chloride  of  ammonium,  in  which  the  fourth  equivalent  of  hy- 
drogen has  its  place  occupied  by  copper ; hence  Graham  terms  it 
chloride  of  cuprammonium  (CuHgKCl)  or  rather 
If  ammoniacal  gas  be  transmitted  through  a hot  concentrated 
solution  of  chloride  of  copper,  till  the  precipitate  at  first  formed  is 
redissolved,  the  liquid  on  cooling  deposits  small  dark-blue,  square 
prisms  and  octohedra,  [IIg-0u'']N2Cl2,(Il4K)2O]. 

It  appears,  therefore,  that  the  following  well-deflned  com- 
pounds may  be  obtained  by  the  reaction  of  the  chlorides  of  copper 
upon  ammonia  or  muriate  of  ammonia  : — 


(2.)  j 

(3.)  (II.eu"N,)"Cl„4  H,N 

(i.-)  (H.Gu"N,)ci„  (rr.]sr),e 

(5.)  (H,Gu"N,)"Cl, 

(6.)  (I-I.eu"N,)"Cl„2  H.NCl 
(7.)  2 H4KCl,eu''Cl2,2  li^e 
(8.)  ii4]s[ci,eib'ci2,2  ii^e 

(883)  Cupreous  bromide.,  OiqBr^,  or  sub-bromide  of  copper 
(CUjBr),  is  insoluble  in  water.  Cupric  bromide  (OuBr^)  is  soluble. 

Cupreous  iodide,  or  subiodide  of  copper  (O1I2I2II2G,  or  Ciql, 
HO),  is  a white  insoluble  powder,  which  becomes  yellow  when 
heated.  It  is  formed  by  pouring  a mixture  of  I equivalent  of  fer- 
rous sulphate,  and  1 of  sulphate  of  copper  into  a solution  of  any 
iodide ; thus  2 GuSO^  + 2 FeSO^ -f- 2 KI^K^SO^-f  Fe23  SO^-f-Oiq 


622 


SULPHATES  OF  COPPER. 


Ij.  Sulphite  of  sodium  may  be  substituted  for  the  sulphate  of 
iron  in  this  experiment.  It  has  been  proposed  to  employ  such  a 
mixture  of  the  two  sulphates  of  iron  and  copper  as  a test  for 
determining  the  quantity  of  iodine  in  kelp,  in  order  to  fix  its 
commercial  value.  Ctijpric  iodide  (Oulg),  if  it  exists,  is  very 
unstable. 

Sulphates  of  Copper. — Copper  forms  a normal  sulphate,  and 
several  basic  sulphates. 

(884)  Sulphate  of  copper^  Blue  vitriol^  or  Cupric  sulphate 
(OuSO^,  5 H„0=159'5  + 90,  or  Cu0,S03,  5 Aq  =79'T+I:5) ; Sp. 
Gr.  anhydrous^  3’631,  crystallized.^  2‘25I : Comp,  in  parts  of 
crystallized  salt.,  OiiO,  31’85  ; SO3,  32*07  ; H^O,  36*08.  — This 
salt  is  manufactured  on  a large  scale,  by  boiling  copper  in  an  iron 
pot  with  sulphuric  acid,  diluted  with  half  its  bulk  of  water  : the 
acid  is  decomposed,  and  the  copper  is  oxidized  at  its  expense 
whilst  the  salt  is  precipitated.  It  may  also  be  formed  from  an 
artificial  sulphide  of  copper,  by  roasting  it  with  free  access  of  air, 
and  lixiviating  the  roasted  mass  to  dissolve  the  sulphate  thus 
produced:  the  heat  must  be  moderate,  or  else  the  sulphate  will 
be  decomposed  during  the  roasting.  If  copper  pyrites  be  used 
instead  of  the  artificial  sulphide,  the  salt  will  contain  a large 
quantity  of  sulphate  of  iron,  which  cannot  be  separated  by  crys- 
tallization ; for  although  the  sulphate  of  copper  does  not  crystal- 
lize alone  vnth  more  than  5 H^O,  yet  when  mixed  with  sulphate 
of  iron,  it,  like  this  salt,  assumes  7 H^O,  and  then  is  isomorphous 
with  the  ferrous  salt.  The  only  plan  in  such  a case  is  to  ignite 
the  mixed  sulphates  feebly : the  salt  of  iron  parts  with  its  acid  at 
a lower  temperature  than  the  copper  salt,  and  by  a second  solution 
the  iron  is  separated  in  the  form  of  an  insoluble  oxide.  Sulphate 
of  copper  is  also  obtained  in  considerable  quantity  as  a secondary 
product  in  the  refining  of  silver  (917) : the  silver  is  precipitated 
from  the  solution  of  its  sulphate  in  the  metallic  form,  by  plates  of 
copper,  and  a pure  sulphate  of  copper  is  thus  furnished. 

Large  quantities  of  the  sulphate  of  copper  are  used  in  calico- 
printing,  and  it  is  the  salt  from  which  most  of  the  pigments  of 
copper  are  formed.  It  is  soluble  in  four  times  its  weight  of 
water  at  60°,  and  crystallizes  in  beautiful  blue  crystals  of  the 
doubly  oblique  rhombic  form.  The  powdered  crystals  absorb 
hydrochloric  acid  gas  rapidly  with  evolution  of  heat,  and  fur- 
nish a deliquescent  mass,  ^hen  sulphate  of  copper  is  heated  to 
212°  it  loses  4 H„0,  and  by  a temperature  of  400°  the  salt  is 
rendered  anhydrous : it  then  assumes  the  appearance  of  a white 
powder,  which  becomes  blue  on  the  addition  of  water.  The  act 
of  combination  with  water  is  attended  with  a hissing  noise,  owing 
to  the  great  rise  of  temperature  which  attends  the  action ; a con- 
siderable evolution  of  heat  also  attends  the  combination  of  the 
compound  -01180^,1130,  with  water.  Sulphate  of  copper  is  insol- 
uble in  alcohol.  When  heated  to  bright  redness  the  elements  of 
sulphuric  anhydride  are  expelled,  and  black  oxide  of  copper  is 
left. 

Sulphate  of  copper  fonns  double  sulphates  both  with  potas- 


NITRATES  AND  CARBONATES  OF  COPPER. 


623 


Slum  and  with  ammonium ; they  are  easily  obtained  by  mixing 
solutions  of  the  salts  in  equivalent  proportions,  and  allowing 
them  to  crystallize.  The  potassium  salt  is  composed  of  (^uSO^, 
H^O ; sp.  gr.  2*244) ; the  ammonium  salt  of  (OuSO„ 
6 sp.  gr.  1*891).  According  to  Graham  a 

hot  saturated  solution  of  double  sulphate  of  copper  and  potas- 
sium deposits  a remarkable  double  salt,  the  composition  of  which 
may  be  represented  by  the  formula  (K2SO^,3-0uSO4,  OuO,4  H^O). 

Basic  Sulphates. — If  a solution  of  1 equivalent  of  sulphate  of 
copper  is  boiled  wdth  less  than  1 equivalent  of  hydrated  oxide  of 
copper,  a green  insoluble  tribasic  sulphate  [GuS04,2  (-GuO,  142^)] 
is  formed.  Brochantite  is  a native  basic  sulphate  of  the  metal, 
composed  of  [GuSO^,  3 (GuO,  H2^)]  5 Denham  Smith  ob- 
tained another  basic  sulphate  consisting  of  (GuSO^,!  GuO,  6 H^O.) 

Anhydrous  sulphate  of  copper  absorbs  dry  ammoniacal  gas ; 
the  compound  consists  of  (GuSO^,  5 liJS ; II.  Rose).  If  am- 
monia be  added  in  excess  to  a solution  of  sulphate  of  copper,  the 
liquid  on  evaporation  yields  dark  blue  crystals  (GuSO^,  4 HjlSr, 
H^O ; Berzelius) ; the  salt,  when  heated  to  300°,  becomes  green, 
losing  two  atoms  of  ammonia  and  one  atom  of  water. 

(885)  Nitrate  of  copper  (Gu  2 R03,6  H^G)  is  easily  made  by 

dissolving  copper  in  nitric  acid : it  forms  a beautiful  blue  deli- 
quescent salt,  which  crystallizes  in  rhomboidal  prisms.  At  tem- 
peratures above  60°  it  crystallizes  with  3 in  deliquescent 

needles  of  sp.  gr.  2*047.  It  is  very  soluble  in  alcohol ; by  heat  it 
is  decomposed,  first  into  a green  basic  nitrate  [Gu  2 RO3,  3(GuG, 
II2O) ; Gerhardt],  which  is  insoluble  ; and  if  the  heat  be  increased, 
it  is  converted  w*hol]y  into  the  black  oxide  of  copper,  the  whole 
of  the  nitric  anhydride  being  expelled.  It  is  this  basic  nitrate 
which  is  formed  when  oxide  of  copper  is  heated  with  monohy- 
drated  nitric  acid,  although  the  acid  may  be  in  considerable  ex- 
cess. If  a few  crystals  of  nitrate  of  copper  are  moistened  and 
wrapped  up  in  tinfoil  they  act  violently  upon  the  metal  and  con- 
vert it  rapidly  into  peroxide  of  tin  with  emission  of  sparks. 

Several  basic  phosphates  of  copper  are  found  native  in  small 
quantities. 

(886)  Carbonates  of  Copper. — All  attempts  to  procure  the 
neutral  carbonate  of  copper  have  hitherto  failed.  A hydrated 
oxy carbonate^  called  chessylite  [GuO,H2G,  2 GuGOg,  or  CuO,IIO, 
2 (Cu0,C02) ; sp.  gr.  3*8],  forms  a beautiful  blue  mineral,  which 
crystallizes  in  oblique  rhombic  prisms.  But  the  most  abundant 
of  the  carbonates  of  copper  is  the  hydrated  dibasic  carbonate,  or 
malachite  (Gue,Il3e,GuGe3,  or  Cu0,II(),Cu(),C03 ; sp.  gr.  3*7 
to  4*0).  It  forms  a very  hard  mineral  of  a silky  lustre,  and  a 
beautiful  green  colour  ; it  is  susceptiljle  of  a high  polish,  l)y  which 
its  concentric  and  often  beautifully  veined  structure  is  advantage- 
ously displayed.  It  is  often  employed  for  ornamental  purposes. 
Malachite  is  occasionally  found  in  oblique  prisms.  Both  the  blue 
and  the  green  carbonate  are  abundant  in  the  copper  ore  furnished 
from  Australia.  A green  precipitate,  sometimes  used  as  a pig- 
ment, which  has  the  same  composition  as  malachite,  and  is  known 


624 


CIIAEACTERS  OF  THE  SALTS  OF  COPPER. 


as  mineral  green^  may  be  obtained  by  mixing  hot  solutions  of  snl- 
pliate  or  nitrate  of  copper  and  carbonate  of  sodium.  If  the  so- 
lutions be  mixed  cold,  a pale  blue  voluminous  precipitate  is 
formed,  wbicli,  according  to  Brunner,  is  tlie  same  compound,  with 
an  additional  atom  of  water  (OiiO,  2 H20,-0u-0O3).  By  boiling 
the  precipitated  carbonate,  it  becomes  first  green  and  then  black, 
losing  nearly  all  its  water  and  carbonic  acid.  A double  carbonate 
of  potassium  and  copper  (K^OOg,  4 OnOG-g,  OuO,  10  H^O)  may 
be  obtained  by  digesting  the  green  carbonate  in  a solution  of  the 
acid-carbonate  of  potassium  : it  is  deposited  in  blue  crystals  by 
spontaneous  evaporation.  Similar  salts  may  be  formed  with  so- 
dium and  ammonium. 

(887)  Characters  of  the  Salts  of  Copper. — 1.  Salts  of  the 
suboxide ^ or  Gujpreons  salts. — Hearly  all  of  them  are  insoluble  in 
water,  but  soluble  in  hydrochloric  acid ; in  this  form  they  absorb 
oxygen  rapidly,  and  are  converted  into  salts  of  the  black  oxide. 
They  are  unimportant,  and  have  been  but  little  studied ; one  of 
their  most  remarkable  properties  is  their  power  when  in  solution 
in  hydrochloric  acid  of  absorbing  carbonic  oxide,  with  which  they 
form  a crystalline  compound. 

2.  Salts  of  the  blach  oxide^  or  Gujprie  salts. — Most  of  these 
salts  of  copper  have  a green  or  a blue  colour  when  hydrated,  but 
they  are  white  when  anhydrous  ; they  are  almost  all  soluble. 
They  have  a strong,  disagreeable  metallic  taste,  and  act  as  poisons 
to  the  animal  frame,  producing  violent  and  irrepressible  vomiting 
and  purging,  followed  by  exhaustion  and  death.  They  form  an 
insoluble  compound  with  albumen,  wdiich  is  nearly  inert ; raw 
whites  of  eggs  should  therefore  be  administered  in  cases  of  poi- 
soning suspected  to  be  occasioned  by  this  metal.  Milk  or  sugar 
mixed  with  iron  filings,  by  reducing  the  salts  of  the  black  oxide 
of  copper  to  salts  of  the  suboxide,  or  to  the  metallic  state,  are 
also  valuable  adjuncts. 

The  salts  of  the  black  oxide  of  copper  are  easily  recognised 
when  in  solution:  though  neutral  in  composition  they  redden 
litmus.  Hydrates  of  jpotash  and  soda  give  in  their  solutions  a 
pale  blue  voluminous  precipitate  of  hydrated  basic  salt ; an  excess 
of  the  alkali  does  not  dissolve  it,  but  converts  it  into  a blue  hy- 
drated oxide,  which  becomes  black  and  anhydrous  when  the  liquid 
is  boiled  with  it.  If  sugar  or  tartaric  acid,  or  certain  other  or- 
ganic substances,  be  present,  the  blue  precipitate  is  redissolved 
by  an  excess  of  the  alkaline  liquid,  and  forms  a blue  solution. 
Ammonia  gives  a similar  blue  precipitate,  but  an  excess  of  the 
alkali  redissolves  it,  forming  a deep  blue  solution,  which  is  very 
characteristic.  The  carbonates  of  potassium  and  sodium  give  a 
pale  blue  hydrated  basic  carbonate,  which  becomes  gradually  con- 
verted into  the  black  oxide  when  boiled  in  the  liquid  with  excess 
of  the  alkaline  carbonate.  GoHonate  of  ammonium  also  gives  a 
blue  precipitate,  but  redissolves  it  if  added  in  excess,  forming  an 
intensely  blue  solution.  Ferrocyanide  of  potassmm  yields  a 
bulky  brown  precipitate,  insoluble  in  hydrochloric  acid,  but  sol- 
uble in  ammonia,  which  leaves  it  unaltered  on  evaporation.  Sul- 


ESTIMATION  OF  COPPER. 


625 


pJiuretted  hydrogen  gives  even  in  acid  solutions  a brownish-black 
hydrated  sulphide.  The  last  two  characters  distinguish  the  salts 
oi*  copxjer  from  those  of  nickel,  which  also  form  a blue  solution 
with  ammonia.  Sulphide  of  copper  is  almost  insoluble  in  am- 
monia, and  in  sulphide  of  ammonium,  but  is  dissolved  by  cyanide 
of  potassium.  Another  characteristic  and  very  delicate  test  of 
the  presence  of  copper  is  afforded  by  the  action  of  a polished 
plate  of  iron^  which,  in  a feebly  acid  solution,  is  speedily  covered 
with  a red  deposit  of  metallic  copper.  Zinc  precipitates  copper 
in  the  form  of  a black  powder,  which  assumes  a metallic  lustre 
under  the  burnisher.  If  a salt  of  copper  be  heated  with  car- 
bonate of  sodium  on  charcoal  hefore  the  blowpipe  in  the  reducing 
flame,  a bead  of  metallic  copper  may  be  obtained,  and  may  be 
recognised  by  its  colour  and  its  malleability.  Most  copper  salts 
when  heated  on  platinum  wire  communicate  an  intense  green 
colour  to  the  oxidizing  flame. 

In  cases  in  which  the  presence  of  copper  is  suspected  in  admix- 
ture with  organic  matters,  as  in  the  contents  of  the  stomach, 
where  it  is  supposed  to  have  acted  as  a poison,  the  material  must 
be  reduced  to  dryness,  and  incinerated  in  an  earthen  crucible. 
The  asli  is  then  to  be  treated  with  nitric  acid,  and  the  liquid 
tested  with  ammonia,  with  ferrocyanide  of  potassium,  and  with  a 
steel  needle.  The  copper-coloured  deposit  on  the  steel  may  be 
further  identified  by  placing  it  in  a narrow  tube  with  a few  drops 
of  ammonia,  which  will  become  blue  in  the  course  of  24  hours  if 
copper  be  present  (Taylor). 

The  salts  of  copper  have  considerable  tendency  to  form  double 
compounds  with  other  salts,  and  frequently  basic  salts  of  this  metal 
may  be  procured  with  various  acids : those  with  the  sulphuric, 
nitric,  carbonic,  and  acetic  acids  are  the  most  important. 

(888)  Estimation  of  copper. — This  is  generally  eftected  in  the 
form  of  the  black  oxide,  100  parts  of  which  correspond  to  79 ’82 
of  the  metal.  If  the  solution  contain  no  metal  precipitable  by 
hydrate  of  potash,  an  excess  of  solution  of  potash  is  added,  and 
the  liquid  is  boiled ; the  precipitate  is  well  washed  witli  boiling 
water. 

Pelouze  {Ann.  de  Ghimie^  III.  xvi.  426)  has  described  a method 
of  estimating  the  quantity  of  copper,  by  bringing  it  into  solution 
with  excess  of  ammonia,  and  ascertaining  the  quantity  of  a standard 
solution  of  sulphide  of  sodium  which  is  required  to  decolorize  the 
liquid.  The  process  is  rapid,  and  admits  of  being  applied  in  a 
large  number  of  cases. 

A still  better  method,  according  to  E.  O.  Brown  {Q.  J.  Chem.. 
Soc.  X.  65),  consists  in  treating  the  solution  of  copper  with  one  of 
iodide  of  potassium ; subiodide  of  copper  (Ou  J^)  is  thus  formed, 
and  iodine  is  set  at  liberty : the  amount  of  the  latter  is  deter- 
mined by  a standard  solution  of  hyposulphite  of  sodium  : in  order 
to  eflect  the  o])eration  a weighed  quantity  of  tlie  ore  is  dissolved  in 
nitric  acid,  boiled  till  red  fumes  cease  to  escape,  and  the  nitrous 
acid  is  all  expelled;  it  is  then  diluted  with  water,  and  carbonate 
of  sodium  added  until  a slight  permanent  precipitate  is  formed. 

40 


626 


LEAD. 


Acetic  acid  in  excess  is  added,  and  afterwards  an  excess  of  iodide  of 
potassium  and  a few  drops  of  a solution  of  starch.  The  quantity 
of  iodine  thus  set  free  is  then  estimated  by  the  number  of  divisions 
of  a standard  solution  of  hyposulphite  of  sodium  required  to  oxidize 
the  iodine,  a point  which  admits  of  most  accurate  determination 
by  the  disappearance  of  the  blue  tinge.  The  solution  of  hypo- 
sulphite is  graduated  by  dissolving  5 grains  of  piiremopper  in 
nitric  acid,  and  subjecting  it  to  a series  of  operations  exactly  cor- 
responding to  those  performed  upon  the  ore,  noting  the  number 
of  divisions  of  the  standard  solution  consumed  in  neutralizing 
the  amount  of  iodine  set  free. 

Copper  may  be  readily  separated  from  the  metals  of  the  first 
five  groups,  with  the  exception  of  cadmium,  by  the  action  of  sul- 
phuretted hydrogen.  The  precipitated  sulphide  of  copper  must  be 
washed  with  water  containing  sulphuretted  hydrogen  in  solution, 
in  order  to  prevent  its  oxidation  on  the  filter.  The  precipitate 
must  be  detached  from  the  filter,  redissolved  in  nitric  acid  (727), 
and  the  oxide  of  copper  precipitated  by  means  of  hydrate  of 
potash. 

If  cadmium  be  present,  Stromeyer  directs  that  the  precipitate 
of  the  mixed  sulphides,  obtained  by  transmitting  sulphuretted  hy- 
drogen through  the  liquid,  be  redissolved  by  nitric  acid,  and  pre- 
cipitated by  an  excess  of  carbonate  of  ammonium,  which,  if  left  to 
stand  for  a few  hours,  dissolves  the  copper,  but  leaves  the  cadmium 
in  the  form  of  carbonate. 

The  separation  of  copper  from  bismuth  may  be  effected  by 
means  of  carbonate  of  ammonium,  as  directed  for  cadmium. 

The  other  metals  of  the  sixth  group  are  separated  by  precipi- 
tating them  with  the  copper  as  sulphides,  and  then  digesting  the 
mixed  sulphides  with  a solution  of  sulphide  of  potassium  (sulphide 
of  ammonium  dissolves  traces  of  copper) ; the  sulphide  of  copper 
alone  remains  undissolved. 

§11.  Lead:  Pb"==  207  or  Pb=103*5.  Sp.  Gr.  11*36; 

Fusing-pointy  617°. 

(889)  Almost  all  the  lead  of  commerce  is  obtained  from  galena, 
the  native  sulphide  of  lead.  It  occurs,  mixed  with  quartz,  blende, 
pyrites,  sulphate  of  barium,  and  fluor-spar,  in  veins  traversing  the 
primitive  rocks,  and  particularly  in  the  clay-slate  in  Cornwall, 
and  mountain  limestone  in  Cumberland.  Small  quantities  of  car- 
bonate and  phosphate  of  lead  are  frequently  met  with,  but  they 
are  unimportant  as  ores  of  the  metal.  Galena  always  contains  a 
small  proportion  of  sulphide  of  silver  ; wdien  the  mineral  is  found 
in  bold,  well-characterized  cubes,  it  is  usually  nearly  pure.  The 
proportion  of  silver  in  galena  is  liable  to  considerable  variation  ; 
a mineral  yielding  120  ounces  of  silver  to  the  ton,  or  0*36  per 
cent.,  is  considered  to  be  extremely  rich.  England  and  Spain 
afford  the  principal  supply  of  this  metal,  about  65,000  tons  of  lead 
being  annually  raised  in  England,  which  furnish  on  the  average 
560,000  ounces  of  silver. 


EXTE ACTION  OF  LEAD. 


627 


(890)  Extraction.  — After  the  lead  ore  has  been  raised  to  the 
surface,  it  undergoes  a careful  mechanical  preparation,  conducted 
upon  the  principles  already  explained  (529) ; and  having  been 
tiius  freed  to  a great  extent  from  its  earthy  impurities,  it  is  ready 
for  smelting. 

If  the  galena  be  tolerably  free  from  siliceous  gangue,  this 
operation  is  sufficiently  simple.  About  1|-  ton  of  the  dressed  ore 
is  mixed  with  from  a fortieth  to  a twentieth  of  its  weight  of  lime, 
and  is  heated  to  dull  redness  in  a reverberatory  furnace,  through 
which  a strong  cimrent  of  air  is  passing.  Fig.  353  exhibits  a sec- 


Fig.  353. 


tion  of  the  reducing  furnace  employed  in  Derbyshire.  A is  the 
fire-grate,  h the  bridge,  h the  hoj^per  by  which  the  charge  is  in- 
troduced ; c c,  the  bed  on  which  the  ore  is  placed,  sloping  down- 
wards towards  a gutter  in  the  centre,  by  wliich  the  melted  metal 
is  drawn  off,  d,  are  doors  for  working  the  charge  and  for  ad- 
mitting air,  the  draught  of  the  furnace  being  completely  under 
control  by  a damper  placed  in  the  flue/*. 

During  the  roasting  a large  cpiantity  of  the  sulphur  burns  off 
as  sulphurous  anhydride,  and  a portion  of  oxide  of  lead  is  formed  : 
another  portion  of  the  sulphide  of  lead  is  converted  into  sulphate 
of  lead,  and  much  of  the  ore  still  remains  undecomposed.  In  the 
course  of  the  operation,  the  mass  is  frequently  stirred,  and  care  is 
taken  not  to  allow  the  temperature  to  rise  sufficiently  high  to  fuse 
it.  When  it  is  considered  that  the  roasting  has  been  carried  far 
enough,  the  materials  on  the  bed  of  the  furnace  are  thoroughly 
mixed  together,  the  furnace  doors  are  closed,  and  the  heat  is  sud- 
denly raised.  The  oxide  and  the  sulphate  of  lead  then  react  upon 
the  undecomposed  sulphide  of  the  metal;  a large  quantity  of  sul- 
])hurous  anhydride  is  evolved,  whilst  metallic  lead  runs  co])iously 
from  the  mass.  The  successive  stages  of  this  operation  may  bo 
traced  as  follows: — 

Two  atoms  of  sulphide  of  lead,  by  combining  with  6 of  oxy- 


628 


REFINING  OF  LEAD. 


gen,  furiiisli  2 atoms  of  oxide  of  lead  and  two  of  sulphurous  anhy- 
dride, as  is  exhibited  by  the  equation  : 2 PbS-f-  3 02=2  PbO  -f 
2 SO2.  If  one  atom  of  galena  unite  with  4 atoms  of  oxygen,  1 atom 
of  sulphate  of  lead  is  formed,  PbS-1-2  O^  = PbSO^.  Both  oxide 
of  lead  and  sulphate  of  lead,  wdien  heated  with  fresh  sulphide  of 
lead,  are  decomposed,  metallic  lead  and  sulphurous  anliydride  being 
in  each  case  the  result  of  the  reaction.  Two  atoms  of  oxide  of  lead, 
and  1 of  galena  furnish  3 of  lead  and  1 of  sulphurous  anhydride  : 
2 PbO  + PbS  = 3 Pb  -f  SO2.  One  atom  of  sulphate  of  lead, 
wdien  heated  with  1 of  galena,  yields  2 atoms  of  lead  and  2 of  sul- 
phurous anhydride  : thus  PbS  PbSO^=  2 Pb  -f  2 SO2.  Dur- 
ing the  roasting  a portion  of  subsulphide  of  lead,  Pb2S,  is  also 
produced.  This  substance  forms  a fusible  matt,  wdiich  flows  from 
the  furnace  wdth  the  metallic  lead,  constituting  a stratum  which 
floats  above  tlie  melted  metal.  This  subsulphide  of  lead  is  again 
returned  to  the  furnace  and  roasted  with  fresh  ore. 

After  the  melted  mass  has  been  drawm  off  into  cast-iron  basins 
placed  for  its  reception,  a few  spadefuls  of  lime  to  which  a quan- 
tity of  fluor-spar  is  sometimes  added,  are  thrown  into  the  furnace, 
with  a view  to  act  upon  the  scorise  which  remain  behind  in  con- 
siderable quantity  : the  lime  decomposes  the  fusible  silicate  of 
lead,  liberates  oxide  of  lead,  and  forms  a less  fusible  silicate  of 
calcium,  and  the  fluor-spar  forms  a fusible  compound  with  the 
sulphate  of  calcium,  or  sulphate  of  barium,  if  either  of  them 
is  present.  The  scoriae  usually  contain  an  excess  of  oxide  and  of 
sulphate  of  lead ; they  are  therefore  mixed  with  coke  or  charcoal, 
and  exposed  to  heat  on  the  bed  of  the  furnace,  after  the  doors 
have  been  carefully  closed  ; the  oxide  of  lead  then  becomes  reduced 
by  the  carbon. 

Refining  of  lead. — Lead  wdiich  contains  antimony  or  tin  is 
harder  than  the  pure  metal,  and  is  subjected  to  a further  opera- 
tion, termed  imjyromng.,  in  order  to  reflne  it.  This  consists  simply 
in  melting  the  lead,  and  heating  it  for  a period,  longer  or  shorter, 
as  may  be  necessary,  in  a shallow  cast-iron  pan  set  in  the  bed  of 
a reverberatory  furnace ; tiie  antimony  and  tin  being  more  oxidi- 
zable  than  the  lead,  are  thus  removed  in  the  pellicle  of  oxide 
which  is  continually  being  formed.  From  time  to  time  the  work- 
man takes  out  a small  sample  of  the  metal  to  examine  the  appear- 
ance which  it  presents  on  cooling.  As  soon  as  it  exibits  a pecu- 
liar flaky  crystalline  appearance  on  the  surface,  the  oxidation  has 
been  carried  far  enough  ; the  metal  is  then  run  off  and  cast  into  pigs. 

(891)  Concentration  of  Silver  in  Lead  hy  Pattinson’s  Pro- 
cess.— Silver  may  be  profitably  extracted  from  lead,  even  when 
the  quantity  does  not  exceed  from  three  to  four  ounces  of  silver 
to  the  ton,  by  a process  introduced  by  Mr.  Pattinson,  of  Kew^- 
castle.  This  gentleman  observed  that  if  melted  argentiferous 
lead  be  briskly  stirred  during  slow"  cooling,  a portion  of  the 
metal  solidifies  first,  in  the  form  of  crystalline  grains,  wdiich 
sink  to  the  bottom  of  the  portion  wdiich  remains  melted.  These 
crystals  consist  of  lead  nearly  free  from  silver,  the  fusing-point  of 
the  argentiferous  alloy  occurring  at  a low^er  temperature  than 


EXTRACTION  OF  SILVER  FROM  LEAD. 


629 


that  of  pure  lead.  This  observation  is  turned  to  account  in  the 
following  simple  manner  : — 

Eight  or  nine  cast-iron  pots,  each  capable  of  containing  about 
five  tons  of  melted  lead,  are  arranged  in  a row,  set  in  brickwork, 
and  each  ^irovided  with  a separate  fireplace  nnderneath.  A 
quantity,  of  lead  is  introduced  into  the  middle  pot,  and  melted  ; 
the  fire  is  then  withdrawn,  and  the  metal  is  briskly  stirred  by  the 
workman  whilst  it  cools  : the  crystals  of  lead  subside  as  they 
form,  and  are  removed  at  intervals  by  means  of  a large  perforated 
iron  ladle,  and  transferred  to  the  next  pot  on  the  right  hand. 
AVhen  about  four-fifths  of  the  metal  have  been  thus  removed  in 
grains,  the  concentrated  argentiferous  alloy  is  ladled  out  into  the 
next  pot  on  the  left-hand  side,  and  the  empty  pot  is  charged  witli 
a fresh  portion  of  lead,  which  is  subjected  to  a similar  treatment. 
When  the  pot  to  the  right  and  to  the  left  has  in  this  manner 
received  a sufficient  quantity  either  of  poor  or  of  argentiferous 
lead,  it  is  subjected  to  a similar  operation  ; the  concentrated 
argentiferous  portion  being  passed  off  continually  to  the  next  pot 
on  the  left,  wdiilst  the  crystalline  or  poorer  portion  is  handed 
over  to  the  next  pot  on  the  right-hand  side.  The  last  pot  to  the 
left  thus  at  length  becomes  filled  with  lead  which  may  contain 
300  ounces  of  silver  to  the  ton  ; it  is  not  found  advantageous  to 
concentrate  it  beyond  this  point : the  lead  which  accumulates  in 
the  last  pot  on  the  right-hand  side  does  not  contain  more  than 
half  an  ounce  of  silver  in  the  ton.  This  poor  lead  is  much  im- 
proved in  quality  by  the  operations  which  it  has  undergone,  and 
is  at  once  cast  into  pigs  for  the  market. 

(892)  Extraction  of  Silver  frorn  Lead  Jby  Ciopellation. — Tlie 
rich  argentiferous  lead  is  now  subjected  to  cujjellation.  This 
process  is  founded  upon  the  circumstance  that  lead,  if  exposed  at  a 
high  temperature  to  a current  of  air,  absorbs  oxygen  rapidly,  and 
is  converted  into  a fusible  oxide,  whilst  silver  does  not  become 
oxidized,  but  is  left  behind  in  the  metallic  state.  The  litharge  or 
oxide  of  lead  melts  at  a high  temperature,  and  flows  off  the  con- 
vex surface  of  the  melted 

metal,  and  thus  continu-  Fig.  354. 

ally  exposes  a fresh  sur- 
face of  lead  to  the  action 
of  the  air. 

In  England  the  cupel- 
lation  is  performed  in  a 
low-crowned  reverberato- 
ry furnace,  the  hearth  of 
which  is  moveable.  The 
hearth  or  cupel  is  shown 
in  the  plan  of  the  furnace 

(Fig.  354)  : it  consist  of  a shallow  oval  basin,  c,  composed  of  a 
mixture  of  bone  ash  with  fern  or  wood  ashes;  this  mixture  is 
slightly  moistened,  and  beaten  into  an  iron  ring  of  about  4 feet  in 
its  long  diamater,  and  2 feet  in  the  shorter : the  cupel  is  intro- 
duced into  the  furnace  from  beneath,  and  is  supported  by  bricks, 


630 


EXTRACTION  OF  SILVER  FROM  LEAD. 


SO  that  it  can  be  readily  removed  and  renewed, — an  operation 
which  is  generally  required  once  a week.  When  dry,  the  fire  is 
cautiously  lighted  and  the  lead  introduced  ; a continual  blast  of 
air  from  a tuyere,  t,  is  made  to  play  over  the  surface  of  the  melted 
metal ; litharge  is  formed  abundantly,  and  runs  off  through  a 
gutter,  y,  into  an  iron  pot,  y?,  placed  beneath  the  furnace  for  its 
reception  ; in  front  is  a hood.  A,  for  carrying  olF  the  fumes  of 
oxide  of  lead  which  would  otherwise  escape  and  injure  the  work- 
men. Fresh  lead  is  added  from  time  to  time  to  supply  the  place 
of  that  which  is  oxidized ; until  at  length  a quantity  of  lead, 
originally  amounting  to  about  5 tons,  is  reduced  to  between  2 
and  3 cwt.  This  melted  metal  is  withdrawn  by  making  a hole 
through  the  bottom  of  the  cupel  ; the  aperture  is  afterwards  closed 
with  fresh  bone  ash,  and  another  charge  is  proceeded  with. 
When  a quantity  of  rich  lead  sufiicient  to  yield  from  3000  to 
5000  ounces  of  silver  has  thus  been  obtained,  it  is  again  placed  in 
a cupel,  and  the  last  portions  of  lead  are  removed.  It  is  found 
advantageous  to  effect  this  final  purification  of  the  concentrated 
silver-lead  separately,  because  in  the  last  stages  of  the  operation 
tlie  litharge  carries  a good  deal  of  silver  down  with  it : these  por- 
tions of  litharge,  therefore,  on  being  reduced,  are  again  subjected 
to  the  desilvering  process. 

The  litharge  from  the  first  fusion  is  either  sold  as  oxide  of 
lead,  or  it  is  reduced  in  a small  reverberatory  furnace  with  an- 
thracite, or  powdered  coal.  The  porous  cupels  absorb  a large 
quantity  of  litharge,  and  they  likewise  are  passed  through  the 
furnace  in  order  to  extract  the  metal. 

A very  beautiful  phenomenon,  known  as  the  fulguration  of 
the  metal,  attends  the  removal  of  the  last  portions  of  lead  from 
the  silver.  During  the  earlier  stages  of  the  process  the  film  of 
oxide  of  lead,  which  is  constantly  forming  over  the  surface  of  the 
melted  mass,  is  renewed  as  rapidly  as  it  is  removed ; but  when 
the  lead  has  all  been  oxidized,  the  film  of  litharge  upon  the  silver 
becomes  thinner  and  thinner  as  it  flows  off ; it  then  exhibits  a 
succession  of  the  beautiful  iridescent  tints  of  Newton’s  rings ; and 
at  length  the  film  of  oxide  suddenly  disappears,  and  reveals  the 
brilliant  surface  of  the  metallic  silver  beneath. 

In  the  Hartz  the  hearth  of  the  cupellation  furnace  is  fixed, 
and  is  made  of  brick,  covered  with  marl,  which  is  renewed  after 
each  operation,  but  the  cover  of  the  furnace  is  moveable.  Karsten 
states  that  the  advantage  of  this  method  is,  that  the  litharge  runs 
off  more  perfectly,  and  that  there  is  less  waste  of  silver  from 
absorption  into  the  cupel,  and  less  expenditure  of  labour  and  fuel 
upon  recovering  the  lead  from  the  bottom  of  the  furnace,  which 
absorbs  but  comparatively  little  litharge. 

(893)  In  the  North  of  England,  the  galena  is  smelted  by  a 
process  somewhat  different : the  ore  is  first  roasted,  and  then 
reduced  in  a small  square  blast  furnace,  or  forge  hearth, — dried 
peat  being  the  fuel  principally  employed.  This  form  of  furnace 
is  known  as  the  Scotch  furnace. 

In  some  parts  of  the  Hartz,  where  the  ores  are  largely  mixed 


COMBINED  ACTION  OF  AIK  AND  WATER  ON  LEAD. 


631 


witli  siliceous  matters,  the  English  method  of  smelting  is  not  ap- 
plicable, as  the  silica  would  combine  with  the  oxide  of  lead,  and 
form  a fusible  slag.  It  is  fonnd  necessary  in  these  cases  to  re- 
duce the  sulphide  of  lead  by  means  of  metallic  iron,  which  is 
added  in  the  form  of  granulated  cast-iron,  in  the  proportion  of 
about  1 part  of  iron  to  20  of  pure  galena.  The  fusion  is  per- 
formed in  a small  blast  furnace,  about  20  feet  high,  and  3 feet 
across  at  the  widest  part. 

These  various  furnace  operations  are  attended  by  a continual 
disengagement  of  white  fumes,  which  consist  principally  of  oxide 
and  sulphate  of  lead,  and  are  technically  termed  froth  of  lead  ; 
in  this  way  nearly  a seventh  of  the  whole  lead  is  volatilized.  In- 
dependently of  the  waste  thus  occasioned,  the  fumes  are  highly 
deleterious  ; it  is  therefore  of  great  importance  to  prevent  as  far 
as  possible  their  diffusion  through  the  air.  It  is  stated,  that  in 
the  Hartz  about  of  the  volatilized  portion  is  arrested  by  causing 
the  gases  from  the  furnaces  to  pass  through  a succession  of  con- 
densing chambers,  before  they  finally  escape  into  the  air. 

(894)  Properties. — Lead  is  a bluish-white  metal,  so  soft  that 
it  may  easily  be  made  to  take  impressions  ; it  leaves  a streak  upon 
paper,  and  may  be  cut  with  the  nail.  It  may  be  laminated  into 
tolerably  thin  sheets,  as  well  as  drawn  into  wire ; but  both  in 
ductility  and  tenacity  it  is  low  in  the  scale.  It  fuses  at  620° 
(Person ; or  617°,  Pudberg),  and  may  with  some  difficulty  bo 
obtained  in  cubic  or  in  octohedral  crystals  as  it  cools ; the  purer 
the  lead  the  larger  the  crystals  (Baker,  quoted  by  Matthiessen). 
Lead  contracts  considerably  at  the  moment  of  its  solidification, 
and  it  is  therefore  not  well  adapted  for  castings.  It  appears  to 
have  the  power,  when  melted,  of  dissolving  a small  quantity  of 
oxide  of  lead,  by  which  the  hardness  of  the  metal  is  much  in- 
creased ; but  its  softness  may  be  restored  by  keeping  it  melted 
under  charcoal  for  some  time,  with  occasional  agitation.  As  a con- 
ductor of  heat  and  electricity,  it  is  inferior  to  many  of  the  metals. 

(895)  Combined  Action  of  Air  a7id  Water  on  Lead. — The  sur- 
face of  a piece  of  lead  when  freshly  cut  presents  a high  metallic 
lustre,  but  it  soon  tarnishes  by  exposure  to  air,  owing  to  the 
formation  of  a thin,  closely  adhering  film  of  oxide,  which  protects 
the  metal  from  further  change.  Lead  undergoes  no  alteration  in 
a perfectly  dry  atmosphere,  and  even  when  sealed  up  in  a vessel 
of  pure  water,  which  has  been  boiled  for  some  time  to  expel  the 
air,  the  metal  will  retain  its  brilliancy  for  an  indefinite  period  ; 
but  if  it  be  exposed  to  the  united  action  of  air  and  pure  water, 
it  is  subject  to  a powerful  corrosion.  As  the  result  of  this  ex- 
])osure  the  lead  becomes  oxidated  at  tlie  surface,  and  the  water 
dissolves  the  oxide  of  lead  ; this  solution  absorbs  carbonic  acid,  a 
film  of  hydrated  basic  carbonate  of  lead  (Pb0Il20,Pb003)  is  de- 
])osited  in  silky  scales,  and  a fresh  portion  of  oxide  is  formed  and 
dissolved  by  the  water ; thus  a rajnd  corrosioTi  of  the  metal  takes 
place.  This  action  is  modified  very  materially  by  the  ])resence  of 
various  salts  in  the  water,  even  though  the  quantity  of  tlu'se  salts 
may  not  exceed  3 or  4 grains  in  the  gallon.  The  corrosion  is 


632 


ACTION  OF  AIK  AND  WATER  ON  LEAD. 


miicli  increased  by  the  chlorides  and  nitrates.  The  presence  of 
very  minute  quantities  of  the  nitrites  in  water  confers  upon  it  a 
corrosive  action  on  lead.  Both  nitrites  and  nitrates  are  often  pre- 
sent in  spring  and  river  waters,  owing  to  the  decomposition  of 
organic  matter  ; and  it  is  not  improbable  that  tlie  unexplained 
corrosive  action  of  certain  soft  waters  upon  lead  may  be  due  to 
the  presence  of  these  salts,  which  might  easily  be  overlooked  in 
the  course  of  the  analysis  (Medlock).  Small  quantities  of  ammo- 
nia also  favour  the  solution  of  the  metal.  On  the  other  hand,  the 
corrosion  is  diminished  by  the  sulphates,  the  phosphates,  and  the 
carbonates.  Oxide  of  lead,  indeed,  is  scarcely  soluble  in  water 
which  contains  these  salts  in  solution.  A solution  of  carbonate 
of  calcium  in  carbonic  acid  is  especially  remarkable  for  the  pre- 
servative influence  which  it  exerts,  and  as  this  latter  is  a very 
usual  impurity  in  water,  few  spring  waters  act  on  the  metal  to  any 
dangerous  extent.  In  these  cases  a fllm  of  insoluble  carbonate  of 
lead  is  formed  upon  the  surface,  and  the  metal  beneath  is  protected 
from  further  injury.  The  action  of  water  on  lead  is  a matter  of 
great  importance  in  its  sanitary  bearings,  on  account  of  the  exten- 
sive employment  of  this  metal  in  cisterns  and  pipes  for  the  storage 
and  supply  of  water.  Rain-water  as  collected  from  the  roofs  of 
houses,  is  for  the  most  part  sufliciently  impure,  especially  in  large 
towns,  to  prevent  its  action  upon  the  metal.  Of  all  the  salts  of 
lead  tlie  hydrated  basic  carbonate  is  the  least  soluble,  pure  water 
not  taking  up  more  than  1 part  in  4 millions,  or  about  a sixtieth 
of  a grain  per  gallon.  If  a solution  of  oxide  of  lead,  in  distilled 
water,  containing  4 or  5 grains  to  the  gallon,  be  exposed  to  the 
air,  it  soon  becomes  fllled  with  silky  crystals  of  the  hydrated  basic 
carbonate,  owing  to  the  absorption  of  carbonic  acid  ; and  in  a few 
hours  the  water  does  not  contain  more  than  ^.o-w.wo  weight 
of  the  metal  in  solution.  Water  highly  charged  with  carbonic 
acid  may  nevertheless  dissolve  lead  to  a dangerous  extent,  owing 
to  the  solubility  of  carbonate  of  lead  in  excess  of  carbonic  acid ; 
when  water  thus  impregnated  with  lead  is  boiled,  the  gas  is  ex- 
pelled, and  the  carbonate  subsides.  So  general,  however,  is  the 
action  of  water  upon  lead  that  it  is  rare  to  And  any  that  has  been 
kept  in  cisterns  of  this  metal  perfectly  free  from  all  traces  of  it. 
Slate  cisterns  are  therefore  greatly  to  be  preferred  to  leaden  ones. 

At  high  temperatures,  lead  absorbs  oxygen  rapidly  from  the 
air  ; it  undergoes  partial  volatilization,  and  emits  white  fumes  of 
oxide.  It  is  not  acted  upon  by  sulphuric  or  hydrochloric  acid  at 
ordinary  temperatures,  and  but  slightly  even  when  boiled  with 
them  ; but  it  is  dissolved  with  extrication  of  nitric  oxide,  by  nitric 
acid,  especially  when  the  acid  is  somewhat  diluted.  Tlie  vapours 
of  acetic  acid  corrode  it  gradually,  and  if  carbonic  acid  be  also  pre- 
sent, convert  it  rapidly  into  wliite  lead.  Green  oak  wood,  from 
the  quantity  of  acetic  acid  which  it  contains,  should  not  be  used 
in  contact  with  lead  for  building  purposes.  The  alkalies  do  not 
exercise  any  decided  influence  upon  lead.  Chlorine  also  slowly 
converts  the  metal  into  chloride,  but  the  fllm  of  this  compound, 
which  is  formed  on  the  surface,  protects  the  metal  beneath.  In 


638 


ALLOYS,  A^T>  OXIDES  OF  LEAD. 

the  presence  of  moisture,  lead  is  corroded  when  in  contact  with 
sulphate  of  calcium  ; hence  in  its  application  to  architectural  pur- 
poses, the  contact  of  stucco  or  plaster  with  lead  should  be  avoided. 

The  lead  of  commerce  is  often  nearly  pure.  The  purest  spe- 
cimens are  the  softest.  Traces  of  tin,  iron,  copper,  and  silver,  and 
sometimes  of  antimony  and  manganese,  are  the  impurities  which 
are  most  often  observed.  In  order  to  obtain  it  perfectly  pure,  it 
should  be  reduced  with  black  flux  from  the  oxide  left  by  igniting 
the  pure  nitrate  or  carbonate  of  the  metal. 

(896)  Uses. — From  its  softness,  fusibility,  durability,  and  the 
ease  with  which  it  may  be  worked,  lead  is  applied  to  a multipli- 
city of  purposes.  The  reception  chambers  in  the  manufacture  of 
sulphuric  acid  are  lined  with  it.  It  forms  the  ordinary  material 
for  cisterns,  water-pipes,  and  gutters,  and  is  frequently  employed 
in  covering  the  roofs  of  houses. 

The  alloys  of  lead  are  numerous  and  important.  Shot  for 
fowling-pieces  is  an  alloy  of  lead  with  a small  proportion  of  arse- 
nic, which  hardens  it  and  facilitates  its  granulation  into  globules  ; 
the  quantity  of  arsenic  varies  with  the  purity  and  softness  of  the 
lead  : usually  it  requires  from  3 to  8 parts  in  the  1000.  The  com- 
mon white  arsenic  of  the  shops  is  added  to  the  lead,  melted  in  a 
covered  vessel;  the  arsenious  anhydride  is  reduced  by  the  lead, 
and  the  oxide  of  lead  thus  formed  rises  as  a him  to  the  surface  of 
the  alloy.  Sonnenschein  observed  an  alloy  of  iron  and  lead 
(FePb^)  wdiich  had  been  accidentally  formed  in  a blast  furnace, 
in  acicular  feathery  crystals ; it  was  yellow,  harder  than  lead,  and 
of  sp.  gr.  10’36  ; it  contained  11T4  per  cent,  of  iron. 

Wlien  lead  is  alloyed  with  about  one-third  of  its  weight  of  an- 
timony it  forms  type  metal : a superior  variety  of  type  consists  of  1 
part  of  antimony,  1 of  tin,  and  2 of  lead ; it  is  harder  and  tougher 
than  the  common  alloy  used  for  this  purpose.  Both  the  alloys  are 
sufficiently  fusible  to  allow  of  being  readily  cast ; they  expand  at  the 
moment  of  solidification,  and  copy  the  mould  accurately ; they  are 
liard  enough  to  bear  the  action  of  the  press,  and  yet  not  so  hard 
as  to  cut  the  paper.  The  ordinary metal  contains  lead,  as 
do  the  various  compounds  called  pewter,  Britannia  metal,  and 
queen’s  metal.  The  solder  used  by  tinplate  workers  and  plumb- 
ers is  a mixture  of  lead  and  tin  (812).  Wlien  lead  is  melted  with 
zinc,  a white,  hard,  ductile  alloy  is  formed ; but  the  two  metals 
separate  into  two  distinct  layers  if  the  fused  mass  be  left  to  cool 
slowly.  Pot-metal  is  an  alloy  of  lead  and  copper,  obtained  by 
throwing  lumps  of  copper  into  red-hot  melted  lead  (Brande) : it  is 
of  a grey  colour,  brittle,  and  granular. 

Other  compounds  of  lead  are  also  largely  enqiloyed  in  the 
arts.  The  red  oxide  is  used  in  large  proportion  in  the  manufac- 
ture of  flint-glass  (599).  The  carbonates,  the  oxychlorides,  and 
the  chromates  are  extensively  employed  as  pigments. 

(897)  Compounds  of  Lead  with  Oxygen. — Lead  forms  four 
oxides;  — an  unimportant  black  suboxide,  Bb^O,  obtained  by 
heating  the  oxalate  to  about  600°,  in  a glass  retort.  A ])rotoxide, 
PbO,  from  which  the  ordinary  salts  of  the  metal  are  formed ; a 


634 


LITHAEGE,  OR  OXIDE  OF  LEAD. 


binoxide,  PbO^,  wbicb  is  insoluble  in  acids ; and  red  lead,  wliich 
is  a compound  of  the  two  oxides  last  mentioned,  usually  in  the 
proportions  indicated  by  the  formula  (2  PbOjPbO^). 

Protoxide  of  Lead  (PbO  = 223,  or  PbO  =:  111*5) ; 8]).  Gr. 
9*2  to  9*5  : Comjo.  in  loh parts ^ Pb,  92*82;  O,  Y*18. — This  oxide 
is  well  known  under  the  name  of  litharge.  Its  colour  varies  ac- 
cording to  the  mode  of  its  preparation.  Usually  it  is  obtained  on 
a large  scale  by  the  oxidation  of  lead  in  a current  of  air,  in  which 
case  it  forms  a scaly  mass,  which,  if  of  a yellow  colour,  is  com- 
monly termed  litharge  of  silver ; if  redder,  it  is  termed  litliarge  of 
gold.  The  former  is  the  purer,  as  the  red  colour  is  due  in  many 
cases  to  the  presence  of  a small  quantity  of  minium.  If  the  oxi- 
dation be  effected  at  a temperature  below  that  required  for  the 
fusion  of  the  oxide,  a yellow  powder  termed  massicot  is  obtained. 
Common  litharge,  when  reduced  to  a fine  powder,  also  has  a dull 
yellow  colour ; when  heated,  it  assumes  a brown-red  hue,  which 
disappears  again  as  it  cools.  If  a hot  solution  of  caustic  soda, 
of  sp.  gr.  1*42,  be  saturated  with  litharge,  the  oxide  is  deposited, 
as  the  liquid  cools,  in  beautiful  anhydrous  rose-coloured  crystals. 
If  the  solution  of  oxide  of  lead  in  caustic  soda  be  allowed  to  eva- 
porate spontaneously  by  exposure  to  the  air,  the  alkali  gradually 
absorbs  carbonic  acid,  and  the  oxide  is  deposited  in  transparent 
anhydrous  dodecahedral  crystals. 

If  the  salt  of  lead  be  precipitated  by  the  addition  of  a caus- 
tic alkali  in  slight  excess,  the  oxide  of  lead  is  precipitated  in  the 
form  of  a white  hydrate  (2  PbO,!!^^).  Another  hydrate  (3  PbO, 
H^O)  may  be  obtained  in  groups  of  transparent  octohedra,  or  of 
four-sided  prisms  mixed  with  anhydrous  crystals,  by  precipitating 
a solution  of  tribasic  acetate  of  lead  by  an  excess  of  ammonia,  at 
a temperature  of  86°. 

Both  litharge  and  the  hydrated  oxide  of  lead  absorb  carbonic 
acid  slowly  from  the  atmosphere. 

Protoxide  of  lead  fuses  at  a heat  above  redness,  and  crystallizes 
on  cooling  in  semi-transparent  scales.  When  fused,  it  combines 
rapidly  with  the  earths  and  with  silica,  speedily  destroying  and 
penetrating  the  crucibles  in  which  it  is  melted.  It  should  not  be 
fused  in  platinum  crucibles,  since  it  becomes  decomposed  into 
peroxide,  and  metallic  lead  ; the  latter  attacking  and  spoiling  the 
crucible.  The  protoxide  is  slightly  soluble  in  water,  to  which  it 
communicates  an  alkaline  reaction.  The  presence  of  a very  small 
quantity  of  saline  matter  diminishes  or  prevents  the  solution  of 
the  oxide ; the  solution  absorbs  carbonic  acid  rapidly  from  the  air, 
and  mere  filtration  in  many  cases  causes  the  deposition  of  a large 
portion  of  the  oxide  in  the  form  of  hydrated  basic  car- 
bonate. 

Oxide  of  lead  is  soluble  in  solutions  of  the  caustic  alkalies  ; in- 
deed it  forms  compounds  with  the  alkalies  and  alkaline  earths 
which  have  been  obtained  in  crystals ; they  are,  however,  decom- 
posed by  simple  exposure  to  the  atmosphere,  owing  to  the  absorp- 
sion  of  carbonic  acid.  The  solution  of  the  oxide  in  lime-water  is 
sometimes  used  as  a hair-dye  : the  lime  softens  and  partially  de- 


MIIsIUM,  OK  KED  LEAD. 


635 


composes  the  hair,  and  the  lead  of  the  oxide,  combining  with  the 
sulphur  of  the  hair,  forms  sulphide  of  lead,  which  stains  the  hair 
of  a permanent  black.  Litharge  is  in  continual  requisition  by 
the  assayer  as  a flux ; it  also  enters  largely  into  the  composition 
of  tlie  glaze  of  common  earthenware.  A mixture  of  1 part  of 
massicot  with  8 or  10  of  hrick-dust,  made  into  a paste  with  linseed 
oil,  forms  Dliil  mastic  / it  sets  exceedingly  hard,  and  is  frequently 
employed  to  repair  defects  in  stone  facings  ; the  stone  should  be 
moistened  before  applying  the  mastic. 

Oxide  of  lead  is  a jDOwerful  base.  It  has  a strong  tendency  to 
form  basic  salts ; those  which  it  yields  with  acetic  acid,  and  some 
of  those  with  nitric  acid,  are  soluble  : they  exert  a strongly  al- 
kaline reaction  upon  test-paper,  and  absorb  carbonic  acid  with 
avidity.  Indeed,  owing  to  the  very  sparing  solubility  of  the  basic 
carbonate  of  lead,  a solution  of  a basic  salt  of  lead  is  the  most 
delicate  test  for  the  presence  of  carbonic  acid,  either  in  a gas  or 
in  distilled  water  ; a mere  trace  of  carbonic  acid  occasions  the  for- 
mation of  the  peculiar  silky  crystalline  precipitate  which  cha- 
racterizes the  basic  hydrated  carbonate  of  lead. 

(898)  Minium^  or  red  lead  {sjp.  gr.  about  9 ‘08),  is  a compound 
of  protoxide  of  lead  with  the  peroxide  of  the  metal.  It  was  ob- 
tained by  Berzelius  as  Pb0,Pb02,  but  its  most  usual  composition 
is  represented  by  the  formula  2 Pb0,Pb02,  though  well  crystal- 
lized samples  have  been  formed,  which  consisted  of  3 Pb0,Pb02. 
All  these  compounds  possess  a brilliant  red  colour.  If  the  latter 
two  be  treated  with  a solution  of  potash,  or  with  one  of  normal 
acetate  of  lead,  the  excess  of  oxide  of  lead  may  be  dissolved  out, 
and  the  compound  Pb0,Pb02  is  left. 

Bed  lead  is  obtained  by  heating  metallic  lead,  so  as  flrst  to 
procure  the  protoxide  or  massicot,  keeping  the  temperature  below 
the  fusing-point  of  the  oxide;  the  oxide  so  obtained  is  finely 
levigated  in  water,  and  the  particles  which  are  held  in  suspension 
are  allowed  to  subside,  dried,  and  exposed,  in  iron  trays,  to  a heat 
of  about  600°,  in  a reverberatory  furnace.  The  additional 
quantity  of  oxygen  is  gradually  absorbed.  If  white  lead  is  sub- 
mitted to  a similar  roasting,  tbe  carbonic  anhydride  is  expelled, 
leaving  protoxide  of  lead,  which  is  converted  into  minium  of  very 
fine  quality  by  the  gradual  absorption  of  oxygen.  The  principal 
use  of  red  lead  is  in  the  manufacture  of  flint  glass.  Much  care 
is  required  in  the  preparation  of  minium  for  this  purpose : it  is 
necessary  that  it  should  be  free  from  the  oxides  of  other  metals, 
which  would  impart  colour  to  the  glass.  In  the  oxidation  of  the 
lead,  which  constitutes  the  flrst  stage  in  the  preparation  of  red 
lead,  the  metals  which  are  more  oxidizable  than  lead  are  removed 
with  the  flrst  portions  of  oxide ; whilst  the  co])per  and  silver  ac- 
cumulate in  the  portions  of  oxide  which  are  ])roduced  last.  The 
intermediate  stage  of  the  o])eration  is  therefore  that  which  fur- 
nishes the  purest  oxide.  Minium  is  better  suited  to  the  glass- 
maker  than  litharge,  because  the  excess  of  oxygen  burns  off  any 
combustible  matter  which  may  accidentally  be  })resent,  and  con- 
verts the  protoxide  of  iron  into  peroxide.  Bed  lead  is  also  used 


636 


PEROXIDE  OF  LEAD. 


for  colouring  the  inferior  kinds  of  red  sealing-wax,  and  for  paper- 
staining. 

If  minium  be  exposed  to  a high  temperature  it  is  decomposed, 
oxygen  is  evolved,  and  the  protoxide  of  lead  remains.  Minium  is 
insoluble  in  the  acids,  but  by  many  of  them,  especially  by  nitric 
acid,  it  is  decomposed  ; a salt  of  the  protoxide  is  formed,  and  the 
brown  peroxide  of  lead  remains  behind. 

(899)  Peroxide  of  lead  (Pb02=239,  orPb02=119-5  ; 8p.  Gr. 
9’45  : Comp,  in  100 parts ^ Pb,  86’61 ; O,  13*39. — This  compound 
is  occasionally  found  native  in  iron-black  brilliant  hexahedral 
prisms,  forming  heavy  lead  ore.  It  is  usually  prepared  by  levi- 
gating minium  very  finely,  and  digesting  the  powder  in  boiling 
nitric  acid,  diluted  with  4 or  5 times  its  bulk  of  water  ; the  residue 
is  washed  with  fresh  nitric  acid,  and  then  with  water,  till  every- 
thing soluble  is  removed.  It  may  also  be  obtained  by  fusing  at  a 
gentle  heat  a mixture  of  4 parts  of  litharge  in  fine  powder,  with 
1 part  of  chlorate  and  8 parts  of  nitrate  of  potassium,  and  wash- 
ing the  product  with  water.  Wohler  prepares  the  peroxide  by 
transmitting  a current  of  gaseous  chlorine  through  the  magma 
obtained  by  mixing^  a solution  of  4 parts  of  acetate  of  lead  with 
a solution  of  3 parts  of  crystallized  carbonate  of  sodium : the  car- 
bonate of  lead  becomes  gradually  but  completely  converted  into 
peroxide  of  lead,  and  must  be  thoroughly  washed;  chloride  of 
sodium  is  formed,  and  acetic  and  carbonic  acids  are  set  free,  as 
follows : — 

Pb  2 e,H3e,-fNa,-ee3-f  ci,-f  2H,e=Pbe,-f2He,H30,-f 
2NaCi4-H3e,ee3. 

Various  other  oxidizing  agents  may  be  employed  to  convert  the 
protoxide  into  the  peroxide  of  lead : thus  acetate  of  lead  when 
heated  with  a solution  of  bleaching-powder  yields  the  peroxide 
in  crystals. 

Peroxide  of  lead  is  insoluble  in  water  and  in  acids ; it  is  con- 
verted by  heat  under  disengagement  of  oxygen  into  the  protoxide ; 
sulphurous  anhydride  instantly  decomposes  it,  forming  sulphate 
of  the  protoxide;  PbO^-l-SOj  = PbSO^ ; hence  it  is  frequently 
employed  in  the  laboratory  to  absorb  sulphurous  anhydride  when 
mixed  with  other  gases.  If  digested  in  a solution  of  ammonia, 
or  subjected  to  a current  of  the  gas,  mutual  decomposition  occurs ; 
water,  nitrate  of  ammonium,  and  protoxide  of  lead  are  formed. 
Cold  diluted  hydrochloric  acid  dissolves  this  oxide,  forming  a rose- 
coloured  solution,  from  which  the  caustic  alkalies  reprecipitate 
the  peroxide  ; but  if  the  acid  be  employed  hot,  or  in  a concentrated 
form,  chloride  of  lead  is  produced,  and  chlorine  is  set  free.  If 
the  peroxide  be  mixed  with  a fifth  of  its  weight  of  sulphur,  the 
mixture  takes  fire  by  friction,  sulphurous  anhydride  and  sulphide 
of  lead  being  produced. 

Peroxide  of  lead  appears  to  possess  feebly  acid  properties.  By 
fusing  the  pure  peroxide  with  excess  of  caustic  potash  or  of  soda, 
in  a silver  crucible,  and  dissolving  the  residue  in  a small  quantity 
of  hot  water,  crystals  of  plumhate  of  potassium  or  of  sodium  are 


COMPOUNDS  OF  SULPHUR  WITH  LEAD. 


637 


formed  as  the  solution  cools  : plumbate  of  potassium  consists  of 
K2pb03,  3 HjO  (Fremy).  Pure  water  decomposes  these  com- 
pounds, and  the  peroxide  of  lead  subsides.  Like  the  peroxides  of 
silver  and  manganese,  tlie  peroxide  of  lead  is  a conductor  of  elec- 
tricity, and  is  formed  at  the  zincode  of  the  battery  when  aqueous 
solutions  of  the  ordinary  salts  of  lead  are  decomposed  by  the  vol- 
taic current. 

(900)  Compounds  of  Sulphur  with  Lead. — The  most  impor- 
tant of  these  is  the  protosulphide,  PbS,  the  galena  of  mineralo- 
gists. Besides  this  a subsulphide,  Pb2S,  is  formed  as  the  lead  matt 
in  reducing  galena : and  a red  persulphide  is  also  obtainable, 
though  its  composition  is  not  accurately  known  : it  is  quickly 
resolved  in  the  liquid  into  protosulphide  of  lead  and  free  sulphur. 
This  persulphide  is  procured  by  adding  a solution  of  a persulphide 
of  one  of  the  metals  of  the  alkalies  to  a solution  of  a salt  of  lead. 

Protosnlpkide^  or  Galena  (PbS=239,  or  PbS  = 119‘5) ; Sj).  Gr. 
7'59  : Comp,  in  100 parts ^ Pb,  86*61 ; S,  13*39. — Galena  is  an 
abundant  mineral,  and  forms  the  principal  ore  of  lead : it  is  a 
brittle  substance,  and  is  found  crystallized,  more  or  less  distinctly, 
in  cubes  of  a deep  leaden  colour  and  strong  metallic  lustre.  It 
may  be  formed  artificially  by  fusing  lead  with  sulphur  ; or  it  may 
be  precipitated  as  a hydrate  by  treating  any  of  its  salts,  either  in 
solution  or  in  suspension  in  water,  with  sulphuretted  hydrogen. 
Sulphide  of  lead  requires  a full  red  heat  for  its  fusion,  and  at  this 
temperature  it  undergoes  partial  volatilization.  When  heated  in 
closed  vessels,  part  of  the  sulphur  is  expelled,  and  a svhsulpliide 
(Pb2S)  left : this  subsulphide  is  formed  on  the  large  scale  in  the 
])rocess  for  reducing  galena  ; it  is  more  fusible  than  the  sulphide, 
and  may  be  melted  at  a high  temperature  without  undergoing 
decomposition  ; but  if  it  be  heated  only  to  tlie  point  at  which  it 
begins  to  soften,  the  subsulphide  is  decomposed,  and  metallic  lead 
melts  out,  leaving  the  less  fusible  protosulphide.  Galena,  when 
iieated  in  contact  witli  air,  is  oxidated,  part  of  the  sulphur  burns  off, 
and  a mixture  of  oxide  of  lead  and  sulphate  of  lead  is  formed.  Kitric 
acid  and  aqua  regia  decompose  it,  converting  it  into  sulphate . 
liydrochloric  acts  but  slowly  upon  it  in  the  cold,  but  at  a boiling 
temperature  it  decomposes  it  freely  and  evolves  sulphuretted 
hydrogen.  When  this  sulphide  is  fused  with  lime  or  with  the 
hydrated  alkalies,  metallic  lead  is  obtained.  If  heated  with  oxide 
of  lead  or  of  iron,  it  is  reduced  with  escape  of  sulphurous  anhy- 
dride. When  heated  with  a small  quantity  of  nitre  a similar 
result  is  obtained.  When  the  sulphide  of  lead  is  heated  with 
metallic  iron  it  is  decomposed,  sulphide  of  iron  and  metallic  lead 
being  the  result.  Advantage  is  taken  of  this  fact  in  the  assay  of 
galena ; 200  grains  of  the  powdered  ore  are  mixed  with  300  of 
black  flux,  3 or  4 blacksmith’s  nails  are  placed  in  a Cornish  cru- 
cible with  their  heads  downwards,  the  mixture  is  introduced,  and 
covered  with  a small  quantity  of  fused  and  powdered  borax.  It 
is  heated  to  full  redness  for  10  minutes  : the  nails  are  withdrawn, 
and,  when  cold,  the  crucible  is  broken,  and  the  button  of  metallic 
lead  is  weighed. 


638 


CHLORIDE,  BRO:MrDE,  AND  IODIDE  OF  LEAD. 


(901)  Chloride  of  Lead  (PbCl2=278,  or  PbCl=139  ; sp.gr. 
5’8  : Comp,  in  100  parts^  Pb,  74-48;  Cl,  25-52)  is  best  prepared 
by  precipitating  a solution  of  nitrate  of  lead  by  the  addition  of 
hydrochloric  acid,  or  of  a solution  of  chloride  of  sodium ; a spar- 
ingly soluble,  white,  heavy  precipitate  occurs.  It  is  soluble  in 
about  33  parts  of  boiling  water,  but  it  is  taken  up  more  sparingly 
if  an  excess  of  hydrochloric  acid  be  present ; the  concentrated 
acid,  however,  dissolves  it  readily,  and  deposits  it  in  long,  delicate, 
six-sided  needles.  It  is  easily  fusible  into  a semi-transparent, 
horny,  sectile  mass,  and  at  high  temperatures  may  be  volatilized. 
If  kept  fused  in  air  till  no  more  fumes  arise,  it  is  converted  into 
an  oxychloride  (PbO,PbCl2).  The  alkalies  at  first  convert  it 
into  an  oxychloride,  and  if  the  action  be  prolonged,  into  pure 
oxide. 

Oxychlorides  of  Lead. — The  chloride  combines  with  oxide  of 
lead  in  several  proportions.  One  of  these  forms  a white,  trans- 
lucent, fasible,  colourless  mineral  (2  PbO.PbCl^),  which  is  found 
in  the  Mendip  Hills  crystallized  in  right  rhombic  prisms.  Pattin- 
son’s  white  oxychloride  of  lead  (PbO,PbCl2)  is  procured  by  grind- 
ing galena  in  a closed  cliert-mill  witli  concentrated  hydrochloric 
acid : sulphuretted  hydrogen  is  liberated  in  large  quantity,  and 
the  sparingly  soluble  chloride  of  lead  is  first  washed  with  com- 
mon water,  and  chalk  added  to  neutralize  every  trace  of  the 
acid : it  is  then  dissolved  in  hot  distilled  water,  and  precipitated 
by  the  addition  of  lime-water  in  quantity  just  sufficient  to  remove 
half  the  chlorine  ; OaO  -f  2 PbCl,  = OaCh -f  Pbe,PbCh.  This 
oxychloride  is  used  to  some  extent  as  a pigment  instead  of  white- 
lead.  Another  oxycliloride  (PbCh,  7 PbOj  is  a pigment  of  some 
importance,  known  under  the  name  of  patent  yellow  or  Turners 
yellow  / it  forms  a very  fusible  compound  of  a bright  yellow 
colour,  which  may  be  obtained  by  heating  together  1 part  of  sal 
ammoniac  and  10  parts  of  litharge. 

When  an  acid  solution  of  chloride  of  lead  is  precipitated  by  a 
current  of  sulphuretted  hydrogen,  the  precipitate  which  is  first 
formed  is  of  a bright  red  colour,  but  by  the  further  action  of  the 
gas  it  becomes  black,  and  furnishes  sulphide  of  lead : the  red  com- 
pound is  a chlorosulphide  of  lead  (3  PbS,  2 PbCy. 

Bromide  of  Lead  (PbBr2=367,  or  PbBr=183-5 ; sp.  gr. 
6-03)  is  white,  sparingly  soluble,  and  fusible  at  a red  heat. 

(902)  Iodide  of  Lead  (PW2— 461,  orPbI=230-5;  sp.  gr. 
0-384)  is  easily  obtained  by  precipitating  a solution  of  the  nitrate 
or  the  acetate  of  lead  by  one  of  iodide  of  potassium  : it  is  thrown 
down  as  a bright  yellow  powder,  sparingly  soluble  in  cold  water, 
but  more  soluble  in  hot  water  ; the  solution  as  it  cools  deposits 
beautiful  yellow  spangles  of  a silky  lustre  ; they  may  be  fused  by 
a moderate  heat. 

The  iodide  of  lead  forms  double  salts  with  the  iodides  of  the 
alkaline  metals.  Several  oxyiodides  of  lead  may  also  be  formed. 

A remarkable  compound  of  oxyiodide  of  lead  with  carbonate 
of  lead  [Bb^ei,  . 4Pbee3,  or  Pbl,  PbOI  . 4 {FhOfiO,}],  of  a 
blue  colour,  may  be  obtained  by  precipitating  the  tribasic  acetate 


SULPHATE,  SULPHITE,  AND  NITRATES  OF  LEAD. 


639 


of  lead  with  a mixture  of  1 atom  of  biniodide  of  potassium  and  2 
of  carbonate  of  potassium. 

‘ Fluoride  of  lead  (PbF^,  or  PbF)  is  white,  insoluble,  and 
fusible. 

(903)  Sulphate  of  Lead  (p-bS0-4=3O3,  or  PbO, 803=151-5) ; 
8p.  Gr.  6*30  : Comp,  in  100  jjarts^  PbO,  73-61 ; SO3,  26-39. — 
This  compound  occurs  native  in  white  prismatic  or  octobedral 
crystals ; it  is  also  found  in  combination  with  carbonate  of  lead. 
W^heii  procured  artificially,  it  forms  a white  powder,  slightly 
soluble  in  nitric  acid,  freely  so  in  a solution  of  acetate  of  ammo- 
nium of  sp.  gr.  1-060,  or  upwards.  An  excess  of  sulphuric  acid, 
however,  throws  down  nearly  the  whole  of  the  lead  as  sulphate 
from  the  acetic  solution.  Tlie  other  salts  of  ammonium  also  pos- 
sess the  property  of  dissolving  sulphate  of  lead,  but  to  a smaller 
extent.  They  form  double  salts  with  the  sulphate  of  lead,  and 
these  compounds  are  slightly  soluble.  Sulphate  of  lead  is  dis- 
solved also,  to  some  extent,  by  concentrated  sulphuric  acid,  hut 
it  is  insoluble  in  pure  water.  Hot  hydrochloric  acid  likewise 
dissolves  it  sensibly,  and  deposits  crystals  of  chloride  of  lead  on 
cooling,  leaving  a portion  of  sulphuric  acid  free  in  the  solution. 
It  may  he  obtained  by  adding  sulphuric  acid,  or  a solution  of  any 
sulphate,  to  a solution  of  one  of  the  salts  of  lead.  It  is  furnished 
in  large  cpiantities  as  a secondary  product  during  the  preparation 
of  acetate  of  aluminum.  Like  all  the  insoluble  compounds  of 
lead,  it  is  gradually  decomposed  by  sulphuretted  hydrogen  ; a 
black  sulphide  of  lead  is  formed,  and  the  acid  is  set  free.  Before 
the  blowpipe  it  yields  metallic  lead  in  the  reducing  fiame,  though 
it  will  hear  a high  temperature  without  decomposition  when 
heated  alone.  Sulphate  and  sulphide  of  lead  when  heated  to- 
gether decompose  each  other,  as  explained  when  speaking  of 
the  process  of  lead  smelting  (890).  The  sulphate  is  reduced 
when  heated  with  carbon,  but  the  products  vary  with  the  pro- 
portion of  carbon  used,  as  may  be  seen  by  the  annexed  equa- 
tions : — 

2 Pbse,  -f  e = 2 Pho + ee^  + 2 SO3 ; 

Pbso, + pb + ee^ + so, ; 

Pbse,  -k  4 e= Pbs  -f  4 00. 

Sulphite  of  lead  (PbS03,  or  PbO, SO,)  is  a white  powder,  in- 
soluble in  water,  but  soluble  in  acids  with  escape  of  sulphurous 
acid  : when  heated  it  is  partially  decopmosed,  with  escape  of  sul- 
phurous anhydride. 

(904)  Nitrates  of  Lead. — Oxide  of  lead  forms  several  salts 
with  nitric  acid,  viz.,  Pb  2 NO, ; Pb  2 N03,Pb0Il,0 ; 2 (Pb  2 NO3, 
2 PbO)  3 11,0 ; and  2 (Pb  2 NO,,  5 PbO)  3 11,0. 

Nitrate  of  Lead  (Pb  2 NOa=331,  or  Pb0,N03=165-6) ; f^p. 
yr.  4-40  : Comp,  in  \t)t) parts ^ PbO,  67-22  ; NjO^,  32-78. — This 
salt  is  easily  formed  by  dissolving  litharge  or  metallic  lead  in 
an  excess  of  nitric  acid  somewhat  diluted:  it  crystallizes  in  regu- 
lar anhydrous  octohedra,  which  arc  sometimes  transparent,  but 
more  commonly  milk-white  and  opaque.  It  is  soluble  in  about 


640 


NITRITES  AND  PHOSPHATES  OF  LEAD. 


8 parts  of  cold  water,  is  sparingly  soluble  in  nitric  acid,  and  in- 
soluble in  alcohol.  If  heated  to  redness,  it  decrepitates  strongly, 
then  fuses  and  is  decomposed  ; oxygen,  and  peroxide  of  nitrogen 
(XO2),  in  the  anhydrous  state,  are  evolved  (367),  while  protoxide 
of  lead  remains.  Caustic  ammonia,  if  added  to  a solution  of  the 
nitrate,  in  quantity  insufficient  to  combine  with  the  whole  of  the 
acid,  throws  down  a sparingly  soluble  dibasic  nitrate  of  lead 
(Pb  2 XO3,Pb0,Il2O).  This  salt  may  be  also  procured  by  boil- 
ing the  normal  nitrate  with  litharge.  It  is  said  to  be  deposited 
from  its  solution  in  hot  water,  in  small  opaque  anhydrous  crystals, 
which  decrepitate  forcibly  when  heated  ; I have,  however,  always 
found  it  to  crystallize  in  leaflets  with  II2O,  and  this  accords  with 
Peligot’s  observation.  By  precipitating  the  nitrate  with  a slight 
excess  of  ammonia,  a tribasic  nitrate  is  formed,  which  falls  as  a 
white  powder,  containing  1^  bj  adding  a large  excess 

of  ammonia  to  the  normal  nitrate,  a kexanitrate  is  formed  ; it  also 
contains  1|-  II^O  (Berzelius.) 

(905)  hTiTRiTEs  OF  Lead. — The  action  of  metallic  lead  on  a 

solution  of  the  nitrate  of  lead  is  remarkable  ; the  solution  of  the 
normal  salt  dissolves  the  metal  without  evolution  of  gas,  whilst 
basic  salts  of  the  lower  oxides  of  nitrogen  are  produced.  Several 
of  these  compounds  may  be  obtained;  the  composition  of  the 
basic  salt  varying  according  to  the  proportions  of  the  normal 
nitrate  and  of  the  metal  employed.  When  a solution  of  331 
parts,  or  1 equivalent  of  nitrate  of  lead,  is  heated  to  about  140°, 
with  207  parts  or  1 equivalent  of  metallic  lead,  perfect  solution 
takes  place,  and  a salt  having  the  formula  (2  PbX03,H20)  crys- 
tallizes on  cooling,  in  yellow  plates;  for  Pb  2 XOg-f  Pb  = 2 Pb 
XO-3.  If  1-|-  equivalent  of  lead  be  employed  instead  of  1 equi- 
valent, another  salt,  composed  of  (7  PbO,HO,  2X04,2Aq),  or 
(4  PbXO-3,  3 PbOH^O),  crystallizes  in  heavy  orange-red  needles. 
By  boiling  a very  dilute  solution  of  the  nitrate  with  2 equiva- 
lents of  lead  for  some  time,  a third  salt,  which  is  a tetranitrite  of 
lead^  composed  of  (Pb  2 . 3 Pb0,H20,  or  4 Pb0,X03,  Aq  ; 

Peligot),  crystallizes  in  hard  rose-red  silky  needles,  which  are  but 
sparingly  soluble  in  hot  water,  and  still  less  so  in  cold  : a normal 
nitrite  of  lead,  Pb  2 XO^,  may  be  formed  by  transmitting  a 
current  of  carbonic  acid  through  the  solution  of  the  basic  ni- 
trite just  mentioned  : a dibasic  nitrite,  Pb  2 X02,Pb0,Il20, 
as  well  as  a tribasic  nitrite,  Pb  2 XO^,  2 PbO,  have  also  been 
formed. 

(906)  Phosphates  of  Lead. — The  salts  of  lead  give  a white 
precipitate  with  the  soluble  salts  of  each  modiflcation  of  phos- 
phoric acid ; these  phosphates  are  principally  interesting  as  fur- 
nishing an  easy  means  of  procuring  the  hydrates  of  these  different 
acids,  by  suspending  the  corresponding  salt  in  water,  and  decom- 
posing it  by  means  of  a current  of  sulphuretted  hydrogen.  All 
the  phosphates  of  lead  are  soluble  in  nitric  acid.  The  pyrophos- 
phate of  lead  (Pb2P207),  before  the  blowpipe  furnishes  a semi- 
transparent globule,  which  becomes  remarkably  cr^^stalline  on 
cooling.  Tribasic  phosphate  of  lead  occurs  both  massive  and 


CARBONATES  OF  LEAD. 


641 


crystallized  in  six-sided  prisms ; the  produce  of  a small  mine  at 
Wissembourg  consists  principally  of  this  compound,  mixed  with 
the  carbonate  of  lead.  A chlorophosjphate  of  lead  [PbCl^,  3 (Pbg  2 
PO4),  gr.  7*01]  is  found  native  in  yellow  six-sided  prisms  : it  is 
readily  fusible. 

Bor  ado  anhydride  may  be  fused  with  oxide  of  lead  in  all  pro- 
portions ; borate  of  lead  enters  into  the  composition  of  Faraday’s 
optical  glass.  The  silicates  of  lead  enter  largely  into  the  forma- 
tion of  flint  glass.  Silica  and  oxide  of  lead  may  be  fused  to- 
gether in  almost  all  proportions  ; the  larger  the  proportion  of  silica, 
the  less  fusible  is  the  compound,  and  the  freer  from  colour  : with 
an  excess  of  oxide  the  glass  is  yellow. 

(907)  Carbonates  of  Lead.  — h7ative  carbonate  of  lead 
(PbOOg,  or  Pb0,C02 ; sp.  gr.  6*46)  is  a beautiful  mineral  met 
with  crystallized  in  transparent  needles,  or  in  flbrous  masses, 
which  are  generally  opaque.  It  is  soft  and  brittle,  and  usually 
accompanies  the  deposits  of  galena,  in  small  quantity.  The 
manufacture  of  carbonate  of  lead,  or  white  lead.,  for  the  painter, 
is  carried  on  upon  a large  scale.  Several  methods  are  in  use  in 
the  preparation  of  this  compound : in  all  of  them,  however,  cer- 
tain peculiarities  in  the  properties  of  the  acetates  of  lead  are 
taken  advantage  of.  There  are  two  acetates  of  lead — a normal 
salt,  Pb  2 PJI3O2,  and  a tribasic  acetate,  (Pb  2 2 PbO). 

A solution  of  the  normal  acetate  in  the  presence  of  an  excess  of 
oxide  of  lead  readily  unites  with  it  to  form  the  basic  salt,  and 
this  basic  acetate,  if  exposed  to  an  atmosphere  containing  car- 
bonic anhydride,  rapidly  absorbs  this  gas,  and  is  thus  converted 
into  carbonate  of  lead  and  normal  acetate.  These  changes  may 
be  thus  represented  : — 

Acetate  of  Lead.  Ox.  Lead.  Tribasic  Acetate  of  Lead. 

Pb  2 O2II3O2  -f  2 PbO=Pb  2 O2H3O2,  2 PbO ; and 

Tribasic  Acetate  of  Lead.  Carb.  Auhyd.  Acetate  of  Lead. 

Pb  2 e^H  A,  2 PbO + 2^2=Pb7oji^2  -f  2 Pboo3. 

The  following  is  the  plan  which  is  known  as  the  Dutch  method 
of  making  white  lead  ; it  is  still  carried  on  extensively  at  Lille : 
— A number  of  small  glazed  earthen  pots  are  partially  tilled  with 
a weak  malt  vinegar,  and  in  each  pot  a thin  sheet  of  cast  lead 
coiled  into  a spiral  form  is  placed ; these  pots  are  then  imbedded 
in  spent  tan,  arranged  in  rows,  and  covered  with  boards ; 
thus  prepared,  they  are  placed  in  tiers  one  above  another  to  a 
depth  of  18  or  20  feet, — the  warmth  given  out  during  the  putre- 
faction of  the  tan  volatilizes  the  vinegar,  and,  under  the  united 
influence  of  the  air  and  acid  fumes,  an  oxide  of  lead  is  formed 
upon  the  surface  of  the  coils  of  metal ; this  oxide  reacts  upon  the 
acetic  acid  which  rises  in  vapour  from  the  vinegar,  and  a basic 
acetate  of  lead  is  thus  produced.  The  carbonic  anhydride  which 
is  supplied  from  the  decomposing  hot-bed  readily  converts  this 
salt  into  carbonate  of  lead  and  the  normal  acetate ; whilst  the 
41 


642 


CARBONATES  OF  LEAD WHITE  LEAD. 


latter  again  combines  with  a fresh  portion  of  newly-formed  oxide,  ^ 
and  produces  the  basic  acetate,  which  is  decomposed  as  before  : 
successive  decompositions  and  recompositions  ensue,  as  the  normal 
acetate  immediately  dissolves  any  oxide  of  lead  presented  to  it, 
forming  the  basic  acetate,  which  again  is  decomposed  under  the 
influence  of  carbonic  anhydride.  Eolled  lead  cannot  be  advanta- 
geously substituted  for  cast  lead  in  this  process,  and  the  purest 
lead  is  always  preferred,  traces  of  iron  being  sufficient  to  impart 
an  objectionable  yellow  tinge  to  the  product. 

Since  the  lead  in  this  process  derives  oxygen  from  the  air,  it  is 
necessary  that  the  atmosphere  be  allowed  to  come  sufficiently  into 
contact  with  the  coils.  The  quantity  of  vinegar  which  is  required 
is  very  small,  1 part  of  pure  acetic  acid  to  100  parts  of  lead  being 
amply  sufficient.  The  carbonate  is  thus  produced  very  slowly, 
and  forms  a compact  layer  upon  the  surface  of  the  coils.  It  al- 
ways contains  an  excess  of  hydrated  oxide  of  lead,  but  the  pro- 
portion of  this  oxide  is  liable  to  vary.  Mulder  found  a specimen 
which  he  examined,  to  contain  PhOH^^,  3 PbOOg ; but  more 
usually  it  consists  of  PbOH^O,  2 PbOOg.  By  unrolling  the  coils, 
the  carbonate  breaks  off  in  flakes  of  a dead- white  colour,  furnish- 
ing the  kind  of  white  lead  most  approved  by  artists  and  colour- 
men.  Before  it  is  fitted  for  their  use,  it  is  subjected  to  the  pro- 
cess of  grinding  and  levigation,  by  which  it  is  reduced  to  an  im- 
palpable powder.  Although  this  pulverization  is  performed  un- 
der water,  the  fine  particles  of  the  carbonate  become  diffused 
through  the  air,  rendering  the  operation  very  deleterious  to  the 
workmen. 

This  circumstance,  combined  with  the  length  of  time  requisite 
for  the  formation  of  the  carbonate,  induced  Thenard  to  substitute 
for  the  foregoing  process  the  direct  decomposition  of  a solution  of 
the  basic  acetate  of  lead,  by  means  of  a current  of  carbonic  anhy- 
dride ; the  carbonate  is  thus  procured  in  a state  of  extreme  divi- 
sion, and  as  rapidly  as  can  be  desired ; it  has,  however,  less  opa- 
city, or  body,  owing  to  its  being  deposited  in  exceedingly  minute 
crystals,  and  is  inferior  as  a pigment  to  that  procured  by  the 
Dutch  method. 

A third  process,  at  one  time  employed  at  Birmingham,  con- 
sisted in  exposing  litharge,  moistened  with  a solution  of  acetate  of 
lead,  to  a current  of  impure  carbonic  anhy chide,  obtained  from 
the  combustion  of  coke. 

Carbonate  of  lead  is  easily  decomposed  by  heat,  giving  off  car- 
bonic anhydride,  and  leaving  a residue  of  protoxide  of  Tead.  It, 
is  insoluble  in  water,  unless  the  water  be  charged  with  carbonic 
acid  to  a large  extent,  when  it  is  slightly  soluble.  It  is  also  solu- 
ble in  most  of  the  acids  with  effervescence,  and  is  likewise  dis- 
solved by  solutions  of  potash  and  soda.  It  is  quickly  blackened 
by  exposure  to  sulphuretted  hydrogen  both  in  the  form  of  gas  and 
when  in  solution  in  water.  This  liability  to  blacken  by  the  action 
of  the  gas  is  possessed  by  all  the  salts  of  lead,  in  common  with  the 
carbonate,  and  is  a serious  objection  to  the  use  of  the  compounds 
of  lead  in  pigments. 


643 


characters  of  the  compounds  of  lead. 

Carbonate  of  lead  is  often  fraudulently  mixed  with  a consider- 
able quantity  of  sulphate  of  barium,  which  is  much  cheaper, 
though  its  whiteness  is  less  intense ; a small  quantity  of  indigo, 
charcoal,  or  sulphide  of  lead  is  usually  added  to  white  lead,  in  or- 
der to  substitute  a bluish  tint  for  the  natural  tendency  of  the 
white  towards  yellow. 

(008)  Characters  of  the  Compounds  of  Lead. — The  salts  of 
lead  with  colourless  acids  are  colourless.  The  soluble  salts,  even 
when  neutral  in  composition,  redden  litmus  ; but  its  basic  salts 
have  an  alkaline  reaction.  They  have  a sweetish  metallic  taste, 
and  exert  a poisonous  action  on  the  system.  In  cases  of  poison- 
ing by  a dose  of  the  soluble  salts  of  lead,  the  best  antidote  is  sul- 
phate of  magnesium,  or  of  sodium,  which  forms  an  insoluble  and 
inert  sulphate  of  lead.  This,  however,  is  of  no  avail  in  the  more 
usual  forms  of  lead  poisoning,  in  which  the  metal  is  introduced  in 
minute  quantities,  unintentionally,  in  water,  or  in  articles  of  diet. 

The  best  tests  for  lead  are  the  formation  of  a white  insoluble 
sulphate  when  sulphuric  acid  or  any  of  the  soluble  sidphates  are 
added  to  its  solutions  ; this  precipitate  is  insoluble  in  cyanide  of 
potassium  and  in  acetic  acid,  but  slightly  soluble  in  nitric  acid, 
more  readily  soluble  in  excess  of  hydrate  of  potash,  freely  soluble 
in  acetate  of  ammonium ; a black  sulphide  with  sulphuretted  hy- 
drogen and  with  sidphide  of  ammonium^  insoluble  in  excess  of 
the  precipitant  and  in  solution  of  the  alkalies  ; a yellow  chromate 
with  chromate  of  potassium  • and  a yellow  iodide  with  iodide  of 
potassium.  Hydrochloric  acid  and  the  soluble  chlorides  give  in 
moderately  diluted  solutions  of  lead,  a white  crystalline  precipi- 
tate of  chloride  of  lead,  readily  soluble  in  excess  of  potash.  ITy- 
drate  of  potash  gives  a white  precipitate  of  the  hydrated  oxide, 
which  is  redissolved  in  an  excess  of  the  fixed  alkalies,  but  is 
nearly  insoluble  in  ammonia.  Carbonate  of  potassium  or  of 
sodium  gives  a dense  white  precipitate  of  white  lead,  which  is 
insoluble  in  excess  of  the  precipitant.  IVIany  other  insoluble 
white  salts  may  be  formed,  as  the  phosphate,  arseniate,  the  ferro- 
cyanide,  and  the  cyanide  : the  latter  is  insoluble  in  excess  of 
cyanide  of  potassium,  but  soluble  in  diluted  nitric  acid.  All  the 
insoluble  salts  of  lead  are  soluble  in  a solution  of  caustic  potash. 
Lead  has  a remarkable  tendency  to  form  basic  salts,  but  the 
number  of  its  double  salts  is  not  great.  From  the  insolubility 
of  many  of  its  organic  compounds,  it  has  been  much  used  to 
determine  the  combining  proportion  of  organic  bodies.  It  is, 
however,  more  advantageous  to  employ  the  oxide  of  silver  for 
this  purpose,  because  the  oxide  of  lead  is  to  a small  extent  volatile. 

Lead,  like  most  other  metals  of  comparatively  weak  attraction 
for  oxygen,  is  easily  precipitated  from  its  solutions  in  the  metallic 
state,  by  the  metals  more  oxidizable  than  itself:  if,  for  instance,  a 
piece  of  zinc  be  suspended  in  a solution  containing  lead,  crystals 
of  lead  are  deposited  in  a beautiful  arborescent  form. 

Before  the  blowpipe  on  charcoal  the  salts  of  lead  yield  a soft 
white  malleable  bead  of  the  metal,  surrounded  by  a yellow  ring  of 
oxide. 


644 


THALLIUM. 


(909)  Estimation  of  Lead. — Lead  is  generally  estimated  in  the 
form  of  the  sulphate,  which  contains  68 per  cent,  of  the  metal. 
More  rarely  it  is  determined  from  the  protoxide,  of  which  100 
parts  correspond  to  92*82  of  lead : porcelain  crucibles  must  be 
employed  for  these  experiments,  since  oxide  of  lead  is  easily 
reduced  to  the  metallic  state,  in  which  case  it  would  form  an 
alloy  with  platinum,  and  would  ruin  a crucible  composed  of 
this  metal. 

Lead  may  be  sej)arated  by  means  of  sulphuric  acid  from  all 
the  metals,  except  its  insoluble  combinations  wdth  the  metallic 
acids.  The  following  is  the  method  to  be  adopted : — If  a galena 
or  an  alloy  of  lead  is  to  be  analysed,  it  should  be  treated  with 
concentrated  nitric  acid  until  it  is  completely  decomposed,  and 
then  evaporated  nearly  to  dryness  with  a small  excess  of  sulphuric 
acid ; the  nitric  acid  is  thus  expelled,  and  the  metals  are  con- 
verted into  sulphates ; the  mass  is  treated  wdth  w^ater,  which  dis- 
solves out  all  the  metals  except  lead,  tin,  and  antimony : quartz, 
or  sulphate  of  barium,  if  present,  would  also  be  contained  in  this 
insoluble  portion.  The  insoluble  residue  is  collected  and  weighed, 
and  then  digested  repeatedly  in  a solution  of  acetate  of  ammonium 
of  sp.  gr.  1*065  ; after  wdiich  the  residue  is  again  washed,  dried, 
and  weighed : the  difference  indicates  the  proportion  of  sulphate 
of  lead  which  is  dissolved  out  from  the  oxides  of  antimony  and 
tin,  and  from  the  quartz  and  sulphate  of  barium.  The  lead  may 
be  obtained  from  its  solution  in  the  acetate  of  ammonium  by  the 
addition  of  sulphide  of  ammonium  : and  the  sulphide  of  lead  thus 
precipitated  may  be  converted  into  sulphate  by  means  of  a mixture 
of  nitric  and  sulphuric  acids.  It  is  evaporated  down  to  dryness, 
ignited,  dried,  and  weighed. 

The  salts  of  lead  with  the  metallic  acids  may  be  decomposed 
by  fusing  them  with  a mixture  of  caustic  potash  and  carbonate 
of  potassium : the  metallic  acid  forms  a salt  with  potassium,  and 
may  be  dissolved  by  the  addition  of  water,  whilst  a portion  of 
the  oxide  of  lead  is  left. 

§ III.  Thallium,  T1=204.  Sp.  Gr.  11*81  to  11*91;  Fusinq- 
jpoint^  561°. 

(910)  This  metal  was  discovered  by  Crookes  in  1861  {Phil. 
Mag.  lY.  xxi.  p.  301),  as  he  was  examining  the  spectrum  reac- 
tions of  a seleniferous  deposit  from  the  sulphuric  acid  manufac- 
tory of  Tilkerode  in  the  Hartz  ; and  in  the  following  year  it  was 
obtained  more  abundantly  from  a similar  source  in  Belgium  by 
Lamy,  to  whose  paper  {Ann.  de  Chimie^  III.  Ixvii.  385)  the 
reader  is  referred  for  details,  and  to  those  of  Crookes,  Phil.  Trans. 
1863,  and  Journ.  Chem.  Soc.  1864,  p.  112. 

The  first  indication  of  its  ju’esence  was  furnished  by  the 
occurrence  of  a single  brilliant  green  line  nearly  coincident  with 
one  of  the  inconspicuous  lines  of  the  barium  spectrum,  fia  5 (p.  151, 
part  I.  fig.  82,  T1  a.)  This  green  colour  suggested  to  Crookes  the 
name  of  thallium  (from  ^aXXocr,  a budding  twig).  In  the  secondary 


THALLIUM.  645 

current  of  an  indnction-coil,  additional  lines  make  their  appearance 
{Proceed.  Boy.  Soc.  1863,  xii.  401). 

Thallium  occurs  hut  sparingly,  and  has  hitherto  been  prin- 
cipally obtained  from  the  Spanish,  Belgian,  and  Bolivian  pyrites. 
Its  compounds  have  been  met  with  by  Bunsen  in  the  mother- 
liquor  of  a spring  from  the  Hartz,  as  well  as  in  some  other 
mineral  waters,  and  particularly  in  that  of  Nauheim,  in  the 
mother-liquor  of  which  Bottger  found  it  associated  with  chlorides 
of  coesium  and  rubidium. 

Pure  thallium  is  a heavy  diamagnetic  metal,  having  a strong 
resemblance  to  lead  in  physical  properties,  though  its  specific 
gravity  is  a little  higher.  The  specific  heat  of  thallium  is  0‘03355, 
Begnault  (or  0*0325,  Lamy),  hence  the  metal,  as  its  compounds 
sliow,  is  of  the  same  class  with  silver,  which  it  in  some  of  its  reac- 
tions resembles  : like  silver  and  the  metals  of  the  alkalies,  it  is  a 
monad  element.  Its  atomic  volume  is  17*2.  The  freshly  cut 
surface  of  thallium  has  a bluish-white  lustre,  resembling  that  of 
zinc,  but  it  quickly  tarnishes  by  exposure  to  the  air,  and  a thin 
film  of  oxide  is  formed.  It  is  sufficiently  soft  to  take  impressions 
from  the  nail  ; it  may  be  hammered  into  foil,  and  pressed  into 
wire,  though  its  tenacity  is  small.  If  rubbed  upon  paper  it  leaves 
a bluish  trace  resembling  that  produced  by  lead,  but  the  streak 
soon  oxidizes  and  becomes  yellowish.  It  melts  at  561°  (Crookes; 
554°  Lamy),  oxidizes  rapidly  in  the  air,  and  if  heated  to  about 
600°  in  oxygen  it  takes  fire  and  burns  with  an  intense  pure  green 
light.  The  metal  does  not  appear  to  be  sensibly  volatile  below  a 
red  heat.  If  heated  with  chlorine  it  burns  vigorously  in  the  gas, 
and  it  also  combines  directly  with  bromine,  with  iodine,  with  sul- 
phur, and  with  phosphorus.  Nitric  acid  attacks  thallimn  with 
great  energy  ; diluted  sulphuric  acid  also  dissolves  it  quickly  with 
evolution  of  hydrogen  ; but  the  action  of  hydrochloric  acid,  even 
when  boiled  upon  it,  is  but  slow,  owing  to  the  insolubility  of  the 
chloride.  The  tarnished  metal  becomes  bright  when  plunged  into 
water,  owing  to  the  solubility  of  the  oxide ; but  the  metal  may  be 
preserved  in  water  unaltered.  Thallium  may  be  easily  alloyed 
with  most  of  the  metals,  and  particularly  with  zinc,  lead,  anti- 
mony, tin,  copper,  silver,  and  platinum. 

The  easiest  mode  of  extracting  the  metal  consists  in  treating 
the  thalliferous  dust  deposited  in  the  flues  of  the  sulphuric  acid 
works  before  they  enter  tlie  chamber,  with  an  equal  weight  of 
boiling  water,  drawing  off  the  clear  liquor,  and  treating  the  uiidis- 
solved  portion  again  in  like  manner.  The  clear  liquors  are  next 
mixed  with  a large  excess  of  strong  hydrochloric  acid,  by  which 
a |)recipitate  of  impure  chloride  of  thallium  is  obtained.  This  is 
then  washed,  pressed,  and  decomposed  by  heating  it  with  an  equal 
weight  of  concentrated  sulphuric  acid.  The  acid  sulphate  of  thal- 
lium thus  formed  is  dissolved  in  about  20  parts  of  water,  filtered, 
and  again  precipitated  as  tolerably  pure  chloride  by  the  addition 
of  hydrochloric  acid  in  excess.  This  ])recipitate  is  washed,  ])ressed, 
and  again  converted  into  sulphate  by  adding  about  two-thirds  of 
its  weight  of  oil  of  vitriol  and  heating  till  all  the  hydrochloric  acid 


OXIDES  AXD  SALTS  OF  THALLIUM. 


Gi6 

is  expelled ; a dense  liquid  is  thus  obtained,  which  as  it  cools  so- 
lidifies to  a white  mass  of  acid  sulphate  of  thalhum.  This  is  dis- 
solved in  about  ten  times  its  weight  of  hot  water,  filtered,  and 
allowed  to  crystallize.  It  may  be  purified  by  recrystaUization, 
and  if  the  solution  be  decomposed  by  metallic  zinc,  or  by  the  vol- 
taic battery,  pure  thallium  is  abundantly  and  easily  obtained.  It 
may  be  melted  in  an  iron  crucible  heated  over  a gas  fiame,  main- 
taining a current  of  coal-gas  through  the  crucible  to  prevent  oxi- 
dation. 

(911)  Oxides  of  Thallium. — Thallium  appears  to  form  three 
oxides — a siiboxide  of  unkno’svn  composition  ; an  oxide  corre- 
sponding to  the  principal  oxide  of  silver,  Tl^O ; and  a superior 
brown  oxide,  possibly  Tl^Oj,  formed  at  the  positive  electrode  dm’- 
ing  electrolysis  of  the  sulphate  of  thallium  by  a weak  current. 

The  most  important  of  these  is  the  oxide  Tl.^0,  which  is  very 
soluble  in  water,  furnishing  an  alkaline  caustic  solution  which 
absorbs  carbonic  acid  from  tlie  air.  The  solution  is  colomless,  and 
by  evaporation  in  vaciw  furnishes  groups  of  pale-yellow,  hydi’ated 
prismatic  needles,  which  blacken  as  the  evaporation  proceeds  ; 
when  heated  to  about  600°  it  becomes  anhydrous,  and  fuses  to  a 
l)rown  liquid  which  becomes  yellow  on  cooling.  A solution  of 
oxide  of  thallium  causes  a precipitate  in  solutions  of  salts  of  mag- 
nesium, manganese,  zinc,  lead,  iron,  and  many  other  metals,  but 
does  not  redissolve  the  precipitate  even  if  the  oxide  of  thallium 
be  in  excess. 

Sulphide  of  thallium  (TI^S)  may  be  obtained  as  a brownish- 
black  curdy  precipitate,  by  adding  sulphide  of  ammonium  to  the 
soluble  salts  of  thallium.  The  precipitate  is  not  soluble  in  excess 
of  the  aUvaline  sulphides.  Acetate  and  oxalate  of  thallium  in 
neutral  solutions  are  precipitated  by  sulphuretted  hydi’ogen. 

Chloride  of  thcdliurn  (TlCl)  is  a yellowish-white  sparingly 
soluble  compound,  less  soluble  in  hydrochloric  acid  than  in  water, 
sparingly  soluble  in  ammonia.  Lamy  also  describes  three  other 
chlorides,  TfiClg  and  TlCfi,  and  one  with  still  more  chlorine,  pos- 
sibly TICI3.  The  protiodide  and  hromide  are  yellow  and  sparingly 
soluble. 

Sulphate  of  thallium  (TfiSOJ  is  a soluble  salt  which  crystal- 
lizes in  anhydrous  six-sided  prisms  which  are  easily  fusible.  With 
sulphate  of  aluminum  it  furnishes  an  octohedi’al  alum.  An  acid 
sulphate  of  thallium  exists. 

Tlie  nitrate  (TIXO3)  crystallizes  in  anhydrous  prismatic  needles 
which  melt  easily:  tliey  are  insoluble  in  alcohol.  It  is  easily 
obtained  by  dissolving  the  metal  in  nitric  acid. 

The  carbonate  (I"l3O0'3)  furnishes  long  flattened  prismatic 
needles,  which  require  about  25  parts  of  cold  water  for  solution. 
It  is  easily  fusible. 

The  phosphate  is  sparins^ly  soluble  and  is  fusible. 

(912)  The  salts  of  thallium  are  poisonous  when  taken  inter- 
nally. They  are  nearly  colourless,  when  formed  with  colourless 
acids : solutions  of  the  salts  of  thalhum  are  easily  decomposed  by 
a feeble  electric  cuiTent,  with  deposition  of  plates  of  the  metal 


INDIUM MEUCURY. 


647 


upon  the  negative  electrode.  Metallic  zinc  also  precipitates  finely 
divided  metallic  thallium,  but  tin  does  not  reduce  the  metal. 

'No  precipitate  is  produced  in  solutions  of  the  sulphate  or  ni- 
trate of  thallium  by  the  hydrated  alkalies  j the  carhonates  give  a 
precipitate  only  in  concentrated  solutions.  Sulphuretted,  hydrogen 
gives  but  little  precipitate  in  solutions  of  the  nitrate,  chloride,  or 
sulphate.  Sulphide  of  ammonium  gives  a brownish-black  preci- 
pitate insoluble  in  the  sulphides  of  the  alkaline  metals.  Chlo- 
rides and  bromides  give  yellowish-white  sparingly  soluble  precipi- 
tates ; the  iodides  give  a reddish-yellow  precipitate ; cyanide  of 
potassium^  a wdiite  precipitate  soluble  in  excess  of  the  precipi- 
tant ; chromate  of  potassium^  a pale  yellow  precipitate  soluble  in 
diluted  acids,  insoluble  in  ammonia.  Wiih.  per  chloride  of  plati- 
num it  forms  a sparingly  soluble  double  salt. 

(912  a)  Indium. — Messrs.  Keich  and  Richter  have  ascertained 
the  existence,  in  a particular  variety  of  zinc  blende  found  at  Frei- 
berg, of  a substance  which,  when  introduced  into  the  flame  of  a 
gas-lamp  and  viewed  by  the  spectroscope,  discloses  2 bright  lines 
in  the  blue  and  indigo,  not  coincident  with  those  of  any  other 
known  body.  They  have  obtained  only  a few  grains  of  this  sub- 
stance, which  furnishes  a white  malleable  metal,  soluble  with  evo- 
lution of  hydrogen  in  hydrochloric  acid,  and  they  have  given  to 
it  the  name  of  indium.  Its  oxide  is  white  and  earthy-looking, 
insoluble  in  solutions  of  ammonia  or  potash,  and  not  precipitated 
by  sulphuretted  hydrogen  from  acid  solutions. — {Phil,  Mag.^ 
March,  1864). 


CHAPTER  XIX. 

GROUP  VIII. — THE  NOBLE  METALS. 

(913)  In  the  group  of  metals  with  which  we  conclude,  there 
is  a less  intimate  natural  relationship  than  in  any  of  the  preceding 
ones.  We  have,  for  instance,  in  silver  a monad  element,  in  mer- 
cury a dyad,  in  gold  a triad,  and  in  platinum  a tetrad  element; 
whilst  the  relations  of  the  remaining  metals  have  been  but  in- 
completely ascertained. 

It  is,  notwithstanding,  convenient  for  the  present  to  group 
them  together.  The  table  on  the  following  page  shows  in  one 
view  some  of  the  most  important  constants  hitherto  ascertained 
of  the  metals  enumerated  in  this  division. 

§ I.  Mercury  : Hg=200,  or  IIg=100.  Sp.  Gr.  as  liquid-  at  32°  F., 
13*596  ; as  vapour.,  6*976  ; Atomic  and  Mol.  Vol.  \ \ |.* 

(914)  Mercury  {hydrargyrum.,  from  vSup,  apyupov,  ‘liquid 
silver,’  or  Quicksilver)  is  one  of  the  metals  which  have  been 

* The  molecule  of  the  vapour  of  mercury  'X)ntains  only  1 atom  of  the  metal  Hg 
like  zinc,  cadmium,  and  other  metallic  dyads. 


648 


EXTKACTION  OF  MEKCUKY. 


Metals. 

Svm- 

bol. 

Atomic 

weight. 

i 

Atomic  1 
voL  I 

1 

Specific 

heat. 

Fusing- 

point. 

j Specific 

1 gravity. 

Electric 
conduc- 
tivitv 
at  32®. 

Mercury 

Hg 

200-0 

14-56  1 

0-0319 

—39 

13-56 

1-63* 

Silver 

^g 

108-0 

10-04  ! 

0-0570 

1873 

10-53 

100-00 

Gold 

Au 

196-7 

10-04  1 

0-0324 

2016 

19-34 

77-96 

Platinum 

Ft 

197-1 

9-12 

0 0324 

21-5 

10-53f 

Palladium 

Pd 

106-5 

9-12 

0-0593 

11-8 

12-641 

Rhodium 

Po 

104-3 

9-12 

0-0580 

12-1 

Ruthenium 

Pu 

104-2 

9-12 

11-4 

Osmium 

Os 

199-0 

9-12 

0-0306 

21-4 

I Iridium 

ir 

197-1 

9-12 

0-0326 

21-15 

longest  known  ; it  is  fonnd  in  but  few  localities,  and  occui’s  most 
frequently  in  the  form  of  the  sulphide  (cinnabar),  usually  accom- 
panied by  small  quantities  of  the  metal  in  its  native  state.  Oc- 
casionally it  is  met  with  combined  as  an  amalgam  with  silver,  and 
sometimes  in  the  form  of  calomel,  and  more  rarely  in  that  of 
iodide.  Generally  speaking,  its  ores  are  found  in  clay-slate,  or  in 
the  red  sandstone  underlying  the  coal,  and  not  unfrequently  among 
the  coal-measures  themselves.  The  most  productive  mines  are 
those  of  Almaden  in  Spain ; very  extensive  and  valuable  deposits 
of  cinnabar  have  likewise  lately  been  found  in  California ; and  the 
mines  of  Idria,  in  Transylvania,  have  long  been  extensively  worked. 
Considerable  quantities  are  likewise  raised  in  China  and  Japan, 
and  from  the  mine  of  Huancavelica,  in  Peru. 

Extraction. — The  metal  may  be  obtained  from  its  ore  either 
by  burning  off  the  sulphur  and  distilling  the  mercury, — a process 
which  is  applicable  both  to  cinnabar  amd  to  the  native  metal ; or 
by  heating  the  cinnabar  with  some  substance  capable  of  com- 
bining witli  the  sulphur,  and  forming  a fixed  compound,  from 
which  the  mercury  is  separated  by  heat.  At  Almaden,  the  metal 
is  extracted  by  the  first  process.  The  ore  employed  yields  about 
10  per  cent,  of  mercury.  Fig,  355  shows  a section  of  the  furnace 
made  use  of : — each  furnace  contains  two  grates,  and  on  the  lower 
one,  a,  provided  with  a chimney,  i,  a fire  ot  brushwood  is  kindled ; 
the  upper  grating  is  formed  by  a brick  arch,  5,  perforated  with 
numerous  apertures ; on  this  arch  the  sulphide  rests,  the  poorer 
pieces  of  ore  being  placed  at  the  bottom.  The  brushwood  quickly 
kindles  the  sulphur  in  the  ore,  which  afterwards  by  its  combustion 
maintains  sufficient  heat  to  continue  the  operation  without  the  use 
of  any  other  fuel : sulphurous  anhydride  is  formed,  and  the  libe- 
rated mercury  distils,  and  is  condensed  in  wide  earthen  pipes,  d, 
connected  with  the  upper  aperture,  c,  of  the  furnaces ; these  pipes 
are  termed  alndeU.  The  aludels  are  supported  on  a doubly  in- 
clined plane  of  masonry ; at  the  lowest  point  a perforation  is  made, 
to  allow  of  the  escape  of  the  mercury  into  a brick  channel, 
tlirough  which  it  runs  into  a well ; the  further  end,  of  the 
aludels  opens  into  a condensing  chamber,  in  which  an  additional 
quantity  of  mercury  is  deposited  in  the  trough,  g : the  sulphurous 
* At  73°.  f At  09-2°.  t At  63°. 


PURIFICATION  OF  MERCURY. 


649 


anhydride  escapes  into  the  air,  through  the  chimney,  A,  Conside- 
rable waste  of  metal  is  incurred  during  this  process,  from  the  in- 
complete manner  in  which  the  condensation  is  effected.  Iron 


Fig.  355. 


pipes,  however,  cannot  be  substituted  for  the  earthen  ones,  as  they 
become  corroded  rapidly  by  the  acid  vapours  produced  in  the 
operation. 

At  Idria  the  process  of  the  extraction  is  the  same  in  principle 
as  at  Almaden,  but  the  condensation  is  effected  more  completely 
by  transmitting  the  mercurial  vapours  through  a succession  of 
chambers  of  masonry,  instead  of  through  aludels. 

Another  plan  which  is  practised  in  the  Palatinate  consists  in 
mixing  the  sulphide  with  slaked  lime,  and  conducting  the  distil- 
lation in  cast-iron  furnaces  and  retorts.  The  mercury  is  condensed 
in  receivers  partly  filled  with  water,  while  sulphide  and  sulphate 
of  calcium  remain  behind  in  the  retort : 4 IIgS  + 4 OaO=4  Hg-f  3 
OaS-fOaSB^.  Iron  filings  also  decompose  cinnabar  when  heated 
with  it,  sulphide  of  iron  being  formed  while  mercury  is  liberated. 
Experience  has  shown  that  unless  the  ore  contain  at  least  of 
its  weight  of  the  metal,  or  3*8  lb.  per  ton,  it  is  too  poor  to  be 
advantageously  worked  by  the  methods  at  present  in  use. 

Pufification. — If  the  ore  contain  any  admixture  of  zinc  and 
bismuth,  small  portions  of  these  metals  are  liable  to  be  distilled 
over  witli  tlie  mercury.  In  this  case  a film  forms  upon  the  sur- 
face of  tlie  fluid  metal  when  it  is  agitated  in  contact  witli  air. 
The  purity  of  the  product  is  easily  seen  by  the  absence  of  this 
film,  and  by  the  perfect  mobility  and  sphericity  of  the  globules, 
which  do  not  wet  the  surface  of  non-metallic  objects.  Violette 
finds  that  the  distillation  of  mercury  on  the  large  scale  is  much 
facilitated  by  transmitting  a current  of  superheated  steam  at 
about  700°  through  the  retort  in  which  the  distillation  is  being 
effected.  A small  quantity  of  mercury  may  be  s])eedily  purified 
by  placing  it  in  a bottle,  with  a little  finely-powdered  loaf-sugar  ; 
the  mercury  should  not  occupy  more  than  one-fourth  of  the 


650 


MEECrEY ITS  PEOPEETIES  AXD  USES. 


capacity  of  the  bottle : the  bottle  is  then  closed,  and  briskly  agi- 
tated for  a fe^y  minutes : after  which  the  stopper  is  withdi*awn, 
and  fi*esh  aii*  is  blown  into  the  bottle  with  a paii*  of  bellows,  and 
the  agitation  is  repeated  : this  is  done  three  or  four  times,  and  the 
mercury  is  then  poured  into  a cone  of  smooth  writing-paper  in  the 
apex  of  which  a pin-hole  is  made  ; the  metal  runs  through,  and 
leaves  the  powdered  sugar  mixed  with  the  oxides  of  the  foreign 
metals,  and  a considerable  quantity  of  finely  diyided  mercmy. 

Generally  speaking,  the  mercury  imported  into  this  country  is 
almost  chemically  pure.  Any  foreign  metals  which  may  be  present 
in  it  may  be  remoyed  by  digesting  it  for  some  days  with  diluted 
nitric  acid  in  the  cold : the  mercury  should  be  placed  in  a shallow 
dish,  so  as  to  expose  a large  sm-face  to  the  acid,  and  it  should  be 
frequently  agitated ; the  acid  exerts  but  little  action  on  the  mer- 
cury so  long  as  any  more  oxidizable  metals  are  present.  A solu- 
tion of  nitrate  of  mercury  may  be  substituted  for  the  nitric  acid 
with  adyantage  ; in  this  case  the  mercury  is  deposited  from  the  so- 
lution and  takes  the  place  of  the  other  metals,  which  are  dissolved. 

(915)  P roperties. — ^lercurv  possesses  a lustre  resembling  that 
of  polished  sdver.  It  is  the  only  metal  that  is  fluid  at  common 
temperatures.  It  freezes  at  — 39°  F.,  and  contracts  considerably 
at  the  moment  of  congelation,  when  it  crystallizes  in  octohedra, 
of  sp.  gr.  about  Id  : in  this  state  it  is  malleable.  When  heated  to 
662°  it  boils,  and  forms  an  invisible,  transparent  vapour,  of  sp. 
gr.  6 ’9 76.  The  metal,  at  all  temperatures  above  40°,  undergoes 
slight  spontaneous  evaporation.  Its  specihc  gravity  at  60°  is  13*56. 
When  pm*e,  it  is  not  tarnished  by  exposure  to  air  and  moisture  at 
ordinary  temperatures,  but  if  heated  to  about  700°  or  800°  it 
absorbs  oxygen,  and  is  gradually  converted  into  the  red  oxide. 
Mercury  enters  into  combination  with  chlorine,  bromine,  and  with 
many  of  the  metals  at  ordinary  temperatures.  It  also  unites  with 
sulphur  and  with  iodine  without  the  aid  of  heat,  if  triturated  with 
them.  Hydrochloric  acid  is  without  action  upon  the  metal,  either 
when  cold  or  hot.  Hydriodic  acid  and  sulphuretted  hydi’ogen  are 
decomposed  slowly  by  it,  with  evolution  of  hydrogen.  Concen- 
trated sulphuric  acid  in  the  cold  produces  no  change,  but  when 
heated  with  it  is  decomposed ; sulphurous  anhydride  being  evolved, 
while  the  mercury  is  oxidized,  and  forms  a sulphate  by  reaction 
with  a portion  of  undecomposed  acid.  Strong  nitric  acid  dissolves 
it  with  rapidity,  extricating  nitric  oxide  in  abundance,  while  mer- 
curic nitrate  is  formed.  If  the  acid  be  dilute,  and  the  metal  in 
excess,  the  mercui*y  is  dissolved  slowly,  and  at  ordinary  tempera- 
tures mercurous  nitrate  is  the  result.  Mercury  may  be  obtained 
- in  a state  of  extreme  division,  by  precipitating  a solution  of  cor- 
rosive sublimate,  by  means  of  the  solution  of  stannous  chloride : 
the  cliloride  of  tin,  if  added  in  suflicient  quantity,  absorbs  all  the 
chlorine,  and  a grey  metallic  powder  subsides ; HgCl,  -f  SnCl, 
=H-hgSnCl^. 

Uses. — Mercury  is  employed  extensively  in  the  extraction  of 
gold  and  silver  from  their  ores,  by  the  processes  of  amalgamation  ; 
great  quantities  are  annually  sent  to  South  America  for  this  pur- 


OXroES  OF  MERCURY. 


651 


pose.  Its  amalgams  are  largely  employed  in  the  processes  of 
silvering  and  gilding.  Mercury  also  combines  readily  with  lead, 
copper,  bismuth,  tin,  and  zinc,  forming  amalgams  which  are  easily 
dissolved  by  an  excess  of  mercury.  Joule  succeeded  in  many 
cases  in  obtaining  definite  compounds  of  various  metals  with 
mercury,  by  subjecting  their  semi-solid  amalgams  to  hydraulic 
pressure,  amounting  to  the  enormous  extent  of  60  tons  upon  the 
square  inch  ; wdth  platinum  1 atom  was  united  with  two  atoms  of 
mercury.  With  silver,  with  copper,  and  wdth  iron,  the  amalgams 
contained  1 atom  of  each  metal ; with  zinc  and  with  lead  the 
amalgam  in  each  case  contained  1 atom  of  mercury  with  2 atoms 
of  the  other  metals,  while  the  amalagam  of  tin  was  represented 
by  the  formula  Sn,Hg. 

Mercury  is  also  used  in  the  preparation  of  vermilion,  which 
is  highly  valued  as  a pigment,  for  the  purity  and  permanence  of 
its  tint.  It  is  indispensable  in  the  construction  of  philosophical 
instruments ; and  it  is  well  known  in  various  forms  as  a valuable 
medicine.  It  exerts  a powerful  action  upon  the  animal  economy, 
producing  salivation,  and  seriously  impairing  the  health  of  the 
workmen  exposed  to  its  vapours,  giving  rise  to  a remarkable 
tremulous  state,  known  as  mercurial  palsy,  consequent  upon  a 
peculiar  form  of  nervous  debility.  By  trituration  with  saccharine 
or  oleaginous  substances,  it  admits  of  being  minutely  subdivided, 
and  a small  portion  of  it  becomes  oxidized,  to  which  the  active 
properties  of  blue-pill  appear  to  be  owing ; the  same  remark 
applies  to  the  mercurial  ointment,  and  the  pulvis  hydrargyri 
cum  cretd. 

(916)  Oxides  of  Mercury. — Mercury  forms  two  oxides,  the 
black  snboxide,  Hg^O,  and  the  red  oxide,  HgO : both  of  them  form 
salts  and  acids. 

Suboxide  of  mercury : Mercurous  oxide  (HgaO-  = 416,  or 
IIg2O=208);  Sp.  Gr.  10’68 : Comp,  in  parts,  Hg,  96*15; 
O,  3*85. — This  oxide,  though  a powerful  saline  base,  is  very 
unstable  when  isolated.  It  is  best  procured  by  triturating  finely 
levigated  calomel  with  a solution  of  potash  or  of  soda,  and  wash- 
ing the  black  precipitate  thus  obtained  with  cold  water.  It  must 
be  allowed  to  dry  spontaneously  in  a dark  place  ; the  oxide  thus 
obtained  is  anhydrous  ; even  when  dry,  mere  exposure  to  light, 
or  a very  gentle  heat,  is  sufiicient  to  convert  it  into  a mixture  of 
red  oxide  and  the  metal. 

(917)  Nitric  oxide.  Mercuric  oxide,  or  Red  oxide  of  mercury 
(HgO=216,  or  IIgO=108);  Sp.Gr.  11*29;  Comp,  in  parts, 
Hg,  92*59 ; 0,  7*41. — This  oxide  may  be  obtained  in  red  scales 
by  heating  metallic  mercury  to  700°  or  800°  in  a matrass : but  this 
process  is  very  slow,  and  not  productive  : it  is  more  conveniently 
prepared  by  the  decomposition  of  the  nitrate  by  lieat,  and  it  then 
has  a bright  scarlet  colour.  It  may  also  be  thrown  down  in  the 
form  of  a yellow  pow*der,  when  potash  or  soda  is  added  to  a solu- 
tion of  corrosive  sublimate,  or  of  mercuric  nitrate.  The  precipi- 
tated oxide  does  not  differ  in  composition  from  the  red  crystallized 
form,  but  it  enters  more  readily  into  combination  ; a cold  solution 


652 


MERCHRAMIXE. 


of  oxalic  acid  is  without  action  on  the  crystallized  oxide,  but  it 
converts  the  precipitated  oxide  into  oxalate ; and  the  yellow  oxide 
when  boiled  with  a solution  of  corrosive  sublimate  is  quickly  con- 
verted into  the  oxychloride  ; but  this  change  is  very  slow  with  the 
crystallized  variety.  The  yellow  oxide,  when  boiled  with  anhydro- 
chromate  of  potassimn,  vields  a basic  mercuric  chromate,  Hgfe*0^, 

2 HgO ; but  the  crystallized  oxide  when  similarly  treated  yields  a 
basic  salt,  with  a larger  excess  of  base,  Hg0i*O^,  3 HgO  (ilillon). 
In  short,  the  crystallized  oxide  obtained  by  the  direct  oxidation 
of  mercury,  and  the  precipitated  oxide  appear  to  be  in  different 
allotropic  conditions. 

The  red  oxide  when  heated  becomes  nearly  black,  but  recovers 
its  colour  on  cooling ; when  exposed  to  a temperature  of  ignition, 
it  is  decomposed  into  metallic  mercury  and  oxygen  gas ; owing 
to  the  volatility  of  the  metal,  this  oxide  may  sometimes  be  use- 
fully employed  as  an  oxidizing  agent  in  some  analytical  opera- 
tions. This  oxide  is  slightly  soluble  in  water ; the  solution  has 
an  acrid  taste,  and  turns  syrup  of  violets  green.  It  forms  with 
baryta  a soluble  compound.  With  ammonia  it  produces  a yel- 
lowish-white insoluble  compound  (Hg^H^XOg)  possessed  of  strong 
basic  powers ; it  enters  into  combination  with  acids,  and  forms 
well-defined  salts. 

(918)  ^[er  cur  amine. — The  best  method  of  preparing  this  re- 
markable base  consists  in  pouring  a pure  solution  of  ammonia 
upon  yellow  precipitated  oxide  of  mercury  in  a bottle  which 
admits  of  being  closed,  to  prevent  the  access  of  carbonic  acid  from 
the  air ; the  colour  of  the  oxide  becomes  paler,  and  eventually  a 
yellowish-white  amorphous  powder  is  obtained,  which,  when 
washed  and  dried  in  a dark  place  over  quicklime,  forms  a hydrate 
of  the  new  base,  containing  (Hg^H^X^Og,  3 H^O,  or  Hor^HjXOg, 

3 HO).  This  compound  was  discovered  by  Fourcroy  and  Thenard, 
but  it  was  first  minutely  examined  by  Millon  (Arm.  de  Chimie^  III. 
xviii.  393).  In  its  isolated  condition  it  is  very  unstable : mere 
exposui-e  to  the  light  decomposes  it.  When  triturated  in  a 
mortar,  it  produces  a series  of  small  detonations.  If  dried  in 
va/iuo  over  sulphuric  acid,  it  loses  2 H,0 ; and  between  212°  and 
266°,  a third  atom  of  water  is  expelled : it  then  becomes  dark 
brown,  and  is  permanent  in  the  air,  containing  (Hg^H^X^Og). 
Chemists  are  not  agreed  as  to  the  probable  arrangement  of  the 
elements  in  this  base.  It  resembles  some  of  the  cobalt  bases  into 
the  composition  of  which  the  elements  of  ammonia  enter.  It 
may  provisionally  be  described  under  the  name  mercuramine^  and 
contains  the  elements  of  hvdrated  oxide  of  teirhydrargammonium 
(Hg".V,©,  5 H,©}. 

Wercuramine  is  a powerful  base ; its  hydrate  (Hg^H^lS  ^Og, 
3 HgO)  absorbs  carbonic  anhydride  from  the  air  almost  as  rapidly 
as  slaked  lime.  It  is  insoluble  in  water  and  in  alcohol,  but  it 
decomposes  solutions  of  the  salts  of  ammonia  and  combines  with 
the  acid.  Definite  salts  with  sulphuric,  nitric,  oxalic,  carbonic, 
hydrochloric,  and  various  other  acids,  have  been  formed.  On  the 
addition  of  hydi-ate  of  soda  or  potash  to  the  solutions  of  these  salts, 


SULPHIDES  OF  MEKCTJHY. 


653 


tlie  hydrate  of  the  base  is  precipitated.  The  formula  of  the  sul- 
phate is  (Hg  ^4 ; of  the  chloride  (Hg  Cl^ ; 

the  latter  salt  may  he  obtained  as  a yellow  precipitate,  by  adding 
a solution  of  corrosive  sublimate  to  a solution  of  ammonia  in 
excess,  and  washing  the  precipitate  with  boiling  w^ater  (924). 

(919)  Sulphides  of  Mercury. — The  two  sulphides  of  mer- 
cury, Hg^S  and  HgS,  correspond  in  composition  to  the  oxides 
and  chlorides  of  the  metal. 

Subsiil^hide  of  Mercury  (Hg2S=432,  or  HgaS  = 216)  is 
scarcely  more  stable  than  the  suboxide  of  the  metal ; it  is  pro- 
cured by  transmitting  a current  of  sulphuretted  hydrogen  through 
a solution  of  a mercurous  salt,  or  by  triturating  16  parts  of 
moistened  sulphur  with  200  of  mercury  ; it  forms  a black  powder, 
wliich  was  formerly  termed  Etliiojfs  mineral.  It  is  decomposed 
by  nitric  acid;  and  if  the  dry  sulphide  be  sublimed,  it  is  con- 
verted into  cinnabar  and  metallic  mercury. 

(920)  Sulphide  of  Mercury.^  or  Cinnabar  (IIgS=:232,  or  HgS= 
116) : S]).  Gr.  of  va/pour,  5-51 ; of  solid ^ 8-2;  Mol.  ml.  | | j ^ 
Comp),  in  pyarts^  Hg,  86*21;  O,  13*79.- — -This  compound  con- 
stitutes the  most  abundant  ore  of  mercury.  It  occurs  sometimes 
crystallized  in  hexahedral  prisms,  but  more  usually  as  a fibrous 
or  amorphous  mass,  and  is  a product  of  considerable  importance 
in  the  arts,  forming  the  pigment  known  under  the  name  of 
mrmilion.  Some  portions  of  the  native  cinnabar  are  of  a suffi- 
ciently delicate  colour  to  be  employed  after  mere  levigation  ; but 
it  is  usually  prepared  artificially.  In  Holland,  this  manufacture 
is  carried  on  to  a considerable  extent.  The  process  adopted  con- 
sists in  triturating  sulphur  with  about  6 times  its  weight  of  mer- 
cury, aiding  the  action  by  a gentle  heat.  The  black  mass  thus 
procured  is  thrown  (in  successive  portions,  to  prevent  too  rapid 
an  action)  into  tall  earthen  pots,  the  lower  parts  of  wdiich  have 
been  previously  brought  to  a red  heat ; the  aperture  at  top  is 
closed  with  an  iron  plate,  and  in  about  32  hours  after  the  intro- 
duction of  the  whole  charge,  the  sublimation  is  complete : when 
cold,  the  pots  are  broken,  and  the  cinnabar,  which  is  found  depo- 
sited in  layers  upon  the  upper  part,  is  carefully  removed ; the 
cinnabar  is  levigated  with  water,  and  the  fine  powder  thus  ob- 
tained is  sold  as  vermilion;  an  excess  of  suljfiiur  is  to  be  avoided, 
as  it  impairs  the  brilliancy  of  the  colour.  Cinnabar  sublimes 
before  undergoing  fusion,  and  forms  a yellowish-brown  vapour. 
Vermilion  may  also  be  ])rocured  in  the  wet  way,  but  the  process 
is  tedious,  and  less  certain.  The  Chinese  vermilion  is  supposed 
by  some  chemists  to  be  ])repared  by  tlie  humid  process.  In 
order  to  produce  vermilion  by  this  means,  Firmenich  recommends 

* The  vapour  volume  of  this  compound  is  anomalous,  the  three  volumes  of 
vapour  having  been  united  without  condensation,  instead  of  being,  as  usual,  reduced 
to  two  volumes — 


Hg  2 vols. 

S 1 vol. 


8p.  Gr. 

or  0'67  4M)12 

0-33  0-737 


3 vols. 


1-00  5-340 


654 


CHLORIDES  OF  MERCTRT CALOMEL. 


the  mercury  to  be  subjected  to  the  action  of  pure  pentasulphide 
of  potassium  in  the  following  manner : — 10  parts  of  mercury  are 
to  be  agitated  for  3 or  4 hours,  with  2 parts  of  sulphur  and  4|- 
of  a saturated  solution  of  pentasulphide  of  potassium ; at  the  end 
of  which  time  the  mixture  becomes  of  a dark  brown  colour.  It 
is  maintained  for  3 or  4 days  at  a temperature  of  from  112°  to 
120°,  witli  occasional  agitation ; it  is  next  drained  upon  a filter, 
and  afterwards  digested  with  caustic  soda  to  remoye  the  excess  of 
sulphur ; it  is  thus  obtained  of  a bright  scarlet,  and  must  then  be 
thoroughly  washed  with  cold  water  and  dried.  {Chem. 

May,  1862,  p.  247.) 

Sulphide  of  mercury  is  thrown  down  as  a black  precipitate  by 
transmitting  sulphuretted  hydrogen  through  solutions  of  the 
mercuric  salts  ; when  dried  and  sublimed  in  yessels  from  which 
air  is  excluded,  it  assumes  its  ordinary  red  colour.  Mhen  heated 
in  the  open  air,  the  sulphur  burns  off,  and  metallic  mercury  is 
liberated.  It  is  upon  this  circumstance  that  the  ordinary  method 
of  extracting  the  metal  is  founded.  The  pure  acids  are  nearly 
without  action  upon  cinnabar,  but  it  is  oxidized  and  dissolyed 
by  acpia  regia.  The  alkalies  in  solution  do  not  decompose  it,  but 
if  ignited  with  it  in  the  dry  state,  a sulphate  and  sulphide  of  the 
alkaline  metal  are  formed,  and  metallic  mercury  sublimes ; 
4lIgS  + 8 IvIIO=4Hg  + Iv2SO^-}-3  ICS  + 4H2O.  It  is  also  de- 
composed if  heated  with  metals  which,  like  iron,  zinc,  and  copper, 
haye  a powerful  attraction  for  sulphur.  Sulphide  of  mercury 
possesses  the  property  of  uniting  with  other  metallic  sulphides, 
and  is  slowly  soluble  in  a solution  of  sulphide  of  potassium  ; it 
also  combines  with  the  nitrate,  the  chloride,  the  iodide,  and  some 
other  mercuric  salts,  forming  peculiar  compounds,  which  are 
produced  by  the  action  of  a small  proportion  of  sulphuretted  hy- 
drogen upon  the  solutions  of  these  salts,  and  cause  the  first  por- 
tions of  the  precipitate  occasioned  in  them  by  the  gas  to  assume 
a white  colour. 

(921)  Chloredes  of  Mercery. — Mercury  forms  two  chlo- 
rides, one  of  which,  HgCl,  is  well  known  as  calomel,  the  other, 
HgCh,  is  commonly  distinguished  as  corrosiye  sublimate. 

Mercurous  chloride^  or  Calomel  SiLbchloriele  of  jner- 

cury^  IIg,Cl= 235-5) ; Sp.  Gr.  of  vapour^  8-35;  of  solid  7-178; 
2I0I.  vol.  ' i j : Comp,  in  100  parts.,  Hg,  84-92  ; Cl,  15-08.^ — This 
compound  may  be  obtained  by  precipitating  a solution  of  mer- 
curous nitrate,  by  one  of  common  salt  ; but  it  is  more  usually 
procured  by  sublimation  : 13  parts  of  mercury  are  triturated  with 
17  of  corrosiye  sublimate,  until  no  metallic  globules  are  yisible, 
the  chloride  haying  been  preyiously  moistened  with  water  or 
alcohol,  to  preyent  the  acrid  particles  from  being  diffused  through 
the  air  ; the  mixture  is  then  sublimed  in  suitable  yessels,  and  the 
calomel  is  deposited  as  a semi-transparent  fibrous  cake.  In  this 
operation  the  additional  mercury  combines  with  half  the  chlorine 

* It  is  possible  that  the  formula  of  calomel,  and  of  mercurous  bromide  and  iodide, 
should  be  doubled  ; but  in  that  case,  their  vapour  volume  would  be  anomalous,  and 
would  represent  4 volumes  instead  of  2 volumes. 


CHLORIDES  OF  MERCURY CALOMEL. 


655 


of  the  chloride  : HgCljd-Hg^SHgCl.  Sometimes  the  vapours  are 
sent  into  a capacious  chamber ; the  deposit  then  assumes  the  form 
of  a fine  powder.  Tlie  salt  may  also  be  obtained  by  the  decom- 
position of  mercuric  sulphate  with  chloride  of  sodium.  For  this 
purpose  2 lb.  of  mercury  may  be  converted  into  sulphate  by  boil- 
ling  it  to  dryness  with  3 lb.  of  sulphuric  acid ; the  residue  is  then  to 
be  intimately  mixed  with  2 lb.  more  of  mercury,  and  subsequently 
triturated  with  1^  lb.  of  chloride  of  sodium,  after  which  it  is  to  be 
sublimed.  The  mercuric  sulphate  which  is  first  obtained  is  con- 
verted into  mercurous  sulphate  by  the  addition  of  the  second  por- 
tion of  mercurjq  and  this  in  its  turn  is  decomposed  into  calomel 
and  sulphate  of  sodium  when  heated  with  chloride  of  sodium  : — 

H2:"SO,-fHg=Hg;se,;  and 
Hg'.Se,  + 2 ]SraCl=Na,SO,  -f  2 Hg'Cl. 

Calomel  may  also  be  prepared  by  forming  a saturated  solution 
of  corrosive  sublimate  in  water  at  120°,  and  transmitting  sul- 
phurous anhydride  into  the  hot  liquid  ; calomel  is  then  precipi- 
tated in  minute  crystals,  whilst  sulphuric  and  hydrochloric  acids 
are  liberated  ; 2 HgCl,H-2  H,e-|-Se,=2  HgCl  + 2 HCl  + H,SO,. 

When  prepared  by  sublimation  calomel  requires  careful 
washing  and  levigation,  because  portions  of  the  undecomposed 
bichloride  always  sublime  with  the  calomel,  and  they  can  only 
be  removed  by  repeated  washing.  It  was  formerly  supposed 
that  the  medicinal  character  of  calomel  was  rendered  milder  bj^  re- 
peated sublimations.  This,  however,  has  been  found  to  be  a serious 
mistake,  for  every  time  that  calomel  is  sublimed,  a small  portion 
of  it  is  reconverted  into  corrosive  sublimate  and  metallic  mercury. 

Properties. — Calomel  sublimes  in  quadrilateral  prisms  termi- 
nated by  four-sided  pyramids  ; when  powdered  it  is  of  a yellow- 
ish-white colour.  It  begins  to  sublime  below  redness,  and  before 
undergoing  fusion.  Calomel  is  tasteless  and  insoluble  in  water  ; 
the  alkalies  decompose  it.  Hydrates  of  soda  and  potash  decom- 
pose it,  wdiilst  mercurous  oxide  is  formed.  Lime-water  has  a 
similar  effect,  and  when  mixed  with  a small  proportion  of  calo- 
mel it  furnishes  what  is  known  as  hlach  wash.  Solution  of 
ammonia  forms  with  calomel  a black  compound,  consisting  of 
Hg'JI^l^Cl  : this  change  is  explained  in  the  subjoined  equation; 
2 HgCl  -h  2 Il3H=Hg2tl2HCl  -f  II^HCl.  This  black  compound  may 
be  regarded  as  chloride  of  ammonium  in  which  two  atoms  of  mer- 
cury have  taken  the  place  of  twm  atoms  of  hydrogen.  Ammonia- 
cal  gas  is  absorbed  by  precipitated  calomel  at  ordinary  tempera- 
tures, and  a compound  containing  (HgllaNCl)  is  formed,  or 
(‘hloride  of  ammonium  in  which  one  of  the  atoms  of  hydrogen 
has  been  disydaced  by  mercury.  Sulphuric  acid  is  without  action 
on  calomel ; boiling  nitric  acid  dissolves  it,  and  forms  corrosive 
sublimate  and  mercuric  nitrate ; a solution  of  chlorine  converts 
it  slowly  into  corrosive  sublimate  ; if  boiled  for  a long  time  with 
hydrochloric  acid  or  chloride  of  sodium,  it  is  resolved  into  corro- 
sive sublimate  and  metallic  mercury : the  same  effect  is  produced, 
but  more  rapidly,  by  boiling  it  in  a solution  of  sal  ammoniac. 


656 


CHLOEIDES  OF  MEKCFTIY COEROSIVE  SUBLIMATE. 


(922)  Bichloride  of  mercury  ; Mercuric  chloride^  or  Corrosive 
sullimate  (H^Cl2=271) ; Sj).  Gr.  of  vapour^  9*8;  of  solid^  5*42; 
Mol.  vol.  I I I : or  (HgCl=135'5) ; Comp,  in  parts ^ Hg,  73*8  ; 
Cl,  26*2.— WTieii  heated  mercnry  is  placed  in  an  atmosphere  of 
chlorine  it  ignites  from  the  rapid  union  of  the  gas  with  the  metal, 
and  the  chloride  is  formed.  It  is  prepared  on  the  large  scale  by 
mixing  intimately  2|-  parts  of  mercuric  sulphate  with  1 part  of 
common  salt,  and  subliming  the  mixture  in  glass  vessels  at  a 
carefully  regulated  heat : sulphate  of  sodium  remains  in  the 
vessel,  and  the  bichloride  sublimes,  as  represented  in  the  equa- 
tion; JigSO^H- 2 NaCl^lN'a^SO,  + HgCl^.  The  fumes  are  ex- 
tremely acrid  and  poisonous. 

Properties. — Corrosive  sublimate  fuses  at  509°  and  boils  at 
563°  ; its  vapours  are  condensed  in  snow-white  crystalline  needles, 
or  in  octohedra  with  a rectangular  base.  As  sold  in  the  shops,  it 
occurs  in  transparent  colourless  masses,  which  have  a crystalline 
fracture.  It  has  an  acrid  burning  taste,  and  disgusting  metallic 
flavour.  It  is  soluble  in  16  parts  of  cold  water,  and  in  less  than 
3 of  boiling  water  ; on  cooling  it  is  deposited  from  a concentrated 
solution  in  transparent  anhydrous  quadrilateral  prisms.  Its  solu- 
tion reddens  litmus ; this  aqueous  solution,  by  long  exposure  to 
light,  is  gradually  decomposed,  and  calomel  is  deposited.  Alco- 
hol when  cold  dissolves  nearly  one-third  of  its  weight  of  the  salt, 
and  its  own  weight  when  boiling  ; ether  also  dissolves  it  freely. 
If  an  aqueous  solution  of  corrosive  sublimate  be  agitated  with 
ether,  almost  the  whole  of  the  salt  will  be  abstracted  by  it  from 
the  water,  and  the  ethereal  solution  will  rise  to  the  surface.  It 
is  very  soluble  in  solutions  of  the  alkaline  chlorides,  with  which 
it  enters  into  combination,  forming  double  salts.  With  chloride 
of  potassium  it  forms  three  distinct  cryst all iz able  compounds, 
KCl,  2 HgCl„2  11,0;  IvCl,IIgCl„H,0 ; and  2 KCl,HgCl„H,0. 
They  are  easily  prepared  by  dissolving  the  salts  in  the  proper 
proportions,  and  allowing  them  to  crystallize.  With  chloride  of 
sodium  only  one  such  compound  is  formed,  2 (I7aCl,iIgCl2)3  IT^O. 
A salt  with  chloride  of  ammonium  (6  H4lsrCl,IIgCl2  . has 

long  been  known  as  sal  alemhi'oth : it  crystallizes  in  flattened 
rhomboidal  tables. 

Similar  compounds  having  a composition  analogous  to  that  of 
the  sodium  salt  may  be  formed  with  most  of  the  soluble  chlorides. 
Chlorides  of  calcium  and  magnesium  form  more  than  one  com- 
pound. An  analogous  but  anhydrous  salt,  IICl,IigCl2,  is  formed 
by  dissolving  corrosive  sublimate  in  hot  hydrochloric  acid,  from 
which  it  crystallizes  on  cooling;  it  is,  however,  decomposed  by 
water. 

Bichloride  of  mercury  combines  with  the  sulphide,  and  forms 
with  it  a white  insoluble  gelatinous  compound,  consisting  of 
2 IIgS,IIgCl2 ; it  is  the  white  precipitate  which  is  always  formed 
at  first,  on  passing  a current  of  sulphuretted  hydrogen  through  a 
solution  of  corrosive  sublimate. 

Corrosive  sublimate  is  decomposed  by  the  hydrates  of  the 
fixed  alkalies  and  alkaline  earths,  a chloride  of  the  alkaline  metal 


OXYCHLOKIDES  OF  MERCFRY. 


657 


and  mercuric  oxide  being  formed.  When  ammonia  is  added  to  a 
solution  of  corrosive  sublimate,  it  separates  only  half  the  chlo- 
rine, uniting  with  the  remainder  to  form  the  compound  called 
white  precipitate  (92d).  Bichloride  of  mercury  acts  powerfully 
on  the  albuminous  tissues,  and  combines  with  them ; it  is  a vio- 
lent and  acrid  poison.  The  best  antidote  in  cases  of  poisoning 
with  this  substance  is  the  immediate  exhibition  of  the  white  sof 
several  raw  eggs,  as  it  coagulates  the  albumen,  and  forms  with  it 
a sparingly  soluble  compound.  It  was  supposed  that  the  bichlo- 
ride was  converted  into  calomel,  but  this  does  not  appear  to  be 
the  case.  Owing  to  this  action  of  the  bichloride  upon  albumen, 
corrosive  sublimate  is  a powerful  antiseptic ; a solution  of  this 
salt  is  hence  often  employed  to  preserve  anatomical  preparations : 
wood,  cordage,  and  canvas,  if  soaked  in  a solution  of  the  salt 
containing  1 part  of  it  in  60  or  80  parts  of  water,  become  much 
less  liable  to  decay  when  exposed  to  the  combined  action  of  air 
and  moisture. 

(923)  Oxychlorides. — Corrosive  sublimate  combines  with  mer- 
curic oxide  in  several  proportions ; these  compounds  are  decom- 
posed by  the  alkalies.  One  of  tliese  is  obtained  in  the  form  of 
dark  brown  insoluble  flakes  (3  iIg0,IigCl2),  when  the  chloride  is 
boiled  with  red  oxide  of  mercury.  Another,  2 HgO,IIgCl2,  is 
obtained  in  blackish  scales  by  acting  Avith  a solution  of  chlorine 
on  red  oxide  of  mercury  (Thaulow).  The  oxychlorides  of  mercury 
are  interesting,  from  the  observations  of  Millon  upon  them,  Avhich 
seem  to  prove  the  persistence  of  the  allotropic  modification  in  a 
body  after  it  has  entered  into  combination.  {Ann.  de  Chimie^ 
III.  xviii.  333.) 

The  three  oxychlorides  described  by  Millon  consist  of  (2  HgO, 
HgCl^),  (3  IIgO,HgCl2),  and  (4  IIgO,iigCl2).  They  may  all  be 
produced  by  the  action  of  carbonate  of  potassium  upon  a solution 
of  corrosive  sublimate.  The  first  may  be  obtained  in  three  differ- 
ent isomeric  conditions,  the  second  in  two,  and  the  third  in  three. 
The  action  of  the  carbonates  of  the  alkali-metals  upon  solutions  of 
corrosive  sublimate  is  peculiar.  The  addition  of  a solution  of  sub- 
limate. to  a solution  of  pure  normal  carbonate  of  sodium  or  potas- 
sium is  attended  with  the  precipitation  of  yellow  oxide  of  mercury. 
If  the  mercurial  solution  be  added  to  a solution  of  an  alkaline  acid- 
carljonate.,  a red  oxychloride  is  formed  ; and  if  eA^en  a small  quan- 
tity of  the  acid-carbonate  of  the  alkali-metal  be  mixed  with  a large 
proportion  of  normal  alkaline  carbonate,  this  red  precipitate  is 
produced  at  first.  This  reaction  may  serve  to  distinguish  the  car- 
bonates from  the  acid-carbonates  in  solution.  If  a cold  saturated 
solution  of  acid-carbonate  of  potassium  be  added  gradually  to  8 
or  10  times  its  volume  of  a cold  saturated  solution  of  sublimate, 
a light  granular  amorphous  preci]ntate  of  a bright  brick-red  col- 
our is  formed  (2  HgO,IIgCl2).  If  the  volume  of  the  solution  of 
sublimate  be  only  3 or  4 times  as  great  as  that  of  the  acid-carbon- 
ate, a precipitate  of  similar  composition  is  formed,  but  it  is  dense, 
crystalline,  and  red,  purple,  or  violet  in  colour.  Both  these  mod- 
ifications, when  decomposed  by  hydrate  of  potash,  yield  the  yeh- 
42 


658 


ACTION  OF  A^mONIA  ON  BICHLORIDE  OF  MERCURf. 


low  oxide  of  mercury  ; but  if  1 volume  of  tlie  solution  of  acid -car- 
bonate be  added  to  2 volumes  of  the  solution  of  sublimate,  stirring 
briskly,  a jet  black  crystalline  precipitate  is  formed,  wliicli  also 
consists  of  2 HgO,HgCl2,  but  which  yields  the  red  crystalline 
oxide  when  decomposed  by  hydrate  of  potash. 

If  equal  volumes  of  the  solutions  be  mixed,  golden-yellow 
plates,  which  gradually  become  brown  or  yellowish,  are  deposited 
(3  Hg0-,IIgCl2).  The  same  body  may  also  be  obtained  in  the 
amorphous  form. 

The  quadribasic  oxychloride  (4  HgO-,HgCl2)  may  be  obtained 
by  adding  a solution  of  corrosive  sublimate  to  a large  excess  of 
the  solution  of  the  acid-carbonate.  Carbonic  acid  gradually 
escapes,  and  brown  crystalline  crusts  are  deposited : caustic  pot- 
ash causes  the  separation  of  the  red  oxide  of  mercury  from  this 
compound.  This  oxychloride  may  also  be  obtained  in  the  form 
of  a brown  amorphous  deposit,  and  in  golden-yellow  plates  ; both 
these  varieties  yield  the  yellow  oxide  when  decomposed  by  hydrate 
of  potash.  The  first  two  oxychlorides  are  converted  by  boiling 
them  with  water  into  the  quadribasic  form,  which  is  deposited 
from  the  solution  in  golden-yellow  scales.  Other  oxychlorides, 
with  5 and  with  6 atoms  of  oxide  of  mercury,  are  described  by 
Roucher  (Ann.  de  Chiinie^  III.  xxvii.  353). 

(921)  Action  of  Ammonia  on  Corrosive  Suhlimate. — When  a 
solution  of  corrosive  sublimate  is  added  to  a solution  of  ammonia 
in  excess,  one-half  of  the  chlorine  only  is  removed  from  the  salt, 
and  the  so-called  %cliite  precipitoie  is  formed,  which,  when  washed 
with  cold  water,  is  completely  soluble  in  nitric  and  in  hydrochloric 
acid,  and  which  therefore  can  contain  no  calomel ; IIgCl2  + 2 
= (IIg''Il2R,Cl)  + II^K Cl.  Kane  considered  this  white  precipitate 
as  a compound  of  chloride  with  amide  of  mercury,  IIgCl,IIgH2K  ; 
but  it  may  also  be  regarded  as  chloride  of  ammonium,  in  which 
2 equivalents  of  hydrogen  are  displaced  by  the  biequivalent  atom 
of  mercury  (Hg'TT^K,!!!).  If  ammonia  be  added  drop  by  drop 
to  a solution  of  corrosive  sublimate,  which  is  purposely  main- 
tained in  considerable  excess,  the  precipitate  consists  of  (Hg^II^ 
K2Clg) ; this  formula  would  be  that  of  chloride  of  mercuramine, 
in  which  the  place  of  the  oxygen  contained  in  tlie  base  is  supplied 
by  an  equivalent  amount  of  chlorine. 

White  precipitate  has  been  made  the  subject  of  numerous  ex- 
periments. If  it  be  heated  to  about  600°,  ammonia  and  the  am- 
moniated  chloride  of  mercury  are  expelled  ; and  a red  crystalline 
powder  remains,  represented  by  the  formula  (2  IIgCl2,iIg3]S’2)  ; 
for  6 (Hg"H,NCl)  = 3 H,]Sf  + (H,N,HgCl,)  + (2  ifgCl^Hg.N,). 
This  red  powder  is  insoluble  in  water  and  in  dilute  acids,  but  it 
is  dissolved  and  decomposed  by  either  boiling  hydrochloric  acid 
or  oil  of  vitriol.  By  raising  the  temperature  still  further  it  is  de- 
composed into  nitrogen,  metallic  mercury,  and  calomel.  It  is  in- 
teresting, as  it  appears  to  contain  a double  atom  of  ammonia  in 
which  the  6 atoms  of  hydrogen  are  displaced  by  3 of  the  biequiv- 
alent mercury. 

When  white  precipitate  is  boiled  in  water  it  is  decomposed, 


BROMIDES  AND  IODIDES  OF  MERCURY. 


659 


and  the  lieavy  insoluble  canary-yellow  chloride  of  mercuraniine  is 
formed,  whilst  chloride  of  ammonium  is  formed  in  the  solution ; 
4 (Hg^'H^lSTCl)  -f  2 -f  2 H^NCl.  This  yel- 

low powder  is  dissolved  easily  by  diluted  nitric  or  hydrochloric 
acid. 

If  a solution  of  corrosive  sublimate  be  added  gradually  to  a 
boiling  solution  of  sal  ammoniac  and  free  ammonia  so  long  as  the 
precipitate  is  redissolved  by  agitation,  a compound  crystallizes  in 
rhombohedra  on  cooling ; and  the  same  substance  is  procured  on 
boiling  ordinary  white  precipitate  in  a solution  of  sal  ammoniac. 
This  compound  fuses  and  undergoes  decomposition  at  a tempera- 
ture of  572°  ; boiling  water  extracts  a large  proportion  of  sal 
ammoniac  from  it,  and  leaves  the  canary-yellow  powder  above 
described.  It  is  freely  soluble  in  acids,  even  in  acetic  acid. 
Kane’s  analysis  of  this  compound  would  allow  of  its  being  repre- 
sented by  the  formula  Hg'^ngK^Clj.  It  is  sometimes  called  fusi- 
ble white  precipitate. 

When  corrosive  sublimate  is  exposed  to  a current  of  dry  am- 
moniacal  gas,  it  fuses  with  extrication  of  heat ; 1 atom  of  the  salt 
absorbs  1 of  ammonia,  producing  Il3]Sr,IIgCl2.  This  compound 
may  be  sublimed  without  change,  but  it  is  decomposed  by  water : 
it  is  a true  ammoniated  chloride  of  mercury. 

The  following  are  the  compounds  wdiich  are  produced  by  the 
combined  action  of  ammonia  and  heat  upon  corrosive  sublimate ' 

(1)  White  precipitate Hg'TT^KCl. 

(2)  Eed  crystalline  compound 2 IIgCl2,Hg"3N2. 

(3)  Chloride  of  mercuramine (IIg4ll4K202)Cl2. 

(4)  Terchloride  of  mercuramine (HgJI^K^ClJCl^. 

(5)  Fusible  white  precipitate IIg^T-IgK2Cl2. 

(6)  Ammoniated  chloride  of  mercury,  Il3K,IIgCl2. 

Besides  the  double  salts,  of  which  one  is — 

(7)  Sal  alembroth 6 H,NCl,IIgCl2,H2e. 

(8)  And  another  is H^KChligCh. 

These  remarkable  compounds  derive  interest  from  their  con- 
nexion with  the  theories  which  have  been  proposed  respecting  the 
nature  of  ammonia,  the  consideration  of  which  will  be  resumed 
when  the  alkaloids  or  organic  bases  are  examined. 

Two  Bromides,  analogous  to  the  chlorides  of  mercury,  may  be 
formed  ; they  yield  corresponding  double  salts ; both  of  them  may 
be  sublimed  without  experiencing  decomposition.  Mercurous 
bromide  ((HgBr ; sp.  gr.  of  vapoitr.^  10'14  ; mol.  vol.  | | |)  is  white 
and  insoluble.  Mercuric  bromide  (HgBrj ; sp.  gr.  of  rapo'iir.^ 
12T6  ; mol.  vol.  \ | |)  is  cryst all iz able  and  soluble. 

(925)  Iodides  of  Mercury. — Mercury  forms  three  iodides : a 
green  iodide,  Hgl ; a red  biniodide,  Hgi2 ; and  an  intermediate 
iodide  (HgI,IIgl2)  of  a yellow  colour,  obtained  by  precipitating 
mercurous  nitrate  by  means  of  iodide  of  potassium  containing 
iodine  in  solution. 

Mercurous  iodide  (Hgl,  or  suhiodide^  IIg2l=327)  is  a green 


660 


BINIODIDE  AND  NITRIDE  OF  MERCURY. 


powder  insoluble  in  water,  wliicli  is  easily  decomposed  by  ex- 
posure to  liglit,  into  mercury  and  the  red  iodide  ; the  same  change 
is  effected  by  heating  it  gently  with  solutions  of  the  soluble 
iodides  or  chlorides,  or  with  hydriodic  or  hydrochloric  acid.  If 
heated  suddenly  it  fuses  and  may  be  sublimed  without  decompo- 
sition : but  if  the  temperature  be  raised  gradually,  it  is  decom- 
posed into  tlie  red  iodide  and  metallic  mercury.  It  is  easily 
formed  by  triturating  5 parts  of  iodine  with  eight  of  mercury, 
moistening  the  mixture  with  a little  alcohol ; or  it  may  be  precip- 
itated from  a solution  of  any  of  tlie  salts  of  mercurous  oxide,  by 
adding  to  them  a solution  of  iodide  of  potassium. 

The  B iniodide  of  mercury  (fler curie  iodide^  Hgl^^ISI) ; Mol. 
vol.  I rn ; (or  IIgI=227) : Sj).  Gr.  of  solid  ^ 6-25  ; ofvapoiir.^  15-68  : 
Comp,  in  y^^parts^  Hg,  41-05  ; I,  55-95. — This  beautiful  compound 
may  be  obtained  by  triturating  5 parts  of  iodine  with  4 of  mer- 
cury, and  subliming  the  mixture ; but  it  is  procured  most  easily 
by  precipitating  a solution  of  corrosive  sublimate  by  means  of  a 
solution  of  iodide  of  potassium  : the  precipitate  is  soluble  in  an 
excess  of  either  salt.  The  precipitate  is  at  first  salmon-coloured, 
but  it  speedily  becomes  converted  into  a brilliant  scarlet  crystal- 
line deposit.  It  fuses  at  about  400°,  and  yields  a vapour  of  ex- 
traordinary density : as  it  cools  it  is  deposited  in  yellow  rhombic 
tables ; this  yellow  colour  is  changed  to  red  by  mere  agitation,  or 
by  scratching  tlie  crystals.  Warington  has  shown  that  this 
change  of  colour  depends  upon  a change  in  the  molecular  consti- 
tution of  the  salt,  in  consequence  of  which  the  rhomboidal  crystals 
are  converted  into  octoliedra  with  a square  base.  Biniodide  of 
mercury  is  nearly  insoluble  in  water,  but  it  is  taken  up  freely  by  hot 
alcohol.  It  is  also  dissolved  by  solutions  of  many  neutral  salts  of 
ammonium,  as  well  as  by  hydrochloric  and  hydriodic  acids.  W ith 
the  soluble  electro-positive  iodides  it  forms  crystalline  double  salts, 
and  it  is  dissolved  easily  by  solutions  of  chlorides  of  the  metals  of 
the  alkalies,  but  it  does  not  form  cry stalliz able  compounds  with 
these  chlorides.  A fusible  double  chloride  and  iodide  of  mercury 
(Hglj^HgCld  may  be  formed  ; and  a soluble  crystallizable  com- 
pound (Ilgla,  2 HgCld  may  be  obtained  by  saturating  a boiling 
solution  of  corrosive  sublimate  with  the  red  iodide  of  mercury, 
and  allowing  it  to  crystallize.  By  adding  a mixture  of  hydrate 
of  potash  and  ammonia  to  a solution  of  iodide  of  mercury  in  one 
of  iodide  of  potassium,  a brown  powder  is  deposited,  to  which 
Nessler  assigns  the  formula  IIg"2AI,Il20.  Biniodide  of  mercury 
also  forms  definite  compounds  with  the  oxide,  and  with  the  sulphide 
of  the  metal. 

(926)  Nitride  of  Mercury. — Plantamour  states,  that  by  trans- 
mitting in  the  cold  a current  of  dry  ammoniacal  gas  over  the 
dried  yellow  oxide  of  mercury  precipitated  from  its  salts  by  an 
alkali,  so  long  as  the  gas  is  absorbed,  and  then  heating  the  dark 
brown  mass  cautiously  to  a temperature  not  exceeding  300°,  so 
long  as  water  is  formed,  an  anhydrous  powder  of  a flea-brown 
colour  is  produced.  It  detonates  powerfully  when  heated,  or 
struck:  the  acids  decompose  it,  forming  salts  of  ammonium  and 


SULPHATES  AND  NITKATES  OF  MERCURY.  661 

mercury.  Its  probable  composition  is  inferred  from 

the  mode  of  preparing  it ; 3 IIgO  + 2Il3bI=HgpN2  + 3 H^O. 

(927)  Sulphate  of  Mercury  ; Mercuric  SulphcUe  (IlgSO^^ 
296,  or  HgO, 803  = 148) ; Sp.  Gr.  6*466. — When  2 parts  of  mer- 
cury are  heated  gently  with  3 of  oil  of  vitriol,  sulphurous  anhy- 
dride is  evolved,  and  mercurous  sulphate  is  procured  ; but  if  the 
heat  be  increased,  and  the  distillation  be  carried  to  dryness, 
mercuric  sulphate  is  formed ; sulphurous  anhydride  being  extri- 
cated, whilst  the  mercury  takes  oxygen  from  the  sulphuric  acid ; 
IIg-f2  112804= HgSO^-l- 602  + 2 li^O.  It  is  a white  crystalline 
poAvder,  Avhich  is  soluble  in  a solution  of  common  salt,  but  is 
decomposed  by  pure  Avater  into  an  insoluble  yelloAV  basic  salt, 
called  turpeth  mineral  (HgSO^,  2lIgO;  sp.  gr.  8*319),  and  a 
soluble  acid  salt,  which  crystallizes  in  deliquescent  needles  ; the 
yelloAV  basic  salt  is  formed  more  rapidly  if  the  sulphate  be  Avashed 
Avith  boiling  Avater.  The  normal  sulphate,  when  treated  with  an 
excess  of  ammonia,  yields  sulphate  of  mercuramine.  The  normal 
sulphate  unites  Avith  sulphate  of  ammonium,  and  forms  a crys- 
tallizable  double  salt. 

(928)  Nitrates  of  Mercury. — Mercury  forms  a larger  number 
of  nitrates  than  any  other  metal.  The  conditions  of  temperature, 
and  dilution  of  acid  necessary  to  ensure  the  production  of  each 
compound,  often  vary  in  eacli  case  but  little,  and  their  accurate 
analysis  is  attended  with  some  difficulty.  Different  chemists 
vary  somewhat  in  their  statements  of  the  results  which  they  ob- 
tained. The  normal  subnitrate^  or  mercurous  nitrate  (Hg'a  2 NO3, 
2 HjO,  or  IIg20,N05 . 2 Aq)  is  obtained  by  digesting  metallic 
mercury  in  an  excess  of  nitric  acid  diluted  with  4 or  5 times  its 
bulk  of  water ; it  crystallizes  in  short  transparent  someAvhat 
effloresceut  prisms  (or  in  rhombic  plates;  Gerhardt);  Avater  de- 
composes it  into  a yelloAV  insoluble  dibasic  salt,  (IIg'22N03,IIg2O, 
II2O)  or  (2  Hg20,N03,II0)  and  a soluble  acid  one.  A soluble 
subnitrate,  AAdiich  is  often  mistaken  for  the  normal  salt,  crystal- 
lizes in  large  transparent  colourless  prisms,  3 (ilg'2  ^ 

II2O,  or  4 lig20,3N03,II0,  and  is  obtained  by  digesting  an  excess 
of  mercury  in  diluted  nitric  acid.  De  Marignac  finds  that  by 
boiling  the  mother-liquors  of  the  preceding  salts  upon  an  excess 
of  mercury  for  several  hours,  doubly  oblique,  rhombic,  colour- 
less prisms  are  deposited,  to  Avliich  lie  assigns  the  formula,  3 (IIg2 
2NO3),  2lig'2e,2ll2e,  or5irg20,  3 NO3,  2 110.  Other  subni- 
trates also  appear  to  exist.  Tliese  various  basic  nitrates  may  be 
distinguished  from  the  normal  salt  by  triturating  them  Avith  chlo- 
ride of  sodium,  when  they  become  grey,  oAving  to  the  separation 
of  black  oxide  of  mercury,  while  calomel  is  formed  ; but  the 
normal  salt  remains  white. 

A normal  mercuric  nitrate  [2  (Hg"2  N03)Il20,  or  2 (IlgO, 
NO3),  IIO]  is  slowly  formed  in  voluminous  crj'stals,  by  dissolving 
the  red  oxide  of  mercury  in  an  excess  of  nitric  acid,  and  eva])orating 
the  liquid  until  it  assumes  a syrupy  consistence.  Another  nitrate 
(fig  2 N03,ffge,  2 1120,  or  2 IIg0,N03,  2 IIO)  is  deposited  in 
acicular  crystals  from  a boiling  solution  of  mercury  in  excess  of 


662 


CHAIiACTEKS  OF  THE  SALTS  OF  MEECCET. 


nitric  acid ; but  it  is  obtained  with  greater  certainty  by  saturat- 
ing nitric  acid,  of  sp.  gr.  l*d,  diluted  with  an  equal  bulk  of 
water,  with  the  red  oxide  of  mercury.  The  solutions  of  both 
these  salts  are  decomposed  when  diluted  freely  with  water,  and  a 
yellow  insoluble  basic  nitrate  (BFg2X03,  2 HgOjH.O,  or  3 H^O, 
XO-,HO)  is  precipitated : by  long-continued  washing  with  hot 
water,  the  whole  of  the  nitric  acid  is  removed  from  this  basic 
salt,  and  oxide  of  mercury  is  left.  Solutions  of  the  mercuric 
nitrates,  when  digested  upon  an  excess  of  the  metal,  are  con- 
verted into  mercm’ous  nitrates. 

(929)  Chaeactees  of  the  Salts  of  Meecley. — Most  of  the 
salts  of  mercury  are  colomdess,  but  some  of  the  basic  mercuric 
salts  are  yellow.  The  following  characters  are  common  to  the 
salts  of  both  oxides.  The  soluble  compounds  have  an  acrid,  nau- 
seous, metallic  taste  : in  large  doses  they  act  as  irritant  poisons. 
All  the  compounds  of  mercury  are  volatilized  by  heat.  If  a 
small  quantity  of  any  of  the  dry  salts  of  this  metal  be  placed  at 
the  bottom  of  a tube  of  the  diameter  of  a quill,  and  be  covered 
to  the  depth  of  an  inch  with  a layer  of  dried  carbonate  of  sodium 
or  of  potassium,  mercmw  may  be  obtained  in  the  form  of  a sub- 
limate of  minute  globules,  by  heating  the  upper  part  of  the  layer 
of  the  carbonate  to  redness,  and  driving  the  vapour  of  the  mer- 
curial compound  slowly  through  it. 

The  presence  of  mercury,  when  in  solution,  may  be  detected 
by  placing  a small  strip  of  zinc,  round  which  a thin  slip  of  gold 
foil  is  twisted,  in  a portion  of  the  liquid  to  be  tested.  The  mer- 
cury will  be  deposited  by  voltaic  action  in  the  form  of  a white 
stain  upon  the  gold.  This  stain  will  disappear  on  heating  the 
gold  to  redness.  The  salts  of  mercury,  whether  soluble  or  in- 
soluble, are  all  reduced  to  the  metallic  state  when  heated  with  a 
solution  of  stannous  chloride.  A strip  of  metallic  copper  becomes 
coated  vdth  a white  amalgam,  if  rubbed  with  a solution  contain- 
ing mercury.  This  test  may  be  employed  for  detecting  the  pre- 
sence of  mercury  in  solution  if  applied  by  the  method  of  Eeinsch 
for  arsenic  (SI6),  a sublimate  of  mercury  in  distinct  globules  being 
obtained  by  heating  the  coated  slip  in  a small  tube. 

1.  — Jlercurous  salts  are  characterized,  when  in  solution,  by 
yielding  with  solutions  of  potash^  of  soda.,  or  of  lime,  a black 
precipitate  of  mercurous  oxide.  Ferrocyanide  of  potassium 
gives  a white  precipitate.  Both  sulphuretted  hydrogen  and  sul- 
phide of  ammonium  yield  a black  sulphide  of  mercury.  Hydro- 
chloric acid  and  solutions  of  the  chlorides  cause  a white  precipi- 
tate of  calomel,  which  is  soluble  in  hot  concentrated  nitric  acid, 
and  in  chlorine  water ; it  is  blackened  by  the  addition  of  an  excess 
of  ammonia.  Iodide  of  potassium  gives  a green  mercurous 
iodide,  and  chromate  of  potassium  a bright  red  basic  mercurous 
chromate. 

2.  — Hercuric  salts,  when  in  solution,  yield  with  solutions  of 
potash,  of  soda  and  of  lime,  a bright  yellow  precipitate  of  mer- 
curic oxide;  with  ammonia,  a white  precipitate;  with  'normal 
carbonate  of  potassium,  a yellow  precipitate  of  oxide;  with  a/nd- 


ESTIMATION  OF  MEKCUKY. 


663 


carbonate  of  potassium^  a red  precipitate  of  oxychloride  of  mer- 
cury (923) : all  these  precipitates  are  soluble  in  hydrochloric 
acid.  Stilphide  of  ammonium  gives  a black  precipitate  ; and 
sulphuretted  hydrogen^  a dirty  wliite  precipitate,  which  passes 
through  red  into  black ; it  is  insoluble  in  nitric  or  in  hydrochloric 
acid ; this  sulphide  is  insoluble  in  the  sulphides  of  the  alkaline 
metals  unless  an  excess  of  alkali  be  present,  in  which  case  the 
precipitate  is  gradually  dissolved.  Iodide  of  potassium  precipi- 
tates a salmon-coloured  iodide  of  mercury,  which  quickly  be- 
comes of  a brilliant  scarlet : this  precipitate  is  soluble  in  excess 
both  of  iodide  of  potassium,  and  of  corrosive  sublimate.  Hydro- 
chloric acid  and  solutions  of  the  chlorides  give  no  precipitate  with 
the  mercuric  salts.  Ferrocyanide  of  potassium  gives  a white 
precipitate,  which  gradually  becomes  blue,  while  cyanide  of 
mercury  is  formed  in  the  solution. 

(930)  Estimation  of  Mercury. — Mercury  is  usually  estimated 
in  the  metallic  form.  If  the  solution  contain  neither  lead  nor 
silver,  metallic  mercury  may  be  precipitated  by  the  addition  of 
stannous  chloride,  acidulated  with  hydrochloric  acid  : the  metal 
must  be  collected  on  a weighed  filter,  and  diled  hi  vacuo  over 
sulphuric  acid. 

When  the  compound  is  in  the  solid  form,  Millon  recommends 
the  following  plan  for  effecting  the  decomposition  of  tlie  combina- 
tions of  mercury,  and  for  collecting  the  metal: — A hard  glass 
tube,  15  or  16  inches  long,  such  as  is  used  in  the  analysis  of 
organic  compounds,  is  drawn  out  in  the  manner  represented  in 
fig.  356,  and  Sit  a sl  small  bulb  is  formed  for  the  reception  of  the 


Fia.  356. 


mercury ; a plug  of  asbestos  is  placed  at  ; the  tube  is  then 
filled  as  far  as  c with  fragments  of  (piicklime,  and  the  mercurial 
compound,  in  quantity  varying  from  15  to  50  grains,  is  introduced 
between  c and  d,  and  the  tu])e  is  filled  up  with  fragments  of 
lime.  If  nitric  acid  be  present  in  the  compound,  metallic  copper 
must  he  substituted  for  quicklime.  The  extremity,  e^  is  con- 
nected with  an  apparatus,  g,  wliich  supplies  a steady  current  of 
pure  dry  hydrogen, — the  tube  being  placed  in  a sheet-iron  fur- 
nace, f wiiile  the  receiver,  a,  projects  beyond  the  furnace,  and  is 


664 


SILVER. 


kept  cool.  As  soon  as  the  apparatus  is  filled  with  the  gas, 
lighted  charcoal  is  applied  to  the  fi-rst  third  of  the  tube  between 
1)  and  c,  and  when  it  is  at  a full  red  heat,  glowing  charcoal  is 
very  gradually  added  until  the  whole  length  of  the  tube  is  red 
liot";  the  mercury  collects  in  a,  and  the  water,  which  is  at  first 
condensed,  is  gradually  removed  by  the  current  of  dry  hydrogen. 
When  the  operation  is  over,  the  narrow  portion  of  the  tube  be- 
tween a and  h is  cut  with  a file,  and  the  detached  portion 
with  its  contents,  is  weighed : the  mercury  is  emptied,  the  bulb 
cleansed  with  nitric  acid  and  water,  then  dried,  and  weighed  a 
second  time ; the  difference  gives  the  weight  of  the  condensed 
mercmw. 

§ II.  Silver  : Ag'=108.  Sp.  Gr.  10*53.  Fusing-pt  1873°. 

(931)  Silver  has  been  known  from  the  earliest  ages,  and  has 
always  been  prized  for  its  rarity,  beauty,  and  its  brilliant  lustre. 
It  has  a white  colom*  with  a tinge  of  red  ; in  hardness  it  is  inter- 
mediate between  copper  and  gold,  and  it  is  endowed  with  con- 
siderable tenacity ; it  may  be  hammered  into  very  thin  leaves, 
and  admits  of  being  drawn  into  very  fine  wire.  By  repeated 
heatings,  however,  this  metal  assumes  a crystalline  texture,  and 
it  then  becomes  brittle.  It  crystallizes  in  forms  belonging  to 
the  regular  system.  Silver  fuses  at  1873°  F.,  and  on  cooling 
expands  forcibly  at  the  moment  of  solidification.  It  is  not 
sensibly  volatilized  if  heated  in  closed  vessels,  but  a silver  wire  is 
dispersed  in  greenish  vapours  when  a very  powerful  electrical  dis- 
charge is  sent  through  it ; when  heated  before  the  oxyhydrogen 
jet  on  lime  (966)  it  may  be  made  to  boil,  and  give  off  vapours 
which  become  oxidized  in  the  cun-ent  of  gas  if  it  contains  an 
excess  of  oxygen.  Silver  is  an  excellent  conductor  both  of  heat 
and  electricity,  and  is  not  inferior  in  these  respects  to  any  known 
substance.  Silver  is  not  oxidized  by  exposure  at  any  temperature 
either  in  a dry  or  a moist  atmosphere.  Pure  silver,  however, 
when  melted,  absorbs  oxygen  mechanically,  to  an  extent  amount- 
ing, it  is  said,  to  22  times  the  bulk  of  the  metal,  but  the  gas  is 
given  ofiP  at  the  moment  of  solidification : if  a mass  of  melted 
silver  be  allowed  to  cool  suddenly,  the  outer  crust  becomes  solidi- 
fied, and  when  the  interior  portion  assumes  the  solid  condition  it 
ruptures  the  crust ; small  tubes  or  globules  of  melted  metal  are 
then  forcibly  expelled  by  the  escaping  oxygen,  aided  by  the  sudden 
expansion  which  the  silver  undergoes  in  the  act  of  solidification. 
This  phenomenon,  which  is  termed  the  spitting  of  the  globule,  is 
entirely  prevented  by  the  presence  of  1 or  2 per  cent,  of  copper. 
Silver  combines  slowly  with  chlorine,  with  bromine,  and  with 
iodine ; if  fused  with  phosphorus  the  two  bodies  enter  into 
combination.  Silver  has  a powerful  attraction  for  sulphur ; 
by  long  exposure  to  the  air  the  metal  becomes  superficially 
blackened  or  tarnished,  from  the  formation  of  a thin  film  of 
sulphide  upon  its  surface,  owing  to  the  decomposing  action  of  the 
metal  upon  the  small  portion  of  sulphuretted  hydrogen  which 


EXTEACTION  OF  SILVER  FROM  ITS  ORES. 


665 


is  constantly  floating  in  the  air,  especially  of  large  towns.  This 
tarnish  is  readily  removed  by  means  of  a solution  of  cyanide  of 
potassium. 

The  best  solvent  for  silver  is  nitric  acid,  which,  if  diluted 
with  an  equal  bulk  of  water,  acts  upon  the  metal  with  great 
violence,  dissohdng  it  rapidly  and  evolving  nitric  oxide,  while 
nitrate  of  silver  is  formed.  Hydrochloric  acid  acts  huts  lightly 
upon  it.  Aqua  regia  attacks  it  more  rapidly.  Diluted  hydriodic 
acid  attacks  it  with  evolution  of  hydrogen.  Boiling  oil  of  vitriol 
dissolves  it  with  evolution  of  sulphurous  anhydride.  If  common 
salt  be  fused  in  a silver  dish,  or  if  it  be  moistened  and  left  in  contact 
with  silver,  it  gradually  corrodes  it ; soda  being  formed  by  the 
absorption  of  oxygen  from  the  air,  while  the  liberated  chlorine 
attacks  the  silver.  Heither  the  hydrated  alkalies  nor  their  ni- 
trates exert  any  considerable  action  upon  it,  wdiether  in  solution 
or  wdien  fused  by  heat,  and  hence  crucibles  for  the  fusion  of  refrac- 
tory minerals  with  caustic  potash  are  commonly  made  of  this  metal. 

The  value  of  silver  as  a medium  of  exchange  has  caused  it  to 
be  adopted  as  such  by  all  civilized  nations  from  the  earliest  ages 
of  the  world.  When  alloyed  with  certain  proportions  of  copper 
it  is  used  for  the  current  coin  of  the  realm,  and  for  the  various 
articles  of  plate.  From  its  superior  power  of  reflecting  light,  it 
forms  the  best  surface  for  the  reflectors  employed  in  lighthouses 
at  sea. 

(932)  Extraction  of  Silver  from  its  Ores. — Silver  is  frequently 
met  with  in  the  native  state  ; either  pure,  when  it  occurs  in  fibrous 
masses,  or  crystallized  in  cubes  or  octohedra  ; or  sometimes  com- 
bined with  gold,  mercury,  or  antimony  : generally,  however,  it  is 
found  in  combination  with  sulphur,  mixed  with  sulphides  of  lead, 
antimony,  copper,  and  iron.  The  mines  of  Peru  and  Mexico  are 
the  most  extensive  sources  of  silver.  In  Europe,  those  of  Kongs- 
berg  in  Norway,  and  of  Schneeberg  and  Freyberg  in  Saxony,  are 
celebrated : there  are  also  numerous  other  mines  from  which 
smaller  quantities  are  obtained.  The  ores  of  silver  occur  usually 
among  the  primitive  rocks,  frequently  in  calcareous  veins,  travers- 
ing either  gneiss,  or  slaty  and  micaceous  deposits.  Sulphide  of 
lead  is  nearly  always  accompanied  by  small  quantities  of  sulphide 
of  silver,  and  a considerable  quantity  of  silver  is  extracted  during 
the  refining  of  lead  by  Pattinson’s  process  (891),  as  well  as  by 
cupellation  (892). 

At  Freyberg,  silver  is  for  the  most  part  obtained  from  the 
sulphide  by  the  method  of  amalgamation.  The  plumbiferous 
ores  are  in  this  case  rejected,  as  they  are  not  adapted  to  this  me- 
thod of  proceeding,  but  are  treated  in  the  manner  already  de- 
scribed. The  ores  are  usually  sorted,  so  that  they  shall  contain 
about  0‘24  parts  of  silver  in  100,  or  about  80  ounces  per  ton  of 
ore,  and  not  more  than  1 per  cent,  of  copper ; the  ])roportion  of 
iron  pyrites  is  not  allowed  to  exceed,  or  greatly  to  fall  short  of  35 
per  cent.  The  metalliferous  mass,  after  being  reduced  to  a coarse 
powder,  is  mixed  with  a tenth  of  its  weight  of  common  salt,  and 
sifted,  to  ensure  its  intimate  incorporation : it  is  then  roasted,  at 


G66 


FKEYBEEG  PROCESS  OF  AMALGAMATION. 


first  at  a low  red  heat ; during  this  operation,  care  is  taken  to 
keep  the  mixture  constantly  stirred,  in  order  as  far  as  possible  to 
pre,vent  it  from  concreting  into  lumps.  Meantime  arsenic  and 
antimony  are  expelled  in  dense  white  fumes  of  arsenious  anhy- 
dride and  oxide  of  antimony,  and  the  sulphides  of  the  other  met- 
als are  partially  oxidized;  the  silver  obtains  chlorine  from  the 
salt,  the  sodium  of  which  unites  with  oxygen  and  sulphur,  chlo- 
ride of  silver  and  sulphate  of  sodium  being  formed;  the  copper 
and  the  iron  are  changed  partly  into  sulphates,  partly  into  chlo- 
rides, and  partly  into  oxides,  as  the  equations  subjoined  will 
show : — 

Ag,S  + 2 XaCl-f  2 e,=2  AgCl  + AXSO, ; 

■0uS-f  2 O2=-0uS04 ; 

2 OuS-fd  KaCl-fd  e,=-eu,Cl,-f  Cl,  + 2 iSXSO,; 

2 FeSj-j-G  hTaCl-l-T  02=Fe2Cl5-f3  AagSO^-f 

During  the  early  stages  of  this  operation,  fumes  of  sulphurous 
anhydride  are  given  ofi’  abundantly  ; and  the  roasting  is  continued 
until  these  have  in  great  measure  given  place  to  those  of  chlorine 
and  perchloride  of  iron.  A charge  of  cwt.  requires  G hours’ 
roasting.  The  roasted  mass  is  now  raked  out  of  the  furnace,  and 
allowed  to  cool : it  is  next  sifted  in  order  to  separate  the  lumps, 
which  are  powdered  and  again  submitted  to  the  same  operation. 
About  85  per  cent,  of  the  silver  is  thus  converted  into  chloride  at 
the  first  roasting.  The  portions  which  have  passed  through  the 
sieve  are  ground  to  powder,  and  passed  through  a bolting  sieve  to 
procure  a very  fine  meal.  The  powder  is  next  placed,  with  from  a 
third  to  half  its  weight  of  water,  in  large  casks,  which  are  charged 
with  half  a ton  of  the  ore.  These  casks  are  caused  to  revolve 
upon  horizontal  axes,  about  20  times  per  minute ; 1 cwt.  of  scrap 
wrought  iron  is  then  introduced  into  each  cask,  and  after  the 
lapse  of  an  hour,  5 cwt.  of  mercury  is  added,  after  which  the 
casks  are  again  made  to  revolve  for  about  20  hours ; during  this 
operation  a slight  rise  of  temperature  is  observed.  The  powder 
when  placed  in  the  casks  consists  principally  of  chloride  of  silver 
mixed  with  large  quantities  of  cupric  sulphate  and  cupreous  chlo- 
ride, as  well  as  of  ferric  chloride,  with  a variable  proportion  of  the 
oxides  of  copper  and  iron.  The  object  of  agitating  the  mixtm’e 
with  the  iron  before  adding  the  mercury  is  to  reduce  the  ferric 
chloride  to  ferrous  chloride  in  the  first  instance ; if  this  precau- 
tion were  not  taken,  the  mercury  would  be  partially  converted 
into  calomel,  which  would  not  subsequently  be  decomposed,  and 
would  thus  be  lost ; the  excess  of  iron  afterwards  removes  the 
chlorine  from  the  chloride  of  silver  and  cupreous  chloride,  and 
the  sulphmdc  acid  from  the  copper. 

Fe-f  Fe,Cle=3  FeCl, ; 2 AgCl-hFe=FeCl-bAg,. 

•GujCl  + Fe = FeClj  2 -Gu ; 0u$0^  -f  Fe = FeSO^  ^u. 

The  presence  of  the  mercmy  favours  this  reaction,  by  establishing 
a voltaic  current,  and  the  silver  and  copper  thus  set  at  liberty 
unite  immediately  with  the  mercury,  forming  a liquid  amalgam. 


AMERICAN  PROCESS  OF  AMALGAMATION. 


667 


amalgam  has  now 


Fig.  357. 


At  the  expiration  of  18  or  20  hours  the  casks  are  filled  up  with 
water,  and  are  again  set  in  motion  for  a couple  of  hours  to  allow 
the  amalgam  to  be  washed  out  of  the  spent  materials  ; after 
which  the  fiuid  amalgam  is  drawn  olF  into  sacks  of  ticking  ; these 
sacks  form  a kind  of  rude  filter  through  which  the  greater  part  of 
the  mercury  runs  into  a stone  trough,  leaving  behind  it  a soft  solid 
containing  from  15  to  IT  per  cent,  of  silver.  The  mud  in  the 
casks  is  again  submitted  to  washing ; the  residual  amalgam  sub- 
sides, owing  to  its  greater  density,  and  the  lighter  portions  are 
rejected.  The  filtered  part  of  the  mercury,  which  retains  a small 
quantity  of  silver,  is  used  again  for  the  amalgamation  of  a 
fresh  portion  of  ore.  The  silver  in  the  solid 
to  he  separated  from  the  remaining 
mercury ; for  this  purpose  it  is  placed 
in  trays,  supported  on  a tripod,  c,  fig. 

357,  under  a large  distillatory  iron  bell, 

B,  round  the  upper  park  of  wdiich  a fire, 

A,  is  lighted  ; the  bell  and  its  contents  are 


thus  brought  to  a red  heat,  by  which 
means  the  mercury  is  driven  off;  its 
vapour  descends,  and  is  condensed  in 
the  water  contained  in  the  vessel,  n. 

The  operation  is  generally  performed 
on  5 cwt.  of  amali^am  at  a time,  and 
occupies  8 hours.  The  residual  spongy 
mass  of  silver  and  copper  is  then  fused 
and  cast  into  ingots,  which  in  the  Saxon 
mines  contain  usually  about  70  per  cent, 
of  pure  silver  and  38  of  copper.* 

(933)  AmeHcan  Process  of  Amalgamation. — In  the  mining 
districts  of  Mexico  and  Chili,  where  fuel  is  expensive,  and  where 


* An  improvement  upon  this  process  has  been  introduced  by  Augustin,  who  dis- 
penses with  the  use  of  mercury  altogether.  After  the  ore  has  been  roasted  first  by 
itself,  and  again  a second  time  with  chloride  of  sodium,  it  is  digested  in  a concen- 
trated solution  of  common  salt ; — such  a solution  dissolves  chloride  of  silver  readily : 
a dilute  solution  of  chloride  of  sodium  exerts  little  or  no  solvent  action ; and  the  con- 
centrated liquid  when  diluted  deposits  the  chloride  of  silver  which  it  had  previously 
dissolved.  In  practice  it  is  found  better,  instead  of  diluting  the  liquid,  to  digest  it 
upon  metallic  copper;  the  chloride  of  silver  is  decomposed,  chloride  of  copper  is 
formed  and  dissolved,  whilst  metallic  silver  is  precipitated.  The  presence  of  chloride 
of  copper  in  the  solution  of  the  chloride  of  sohum  does  not  prevent  the  liquid  from 
being  employed  again  for  the  extraction  of  chloride  of  silver  from  fresh  portions  of 
the  roasted  ore. 

Another  important  improvement  in  the  operation  was  made  by  Ziervogel.  He 
avoids  the  preparation  of  chloride  of  silver  entirely,  and  merely  roasts  the  sulphurous 
ores  in  such  a manner  that  the  sulphates  of  iron  and  copper  are  completely  decom- 
posed, whilst  the  sulphate  of  silver,  which  vdthstands  a much  higher  temperature, 
remains  undecomposed  in  the  mass.  In  this  operation  the  powdered  ore  is  roasted 
till  it  gives  off  no  odour  of  sulphurous  anhydride  and  yields  no  sensible  amount  of 
sulphate  of  copper  when  thrown  red  hot  into  water : boiling  water  then  dissolves  out 
the  sulphate  of  silver,  but  the  oxides  of  copper  and  iron  remain  undissolved.  The 
silver  is  precipitated  from  the  liquid  by  means  of  metallic  copper  as  before.  A small 
quantity  of  silver  is  still  retained  in  the  uudissolved  residue,  from  which  it  may  be 
advantageously  extracted  by  the  method  of  Augustin.  Both  these  processes  have 
been  patented  and  practised  on  a large  scale  in  England. 

Percy  has  suggested  the  use  of  hyposulphite  of  sodium  as  a solvent  for  the  chlo- 
ride of  silver.  The  mineral  after  roasting  with  chloride  of  sodium  is  washed  first 


668 


AMERICAN  PROCESS  OF  AMALGAMATION. 


ores  are  often  worked  of  a mncli  poorer  description  than  in 
Europe,  the  process  of  amalgamation  is  different.  A good  deal 
of  the  silver  occurs  in  the  native  state,  so  that  it  unites  directly 
with  the  mercury.  The  mineral  is  stamped  and  ground  to  a 
fine  powder  in  mills,  then  moistened  with  water,  and  mingled 
with  from  1 to  5 per  cent,  of  salt ; the  mixing  is  effected  by  the 
trampling  of  horses  during  6 or  8 hours.  The  ore  thus  blended 
with  the  salt  is  allowed  to  remain  undisturbed  for  some  days,  after 
which  an  addition  of  or  of  its  weight  of  what  is  techni- 
cally termed  magistral  is  made.  This  substance  consists  of  roasted 
copper  pyrites,  and  contains  about  10  per  cent,  of  sulphate  of 
copper,  the  remainder  being  sulphate  of  iron  and  other  impurities ; 
mercury,  to  the  extent  of  twice  the  quantity  of  silver  that  the  ore 
contains,  is  then  added,  the  mixture  being  effected,  as  before,  by 
the  trampling  of  horses.  It  is  again  allowed  to  rest  for  16  or  20 
days : during  this  period  a considerable  portion  of  the  silver  be- 
comes united  with  the  mercury,  forming  a hard,  brilliant  amal- 
gam, and  at  the  same  time  a large  quantity  of  calolnel  is  formed. 
Another  equal  quantity  of  mercury  is  added,  and  a still  longer 
interval  of  rest  is  allowed ; then  a third  dose  of  mercury  to  the 
same  extent  follows ; by  this  last  addition  a fluid  amalgam  is  ob- 
tained, which  is  separated  by  washing,  filtered,  and  the  mercury 
is  expelled  from  the  silver  by  distillation.  The  quantity  of  mer- 
cury consumed  in  this  process  varies  from  130  to  150  parts  for 
each  100  parts  of  silver  extracted,  great  waste  being  incurred 
owing  to  the  formation  of  calomel,  which  is  not  recovered.  It  is 
calculated  that  up  to  the  close  of  the  last  century,  6 million  cwt. 
of  mercury  had  thus  been  lost  by  the  processes  adopted  in  the 
American  mines  in  the  course  of  200  years.* 

The  theory  of  this  operation  is  rather  obscure.  The  sulphate 
of  copper  of  the  magistral,  and  the  chloride  of  sodium  decompose 
each  other,  cupric  chloride  and  sulphate  of  sodium  being  formed. 
Cupric  chloride,  in  the  presence  of  metallic  silver,  is  converted 
into  cupreous  chloride,  whilst  chloride  of  silver  is  produced; 
2 Ou'^Cl^  + Ag2  ^Ou'^Cla  -f  2 AgCl.  When  cupreous  chloride,  with 
excess  of  common  salt  and  water,  is  brought  into  contact  with 
sulphide  of  silver,  the  cupreous  chloride  is  dissolved  by  the  solu- 
tion of  chloride  of  sodium ; this  solution  of  cupreous  chloride  de- 
composes the  sulphide  of  silver,  and  is  converted  into  cupreous 
sulphide,  whilst  chloride  of  silver  is  formed ; ■0u'2Cl2-f- Ag^S^Ou'^S 
-h  2 AgCl.  The  excess  of  salt  dissolves  the  chloride  of  silver,  and 
the  addition  of  mercury  decomposes  this  dissolved  chloride ; calo- 
mel is  formed,  and  an  amalgam  of  silver  is  procured;  2 AgCl-f 

witli  hot  and  then  with  cold  water,  and  afterwards  is  digested  in  a dilute  solution  of 
the  alkaline  hyposulphite,  which  dissolves  the  chloride  of  silver ; from  this  solution 
the  silver  is  precipitated  as  sulphide,  by  means  of  sulphide  of  sodium,  whilst  hypo- 
sulphite of  sodium  is  reproduced  as  before. 

* Dumas  proposes  to  recover  this  mercury  by  treating  the  washed  residue  with  a 
quantit}^  of  chloride  of  lime  or  nitrate  of  sodium,  proportioned  to  the  mercury  they 
contain,  then  adding  hydrochloric  acid  in  slight  excess ; the  calomel  would  thus  be 
converted  into  corrosive  sublimate.  This  is  to  be  removed  by  methodical  washiiig, 
and  the  mercury  precipitated  by  copper.  The  solution  of  copper  thus  obtained  would 
furnish  the  magistral  required  for  a new  operation  upon  fresh  ore. 


LIQUATION PLATING  AND  SILVEKING. 


669 


2Hg— 2HgCl  + Ag,.  If  too  inucli  magistral  be  added,  an  excess 
of  cupric  chloride  (OuCl^)  is  produced;  this  state  of  the  mix- 
ture is  easily  perceived,  for  in  such  a case  the  globules  of  mercury 
in  the  mixture  appear  to  be  too  minutely  divided ; the  addition  of 
lime  then  becomes  necessary  in  order  to  decompose  the  excess  of 
the  cupric  chloride,  otherwise  this  salt  would  reconvert  the  silver 
into  chloride,  and  the  mercury  into  calomel. 

(934)  Separation  of  Silver  from  Copper  hy  Liquation. — It  oc- 
casionally happens  that  a copper  ore  contains  a considerable  amount 
of  silv^er,  which,  under  certain  circumstances,  it  may  be  desirable 
to  extract  by  the  process  of  liquation.  For  this  purpose  the  cop- 
per, having  been  brought  to  the  stage  of  blister  copper  (870),  is 
melted  with  from  3 to  4 times  its  w^eight  of  lead : the  mixture  is 
cast  into  circular  ingots  in  iron  moulds,  which  suddenly  cool  the 
alloy,  and  cause  it  to  solidify  before  the  copj)er  and  lead  have 
time  to  separate  from  each  other.  The  proportion  of  lead  should 
not  be  less  than  500  times  that  of  the  silver  in  the  mass.  These 
cakes  are  then  subjected  to  the  action  of  a moderate  heat ; the 
lead,  combined  with  nearly  all  the  silver,  and  a small  proportion 
only  of  copper,  gradually  runs  from  tlie  mass,  leaving  a s^^ongy 
residue,  consisting  chiefly  of  copper,  but  still  retaining  a small 
proportion  of  lead.  The  argentiferous  lead  is  afterwards  subjected 
to  the  process  of  cupellation,  whilst  the  copper  from  which  it  has 
been  separated  is  subjected  to  a patient  roasting  in  order  to  oxidize 
the  remainder  of  the  lead,  and  it  is  then  reflned  much  in  the  usual 
manner. 

(935)  Plating  and  Silvering. — Silver  is  frequently  employed 
to  give  a coating  to  the  surface  of  less  expensive  metals.  Goods 
so  prepared  are  said  to  be  plated.^  if  the  proportion  of  silver  be 
considerable,  and  sihered  if  it  be  small.  Plating  on  copper  is 
effected  by  polishing  the  upper  surface  of  the  ingot  which  is  to  be 
plated,  and  then  placing  upon  it  a bright  slip  of  silver,  the  super- 
flcial  area  of  which  is  a little  smaller  than  that  of  the  copper 
which  it  is  intended  to  cover : the  thickness  of  the  plate  of  silver 
in  proportion  to  that  of  the  copper  varies  with  the  value  of  the 
goods.  The  compound  ingot  is  then  exposed  to  a temperature 
pist  below  the  fusing-point  of  the  silver,  wdiich  softens  at  its 
surface.  By  hammering  or  rolling  out  at  this  high  heat,  the  two 
metals  are  sweated  together,  as  it  is  termed,  and  become  insepa- 
rably united.  ISo  solder  is  used  in  this  process,  but  a small 
])ortion  of  powdered  borax  is  placed  round  the  edge  of  the  silver 
to  prevent  the  surface  of  the  copper  from  becoming  oxidated. 
The  ingot  is  then  rolled  until  it  is  reduced  to  the  required  degree 
of  tenuity. 

Iflating  on  steel  is  effected  rather  differently.  The  article  (a 
dessert  knife,  for  example),  having  been  first  brought  to  the  shape 
required,  is  tinned  upon  its  surface,  and  then  a slip  of  silver  foil 
is  soldered  on.  After  the  silver  has  been  attached,  the  super- 
fluous portion  is  removed,  and  the  article  is  finished  up  and 
])olished. 

These  methods  of  plating  have,  however,  been  in  a great 


670 


SILVERING  OF  MIRRORS. 


degree  superseded  by  the  process  of  electro-plating,  in  wliicli  tlie 
silver  is  deposited  upon  the  surface  by  voltaic  action  (295). 

Silvering  may  be  effected  either  by  the  wet  or  by  the  dry 
method.  The  wet  method  is  usually  adopted  for  such  purposes  as 
the  silvering  of  thermometer  scales.  It  is  generally  executed 
either  on  brass  or  on  copper : the  surface  of  these  metals  is 
cleaned  by  dipping^  or  momentary  immersion  of  the  articles  in 
nitric  acid,  to  remove  the  film  of  oxide  which  always  forms  from 
exposure  to  the  atmosphere,  even  for  a few  hours.  After  rinsing 
them  in  water  to  remove  the  nitric  acid,  they  are  rubbed  over 
with  a mixture  of  100  parts  of  cream  of  tartar,  10  of  chloride  of 
silver,  and  1 part  of  corrosive  sublimate.  The  mercury  appears 
to  act  as  a kind  of  solder  to  the  silver,  the  copper  combining  with 
the  chlorine  both  of  the  chloride  of  silver  and  of  the  sublimate ; 
the  surface  is  afterwards  polished. 

Dry  silvering  is  effected  by  dissolving  a certain  quantity  of 
silver  in  mercury  ; the  ‘ dipped  ’ articles  are  agitated  with  a por- 
tion of  this  amalgam,  which  thus  becomes  diffused  uniformly  over 
the  surface.  By  the  application  of  heat  the  mercury  is  expelled, 
leaving  a very  tbin  film  of  silver  behind : on  polishing  the  trinkets 
a bright  silvered  surface  is  obtained. 

(936)  Silvering  of  Mirrors. — Some  of  the  salts  of  silver  when 
rendered  slightly  ammoniacal  and  mixed  with  certain  organic  solu- 
tions, such  as  aldehyd  and  salicylous  acid,  are  reduced  to  the 
metallic  state,  the  silver  being  deposited  upon  the  surfaces  of  glass 
vessels  in  which  the  experiment  is  made,  in  the  form  of  a bril- 
liant, adhering,  mirror-like  coating.  Mr.  Drayton -some  years 
ago  proposed  to  apply  this  observation  to  the  silvering  of  mirrors 
upon  a large  scale,  as  the  coating  adapts  itself  not  only  to  flat  sur- 
faces, but  to  those  also  which  are  curved,  or  cut  into  patterns. 
This  process  is  now  successfully  practised  in  Paris,  as  follows  : — • 
600  grains  of  pure  neutral  nitrate  of  silver  are  dissolved  in  1200 
grains  of  water.  To  this  solution  are  added : 1st,  75  grains  of  a 
liquor  prepared  from  25  parts  of  distilled  water,  10  of  sesquicar- 
bonate  of  ammonium,  and  10  of  a solution  of  ammonia  of  sp.  gr. 
0*980;  2nd,  30  grains  of  a solution  of  ammonia  of  sp.  gr.  0*980; 
and  3rd,  1800  grains  of  alcohol  of  sp.  gr.  0*850.  The  mixture  is 
left  at  rest  to  become  clear.  The  liquid  is  decanted  or  filtered, 
and  a mixture  of  equal  parts  of  alcohol  (sp.  gr.  0*850)  and  oil  of 
cassia  is  added  in  the  proportion  of  1 part  of  this  essence  of  cassia 
to  15  parts  of  the  solution  of  silver ; the  mixture  is  agitated  and 
left  to  settle  for  several  hours,  after  which  it  is  filtered.  Just 
before  pouring  it  upon  the  glass  to  be  silvered,  it  is  mixed  with 
tV  of  its  bulk  of  essence  of  cloves  (composed  of  1 part  of  oil  of 
cloves,  and  3 of  alcohol,  sp.  gr.  0*850).  The  glass,  having  been 
thoroughly  cleansed,  is  covered  with  the  silvering  liquid,  and 
warmed  to  about  100°  F.,  at  which  temperature  it  is  maintained 
for  two  or  three  hours : the  liquid  is  then  decanted,  and  may  be 
employed  for  silvering  other  glasses.  The  deposit  of  silver  upon 
the  glass  is  washed,  dried,  and  then  varnished.  (Pelouze  and 
Fremy,  Traite  de  Chimie^  2nd  Ed.,  iii.  347.) 


SILVEEING  OF  MEKOKS — ALLOYS  OF  SILVEE.  6Yl 

An  alcoholic  solution  of  grape-sugar  produces  the  same  result, 
if  substituted  for  the  oils  of  cassia  and  cloves,  but  the  deposit 
occurs  much  more  slowly.  Liebig’s  method  of  reducing  an  am- 
moniacal  solution  of  nitrate  of  silver  alkalized  with  soda  or  potash, 
by  means  of  milk-sugar,  at  ordinary  temperatures,  has  been  suc- 
cesfully  applied  by  Steinheil,  in  the  following  manner,  to  the  sil- 
vering of  mirrors  for  telescopes  {Liebig’s  Annal.  xcviii.  132) : — 
Dissolve  in  200  measures  of  water  of  their  weight  of  pure 
nitrate  of  silver,  and  add  to  the  liquid  a solution  of  caustic  am- 
monia in  quantity  just  sufficient  to  redissolve  the  oxide  of  silver 
which  is  at  hrst  precipitated ; add  to  this  solution  450  measures  of 
a solution  of  caustic  soda  (of  sp.  gr.  1-035)  free  from  chloride, 
and  immediately  redissolve  the  dark  brown  precipitate  thus  pro- 
duced, by  the  cautious  addition  of  caustic  ammonia,  after  which 
dilute  the  liquid  with  water  to  1450  measures ; then  add  a solu- 
tion of  nitrate  of  silver  till  a decided  permanent  grey  precipitate 
is  formed,  and  finally  pour  in  water  till  the  mixture  occupies 
exactly  1500  measures:  then  leave  it  to  stand,  and  decant  the 
clear  liquid.  Immediately  before  the  solution  is  to  be  used,  it  is 
to  be  mixed  with  an  eighth  or  an  tenth  of  its  volume  of  a solution 
of  milk-sugar  in  ten  times  its  w^eight  of  water.  The  solution  is 
to  be  placed  in  a shallow  vessel,  and  the  glass  to  be  silvered  sup- 
ported just  at  the  surface  of  the  liquid : a beautiful  coherent  film 
of  silver  is  deposited  upon  the  under  surface  of  the  glass,  and  a 
copious  precipitation  of  silver  occurs  upon  the  sides  of  the  vessel. 

Another  very  good  method  of  silvering  glass  is  that  of  Petit 
Jean  {Chem.  Gaz,^  1856,  p.  319),  in  which  an  ammoniacal  solution 
of  tartrate  of  silver  is  employed  at  a gentle  heat;  by  using  a 
solution  of  ammonio-citrate  of  gold,  it  is  easy  to  gild  upon  glass ; 
and  in  a similar  manner  the  surface  may  be  platinized  if  a solu- 
tion of  sodio-tartrate  of  platinum  be  employed. 

(937)  Alloys  of  Silver. — Y arious  alloys  of  silver  may  be  ob- 
tained with  facility,  but  the  only  one  extensively  used  is  the  alloy 
of  silver  with  copper.  Pure  silver  is  too  soft  for  ordinary  uses, 
such  as  the  fabrication  of  coin,  and  jeweller’s  work,  and  would 
soon  waste  by  the  constant  friction  it  -would  experience.  In  order 
to  confer  a sufficient  degree  of  hardness  upon  the  silver,  it  is  com- 
bined with  a small  quantity  of  copper.  The  proportion  of  copper 
in  the  ‘ standard  ’ silver  employed  for  coinage  varies  in  different 
countries:  in  England  it  amounts  to  7*5  per  cent.,  in  France  to 
10  per  cent.,  and  in  Prussia  to  25  per  cent.  Silver  and  copper 
in  uniting  to  form  an  alloy  expand  slightly,  so  that  the  density  of 
the  mixture  is  somewhat  less  than  the  calculated  mean.  English 
standard  silver  has  a density  of  10-20,  instead  10-35.  Experi- 
ence has  shown  that  an  alloy  of  silver  and  co]>per,  however  care- 
fully the  two  metals  be  incorporated,  undergoes  a species  of  liqua- 
tion during  the  slow  solidification  of  tlie  melted  mass : wlien  cast 
into  ingots,  the  interior  parts  of  tlie  bars  have  a composition  dif- 
ferent from  that  of  the  superficial  portions ; a circumstance  of 
some  importance  in  the  preparation  of  standard  silver  for  the  pur- 
poses of  coinage.  The  only  alloy  in  which  this  partial  separation 


672 


ASSAY  OF  SILYEE  BY  CtTPELEATION. 


of  tlie  two  metals  was  found  not  to  occur  is  stated  by  Levol  {Ann. 
de  Chimie^  III.  xxxvi.  220),  to  consist  of  719  parts  of  silver  and 
281  of  copper,  corresponding  to  tlie  formula  Agg-Bu^.  Tins  liqua- 
tion is  comparatively  trilling  in  amount  in  bars  which  contain 
950  parts  of  silver  and  upwards  in  1000 : in  bars  which  contain  a 
larger  proportion  of  silver  than  719  in  1000  of  alloy,  the  central 
portions  of  the  ingot  were  found  to  be  richer  than  those  upon  the 
surface ; but  in  the  alloys  of  lower  value  the  proportion  of  silver 
was  greatest  on  the  surface  of  the  ingot.  Silver,  when  alloyed 
with  many  of  the  metals  in  small  quantity,  is  rendered  brittle  and 
unlit  for  the  purposes  of  coinage.  This  is  the  case,  for  instance, 
when  the  silver  contains  tin,  zinc,  antimony,  bismuth,  lead,  or 
arsenic.  These  metals  are,  however,  all  easily  removed  in  the 
ordinary  course  of  relining.  The  alloy  used  as  a solder  for  silver 
consists  of  6 parts  of  brass,  5 of  silver,  and  2 of  zinc.  Silver 
appears  to  have  the  power  of  dissolving  its  sulphide : a quantity 
of  sulphide  not  exceeding  1 per  cent,  renders  the  mass  so  brittle 
that  it  cannot  be  rolled. 

(938)  Assay  of  Silver  hy  Gupellation. — From  the  high  price 
of  silver,  compared  with  that  of  the  metals  used  to  harden  it,  it 
has  become  an  object  of  great  importance  to  be  able  to  determine 
with  facility  and  with  accuracy  the  proportion  of  silver  in  any 
compound.  Jeweller’s  silver  must  according  to  law  be  of  a cer- 
tain degree  of  fineness.  In  this  country  each  article,  previously 
to  being  sold,  is  tested  at  Goldsmith’s  Hall,  and  if  approved  is 
stamped.  The  method  of  testing  commonly  employed  is  termed 
assaying  or  cujyellation.  In  principle  it  depends  upo^i  the  prop- 
erty which  lead  possesses  of  absorbing  oxygen  at  a high  tempera- 
ture, and  of  forming  with  it  an  easily  fusible  oxide,  which  imparts 
oxygen  with  facility  to  all  those  metals  wdiich  yield  oxides  not 
reducible  by  heat  alone.  Most  of  the  oxides'^  thus  formed  unite 
with  the  oxide  of  lead,  and  produce  a fusible  glass  which  is  easily 
absorbed  by  a porous  crucible  made  of  burnt  bones,  termed  a cupel  ‘ 
whilst  any  silver  that  the  mixture  contains  is  left  behind  in  a 
bright  globule,  which  admits  of  being  accurately  weighed.  The 
cupel  and  its  contents  are  shown  in  section  in  fig. 
358.  These  cupels  are  prepared  from  bone  ash 
(burnt  to  wdiiteness,  and  ground  to  a fine  powder), 
by  moistening  it  with  water : a suitable  quantity  of 
the  mixture  is  placed  in  a mould,  and  the  required 
form  and  coherence  is  given  to  it  by  the  blow  of  a 
mallet  or  of  a press  : the  cupels  are  allowed  to  dry  thoroughly 
before  they  are  used.  The  assay  may  be  conducted  upon  quanti- 
ties of  silver  varying  from  10  to  20  grains  in  weight.  The  plan 
of  proceeding  is  as  follows  : — In  a convenient  furnace,  such  as  is 
shown  in  section  at  a a,  fig.  359,  is  placed  an  earthenware  oven  or 
mufiie,  B,  of  semi-cylindrical  form,  closed  at  one  end,  and  open  at 
the  other,  with  slits  in  the  sides  to  allow  the  free  circulation  of  the 

* Oxides  of  tin,  zinc,  nickel,  and  iron,  do  not  form  a fusible  combination  with 
litharge,  and  the  alloys  which  these  metals  yield  with  sUver  are  consequently  not 
adapted  for  cupellation. 


ASSAY  OF  SILVER  BY  CUPELLATION. 


673 


air : upon  tlie  floor  of  the  muffle,  a number  of  cupels  are  arranged 
in  rows,  and  the  temperature  is  raised  to  bright  redness.  Equal 
portions  of  the  various  samples  of  silver  to  he  assayed  are  in  the 
meantime  accurately 
weighed,  and  wrapped 
in  a quantity  of  pure 
thin  sheet-lead,  the 
weight  of  which  va- 
ries with  the  purity  of 
the  alloy;  the  larger 
the  proportion  of  for- 
eign metals  that  it  con- 
tains, the  greater  is  the 
quantity  of  lead  need- 
ed. Each  piece  for 
assay  is  now  placed  in 
its  allotted  cupel,  by 
means  of  a long  pair 
of  tongs.  It  quickly 
fuses ; fumes  of  oxide 
of  lead  are  seen  rising 
from  the  cupels,  hut 
the  greater  part  of  the 
oxide  is  absorbed  by 
the  cupel,  and  the 
silver  is  left  behind  in  a state  of  purity.  At  the  moment  that  the 
last  portion  of  lead  undergoes  oxidation,  the  surface  of  tjie  silver 
flashes,  or  lightens  as  it  is  technically  termed,  owing  to  the  cause 
already  explained  (892).  This  phenomenon  indicates  that  the 
process  is  completed.  The  button  is  allowed  to  cool  very  gradu- 
ally, to  prevent  the  loss  of  silver  by  dispersion  from  spitting  (931) ; 
it  is  then  detached  from  the  cupel,  brushed,  and  accurately 
weighed.  If  the  piece  of  alloy  originally  taken  weighed  10 
grains,  the  weight  of  the  button  in  hundredths  of  a grain  gives 
the  number  of  parts  of  silver  in  1000  parts  of  alloy.  A minute 
quantity  of  silver  always  passes  into  the  cupel  during  the  process, 
for  which  an  allowance  must  be  made  in  weighing  the  button ; 
and  if  the  proportion  of  lead  be  too  great  this  loss  is  increased, 
but  if  too  little  be  used,  part  of  the  copper  is  left  in  the  bead. 
Upon  an  alloy  which  contains  925  parts  of  silver  to  75  of  copper, 
the  loss  is  about  4 per  1000  ; and  upon  silver  which  contains  900 
parts  in  1000,  the  loss  on  the  button  is  about  5 parts  in  1000.  In 
order  to  be  able  to  estimate  the  amount  of  this  loss  in  each  opera- 
tion, the  best  plan  is  to  pass  three  or  four  with  eacli  set  of 

assays.  These  proofs  consist  of  pieces  of  fine  silver  of  known 
weight,  which  are  mixed  with  quantities  of  lead  and  copper,  ap- 
proximatively  of  the  same  amount  as  those  present  in  the  assays 
under  trial.  The  loss  experienced  by  these  proofs  affords  a method 
of  checking  the  results  of  the  assay.  The  amount  of  this  loss 
varies  with  the  temperature. 

The  most  convenient  system  of  reporting  the  fineness  of  sil- 
43 


Fig.  359. 


674 


ASSAY  OF  SILVER  BY  THE  HUMID  PROCESS. 


ver  is  the  decimal  method,  which  is  employed  in  most  countries 
with  the  exception  of  England.  The  practice  of  reporting  both 
gold  and  silver  decimally  was  introduced  a few  years  ago  by  Sir 
J.  Herschel  into  the  Mint  of  this  country,  and  it  probably  will 
gradually  supersede  the  cumbrous  and  artificial  method  which  is 
still  generally  employed  by  the  English  assay ers.  Upon  the  de- 
cimal system,  fine  silver  is  termed  1000*0,  and  the  report  upon 
any  sample  of  alloy  simply  indicates  the  number  of  parts  of  pure 
silver  in  1000  which  it  contains.  Thus  English  standard  silver 
contains  925  parts  of  silver,  and  75  of  copper  in  1000  of  the  alloy. 
Erench  standard  contains  900  parts  of  silver,  and  100  of  copper 
in  1000  of  alloy.  English  standard  would  therefore  be  reported 
as  925  ; French  standard  as  900. 

The  proportions  of  lead  which  are  generally  employed  for  the 
cupellation  of  difierent  alloys  are  the  following  : — 


1000  parts  of  the  alloy  contain 

It  will 

[ require  of  lead 

1000 

parts  of  fine  silver  ...... 

half 

its  weight. 

950 

u 

3 times  its  weight. 

925 

a 

H 

u 

900 

a 

7 

a 

850 

u 

9 

u 

800 

u 

10 

n 

700 

a 

12 

u 

600 

u 

14 

a 

500, 

or  less  

16  or 

17  “ 

A skilful  assayer  will  generally  be  able  at  once  to  determine 
the  comparative  fineness  of  an  article  from  its  mere  appearance, 
and  will  judge  accordingly  of  the  proportion  of  lead  which  it  will 
require.  Great  care  is  needful  in  regulating  the  temperature  of 
the  furnace  during  the  cupellation  ; if  too  high,  a part  of  the  sil- 
ver will  be  lost  by  volatilization  ; if  too  low,  portions  of  lead  and 
copper  are  liable  to  be  retained.  When  the  assay  is  properly 
performed,  the  button  is  brilliant,  well  rounded,  free  from  irregu- 
larities, and  somewhat  granular  upon  its  surface  : it  is  readily 
detached  from  the  cupel.  If  the  assay  adheres  strongly  to  the 
cupel,  or  is  irregular  in  its  outline,  it  retains  a portion  of  alloy. 

(939)  Assay  of  Silver  hy  the  Humid  Process. — The  results  of 
the  process  of  the  assay  by  cupellation,  even  in  experienced  hands, 
may  vary  as  much  as  2 parts  in  1000  : this  circumstance  induced 
Gay-Lussac  to  contrive  a different  method,  which  is  now  adopted 
not  only  in  the  French  Mint,  but  is  employed  in  the  Mints  of 
Great  Britain  and  the  United  States,  as  well  as  in  almost  all  the 
Mints  of  Europe  ; it  admits  of  an  accurate  estimate  of  the  value 
of  an  alloy  to  within  0*5  in  1000.  This  process  depends  upon  the 
solution  of  the  alloy  in  nitric  acid,  the  precipitation  of  the  silver 
from  the  nitrate  in  the  form  of  an  insoluble  chloride,  and  the 
measurement  of  the  amount  of  a standard  solution  of  chloride  of 
sodium  which  is  required  to  effect  the  complete  precipitation  of 
the  silver  in  a given  weight  of  the  alloy.  Chloride  of  silver  easily 
collects  into  dense  flocculi  by  agitation  in  a solution  which  is 


ASSAY  OF  SILVER  BY  THE  HUMID  PROCESS. 


675 


acidulated  with  nitric  acid,  and  which  contains  no  excess  of  so- 
luble chlorides ; so  that  the  exact  point  at  which  the  precipitate 
ceases  to  be  formed  is  readily  perceived. 

A solution  of  common  salt  is  prepared  of  such  a strength  that 
1000  grains  of  it  are  exactly  sufficient  to  precipitate  10  grains  of 
pure  silver.  10  grains  of  the  alloy  for  examination  are  placed 
in  a stoppered  bottle  capable  of  holding  about  6 oz.  of  water,  and 
by  the  aid  of  a gentle  heat,  are  dissolved  in  2 drachms  of  nitric 
acid  of  specific  gravity  1*25  : the  solution  of  salt  is  then  placed 
in  a burette  (fig.  360)  capable  of  holding 
rather  more  than  1000  grains.  The  bu-  360. 

rette,  when  filled  with  the  solution,  is 
weighed  before  being  used,  and  the  li- 
quid is  added  to  the  nitrate  of  silver  in 
the  bottle  ; when  it  is  supposed  that  the 
silver  is  nearly  all  precipitated,  the  liquor 
is  briskly  agitated  in  the  bottle,  and  the 
precipitate  is  allowed  to  subside ; a drop 
or  two  more  of  the  solution  of  salt  is  then 
added : if  a precipitate  be  produced,  the  liquid  is  again  agitated  ; 
and  when  clear,  more  of  the  solution  is  added,  as  before,  so  long 
as  any  turbidity  is  produced  by  the  addition.  When  a cloud 
ceases  to  be  formed,  the  proportion  of  solution  of  salt  wliich  has 
been  added,  is  ascertained  by  weighing  the  burette  a second  time. 
The  number  of  grains  of  the  solution  employed  indicates  the 
degree  of  fineness  of  the  alloy.* 

When,  as  in  the  assay  of  bars  for  coin  or  for  jeweller’s  work, 
a large  number  of  assays  must  be  executed,  all  very  nearly  of  uni- 
form fineness,  the  operation  may  be  reduced  to  a system  by  which 
its  precision  may  be  increased,  at  the  same  time  that  it  is  ren- 
dered much  more  easy  of  execution.  For  this  purpose,  two  so- 
lutions of  salt  are  employed : one,  the  standard  solution^  con- 
taining in  1000  grains  a sufficient  quantity  of  commercial  chloride 
of  sodium  to  precipitate  10  grains  of  silver  ;‘f'  tJie  second  solution, 
the  decimal  solution^  having  one-tenth  of  the  strength  of  the  first, 
and  being  prepared  by  diluting  1 pint  of  the  standard  solution 
wdth  9 pints  of  water.  These  solutions  are  to  be  preserved  in 
well-closed  bottles.  The  standard  solution  is  prepared  in  large 
quantities  at  a time,  and  kept  in  stoneware  jars,  a,  fig.  361,  ca- 
pable of  containing  20  or  25  gallons : is  a tube  open  at  botli 
ends,  which  passes  nearly  to  the  bottom  of  the  jar,  to  admit  air, 
whilst  the  liquid  is  drawn  off  by  the  stopcock,  <?,  without  allowing 
any  loss  by  evaporation  ; cZ  is  a gauge  by  whicli  the  quantity  of 

* In  the  Calcutta  Mint  this  precipitate  is  washed  by  subsidence  in  the  vessel  in 
which  it  is  formed,  and  is  then  collected  in  a small  porcelain  crucible,  as  in  the  pro- 
cess of  collecting  gold,  in  the  operation  of  parting  (958).  The  chloride  is  dried,  and 
then  weighed,  and  the  corresponding  value  of  the  silver  is  calculated. 

f This  solution  contains  approximatively  380  grains  of  chloride  of  sodium  in  a 
gallon  : but  as  the  commercial  salt  contains  chloride  of  maj^esium,  the  exact  strength 
must  be  determined  by  dissolving  10  grains  of  fine  silver  in  acid,  and  precipitating  it 
by  the  addition  of  1000  grains  of  the  solution,  ascertaining  the  amount  of  the  excess 
or  deficiency  of  chloride  in  the  manner  about  to  bo  detailed,  and  then  adding  water 
or  salt  as  may  be  needed. 


676 


ASSAY  OF  SILVER  BY  THE  HUMID  PROCESS. 


liquid  within  is  indicated. 

Fm.  361. 


series  of  bottles,  capable  of  con- 
taining about  6 fluid 
ounces  each,  is  fitted 
with  ground  stoppers, 
numbered  consecutively 
from  1 upwards  : into 
each  bottle  10  grains  of 
the  alloy  for  assay  are 
weighed;  2 drachms  of 
nitric  acid  are  added  to 
each  bottle,  which  is 
placed  in  a shallow 
vessel  containing  water, 
and  gradually  raised  to 
the  boiling-point  ; in 
ten  minutes  the  alloy 
is  completely  dissolved. 

The  precipitation  of 
the  silver  in  the  form  of 
chloride  is  then  effected 
by  the  aid  of  the  appara- 
tus now  to  be  described : 
— y,  fig.  361,  is  a glass 
pipette  which  can  be 
filled  with  the  standard 
solution.  The  quantity 
of  liquid  introduced  into 
the  pipette  is  regulated 
by  means  of  the  stop- 
cock, e the  peculiar 
construction  of  which  is 
shown  on  a larger  scale 
in  fig.  362,  in  which  e 
represents  an  ordinary 
stopcock  (constructed  of  silver  to  resist  the  action  of  the  solution), 
terminating  below  in  a long  tube,  c ; at  is  an 
opening  for  the  escape  of  air,  which  can  be  closed 
at  pleasure  by  the  plug,  a.  Suppose  it  be  desired 
to  fill  the  pipette,  y,  fig.  361 ; the  lower  opening 
of  the  pipette  is  closed  by  the  forefinger,  the 
solution  is  admitted  by  opening  the  stopcock, 
whilst  the  air  escapes  at  /*,  which  is  open ; as 
soon  as  the  liquid  has  risen  a little  above  the 
mark,  both  the  stopcock,  and  the  plug 
at  f are  closed,  and  the  finger  is  withdrawn. 
In  this  position  the  pipette  will  retain  its  charge 
for  an  indefinite  time.  The  apparatus  repre- 
sented at  m I is  intended  to  facilitate  the  exact 
emptying  of  the  pipette ; the  tray,  li  % slides 
easily  between  two  grooves,  in  which  its  motion 
is  limited  by  the  stops  I and  m • A is  a compart- 


Fig.  362. 


ASSAY  OF  SILVER  BY  THE  HTOIB  PROCESS. 


677 


ment  for  the  reception  of  the  assay  bottle,  so  adjusted  that  when 
the  tray  rests  against  the  stop  m,  the  pipette  shall  empty  itself 
into  the  bottle  without  wetting  its  neck  ; i is  another  compart- 
ment for  receiving  the  superfluous  solution  of  salt,  and  ^ repre- 
sents a piece  of  sponge,  the  object  of  which  is  to  remove  tlie 
drop  which  hangs  to  the  lower  end  of  the  pipette ; the  stop  I 
is  so  placed,  that  when  the  slide  rests  against  it,  the  sponge 
shall  just  touch  the  lower  extremity  of  the  pipette.  The  sponge, 
X’,  having  been  brought  to  touch  the  lower  end  of  the  pipette,  the 
plug  at  / is  slightly  relaxed  to  allow  the  air  to  enter,  and  a por- 
tion of  the  liquid  gradually  to  escape,  until  it  has  fallen  exactly 
to  the  mark  n.  The  slide  is  now  moved  until  the  bottle,  A, 
is  directly  underneath  the  pipette,  and  on  opening  the  plug 
at  f to  its  full  extent,  the  charge  flows  freely  into  the  bottle. 

Suppose  now  the  ob- 
ject of  the  assay  be  to 
ascertain  whether  a cer- 
tain number  of  bars  be 
of  the  fineness  of  Eng- 
lish standard  silver,  or 
if  not,  what  is  the 
amount  of  their  varia- 
tion from  standard.  The 
pipette,  y,  is  so  gradua- 
ted that  when  filled  up 
to  the  mark  it  shall  de- 
liver exactly  922  grains 
of  the  standard  solution, 
which  will  contain  a 
sufficient  amount  of 
common  salt  to  precipi- 
tate 9 •.22  grains  of  sil- 
ver ; a quantity  which 
is  purposely  rather  less 
than  the  assay  is  expect- 
ed to  contain  ; 10  grains 
of  alloy,  if  of  correct 
composition,  containing 
9 "25  grains  of  silver. 

When  each  bottle  in 
succession  has  received 
from  the  pipette  a 
charge  of  exactly  the 
same  value,  the  bottles 
are  transferred  to  the  agitator^  shown  at  fig.  363,  wliicli  is  sus- 
pended from  an  iron  arm,  between  two  strong  springs, 
made  of  vulcanized  caoutchouc.  Tliis  agitator  is  usually  con- 
structed to  contain  10  bottles,  which  are  lodged  in  the  comj)art- 
ments,  a j the  stoppers  are  secured  in  their  places  by  the  rims, 
J,  one  of  which  is  represented  in  the  figure  as  thrown  back  for 
the  admission  of  the  bottles ; the  rims  when  closed  are  confined 


678 


rSE  OF  THE  DECIMAL  SOLUTION  OF  SALT. 


by  tlie  springs  shown  at  c,  c.  On  agitating  the  apparatus  briskly 
for  60  or  80  seconds,  the  solutions  become  clear,  and  the  bottles 
are  removed  from  the  agitator,  and  transferred  to  a stand,  behind 
which  is  a black  board  di^dded  into  10  numbered  compartments, 
each  bottle  being  placed  opposite  the  compartment  which  corre- 
sponds with  its  number. 

The  adjustment  of  the  remaining  portion  of  the  assay  is  made 
by  means  of  the  decimal  solution.  This  is 
contained  in  a small  bottle  of  10  or  12 
ounces  in  capacity,  fig.  364,  pro^dded  with 
a tube  or  small  pipette,  open  at  both  ends, 
but  drawn  out  to  a narrow  aperture  below. 
On  this  small  pipette  a mark,  is  made  at 
a height  corresponding  exactly  to  10  grains 
of  the  liquid,  10  grains  of  this  solution  con- 
taining sufficient  chlorine  to  precipitate 
O’Ol  g]-ain  of  silver. 

The  assayer  now  plunges  this  small 
pipette  into  the  decimal  solution,  and  clos- 
ing the  upper  opening  of  the  tube  with  his 
forefinger,  partially  withdraws  it  from  the 
bottle,  and  allows  the  liquid  to  escape  until  it  stands  exactly  at 
the  line  of  the  graduation,  c / he  then  transfers  the  pipette  to  the 
first  bottle,  and  allows  the  solution  to  flow  into  it.  The  same 
operation  is  repeated  with  each  assay  bottle  in  succession.  A 
mark  is  next  made  with  a piece  of  chalk,  opposite  to  each  bottle 
in  which  a precipitate  is  occasioned.  These  bottles  are  then  re- 
placed in  the  agitator  and  shaken  a second  time ; the  solutions 
having  thus  again  been  rendered  clear,  are  replaced  upon  the 
table,  and  a second  pipette  of  the  decimal  solution  is  added  to 
each  of  the  bottles  in  which  a precipitate  is  first  produced.  This 
operation  is  repeated  until  in  each  bottle  no  further  precipitate  is 
occasioned.  The  contents  of  the  pipette,  of  the  standard  solu- 
tion, which  have  been  added  to  each  assay,  occasion  a precipitate 
out  of  the  10  grains  equal  to  9*22,  or  of  922  parts  out  of  1000 
parts  of  alloy.  Each  pipette  of  decimal  solution  is  equivalent  to 
^ 0 of  fine  silver  in  the  alloy,  and  by  counting  the  number  of 

marks  against  each  bottle,  reckoning  the  last  only  as  equal  to 
half  a thousandth,  since  a portion  of  it  probably  remains  in  the 
liquid  in  excess,  the  assayer  ascertains  the  value  of  each  bar.  If, 
for  instance,  two  marks  stand  opposite  to  any  bottle,  the  fineness 
of  the  bar  will  be  more  than  923,  but  less  than  924,  and  may  be 
reported  as  923’5. 

But  suppose  that  there  be  some  bottles  in  which  the  addition 
of  the  first  pipette  of  the  decimal  solution  produces  no  precipi- 
tate ; these  samples  must  be  either  exactly  of  the  fineness  922,  or 
below  that  point.  The  following  method  is  adopted  for  completing 
the  assay  of  these  samples  : a decimal  solution  of  silver  is  prepared 
by  dissolving  10  grains  of  pure  silver  in  nitric  acid,  and  diluting 
it  with  distilled  water  till  the  solution  occupies  the  bulk  of  10,000 
grain-measures  of  water ; each  10  grains  of  this  liquid  will  then 


USE  OF  THE  DECIMAL  SOLUTION  OF  SALT. 


679 


contain  exactly  0*01  grain  of  silver.  A bottle  of  tins  solution  is 
provided  with  a pipette  similar  to  that  shown  in  fig.  364,  but 
graduated  to  dehver  50  grains  of  the  liquid  from  the  mark  d. 
Each  of  the  assay  bottles,  which  indicates  a fineness  below  922,  is 
supplied  with  50  grains  of  this  decimal  silver  solution,  or  with 
0'05  grain  of  silver;  a mark  of  —5  is  made  upon  the  board 
against  each  of  these  bottles.  The  bottles  are  then  agitated  as 
before,  and  a fresh  dose  of  10  grains  of  the  decimal  salt  solution 
is  now  added  to  each : if  a cloud  be  thus  produced,  a mark  is 
chalked  against  each  bottle  in  which  a precipitate  is  observed, 
and  the  bottles  are  again  agitated,  and  another  dose  of  decimal 
salt  liquid  is  added,  and  so  on  until  a precipitate  ceases  to  be 
formed.  Suppose  that  the  first  two  pipettes  of  the  solution  pro- 
duce a cloud,  but  that  the  third  does  not ; each  bottle,  it  will  be 
remembered,  received  a dose  of  salt  solution  in  the  first  instance, 
as  usual,  in  addition  to  the  quantity  received  after  the  decimal 
silver  solution  was  added ; the  quantity  of  salt  which  has  produced 
a precipitate  is  therefore  equivalent  to  922-f  1 + 1|-,  or  924‘5  ; but 
since  5 of  silver  have  also  been  added  beyond  that  which  the  alloy 
originally  contained,  the  amount  to  be  reported  becomes  924-5  — 5, 
or  the  fineness  of  the  bar  is  919*5.  It  is  preferable,  in  cases 
where  the  bars  are  below  the  standard,  to  add  an  excess  of  silver 
solution  at  once,  and  then  to  estimate  the  excess  of  silver  in  the 
manner  above  described  ; because  if,  instead  of  acting  thus,  suc- 
cessive doses  of  O’Ol  of  silver  be  added  until  no  further  precipi- 
tate is  formed,  it  becomes  very  difficult  to  render  the  solution  clear 
by  agitation. 

The  standard  solution  of  salt  is  prepared  at  a temperature,  say, 
of  60°,  consequently  the  pipette,  will  only  deliver  a volume  of 
liquid  rigorously  equal  to  9*22  grains  of  silver,  at  that  temperature. 
At  a higher  temperature  the  liquid  will  expand,  and  a given 
volume  wdll  therefore  contain  a smaller  amount  of  chloride  of 
sodium,  whilst  at  a lower  temperature  it  will  contract,  and  will 
contain  a larger  amount.  A correction  for  this  variation  in  the 
strength  of  liquid  is  therefore  required.  This  is  made  very  simply 
in  the  following  manner  : — Each  time  that  a number  of  assays  is 
made,  a piece  of  fine  silver,  equal  to  9*25  grains,  is  weighed  ofiT, 
dissolved  in  nitric  acid,  and  assayed  as  above  directed.  The  num- 
ber of  pipettes  of  the  decimal  solution  of  salt  which  is  required 
to  complete  the  precipitation  is  noted,  and  the  value  of  the  con- 
tents of  the  large  pipette,  is  thus  verified  upon  each  occasion. 
If,  for  example,  2^  pipettes  were  required  for  completing  this  pre- 
cipitation, the  large  pipette  would  deliver  a quantity  of  the  solu- 
tion sufficient  to  precipitate  9*225  grains  on  that  day,  instead  of 
9*22.  Any  deviation  from  the  calculated  value  is  allowed  for,  and 
a correction  is  made  upon  the  assays  by  means  of  a table  con- 
structed for  the  purpose. 

It  is  easy  to  apply  this  apparatus  to  the  assay  of  silver  of  other 
degrees  of  fineness  ; but  it  is  necessary  to  know  a])])roximatively 
the  value  of  the  alloy,  in  order  that  a suitable  weight  of  it  may 
be  dissolved  in  nitric  acid.  Suppose,  for  instance,  a number  of 


680 


PREPARATION  OF  FINE  SILVER. 


bars  approximatively  of  tlie  value  of  900  (the  French  standard) 
are  to  be  assayed ; a piece  of  the  alloy,  which  contains  approxi- 
mativelv  9*25  grains  of  fine  silver,  must  be  taken  ; the  quantity 
required  is  easily  calculated,  since  the  weight  of  the  alloy  needed 
Avill  be  inversely  as  its  fineness  ; for  900  : 925  : : 10  grs.  : 10-277  grs. 
The  weight  required  in  this  case  will  consequently  be  10 '2 77  grains. 

Mercury  is  the  only  metal  the  presence  of  which  interferes 
with  the  accuracy  of  the  assay  by  the  humid  method : but  the  pro- 
cess may  be  modified  so  as  to  give  correct  results  even  in  this  case. 

(910)  Preparation  of  Fine  Silver.  — In  order  that  the  fore- 
going process  shall  be  accurately  performed,  it  is  necessary  to  be 
provided  with  silver  of  absolute  purity.  The  following  is  the  best 
method  of  procuring  the  metal  in  this  condition.  Standard  silver 
is  dissolved  in  nitric  acid : the  liquid  is  diluted,  and  decanted  or 
filtered  from  undissolved  particles  of  gold  or  of  sulphide  of  silver, 
and  the  solution  is  precipitated  by  the  addition  of  a solution  of 
chloride  of  sodium  in  slight  excess.  The  precipitate  is  washed  in 
a large  jar  by  subsidence,  until  the  washings  are  tasteless.  The 
chloride  is  then  mixed  with  oil  of  vitriol,  in  the  proportion  of  3 
ounces  to  each  pound  of  chloride,  and  several  bars  of  zinc  are 
placed  in  the  mass : the  zinc  speedily  becomes  converted  into 
chloride  of  zinc,  which  is  dissolved,  whilst  the  silver  is  reduced 
to  the  metallic  state,  and  by  a voltaic  action  the  reduction  gra- 
dually extends  through  the  mass  ; Zn  4-  2 AgCl  = Ag^  + ZnCl^. 
The  mixture  is  not  to  be  agitated.  In  the  course  of  a day  or  two 
the  decomposition  is  usually  completed.  If  a portion  of  the 
reduced  silver,  after  being  thoroughly  washed,  is  entirely  soluble 
in  nitric  acid,  the  reduction  is  complete.  The  bars  of  zinc,  with 
the  crust  which  adheres  to  them,  are  then  carefully  removed,  and 
the  reduced  metal  is  digested  for  two  days  with  diluted  sulphuric 
acid,  to  remove  any  portions  of  the  basic  salts  of  zinc  which  are 
occasionally  formed,  and  is  washed  in  a large  vessel  by  subsidence, 
until  the  washings  cease  to  precipitate  nitrate  of  silver.^  The 
reduced  silver  is  now  redissolved  in  nitric  acid,  and  a second  time 
precipitated  as  chloride,  pure  hydrochloric  acid  being  employed 
for  this  purpose  : the  precipitated  chloride  is  again  washed  by  sub- 
sidence until  the  washings  no  longer  redden  litmus.  The  chlo- 
ride of  silver  is  next  dried  until  it  ceases  to  lose  weight,  100  parts 
of  the  chloride  are  mixed  with  70-1:  of  chalk,  and  4-2  of  powdered 
charcoal,  and  the  mixture  is  heated  in  a deep  clay  crucible.f  The 
temperature  is  kept  at  a dull  red  heat  for  half  an  hour,  after  which 
it  is  gradually  raised  to  full  redness : a considerable  disengage- 
ment of  gas  takes  place,  owing  to  the  evolution  of  carbonic  anhy- 
dride and  carbonic  oxide,  and  oxychloride  of  calcium  is  formed, 
constitutino;  a fusible  slas:,  beneath  which  the  pure  silver  collects  ; 

2 AgCi-f 2"eaee3-po=ee+2  ee,  -p  eae,eaci  + Ag,.  The 

* The  reduced  silver  may  he  dried,  and  cast  into  ingots  if  desired.  The  metal  is 
refined  in  large  quantities  for  commercial  purposes  in  this  manner.  It  is  not  abso- 
lutely pure,  and  therefore,  for  delicate  chemical  operations,  it  undergoes  the  further 
process  of  purification  described  in  the  text. 

\ The  washed  chloride  may  also  be  reduced  without  difficulty  by  fusion  with 
about  half  its  weight  of  dried  carbonate  of  sodium. 


OXIDES  OF  SILVEE FULMINATIXO  SILYEE. 


681 


silver  may  be  ponred  into  an  ingot  mould,  remelted  in  order  to 
free  it  from  slag,  and  afterwards  rolled  into  sheets.  Silver  suffi- 
ciently pime  for  all  ordinary  purposes  may  also  be  obtained  in  a 
crystalline  form  by  boiling  a slightly  acid  solution  of  nitrate  or 
other  salt  of  silver  wuth  sheet  copper  : the  precipitated  silver  is 
vrell  washed,  digested  in  a solution  of  ammonia,  to  remove  any 
traces  of  adhering  oxide  of  copper,  and  again  washed. 

(941)  Oxides  of  Silvee. — Silver  forms  three  oxides  ; a sub- 
oxide, Ag^O;  argentic  oxide,  Ag^O,  which  is  the  basis  of  the 
salts  of  the  metal ; and  a peroxide,  probably  Ag^Oa,  which  does 
not  combine  with  acids. 

Argentous  oxide,  or  Suhoxide  of  silver  (Ag^O,  or  Ag^O). — 
According  to  Wohler,  if  the  citrate  of  silver  be  heated  to  212°  in 
a current  of  hydrogen,  the  salt  loses  half  an  equivalent  of  oxygen, 
and  a compound  is  produced  which  is  sparingly  soluble  in  water, 
forming  with  it  a brown  solution,  from  which,  on  the  addition 
of  hydrate  of  potash,  a suboxide  of  silver  is  precipitated.  This 
compound  is  very  unstable  ; hydrochloric  acid  converts  it  par- 
tially into  subchloride,  but  it  is  decomposed  by  other  acids,  and 
by  ammonia,  into  argentic  oxide  and  metallic  silver.  A mixture 
of  metallic  silver  and  argentous  oxide  is  also  obtained  by  boiling 
the  yellow  arsenite  of  silver  with  a strong  solution  of  caustic  soda, 
arseniate  of  sodium  being  formed  in  the  liquid,  2 AggAsOg  + G IN^a 
IIO=Ag^O-}- Agg-}-2  ISTugAsO^  + S IlgO. 

Argentic  oxide,  or  Protoxide  of  silver  (AggO=232,  or  AgO 
= 116) : Comp,  in  100  parts,  Ag,  93T  ; O,  69. — This  oxide  may 
be  procured  by  adding  a solution  of  potash  or  of  soda  to  a solu- 
tion of  the  nitrate  or  any  soluble  salt  of  silver.  A brown  hydrate 
ed  oxide  falls,  which  readily  parts  with  its  w^ater,  and  if  dried 
at  a temperature  above  140°,  becomes  anhydrous ; it  gives  off 
oxygen  below  a red  heat,  and  is  reduced  to  tiie  metallic  state. 
L^lit  also  reduces  it,  and  hydrogen,  even  at  212°,  has  a similar 
effect ; contact  under  water  with  metallic  tin  or  copper  also  de- 
prives it  of  oxygen.  Oxide  of  silver  is  a powerful  base  ; it  com- 
bines easily  with  acids,  yielding  salts  which  in  some  cases  are 
isornorphous  with  the  corresponding  salts  of  sodium.  It  forms 
with  nitric  acid  a salt  wdiich  is  not  acid  in  its  reaction  upon 
litmus.  It  is  slightly  soluble  in  pure  water,  to  wdiich  it  com- 
municates a feebly  alkaline  reaction.  Oxide  of  silver  combines 
wdth  the  fusible  silicates,  and  is  sometimes  employed  for  produc- 
ing a yellow  glass.  Hydrates  of  potash  and  soda  do  not  dissolve 
the  oxide,  but  it  is  freely  soluble  in  ammonia,  and  the  solution, 
by  exposure  to  the  air,  deposits  a black  micaceous  powder,  wdiich 
is  pow^erfully  explosive,  and  which  has  received  the  name  of  ful- 
minating silver. 

(942)  Fulminating  silver  is  also  produced  if  a concentrated 
solution  of  ammonia  be  digested  for  some  hours  upon  freslily  pre- 
cipitated oxide  of  silver  ; a black  powder  is  formed  wdiich  is 
allow'ed  to  dry  in  minute  quantities  on  separate  jiieces  of  filtering 
paper.  The  same  compound  is  formed  on  ])reci})itating  an  am- 
moniacal  solution  of  nitrate  or  chloride  of  silver  by  the  addition 


6S2 


PEEOXTDE  A^T)  SULPHIDE  OF  SELYEE. 


of  liydi'ate  of  potash.  It  is  necessary  to  be  aware  of  these  facts, 
as  it  is  a most  dangerous  substance,  and  might  be  produced  un- 
intentionally. Friction  or  pressui’e,  eyen  when  under  water, 
occasions  it  to  explode  : and  when  diy,  its  detonation  often  occurs 
without  any  assignable  cause.  Acids  immediately  decompose 
it  into  an  ammoniacal  salt,  and  the  corresponding  salt  of  silver. 
The  composition  of  this  body,  owing  to  its  dangerous  character, 
has  not  been  accurately  determined,  but  it  is  generally  supposed 
to  be  a nitride,  similar  to  that  which  is  obtainable  from  mercury. 

Peroxide  of  silver  (Ag^O^  or  AgO^  ?)  ; Sj?.  Gr.  5 ATI. — This 
compound  is  procui'ed  in  dark  grey  acicular  crystals,  when  a di- 
lute solution  of  nitrate  of  silver  is  decomposed  by  means  of  the 
voltaic  current.  The  peroxide  of  silver  accumulates  upon  the 
positive  plate,  but  it  always  retains  a certain  quantity  of  unde- 
composed nitrate  of  silver.  It  is  a conductor  of  the  voltaic  cur- 
rent. Acids  decompose  it,  forming  a salt  of  argentic  oxide,  whilst 
ox;\'gen  gas  escapes.  It  is  also  decomposed  by  ammonia,  with 
eftervescence,  owing  to  escape  of  nitrogen. 

(913)  Sulphide  of  Silver  (Ag2S=2I8,  or  AgS  = 12I);  Sp. 
Gr.  7'2  : Comp,  in  100  Ag,  8T‘l;  S,  12‘9. — This  compound 
is  the  principal  ore  of  silver.  It  is  found  native,  sometimes  crys- 
tallized in  cubes  or  octohedra,  at  other  times  massive.  It  has  a 
leaden-grey  metallic  lustre,  from  which  it  derives  its  mineralogi- 
cal  name  of  silver  glance.  Sulphide  of  silver  is  isomorphous  with 
subsulphide  of  copper,  and  sometimes  displaces  it  in  certain  mine- 
rals, such,  for  example,  as  polybasite,  aud  fahlerz  or  grey  copper 
ore  (879). 

Silver  has  a very  powerful  attraction  for  sulphur.  The  metal 
becomes  tarnished,  owing  to  the  formation  of  a film  of  sulphide, 
if  it  be  exposed  to  the  action  of  sulphui'etted  hydrogen  in  the 
gaseous  state,  eyen  though  largely  diluted  with  air ; and  a black 
spot  is  immediately  produced  upon  its  siuTace  by  contact  with  a 
solution  of  a sulphide  of  one  of  the  metals  of  the  alkalies  or  alka- 
line earths.  Sulphide  of  silver  may  be  prepared  by  transmitting 
a current  of  sulphuretted  hydrogen  through  solutions  of  the  salts 
of  silver,  in  which  it  forms  a black  precipitate  ; or  it  may  be  ob- 
tained by  heating  silver  with  an  excess  of  sulphur  in  a covered 
crucible.  Tlie  sulphide  of  silver  fuses,  and  forms  a dark  grey 
crystalline  mass  as  it  cools,  and  the  excess  of  sulphur  is  volatilized. 

Sulpiiide  of  silver  is  soft  enough  to  allow  of  its  being  cut  with 
a knife  ; it  also  possesses  sufficient  malleability  to  receive  impres- 
sions from  a die.  It  is  not  a conductor  of  the  voltaic  current 
when  cold,  but  if  heated  it  readily  transmits  the  cuiTent  without 
undergoing  decomposition.  It  is  easily  fusible,  and  if  heated  in 
closed  vessels  may  be  melted  without  becoming  decomposed ; but 
if  roasted  in  the  air,  the  sulphur  is  gradually  converted  into  sul- 
phurous anhydilde,  and  metalhc  silver  is  left : during  this  opera- 
tion a portion  of  it  is  usually  converted  into  sulphate  of  silver, 
which  afterwards  requires  an  elevated  temperature  for  its  decom- 
position. 

Sulphide  of  silver  is  decomposed  when  boiled  with  concen- 


CHLOKroES  OF  SILVER. 


683 


trated  sulphuric  acid,  sulphurous  anhydride  and  sulphate  of  silver 
being  formed.  Strong  nitric  acid  also  dissolves  it  by  the  aid  of 
heat.*  Boiling  hydrochloric  acid  converts  it  into  chloride  of  sil- 
ver, with  evolution  of  sulphuretted  hydrogen.  Chloride  of  cop- 
per converts  it  into  chloride  of  silver,  with  the  formation  of 
cupreous  chloride  and  sulphide  of  copper : this  change  is  much 
facilitated  by  the  presence  of  chloride  of  sodium  in  a moist  state, 
as  by  its  means  both  the  chloride  of  silver  and  the  cupreous  chlo- 
ride are  dissolved  at  the  moment  of  their  formation.  These 
reactions  become  important  in  the  extraction  of  silver  from  its 
ores  (931).  Sulphide  of  silver  is  also  decomposed  when  heated 
with  the  alkalies,  and  a similar  effect  is  produced  by  igniting  it 
with  iron,  copper,  lead,  and  many  other  metals. 

Sulphide  of  silver  is  not  soluble  in  solutions  of  the  sulphides 
of  the  alkaline  metals  ; but  it  may  be  made  to  unite  with  many 
other  metallic  sulphides  when  fused  with  them.  A native  com- 
pound of  this  description  is  found  in  red  silver  ore^  which  is  a 
double  sulphide  of  silver  and  antimony,  3 Ag2S,Sb2S3.  In  this 
mineral  a portion  of  sulphide  of  antimony  is  often  displaced  by 
sulphide  of  arsenic. 

(944)  Chlorides  of  Silver. — There  are  two  chlorides  of  sil- 
ver, the  subchloride,  Ag^Cl,  and  the  protochloride,  AgCl. 

Sicbchloride  of  silver  (Ag^Cl)  does  not  appear  to  have  been  ob- 
tained in  a perfectly  pure  form.  It  is  usually  directed  to  be  pro- 
cured by  digesting  leaves  of  pure  silver  in  a solution  of  chloride  of 
copper  or  of  perchloride  of  iron  ; it  forms  black  scales  which  are 
not  acted  upon  by  nitric  acid,  but  are  resolved  by  ammonia  into 
chloride  of  silver  and  metallic  silver. 

Chloride  of  silver  (AgCl  = 143*5);  Sjp.  Gr.  5*552  : Comp,  in 
1()0 parts ^ Ag,  75*27 ; Cl,  24*73. — This  compound  is  found  native, 
either  crystallized  in  cubes,  or  as  a compact  semi-transparent  mass, 
known  by  the  name  of  horn  silver.  It  is  procured  as  a dense 
white  flocculent  precipitate  on  adding  hydrochloric  acid  or  the 
solution  of  any  chloride  to  a soluble  salt  of  silver  : when  moist  it 
quickly  assumes  a violet  colour  by  exposure  to  the  sun’s  light ; a 
similar  change  is  produced  gradually  by  diffused  daylight.  The 
subchloride  appears  to  be  formed  under  these  circumstances,  and 
chlorine  is  set  free.  If  the  chloride  be  moistened  with  a solution 
of  nitrate  of  silver  and  exposed  to  the  sun  in  a thin  layer,  a strong 
odour  of  hypochlorous  acid  is  immediately  developed. 

Chloride  of  silver  is  insoluble  in  pure  water,  and  in  all  the 
diluted  acids.  A solution  of  silver  containing  not  more  than  1 
part  of  the  metal  in  200,000  of  water  is  immediately  rendered  opa- 
lescent by  the  addition  of  hydrochloric  acid.  Cldoride  of  silver 
is  however  taken  up  by  boiling  hydrochloric  acid  and  by  strong 
solutions  of  the  chlorides  of  metals  of  the  alkalies  and  alkaline 
earths,  with  which  it  forms  crystallizable  double  salts ; they  are 


* Nitrate  of  silver  forms  with  the  sulphide  a yellow  compound,  AgaSjAgNOs,  in- 
soluble in  cold  nitric  acid,  but  it  is  decomposed  when  washed  with  boilinj:^  water.  It 
is  left  in  the  form  of  a yellow  powder  when  silver  containing  sulphide  is  dissolved  in 
warm  nitric  acid  of  sp.  gr.  about  1’2. 


68i 


BKOMTDE  OF  SILYEE. 


decomposed  if  tlieir  solutions  are  diluted  ; advantage  is  taken  of 
this  circumstance  in  the  extraction  of  silver  {note^  p.  667).  Chlo- 
ride of  silver  is  decomposed  by  digestion  with  a solution  of  bro- 
mide or  of  iodide  of  potassium,  bromide  or  iodide  of  silver  being 
produced,  while  chloride  of  potassium  is  obtained  in  solution. 
Field,  by  whom  this  result  was  observed  (^.  J.  Cliem.  Soc.  x.  236), 
has  proposed  to  employ  it  for  determining  the  proportions  of  chlo- 
rine, bromine,  and  iodine  in  the  analysis  of  a mixture  in  which  they 
occur  together. 

Chloride  of  silver  melts  at  a temperature  of  about  500°,  and 
when  strongly  heated  it  is  partially  volatilized ; on  cooling  it  forms 
a horny,  semi-transparent,  sectile  mass.  It  is  not  decomposed 
when  heated  with  carbon  ; but  it  is  easily  reduced  by  hydrogen  if 
it  be  heated  in  a current  of  the  gas,  hydrochloric  acid  being 
formed,  whilst  metallic  silver  is  set  free  ; zinc,  and  u’on,  and  many 
of  the  easily  oxidizable  metals,  also  reduce  moist  chloride  of  silver. 
On  the  large  scale  this  process  is  turned  to  account  in  the  refining 
of  silver  (910).  It  is  not  necessary  that  the  chloride  of  silver  be 
freshly  precipitated,  though,  if  it  be,  the  operation  is  more  rapid  ; 
if  a cake  of  the  fused  chloride  be  laid  upon  zinc  or  on  iron  and 
covered  with  acidulated  water,  it  will  after  some  days  be  complete- 
ly reduced  to  a spongy  mass  of  metallic  silver. 

'\Y eak  alkaline  leys  do  not  act  upon  chloride  of  silver,  but  if  a 
concentrated  solution  of  potash  be  boiled  upon  it,  chloride  of  potas- 
sium is  formed,  and  a dense  black  oxide  of  silver  is  produced ; the 
addition  of  sugar  to  this  mixture  reduces  the  oxide  rapidly  to 
the  state  of  metallic  silver.  A solution  of  ammonia  dissolves  the 
chloride  freely,  and  deposits  it  again,  by  evaporation  at  ordinary 
temperatures,  in  transparent  colourless  crystals  ; if  the  solution  be 
boiled  with  potash,  fulminating  silver  is  deposited.  The  solid  chlo- 
ride absorbs  ammoniacal  gas  rapidly,  and  leaves  it  unaltered  when 
heat  is  applied  (369).  When  chloride  of  silver  is  ignited  with  the 
carbonates  of  the  alkali-metals,  chlorides  of  their  basyls  are  formed 
and  pure  silver  is  left : this  reaction  furnishes  a means  of  procur- 
ing large  quantities  of  silver  in  a state  of  purity ; 4 AgCl  + 2 Aa, 
0^3=4  Is  aCl  + 2 00-2 -f  02  + 2 Ag^.  Chloride  of  silver  is  solu- 
ble in  solutions  of  the  hyposulphites,  forming  compounds  of  an 
intensely  sweet  taste : by  evaporating  these  solutions  crystalline 
double  hyposulphites  may  be  procured  (419)  Cyanide  of  potas- 
sium likewise  dissolves  chloride  of  silver,  forming  chloride  of 
potassium  and  a double  cyanide  of  silver  and  potassimn.  The 
soluble  sulphites  also  dissolve  chloride  of  silver. 

(945)  Bromide  of  Silver  (AgBr  = 1S8) ; Sj?.  Gr.  6'353 : 
Comp,  in  parts Ag,  57*44  ; Br,  42*56. — This  constitutes  a rare 
mineral  which  has  been  found  in  Chili ; but  it  occurs  in  com- 
bination with  chloride  of  silver  in  variable  proportions  in  tolerable 
abundance  at  the  mine  of  Chanarcillo,  in  Atacama.  The  bromide 
may  be  formed  artificially  by  adding  a solution  of  bromide  of 
potassium  to  one  of  nitrate  of  silver.  It  is  of  a yellowish  colour, 
is  insoluble  in  water,  and  is  much  less  soluble  in  ammonia  than 
the  chloride.  Acids  do  not  dissolve  it,  but  chlorine  disengages 


IODIDE,  FLDOKIDE,  AND  SULPHATE  OF  SILVEE. 


685 


vapours  of  bromine  from  it,  and  cliloride  of  silver  is  produced. 
Eromide  of  silver  fuses  below  a red  heat.  It  is  soluble  in  a con- 
centrated solution  of  bromide  of  potassium,  and  in  other  bromides, 
with  which  it  forms  double  salts,  which  are  decomposed  by  dilu- 
tion with  water.  Both  the  bromide  and  the  iodide  of  silver  are 
soluble  in  a solution  of  hyposulphite  of  sodium. 

(916)  Iodide  of  Silver  (Agl  = 235) ; Sjp.  Gr.  5*5 : Comp,  in 
100  parts.,  Ag,  45*96  ; 1, 54*04.— This  compound  is  found  in  Mexico, 
mixed  with  carbonate  of  calcium,  native  silver,  and  sulphide  of 
lead.  It  may  be  procured  artifically  by  precipitating  a solution 
of  the  nitrate  of  silver  by  one  of  iodide  of  potassium,  when  a pale 
yellow,  hocculent  deposit  occurs,  which  is  but  slowly  acted  on  by 
light,  is  insoluble  in  acids,  and  almost  so  in  ammonia.  It  may 
also  be  obtained  by  acting  upon  metallic  silver  with  hydriodic 
acid,  Avhich  dissolves  the  metal  with  evolution  of  hydrogen,  and 
gradually  deposits  six-sided  prisms  of  the  iodide.  It  fuses  easily 
into  a mass  which  becomes  yellow  and  opaque  on  cooling.  It 
is  decomposed  by  zinc  in  the  i^resence  of  moisture.  Chlorine 
displaces  the  iodine  from  the  salt.  Iodide  of  silver  is  soluble  in 
a hot  solution  of  hydriodic  acid,  which  on  cooling  deposits  flaky 
crystals  of  a compound  of  the  acid  with  iodide  of  silver  (AgI,ITI). 
The  iodide  is  likewise  soluble  in  concentrated  solutions  of  iodide 
of  potassium. 

Fluoride  of  silver  (AgF=127)  is  freely  soluble  in  water  ; it 
is  obtained  by  dissolving  the  oxide  or  the  carbonate  of  silver  in 
diluted  hydrofluoric  acid,  but  it  is  partially  decomposed  on  evapo- 
rating its  solution. 

(947)  Sulphate  of  Silver  (Ag2S04=:312,  or  Ag0,S03— 156) ; 
Sp.  Gr.  5*322;  Comp,  in  parts ^ Ag^O,  74*36;  SO3,  25*64. — 
When  silver  is  boiled  with  sulphuric  acid,  a portion  of  the  acid 
is  decomposed  and  gives  oxygen  to  the  silver,  which  is  converted 
into  a sulphate,  while  sulphurous  anhydride  escapes  : the  sulphate 
is  dissolved  by  the  excess  of  acid,  but  is  deposited  in  great  part 
on  the  addition  of  water,  of  which  it  requires  90  times  its  weight 
for  solution.  It  may  be  obtained  in  small  rhombic  prisms,  which 
are  isomorphous  with  those  of  sulphate  of  sodium.  They  fuse 
readily ; for  their  decomposition  they  require  a temperature  higher 
than  is  needed  to  decompose  the  sulphates  of  iron  or  copper.  (See 
note^  p.  667.)  Small  quantities  of  gold  are  separated  from  silver 
on  the  large  scale,  by  boiling  1 part  of  the  alloy,  finely  granulated, 
in  cast-iron  vessels  with  2^  parts  of  oil  of  vitrol  ; the  gold  is  left 
behind  as  a fine  powder.  The  solution  of  silver  is  afterwards  diluted 
till  of  a specific  gravity  of  1*200,  introduced  into  leaden  vessels,  and 
the  silver  precipitated  in  the  metallic  form  from  the  solution  by  bars 
of  metallic  copper.  This  process  has  been  economically  applied  to 
the  extraction  of  the  gold  contained  in  old  silver  coin,  even  where 
the  proportion  of  gold  did  not  exceed  1 part  in  2000,  It  cannot 
be  advantageously  practised  upon  alloys  containing  more  than 
about  200  parts  of  gold  per  1000.  If  cop])er  be  present,  its  pio- 
portion  should  not  exceed  4 per  cent,  of  the  mass  ; otherwise  the 
sulphate  of  copper,  owing  to  its  sparing  solubility  in  the  acid. 


686 


NITEATE  AND  PHOSPHATES  OF  SILVER. 


impedes  the  operation.  Crystallized  sulphate  of  silver  absorbs 
1 equivalent  of  ammonia  with  rapidity.  A hot  solution  of  am- 
monia dissolves  the  salt  freely,  and  on  cooling  deposits  crystals 
composed  of  (4  HghTjAg^SO^). 

(948)  Aitrate  of  Silver  (AgAOg,  or  AgOjhTOj  = 170) ; Sj>. 

(XT’.  4-336 : Comp,  in  100  parts Ag^O,  68’23  ; 31*77,  or 

Ag,  63-51. — This  salt  is  readily  formed  by  dissolving  silver  in 
moderately  strong  nitric  acid.  If  standard  silver  be  employed  in 
its  preparation,  the  oxide  of  copper  is  easily  separated  from  the 
solution  by  boiling  it  upon  freshly  precipitated  oxide  of  silver, 
which  may  be  obtained  by  precipitating  a portion  of  the  same 
solution  by  caustic  potash,  and  washing  the  precipitate,  the 
presence  of  oxide  of  copper  being  unimportant.  It  crystallizes  in 
square,  colourless,  anhydrous  tables,  which  require  an  equal  weight 
of  cold  water  for  solution.  Boiling  alcohol  dissolves  about  a 
fourth  of  its  weight  of  the  salt,  but  deposits  most  of  it  on  cooling. 
The  nitrate  fuses  at  426°  when  heated,  and  if  then  cast  into 
cylindrical  moulds,  it  forms  the  sticks  of  lunar  caustic  (from  lima., 
the  alchemical  name  for  silver)  employed  by  surgeons  as  an 
escharotic.  By  a more  elevated  temperature  it  is  decomposed, 
nitrite  of  silver  is  produced,  and  at  a still  higher  temperature  me- 
tallic silver  is  left. 

Aitrate  of  silver,  when  pure,  undergoes  no  change  by  the 
action  of  light ; but  it  is  readily  decomposed  by  the  combined 
action  of  light  and  organic  matter,  which  it  usually  stains  black. 
The  stain  thus  produced  cannot  be  removed  by  washing  with  soap 
and  water ; from  this  property  it  has  been  employed  as  the  basis 
of  an  ink  for  marking  linen,  which  may  be  prepared  as  follow  : — 
Dissolve  2 drachms  of  nitrate  of  silver  and  1 drachm  of  gum 
arable  in  7 drachms  of  water,  and  colour  the  liquid  with  Indian 
ink  (Brande).  It  is  requisite  to  prepare  the  cloth  first,  by  moisten- 
ing the  spot  to  be  marked,  with  a solution  of  carbonate  of  sodium, 
which  is  allowed  to  become  dry.  This  preparatory  solution  may 
consist  of  2 ounces  of  crystallized  carbonate  of  sodium,  and  2 
drachms  of  gum,  dissolved  in  4 ounces  of  water.*  The  black 
stains  of  nitrate  of  silver  may  be  removed  from  the  hands  or  from 
linen  by  the  employment  of  a strong  solution  of  iodide  of  potas- 
sium ; cyanide  of  potassium  is  still  more  effectual.  Dry  nitrate 
of  silver  absorbs  3 atoms  of  ammonia,  and  if  ammoniacal  gas  be 
passed  into  a concentrated  solution  of  the  salt,  crystals  having  the 
composition  (2  Il3A,AgA03)  are  deposited. 

When  metallic  silver  in  fine  powder  is  digested  in  a solution 
of  nitrate  of  silver,  it  is  dissolved,  and  a yellow  solution  is  formed 
analogous  to  that  obtained  when  lead  is  similarly  treated  (905). 

(949)  Triphosphate  of  Silver  (AggPO,,  or  3 Ag0,P06=419  ; 
sp.  gr.  7*321)  is  of  a yellow  colour,  which  is  speedily  changed  by 
the  action  of  light.  The  salt  is  very  soluble  in  excess  both  of 
nitric  acid  and  of  ammonia.  It  is  easily  procured  by  precipitating 
a solution  of  the  ordinary  phosphate  of  sodium  by  one  of  nitrate 

* a'  solution  of  coal-tar  in  naphtha  forms  a cheap  indelible  marking  ink  which 
resists  the  action  of  chlorine,  and  is  used  by  bleachers  to  mark  their  goods. 


CHAHACTERS  OF  THE  SALTS  OF  SILVER. 


687 


of  silver ; it  fuses  if  heated  above  redness.  The  pyrophosphate 
(Ag^P^O,,  or  2 AgOjPOg ; sp.  gr.  5’306)  is  obtained  in  like  manner 
by  precipitating  the  nitrate  of  silver  by  pyrophosphate  of  sodium ; 
it  is  a white  precipitate  slowly  darkened  by  light,  and  is  easily 
fusible.  The  metaphosphate  (AgPOg,  or  AgOjPO^)  is  obtained  by 
precipitation  from  the  nitrate  of  silver  by  the  metaphosphate  of 
sodium ; it  forms  a gelatinous  mass,  which  softens  even  at  a heat 
of  212°,  and  is  soluble  in  excess  of  nitrate  of  silver.  If  boiling 
w'ater  be  poured  upon  this  precipitate,  it  fuses ; acid  is  removed, 
and  a submetaphosphate  is  left,  consisting  of  (AggP^O^g,  or  3 AgO, 
2 POg ; Graham). 

(950)  Characters  of  the  Salts  of  Silver. — The  soluble 
salts  of  this  metal  are  colourless,  and  nearly  all  are  anhydrous ; 
they  do  not  redden  litmus ; they  have  a powerfully  acrid,  metallic, 
astringent  taste,  and  act  as  irritant  poisons.  Before  the  blowpipe 
they  are  all  readily  reduced  on  charcoal  to  the  metallic  state, 
especially  when  mixed  with  carbonate  of  sodium.  They  give  a 
yellowish  bead  with  microcosmic  salt  in  the  oxidating  flame.  In 
solution  the  salts  of  silver  present  the  following  reactions : — 

The  hydrates  of  the  fixed  alkalies  give  a brown  hydrated  oxide, 
insoluble  in  excess  of  the  precipitant ; ammonia^  a brown  precipi- 
tate, readily  soluble  in  excess  of  ammonia ; carbonates  of  potas- 
sium and  soduim^  a white  carbonate  of  silver  insoluble  in  excess, 
but  soluble  in  carbonate  of  ammonium.  Sulphuretted  hydrogen 
and  sulphide  of  ammonium  give  a black  precipitate  of  sulphide  of 
silver,  not  soluble  in  ammonia  or  in  the  sulphides  of  the  alkaline 
metals.  But  the  most  characteristic  test  is  the  action  of  hydro- 
chloric acid^  or  of  a soluble  chloride^  wdiich  produces  a white  curdy 
precipitate  of  chloride  of  silver,  insoluble  in  nitric  acid,  but  readily 
soluble  in  ammonia ; it  is  also  soluble  in  hyposulphite  of  sodium, 
wdth  wdiich  it  forms  an  intensely  sweet  solution  ; cyanide  of  jiotas- 
sium  also  dissolves  it : chloride  of  silver  speedily  assumes  a violet 
tinge  wdien  exposed  to  light ; this  change  is  impeded  by  the  pre- 
sence of  free  chlorine  as  well  as  by  that  of  free  nitric  acid,  and  is 
prevented  by  the  admixture  of  a small  proportion  of  chloride  of 
mercury.  Iodide  or  bromide  of  p)otassium  gives  a yellowish-wdiite 
precipitate  of  iodide  or  of  bromide  of  silver,  sparingly  soluble  in 
ammonia.  Hydrocyanic  acid  and  cyanide  of  potassium  give  a 
w^hite  curdy  precipitate  of  cyanide  of  silver,  wdiich  is  soluble  in 
excess  of  cyanide  of  potassium,  easily  soluble  in  ammonia,  insol- 
uble in  diluted  nitric  acid,  but  soluble  in  boiling  nitric  acid  if 
concentrated.  Phosphoric^  chromic^  oxalic^  tartaric^  and  citric 
acids  all  form  insoluble  precipitates  wdth  salts  of  silver.  Indeed, 
silver  furnishes  a greater  number  of  insoluble  salts  than  any  other 
metal ; they  are  almost  all  neutral  in  composition,  and  generally 
of  a dazzling  wdiite  colour.  Most  of  them,  however,  become 
black  when  exposed  to  the  action  of  light.  Nearly  all  of  them  are 
soluble  in  ammonia,  and  many  of  them  also  in  nitric  acid.  Mary 
metals  reduce  solutions  of  the  salts  of  silver,  and  throw'  dowm  the 
silver  from  them  in  a metallic  state,  as  is  beautifully  showm  by 
the  action  of  mercury,  which  produces  a crystalline  deposit  con- 


6SS 


ESTIMATION  OF  SILYEE GOLD. 


sisting  of  an  amalgam  of  silver,  forming  what  has  been  termed 
the  arhor  Diance.'^  Cojiper  and  zinc  also  precipitate  silver  from 
its  solutions.  Phosphorus  becomes  coated  with  metallic  silver  if 
placed  in  a solution  of  any  of  its  salts.  A solution  of  ferrous 
sulphate  also  precipitates  silver  in  the  metallic  form  fi’om  its  solu- 
tions, if  they  do  not  contain  free  nitric  acid.  If  a solution  of 
ammonia-nitrate  of  silver  be  added  to  one  of  ferrous  sulphate,  an 
intensely  black  precipitate  (Ag^O,  2 Fe0,Fe203 ; H.  Eose)  is  pro- 
duced. This  reaction  is  extremely  sensitive  for  very  small  quan- 
tities of  iron. 

The  compounds  of  silver  exliibit  a less  strongly  marked  ten- 
dency to  form  double  salts  than  is  the  case  Avith  the  other  noble 
metals. 

(951)  Estimation  of  Silver. — Silver  may  be  estimated  either 
in  the  metallic  state,  as  in  the  process  of  cupellation, — or  in  the 
form  of  chloride,  100  parts  of  which,  after  tusion,  correspond  to 
V5-27  of  the  metal.  This  precipitation  is  best  effected  by  acidu- 
lating the  liquid  with  nitric  acid,  and  adding  hydrochloric  acid  in 
slight  excess.  After  the  precipitate  has  been  collected  and  dined, 
it  should  be  detached  from  the  filter,  and  fused  in  a porcelain  cap- 
sule ; on  burning  the  filter,  the  portions  of  chloride  retained  by  it 
are  reduced  partially  to  the  metallic  state  by  the  hydrogen  of  the 
paper ; the  ash  must  therefore  be  moistened,  first  with  nitric,  and 
then  with  hydrochloric  acid,  to  reconvert  it  into  chloride  : the 
excess  of  acid  must  afterwards  be  expelled  by  heat. 

(952)  Separation  of  Silver  from  other  Metals. — This  is  readily 
effected  by  means  of  hydrochloric  acid.  If  lead  be  present,  the 
solution  must  be  diluted  largely : should  mercury  be  in  solution, 
it  must  be  com^erted  into  a salt  of  the  red  oxide  by  boiling  the 
liquid  with  nitric  acid,  after  which  the  silver  may  be  precipitated 
in  the  form  of  chloride. 

§ III.  Gold:  Au=196'6.  Sj).  Gr.  19-31;  Fusingpt.  2016°. 

(953)  This  valuable  metal  has  been  prized  from  the  earliest 
ages  of  the  world.  It  is  found  in  small  quantities  in  numerous 
localities,  and  always  occurs  in  the  native  state,  either  crystallized  in 
cubes,  octohedra,  or  tetrahedra, — or  in  plates,  in  ramified  masses, 
or  in  nodules  or  nuggets.^  which  sometimes  weigh  many  pounds.! 
Aative  gold  is  always  alloyed  with  silver;  small  quantities  of 
osmium  and  iridium,  copper,  antimony,  and,  in  some  rare  instances, 
tellurium,  are  found  accompanying  it.  Ao  regular  veins  of  gold 
are  met  with ; it  commonly  occurs  either  in  primitive  or  volcanic 
rocks,  or  in  the  alluvial  deposits  of  certain  rivers.  Its  most  cele- 
brated mines  are  those  of  California  and  Australia ; and  those  of 
Mexico,  Chili,  Brazil,  and  Peru.  In  California  the  gold  is  chiefly 
found  upon  the  Sacramento  and  its  tributary  streams,  in  deposits 

* On  one  occasion  I found  the  long  prismatic  thin  crystals  to  hare  the  compo- 
sition AgaHgj,  containing  26-45  per  cent,  of  metallic  silver. 

f A specimen  of  native  gold,  nearly  free  from  earthy  impurities,  from  the  Kingower 
diggings,  Australia,  weighing  1743  oz.,  was  exhibited  in  England  in  the  early  part  ot 
1858,  and  still  larger  masses  have  been  found  subsequently. 


EXTKACTION  OF  GOLD. 


689 


formed  by  tlie  disintegration  of  qnartz  and  granite.  In  Australia 
the  gold  is  also  associated  with  quartz,  and  occurs  in  slate  rocks 
equivalent  to  the  Cambrian  formations  of  England  and  Wales,  in 
the  detritus  of  which  the  most  productive  gold-fields  occur,  in  the 
deep  gullies  at  the  base  of  the  rocky  ranges  of  clay-slate,  mica 
schist,  red  and  yellow  sandstone.  In  the  alluvial  portion  the  gold 
is  usually  found  at  a depth  of  from  10  to  40  feet,  resting  upon  a 
“bottom”  of  pipeclay.  A good  deal  of  gold  is  also  obtained  from 
the  Ural  Mountains ; gold  has  also  been  obtained  in  Wales,  in  the 
Cader  Idris  district.  Many  of  the  rivers  of  Africa  likewise  contain 
it  among  their  sands,  as  do  those  of  Hungary,  Transylvania,  and 
Piedmont : in  these  countries  it  is  principally  extracted  from  the 
river  sands  by  gipsies. 

Extraction. — The  operations  for  obtaining  gold  from  its  de- 
posits differ  from  those  required  by  almost  every  other  metal,  in 
being  for  the  most  part  purely  mechanical.  According  to  Mr. 
Wathen  {The  Golden  Colony^  p.  71),  the  Australian  digger  for- 
merly used  a cradle  for  washing  the  ore,  but  this  is  not  adapted  to 
the  stifi'  clays  of  the  Australian  gold-fields.  The  miner  now,  after 
having  raised  the  “washing  stufi*”  from  the  pit,  introduces  it  into 
the  “ puddling  tub,”  which  is  merely  one-half  of  a porter-cask. 
The  tub  is  half  filled  with  the  washing  stuff,  w^ater  is  baled  in 
from  the  creek,  and  the  whole  worked  about  with  the  spade 
until  the  clay  has  become  diftused  through  the  water ; this  turbid 
water  is  poured  off  and  fresh  water  added,  until,  by  repetition  of 
the  washing,  “ nothing  but  clean  gravel,  sand,  and  gold  remains. 
Tlie  gold  is  now  readily  separated  from  the  gravel  by  means  of  a 
cradle,  or  simply  by  a tin  dish.  In  the  latter  case,  the  dish  is  held 
half-immersed  obliquely  in  water,  and  the  gravel  gradually  w^ashed 
away  from  the  gold  by  the  dexterous  handling  of  the  dish.” 

The  Californian  “Long  Tom”  consists  of  a trough  about  16 
inches  wide,  and  10  or  12  feet  long,  inclined  so  as  to  cause  the 
water  to  run  rapidly  down  : an  iron  grating,  perforated  with  holes 
as  large  as  a sixpence,  forms  the  lower  end,  and  is  tilted  in  an  op- 
posite direction  to  the  trough.  Through  the  trough  a current  of 
water  is  kept  constantly  fiowing.  The  auriferous  earth  is  thrown 
in  at  the  head,  and  as  it  is  washed  down  by  the  stream,  it  is  worked 
about  with  the  spade ; the  earth  and  clay  are  quickly  washed 
away ; when  the  clean  gravel  reaches  the  lower  end,  it  is  arrested 
by  the  iron  grating,  and  removed  with  a shovel,  while  tlie  gold 
and  sand  fall  through  into  a box  placed  beneath.  The  contents 
of  the  box  are  again  washed  to  extract  the  gold. 

Auriferous  quartz  is  first  crushed,  then  stamped  and  ground 
to  powder,  and  from  the  powder  the  gold  is  subsequently  extracted 
by  amalgamation. 

Much  of  the  gold  in  circulation  before  the  discovery  of  the 
deposits  in  Australia  and  California  was  obtained  from  auriferous 
pyrites.  This  mineral  is  coarsely  pulverized,  either  before  or  after 
roasting,  and  washed : the  heavier  particles  of  gold  subside,  and 
are  extracted  from  this  concentrated  jiortion  by  amalgamation, 
the  excess  of  mercury  being  separated  by  distillation.  Various 
44 


G90 


PROPEETIES  AXD  PEEPAPATIOX  OF  GOLD. 


methods  are  adopted  for  washing  the  anriferons  material : in 
Mexico  this  operation  is  nsnallv  performed  by  negresses,  who 
ha^dng  pulverized  the  ore  under  flat  stones,  agitate  it  in  wide, 
shallow,  wooden  dishes,  separating  the  lighter  portions  with  much 
dexterity.  In  Eimope,  the  pyrites  is  ground  and  amalgamated, 
in  mills  constnicted  for  the  purpose.  Those  who  wash  the  river 
sands  usually  select  some  spot  at  the  bend  of  the  stream,  where 
the  mud  appears  to  be  black  or  reddish  ; as  it  is  here,  if  anywhere, 
that  the  gold  is  found.  The  most  favourable  time  is  when  the 
waters  are  subsiding  after  storms  or  heavy  rains ; the  sand  is  con- 
centrated either  by  washing  it  in  shallow  vessels,  or  else  by  allow- 
ing it  to  pass  through  a succession  of  troughs.  Amalgamation  is 
afterwards  resorted  to,  and  the  product  is  distilled,  as  in  the  ana- 
logous process  for  obtaining  silver. 

(951)  Properties. — Gold  is  of  a rich  yellow  colour  and  high 
metallic  lustre.  It  is  not  remarkable  for  its  hardness,  being,  when 
in  a pure  state,  nearly  as  soft  as  lead.  Its  ductility,  however,  is 
considerable,  ranking  next  to  silver,  so  that  it  may  be  drawn  into 
very  fine  wire.  As  already  mentioned,  it  is  the  most  malleable  of 
the  metals,  and  so  extreme  is  the  thinness  to  wliich  it  may  be  re- 
duced by  hammering,  that  280,000  leaves  placed  upon  one  another 
would  be  required  to  occupy  the  thickness  of  one  inch.  The 
thickness  of  the  film  may  be  still  fm-ther  reduced  by  floating  it 
upon  a dilute  solution  of  cyanide  of  potassimn.  Faraday  found 
that  such  a film  when  attached  to  a plate  of  glass  still  retained  its 
power  of  reflecting  yellow  light  and  transmitting  green : if,  how- 
ever, the  temperature  were  maintained  for  a short  time  at  a point 
not  exceeding  600°  F.,  the  metallic  lustre  disappeared  entirely, 
and  the  transmitted  light  became  of  a pure  ruby  red.  The  pres- 
sure of  agate,  or  of  any  kind  of  hard  body  upon  the  fihn,  changed 
the  colom*  of  the  transmitted  light  at  that  spot  again  to  green. 
{Phil.  Trans.  185 T.)  Gold  fuses  at  a temperatime  of  2016°.  It 
cannot  be  advantageously  employed  for  castings,  as  it  shrinks 
greatly  at  the  moment  of  solidifying.  It  is  but  very  slightly  vol- 
atile in  the  heat  of  the  furnace,  tliough  by  a powerful  electric 
discharge,  by  the  concentration  of  the  sun’s  rays  with  a large 
convex  lens,  or  by  the  intense  heat  of  the  oxyhydrogen  jet,  it  may 
be  dispersed  in  purple  vapours.  It  is  one  of  the  most  perfect  con- 
ductors both  of  heat  and  of  electricity.  Gold  suffers  no  change 
by  exposm’e  to  ah  and  moistm-e  at  any  temperatm’e.  Xone  of  the 
simple  acids,  with  the  exception  of  the  selenic,  have  any  efiect 
upon  it,  but  it  is  dissolved  iDy  any  mixture  which  liberates  chlo- 
rine. Its  usual  solvent  is  aqua  regia,  which  for  this  purpose  is 
generally  prepared  by  mixing  1 part  of  nitric  acid  and  I parts  of 
hydrochloric  acid,  the  hydi’ated  alkalies  do  not  affect  it ; a cru- 
cible of  gold  is  consequently  a valuable  instrument  in  the  ana- 
lysis of  minerals  which  require  fusion  with  the  caustic  alkalies, 
the  metal  combines  directly  with  fluorine,  chlorine,  and  bromine, 
without  the  aid  of  heat,  and  with  phosphorus  when  heated. 

(955)  Preparation  of  Fine  Gold. — Gold  is  best  obtained  in  a 
state  of  purity  by  dissolving  the  metal  in  aqua  regia,  and  evapo- 


rSES  OF  GOLD GILDING. 


691 


rating  the  solution  of  chloride  of  gold  thus  obtained  with  an  excess 
of  hydrochloric  acid,  for  the  purpose  of  destroying  the  excess  of 
nitric  acid : the  solution  is  then  largely  diluted  with  water,  to  pre- 
cipitate the  chloride  of  silver,  from  which  it  is  afterwards  decanted. 
A solution  of  ferrous  sulphate  is  next  prepared  and  added  to  the 
solution  of  chloride  of  gold : 1 part  of  gold  requires  between  4 
and  5 parts  of  the  crystallized  sulphate  [6  FeSO^  + 2 AuClg  = 
2 (Fe^  3 SO4)  + Fe^Clg  -|-  2 Au].  Metallic  gold  is  thus  precipi- 
tated in  the  form  of  a finely  divided  powder,  which,  when  sus- 
pended in  water,  is  brown  by  refiected,  but  purple  when  viewmd 
by  transmitted  light.  For  commercial  purposes  it  would  be  suf- 
ficient now  to  collect  the  gold,  dry  it,  and  after  fusing  it  with 
borax,  to  cast  it  into  ingots  ; but  when  required  to  be  perfectly 
free  from  silver,  the  gold  is  not  melted  at  this  stage,  but  the  pre- 
cipitated metal  is  boiled  with  hydrochloric  acid  of  sp.  gr.  1*1. 
The  acid  is  decanted,  and  the  residue  is  boiled  twice  with  fresh 
acid  without  washing  the  gold  between  these  successive  additions 
of  acid.  The  last  traces  of  iron  and  nearly  all  the  chloride  of  sil- 
ver are  thus  removed.  The  gold  is  then  washed,  dried,  and  mixed 
with  its  own  weight  of  acid  sulphate  of  potassium,  and  fused  in  a 
Hessian  crucible.  The  last  portions  of  chloride  of  silver  are  thus 
removed,  and  the  gold  is  perfectly  pure.  When  thus  prepared  its 
surface  often  exhibits  a crystalline  appearance,  being  embossed 
with  aggregations  of  tetrahedra  if  the  metal  be  allowed  to  cool 
slowly. 

Levol  prefers  to  precipitate  the  gold  from  an  acid  solution  of 
its  chloride  by  means  of  an  acid  solution  of  terchloride  of  anti- 
mony : 3 SbClg  + 2 AuClg  = 3 SbCl^  + 2 Au.  The  hydrochloric 
solution  retains  any  traces  of  chloride  of  silver  which  may  be 
present. 

Uses. — Gold  is  employed  in  its  finely  divided  state  for  gilding 
porcelain,  which  is  first  painted,  with  an  adhesive  varnish  and 
allowed  to  become  partially  dry ; the  powdered  metal  is  then 
dabbed  on  wdth  a dry  pencil  (having  been  previously  mixed  with 
a fusible  enamel),  after  which  the  article  is  fired  ; the  gilt  portions 
are  subsequently  burnished  and  take  a high  polish.  It  commu- 
nicates a fine  ruby  colour  to  glass,  and  is  the  colouring  ingredient 
in  the  beautiful  red  glass  manufactured  in  Bohemia.  The  uses  of 
gold  in  the  fabrication  of  ornamental  articles  and  in  coinage  are 
well  known  ; like  silver  it  is  too  soft  to  be  employed  in  a pure 
state. 

(956)  Gilding  upon  woodwork,  papier-mache,  or  plaster,  is 
effected  by  means  of  gold  leaf  which  is  attached  to  tlie  surface  by 
an  adhesive  varnish,  sucli  as  gold-size.  Gilding  upon  metals  is 
effected  either  through  the  medium  of  mercury,  as  in  one  of  the 
processes  for  silvering  (935),  or  by  voltaic  action,  as  in  the  process 
of  electro-silvering  already  mentioned  ; for  this  purpose,  a solution 
either  of  the  cyanide  of  gold  and  Y)otassium,  or  of  sulphide  of  gold  in 
sulphide  of  potassium,  is  used  (296). 

Some  years  ago,  a means  of  gilding  by  immersion  was  intro- 
duced by  Mr.  Elkington,  by  w*hich  copper  trinkets  and  stamped 


692 


ALLOYS  OF  GOLD. 


articles  can  be  coated  with  a thin  film  of  gold  ; this  method  has 
been  very  largely  practised.  The  process  has  been  carefully  in- 
yestigated  by  Barral  {Aim.  de  Chimie,  III.  x^dii.  5).  The  gilding 
bath  is  prepared  by  dissolying  1 part  of  fine  gold  in  aqua  regia, 
and  expelling  the  excess  of  acid  by  eyaporation  ; the  chloride  is 
dissolyed  in  a small  quantity  of  water  ; to  this  solution  30  parts 
of  the  acid-carbonate  of  potassium  (lyHOOg)  are  gradually  added. 
This  liquid  is  then  mixed  with  a solution  of  30  parts  more  of  the 
acid-carbonate,  dissolyed  in  200  parts  of  water,  and  the  liquid  is 
boiled  for  two  hours  : during  this  operation,  the  acid-carbonate  of 
potassium  is  conyerted  into  the  sesquicarbonate,  and  the  yellow 
liquid  passes  into  green  ; after  this,  the  solution  is  ready  for  use. 
The  trinkets  liaying  been  annealed  are  cleansed  from  adhering 
oxide  by  a momentary  immersion  in  a mixture  of  equal  parts  of 
sulphuric  and  nitric  acids,  to  which,  when  the  gold  is  intended 
to  haye  a dead  appearance,  a little  common  salt  is  added. 
The  articles  are  washed  in  water  and  then  plunged  into  the 
hot  gilding  liquid,  where  they  are  left  for  about  half  a minute, 
after  which  they  are  washed  in  water  and  dried  in  hot  sawdust. 
The  layer  of  gold  deposited  in  this  operation  is  always  excessively 
thin,  and  cannot  be  increased,  because  as  soon  as  the  alloy  is  once 
covered  with  a film  of  gold  no  further  deposition  occurs.  This 
bath  may  also  be  employed  for  gilding  on  German  silver,  platinum, 
or  silver,  by  immersing  the  objects  composed  of  these  metals  in 
the  liquid  in  contact  with  wires  of  copper  or  of  zinc.  During 
this  process  of  gilding,  a remarkable  reaction  occurs, — the  gold 
imparts  a portion  of  its  chlorine  to  the  excess  of  potash  contained 
in  the  bath,  forming  chlorate  of  potassium  ; protochloride  of  gold 
is  formed  and  is  decomposed  by  the  copper,  cupric  chloride  being 
produced,  whilst  metallic  s^old  is  deposited  upon  the  surface  of  the 
trinkets:  6 AuCl3-f3  1^-003 4-6  011=6  euCl,  + 5 KCI  + KCIO, 
4-  6 Au  4-  3 0O3.  In  the  com’se  of  the  operation  a black  pow- 
der is  precipitated,  which  contains  hydrated  carbonate  of  copper, 
mixed  with  a small  proportion  of  the  purple  of  Cassius  deriyed 
from  the  action  of  the  gilding  solution  upon  the  tin  contained 
in  the  solder  of  the  trinkets. 

AVith  mercury,  gold  forms  a semi-solid  amalgam  of  a yellowish 
colour,  which  is  soluble  in  an  excess  of  mercury.  This  excess 
may  be  remoyed,  as  in  the  case  of  silyer  amalgam,  by  filtering, 
and  squeezing  it  through  chamois  leather.  It  is  this  amalgam 
which  is  formed  during  the  extraction  of  gold  from  its  ores  ; it  is 
also  extensiyely  prepared  for  the  purposes  of  gilding.  A combina- 
tion of  mercury  with  gold  (Augilg)  may  be  obtained  cr^'stallized 
in  brilliant  four-sided  prisms  by  acting  with  diluted  nitric  acid, 
aided  by  a gentle  heat,  upon  an  amalgam  of  gold  containing 
about  1 part  of  gold  to  1000  of  mercury  (T.  H.  Henry) : these 
crystals  are  insoluble  in  nitric  acid. 

(957)  AUoys  of  Gold. — The  ductility  of  gold  is  much  im- 
paired by  alloying  it  with  other  metals,  though  its  hardness  and 
soncuousness  are  increased : these  alloys  are  generally  formed 
without  difficulty.  If  a proportion  of  tin,  of  cobalt,  of  nickel,  or 


ALLOYS  OF  GOLD PARTING. 


693 


of  zinc,  greater  than  2 per  cent,  of  the  mass  he  present  in  the 
alloy,  it  is  unfit  for  coinage ; and  still  smaller  quantities  of  lead, 
of  arsenic,  of  antimony,  or  of  bismuth,  render  gold  brittle.  Pal- 
ladium is  a still  more  inconvenient  impurity,  since  it  not  only 
renders  the  gold  brittle,  but  it  requires  special  treatment  in  order 
to  extract  it,  as  it  is  not  removed  by  the  ordinary  operations  of 
the  refiner.  A similar  remark  is  applicable  to  the  alloy  of  plati- 
num with  gold.  Small  quantities  both  of  platinum  and  of  palla- 
dium render  the  gold  nearly  white.  The  native  alloy  of  osmium 
and  iridium  which  frequently  accompanies  the  Californian  gold, 
does  not  combine  with  the  metal,  but  remains  disseminated 
through  it  in  distinct  grains  after  the  gold  has  been  melted. 
These  grains  occasion  much  inconvenience;  they  often  escape 
notice  until  the  metal  passes  through  the  coining  press,  where 
they  make  themselves  apparent  by  their  hardness,  and  by  the 
injury  which  they  consequently  inflict  upon  the  dies. 

Silver  and  gold  may  be  alloyed  with  each  other  in  all  propor- 
tions. The  alloy  which  they  form  lias  a pale  greenish-yellow 
colour,  but  it  becomes  nearly  white  when  the  quantity  of  silver 
exceeds  50  per  cent.  The  malleabilit}"  of  gold  is  less  diminished 
by  the  presence  of  silver  than  by  that  of  any  other  metal.  In  the 
arts  it  frequently  becomes  necessary  to  separate  these  two  metals, 
and  this  is  usually  effected  by  the  method  termed  quartation  or 
qyarting.  This  operation  depends  on  the  solubility  of  silver  in 
nitric  acid,  and  the  insolubility  of  gold  in  this  liquid.  It  is 
necessary  that  the  silver  should  amount  to  at  least  three  times 
the  weight  of  gold,  otherwise  portions  of  silver  would  be  mechani- 
cally protected  from  the  action  of  the  acid,  and  the  separation 
would  be  incomplete.  If,  therefore,  the  alloy  be  found  to  contain 
more  than  a fourth  of  its  weight  of  gold,  sufficient  silver  is  added 
to  reduce  it  to  this  proportion,  and  hence  the  origin  of  the  term 
“ quartation.”  The  metals  are  fused  together,  g]-aimlated  by 
being  poured  into  water,  and  they  are  then  digested  in  the  acid. 
The  gold  is  afterwards  melted  into  ingots,  the  silver  is  precipi- 
tated as  chloride,  by  common  salt,  and  the  chloride  is  reduced 
either  by  zinc  (940),  or  by  fusion  with  an  alkali  (944).  On  the 
large  scale  sulphuric  acid  is  usually  substituted  for  nitric  acid ; it 
is  much  cheaper,  and  is  quite  as  effectual  in  dissolving  the  silver 
if  boiled  upon  it  (947).  Indeed,  in  refining  upon  the  large  scale, 
when  sulphuric  acid  is  used  the  gold  may  be  obtained  containing 
998  or  999  thousandths  of  the  pure  metal;  whereas  when  nitric 
acid  is  used  it  is  seldom  finer  than  from  993  to  995  tliousandths. 

The  most  useful  alloy  of  gold  is  that  whicli  it  forms  with 
copper:  it  is  of  a redder  colour  than  pure  gold,  and  considerahly 
harder  and  more  fusible,  but  it  is  less  ductile  and  malleable.  It 
is  this  alloy  which  is  used  for  coinage.  British  standard  gold  con- 
tains 8*33  per  cent,  of  copper,  or  11  parts  of  gold  to  1 ])art  of 
copper.  The  specific  gravity  of  this  mixture  is  17T57,  instead 
of  18*47,  the  two  metals  expanding  a little  when  they  unite.  In 
France  and  in  the  United  States  the  standard  gold  contains  10 
per  cent,  of  copper.  Jewellers  frequently  alloy  their  gold  with  a 


694: 


ASSAY  OF  GOLD. 


mixture  of  copper  and  silver.  The  alloys  of  gold  and  copper, 
when  once  the  materials  have  been  well  mixed,  do  not  exhibit  the 
tendency  to  liquation  which  occasions  so  much  trouble  in  the  case 
of  silver  (937).  The  solder  nsed  for  uniting  pieces  of  gold  is  an 
alloy  of  gold  with  copper,  which  melts  at  a lower  temperature 
than  pure  gold. 

(958)  Assay  of  Gold. — In  the  assay  of  gold  a combination  of 
the  processes  of  cupellation  and  qnartation  is  employed.  In  the 
cupellation  of  gold  the  quantity  of  lead  which  is  needed  is  about 
double  tliat  employed  for  silver  ; 1 part  of  copper  requiring  about 
32  parts  of  lead.  The  assay  of  gold  furnishes  results  which  are 
more  accurate  than  those  obtained  in  the  cupellation  of  silver. 
The  loss  of  gold  by  volatilization  is  very  much  smaller,  and  scarcely 
any  of  the  metal  is  carried  into  the  cupel  by  an  excess  of  lead. 

The  following  is  an  outline  of  the  method  adopted  in  the  assay 
of  gold  : — The  quantity  of  the  alloy  for  assay  having  been  accu- 
rately weighed,  it  is  wrapped  in  a piece  of  paper,  with  a propor- 
tion of  silver  equal  to  about  3 times  that  of  the  gold  which  the 
alloy  is  supposed  to  contain,*  and  this  is  submitted  to  cupellation 
in  the  manner  already  described  when  speaking  of  the  assay  of 
silver  (938).  By  this  means  the  silver  and  the  gold  become 
thoroughly  incorporated,  and  the  copper  is  oxidized  and  absorbed 
by  the  cupel  with  the  oxide  of  lead.  The  auriferous  button  is  then 
hammered  into  a flattened  disk,  of  about  the  size  of  a sixpence, 
and  annealed,  by  heating  it  to  redness.  It  is  next  passed  between 
a pair  of  laminating  rollers,  by  which  its  thickness  is  reduced 
to  that  of  an  ordinary  address  card,  after  which  it  is  a second 
time  annealed.  These  operations  render  it  sufficiently  flexible  to 
allow  of  its  being  coiled  into  a small  sjDiral  by  rolling  between  the 
linger  and  thumb.  The  cornet  thus  obtained  is  next  introduced 
into  a flask  which  contains  about  an  ounce  of  nitric  acid  of  sp.  gr. 
1T80,  heated  nearly  to  the  boiling-point.  Brisk  evolution  of 
nitrous  fumes  immediately  ensues  ; the  silver  is  gradually  dissolved 
away,  and  the  gold  is  left  in  the  form  of  the  original  cornet,  as  a 
brown,  porous,  very  brittle  mass.  After  this  first  boiling  has 
been  continued  for  10  minutes,  the  flask  is  removed  from  the  fire, 
the  acid  solution  is  poured  off,  and  the  cornet  is  washed  by  care- 
fully pouring  distilled  water  upon  it ; and  this  water,  after  stand- 
ing for  a couple  of  minutes,  is  again  poured  off.  Some  traces  of 

* An  approximative  estimate  of  the  composition  of  the  alloy  is  sometimes  made 
by  the  use  of  the  touchstone,  though  it  is  seldom  employed  by  the  practised 
assayer : — A number  of  pieces  of  alloy  are  formed  containing  known  quantities  of 
gold  and  copper,  or  of  gold  and  silver;  the  first  consisting  of  pure  gold;  the  second 
of  23  parts  of  gold  and  1 part  of  copper;  the  third  of  22  of  gold  and  2 of  copper,  and 
so  on;  the  assayer  selects  one  of  these  alloys,  or  ‘ needles,’  which  from  its  colour  he 
judges  to  approach  nearest  in  composition  to  the  alloy  which  he  is  about  to  assay ; 
this  he  rubs  upon  a hard,  black  stone,  ‘ touchstone,’  which  is  a peculiar  kind  of  bitu- 
minous quartz  formerly  obtained  from  Lydia,  in  Asia  Minor;  black  basalt,  however, 
may  be  employed  for  the  purpose;  the  alloy  leaves  a streak  upon  the  stone,  the 
colour  of  which  is  redder  in  proportion  as  the  copper  preponderates.  The  streak 
formed  by  the  alloy  for  assay  is  then  compared  with  that  of  the  needles,  until  one  of 
these  is  found  to  which  it  nearly  corresponds.  The  judgment  may  be  further  aided, 
by  moistening  the  streaks  obtained  with  a little  nitric  acid,  which  attacks  the  copper 
or  silver,  but  leaves  the  gold. 


ASSAY  OF  GOLD. 


695 


silver  are,  however,  still  retained  by  the  gold,  and,  in  order  to 
remove  these,  the  cornet  is  again  boiled  with  nitric  acid,  which, 
this  time,  mnst  be  of  sp.  gr.  1‘280.  In  this  second  boiling,  which 
must  be  continued  for  20  minutes,  a small  fragment  of  charcoal 
should  be  introduced  into  the  flask,  in  order  to  prevent  the  ebulli- 
tion from  taking  place  irregularly,  with  sudden  bursts,  as  it  is  very 
apt  to  do  if  this  precaution  be  neglected. 

The  acid  having  been  poured  off,  the  flask  is  fllled  up  com- 
pletely with  distilled  water.  A small,  smoothly  finished,  porous 
clay  crucible  is  placed  over  the  mouth  of  the  flask,  and  tlie  flask 
and  crucible  are  inverted,  so  that  the  cornet  shall  fall  gently 
through  the  water  into  the  crucible : by  a dexterous  movement 
of  the  hand,  the  flask  is  then  withdrawn  in  such  a manner  as  to 
prevent  the  overflow  of  any  liquid  from  the  little  crucible : the 
water  is  afterwards  carefully  poured  off  from  the  cornet,  and  the 
crucible  is  heated  to  redness  in  the  muffle.  By  this  means  the 
gold,  though  it  is  not  fused,  is  rendered  much  more  compact ; it 
shrinks  in  bulk,  loses  its  brown  appearance,  and  assumes  the 
peculiar  colour  and  lustre  of  the  metal.  When  cold,  the  cornet 
is  weighed  with  the  same  precision  as  the  original  alloy.  The 
assayer  calls  the  arbitrary  weight  of  the  alloy  upon  which  he 
operates,  1000 ; his  weights  are  all  subdivided  so  as  to  give  him 
the  value  of  the  alloy  in  thousandths  of  this  original  quantity ; so 
that  if  he  And  a portion  of  the  alloy  which  originally  weighed 
1000  of  these  arbitrary  units,  to  yield  a quantity  of  gold  equal  to 
916-1  of  these  parts,  he  reports  it  as  916'6.  1000  ounces  of  such 

an  alloy  would  contain  916 ’6  ounces  of  fine  gold. 

The  amount  of  alloy  upon  wdiich  it  is  most  convenient  to 
operate  in  assaying  is  half  a gramme,  or  between  7 and  8 grains. 

The  gold  contained  in  the  cornet  is  never  absolutely  pure : 
it  retains  a small  quantity  of  lead  and  of  silver,  and  frequently 
also  traces  of  copper,  which  render  its  weight  a little  higher  than 
it  ought  to  be.  In  order  to  ascertain  the  amount  of  this  error, 
a number  of  proofs  are  passed  through  the  muffle  simultaneously 
with  the  alloys,  and  subjected  to  the  same  process  as  the  alloys 
themselves.  These  proofs  consist  of  weighed  portions  of  fine  gold, 
to  each  of  which  is  added  a proportion  of  copper  equal  to  that 
estimated  to  exist  in  the  alloys  under  examination.  The  excess 
of  weight  which  these  proofs  indicate  shows  the  amount  of  the 
correction  which  it  becomes  necessary  to  make.  This  correction 
is  liable  to  daily  variation,  according  to  the  temperature  of  the 
furnace,  the  more  or  less  perfect  softening  of  the  buttons  during 
annealing,  the  thickness  of  the  cornets,  &c. ; but  it  usually  varies 
from  0*2  to  0*5  parts  in  1000.  Most  assayers  vary  tlie  quantity  of 
lead  according  to  the  proportion  of  copper  in  the  alloys.  I have 
found  it  advantageous  to  use  the  same  amount  of  lead  in  all  cases ; 
the  correction  then  becomes  uniform  for  all  the  assays  passed  at 
one  operation. 

When  the  alloy  contains  very  little  co]q)er,  as  commonly 
occurs  with  native  gold,  the  button  of  alloy  is  liable  ‘to  s})it’  as  it 
cools  after  the  cupellation  ; this  mischance  may  easily  be  prevented 


696 


OXIDES  OF  GOLD. 


by  tlie  addition  of  a small  fragment  of  copper,  not  exceeding  | 
of  a grain  in  weight,  before  introducing  the  alloy  into  the  cupel. 

It  frequently  happens  that  it  is  necessary  to  ascertain  the  pro- 
portion both  of  gold  and  of  silver  in  a given  alloy.  If  the  propor- 
tion of  gold  preponderate,  the  quantity  of  gold  is  determined  in 
tlie  manner  above  described,  and  that  of  the  gold  and  silver  to- 
gether is  ascertained  by  submitting  a portion  of  the  alloy  to  cu- 
pellation  with  the  lead,  as  if  it  consisted  of  silver  only  (938).  The 
two  metals,  gold  and  silver,  remain  upon  the  cupel,  whilst  the 
copper  and  more  oxidizable  metals  are  absorbed.  The  weight  of 
the  residual  button  gives  the  united  weight  of  the  gold  and  silver, 
and  the  difference  between  this  weight  and  that  of  the  gold  alone 
will  of  course  furnish  the  proportion  of  silver. 

When  the  proportion  of  gold  is  very  small  compared  with  that 
of  the  silver,  the  two  metals  are  treated  with  nitric  acid  at  once 
(without  submitting  them  to  the  usual  assay  for  gold),  the  acid 
dissolves  the  silver  and  other  metals  which  may  be  present,  leav- 
ing the  gold  in  the  form  of  a black  powder : this  powder  must  be 
collected  by  subsidence  in  one  of  the  small  porous  crucibles  used 
for  annealing  gold  cornets,  in  which  it  is  ignited,  and  can  after- 
wards be  weighed  without  difficulty. 

(959)  Oxides  of  Gold. — There  are  two  oxides  of  gold:  a 
suboxide,  Au^G,  and  a peroxide,  Au^Og : the  latter  possesses  acid 
properties,  and  is  frequently  termed  auric  acid. 

The  suboxide  (Au2O=4:09*2),  or  protoxide  (AuO=:204:-6)  is 
obtained  as  a dark  green  powder  by  precipitating  the  protochlo- 
ride of  gold  by  a dilute  solution  of  potash  ; it  is  slightly  soluble 
in  excess  of  the  alkali : when  digested  with  ammonia  it  forms 
fulminating  gold ; hydrochloric  acid  converts  it  into  metallic  gold 
and  terchloride  of  the  metal.  Protoxide  of  gold  undergoes  a 
suspension  in  pure  water,  and  passes  through  the  filter  ; but  boil- 
ing the  solution  after  adding  any  saline  compound  causes  its  pre- 
cipitation. 

Peroxide  of  gold  Auric  acid  (AugOg— 44:1’2,  or  AuOg=220*6). 
— This  compound  is  best  obtained  by  decomposing  a solution  of 
the  terchloride  of  gold  by  magnesia  ; for  if  solutions  of  the  alka- 
lies be  used,  they  adhere  strongly  to  the  precipitate : it  falls  in 
combination  with  the  earth,  which  may  be  removed  by  means  of 
diluted  nitric  acid,  and  the  oxide  of  gold  remains  as  a yellow  hy- 
drate, if  the  acid  used  be  weak,  or  as  a brown  anhydrous  oxide  if 
strong ; it  is  very  readily  reduced  by  exposure  to  light,  and  at  a 
temperature  of  about  470°  it  is  resolved  into  metallic  gold  and 
free  oxygen.  It  is  taken  up  by  strong  nitric  and  sulphuric  acids, 
but  no  true  salts  are  formed  ; the  oxide  being  deposited  again 
from  these  solutions  in  a pure  state  on  dilution.  Peroxide  of  gold 
is  dissolved  by  hydrochloric,  hydrobromic,  and  hydriodic  acids, 
forming  terchloride,  terbromide,  and  teriodide  of  gold. 

When  hydrated  it  is  readily  acted  on  by  the  hydrated  alkalies, 
forming  salts  that  have  been  termed  aurates^  which  are  soluble  in 
water,  and  form  yellow  solutions.  Aurate  of  potassium  crystal- 
lizes in  yellowish  needles  (KAuOg,  3 II2O,  or  KO,AuOg  . 6 Aq) ; 


SULPHIDES  AND  CHLORIDES  OF  GOLD. 


697 


its  solution  may  be  used  in  electro-gilding.  Most  of  the  com- 
pounds of  auric  acid  with  the  earths  and  other  metallic  oxides 
are  insoluble. 

Peroxide  of  gold  forms  wdth  ammonia  a dark  olive-brown  ful- 
minating compound,  analogous  to  that  furnished  by  silver  (94:2)  ; 
the  same  compound  may  be  formed  by  adding  ammonia  to  the 
terchloride,  but  in  this  case  it  is  of  a reddish-yellow  colour,  owing 
to  the  admixture  of  a little  ammoniacal  subchloride  of  gold.  So 
great  is  the  attraction  of  peroxide  of  gold  for  ammonia,  that  it 
decomposes  the  neutral  salts  of  ammonium,  such  as  the  sulphate, 
and  sets  the  acid  at  liberty. 

(960)  Sulphide  or  hisidphide  of  gold  (Au^S4=914'4:,  or  AuS^, 
= 228'6). — When  a current  of  sulphuretted  hydrogen  is  trans- 
mitted through  a cold  solution  of  terchloride  of  gold,  a black  pre- 
cipitate is  produced,  which,  according  to  Levol,  is  a l)isulphide,  or 
rather  (Au^SjAu^Sg).  It  is  soluble  in  the  solutions  of  the  sul- 
phides of  the  alkaline  metals : its  solution  in  sulphide  of  sodium 
yields  a colourless  salt  which  is  soluble  in  alcohol ; it  crystallizes 
in  six-sided  prisms,  consisting  of  (hTaAuS  . 4 HaO,  or  NaS,AuS  . 
8 Aq;  Yorke),  2 AuS-f2  Na^S  becoming  2 AuYaS-f ISTaaSa.  If 
finely  divided  gold  be  heated  with  sulphur  in  contact  with  car- 
bonate of  potassium,  a double  sulphide  of  gold  and  potassium  is 
formed ; it  resists  a red  heat,  and  is  very  soluble  in  water : this 
sulphur  salt  is  used  for  gilding  china,  and  produces  the  colour 
known  as  Burgos  lustre. 

(961)  Chlorides  of  Gold. — Gold  forms  twm  compounds  with 
chlorine, — a protochloride,  AuCl,  and  a terchloride,  AuClg. 

Protochloride  of  gold  (And  = 232*1). — When  terchloride  of 
gold  is  exposed  to  a gentle  heat,  it  fuses,  without  undergoing  de- 
composition ; but  if  the  temperature  be  raised  to  about  350°, 
chlorine  is  gradually  expelled,  and  a pale  yellow,  sparingly  soluble 
powder  is  left,  which  is  the  protochloride.  It  is  an  unstable  com- 
pound, but  it  may  be  washed  wdth  cold  w^ater  to  remove  any  un- 
decomposed terchloride  ; boiling  water  converts  it  into  a mixture 
of  the  terchloride  with  metallic  gold,  and  a similar  change  is  pro- 
duced by  exposing  it  to  light.  If  the  tem^^erature  be  raised  a 
little  beyond  400°,  the  whole  of  the  chlorine  is  expelled.  Proto- 
cldoride  of  gold  when  digested  in  a solution  of  caustic  potash 
yields  hydrated  suboxide  of  gold  and  chloride  of  potassium. 

Terchloride  of  gold  (AuCl3=303):  Comp,  in  100  parts.,  Au, 
64*89  ; Cl,  35*11. — This  compound  is  produced  when  the  metal  is 
dissolved  in  aqua  regia ; on  evaporating  the  solution  to  dryness 
at  a temperature  not  exceeding  250°,  taking  care  to  maintain  tlie 
liydrochloric  acid  in  excess  over  the  nitric,  this  salt  remains  be- 
liind  as  a red  deliquescent  mass;  but  usually  a portion  of  tlie  ter- 
chloride is  reduced  to  the  state  of  insoluble  protochloride  : indeed 
it  is  difficult  to  get  rid  of  the  last  portion  of  acid.  It  forms  with 
water  an  orange-coloured  solution,  which  preserves  its  colour  even 
when  very  largely  diluted  ; alcohol  also  dissolves  the  chloride, 
and  ether  takes  it  up  so  freely  as  to  separate  it  from  its  aqueous 
solution  when  agitated  with  it.  Chloride  of  gold  forms  a crystal- 


698 


TEEBROMIDE  AND  IODIDES  OF  GOLD. 


line  compound  witli  liydrochloric  acid:  it  also  unites  witli  tlie 
chlorides  of  many  of  the  basylous  metals  to  form  double  salts  : 
that  with  potassium  crystallizes  in  efflorescent  striated  prisms, 
consisting  of  2 (KCljAuClg)  . 5 that  with  sodium  forms 

four-sided  prisms,  (NaCl,AuCl3,  2 H^O).  The  chlorides  of  most 
of  the  organic  bases  also  form  cry stalliz able  double  salts  with  ter- 
chloride  of  gold  : these  compounds  are  often  employed  to  deter- 
mine the  combining  number  of  the  organic  alkali.  The  chloride 
of  gold  is  easily  reduced  by  many  substances ; the  reaction  of 
ferrous  sulphate  in  presence  of  an  excess  of  acid  has  already  been 
mentioned,  so  likewise  has  that  with  terchloride  of  antimony  (955). 
Oxalic  acid  produces  a similar  precipitate  of  metallic  gold  even 
in  acid  solutions;  for  instance,  2 AuClg-fS  Au-f 

6 HCl-t-6  OO^ : the  powder,  when  viewed  by  reflected  light,  ap- 
pears to  be  of  a brown  colour,  but  by  transmitted  light,  whilst 
suspended  in  water,  it  has  a purple  tint.  Many  organic  sub- 
stances, if  moistened  with  a solution  of  the  chloride  of  gold,  also 
exert  a reducing  effect  upon  it ; hence  the  lingers,  or  writing-paper, 
if  washed  over  with  the  solution,  become  stained  of  a violet  colour 
when  exposed  to  the  sun’s  light.  Metallic  gold  is  also  readily  ob- 
tained from  the  solution  of  this  salt  by  other  means.  A solution 
of  sulphurous  acid,  or  a current  of  the  gas  transmitted  through 
the  solution,  or  a solution  of  one  of  the  sulphites,  precipitates  the 
gold  completely;  2 AuClg-fS  HCl-f 3 H^SO^ 

-{-  2 Au.  Phosphorous  and  hypophosphorous  acids,  and  solutions 
of  their  salts,  produce  the  same  effect ; and  a similar  result  is  ob- 
tained by  contact  with  many  of  the  metals,  such  as  mercury,  cop- 
per, iron,  and  zinc.  A stick  of  phosphorus  when  immersed  in  a 
solution  of  chloride  of  gold,  soon  becomes  coated  with  the  reduced 
metal ; and  if  a few  drops  of  a solution  of  phosphorus  in  ether, 
or  in  bisulphide  of  carbon,  be  mixed  with  a very  dilute  solution 
of  neutral  chloride  of  gold,  containing  from  0’6  to  1*0  of  a grain 
of  the  metal  in  a quart  of  water,  the  gold  will  be  reduced  in  the 
course  of  a few  hours.  Provided  that  the  bottle  containing  the 
solutions  be  chemically  clean,  the  metal  will  be  separated  in  par- 
ticles of  such  extreme  tenuity  that  it  will  remain  suspended  in 
the  liquor  for  months ; giving  to  it  a ruby  red  or  amethystine  col- 
our when  viewed  by  transmitted  light,  though  it  appears  to  be 
turbid  and  brown  when  seen  by  reflected  light.  If  this  red  liquid 
be  mixed  with  a small  quantity  of  a solution  of  common  salt,  the 
ruby  tint  is  immediately  changed  to  purple,  the  state  of  aggrega- 
tion of  the  metal  undergoing  an  instantaneous  alteration,  in  con- 
sequence of  which  the  liquid  becomes  colourless  in  a few  hours, 
and  the  whole  of  the  suspended  particles  of  gold  are  deposited  in 
a purple  but  perfectly  metallic  powder  (Faraday). 

(962)  A terbromide  of  gold  may  be  formed ; it  crystallizes 
easily,  and  forms  numerous  double  salts  with  other  soluble  bromides. 

There  are  two  iodides  of  gold,  corresponding  to  the  chlorides. 
The  protiodide  is  a yellow  insoluble  powder.  The  teriodide  is 
unstable  ; it  is  green  and  sparingly  soluble  ; it  forms  double  salts 
with  the  iodides  of  the  alkaline  metals. 


CHAEACTERS  OF  THE  SALTS  OF  GOLD PLATLNTJM. 


699 


(963)  P%irple  of  Cassius. — When  a mixture  of  stannous  and 
stannic  chloride  very  much  diluted  is  added  drop  by  drop  to  a 
dilute  neutral  solution  of  terchloride  of  gold,  a flocculent  purple 
deposit  takes  place.  The  same  compound  is  readily  formed  by 
digesting  metallic  tin  in  a neutral  solution  of  terchloride  of  gold ; 
metallic  gold  and  the  purple  of  Cassius  being  formed.  The  true 
nature  of  this  compound  has  been  the  subject  of  much  discussion. 
Berzelius  concluded  from  the  researches  of  Figuier  {A7in.  de 
Chimie^  III.  xi.  351)  that  it  consists  of  a hydrated  double  stannate 
of  gold  and  tin  (Sn^Wu^Sn^Og  4 or  AuOjSnO^ . SnOjSnO^jd 
Aq).  Purple  of  Cassius  undergoes  a suspension  in  pure  water, 
and  passes  through  the  filter,  but  it  is  separated  on  adding  a salt 
to  the  liquid  and  boiling  it.  It  is  insoluble  in  solutions  of  potash 
and  soda,  but  soluble  in  ammonia,  forming  a deep  purple  solution, 
from  which  it  is  deposited  unchanged  if  the  ammonia  be  expelled 
by  heat,  or  neutralized  by  an  acid.  This  solution  is  bleached  by 
the  action  of  light,  and  gold  is  deposited.  Purple  of  Cassius  is 
decomposed  by  the  acids,  metallic  gold  being  left ; but  it  is  not 
changed  by  the  action  of  light.  If  heated  to  redness  water  is  ex- 
pelled, and  a red  powder  is  left,  which  is  a mixture  of  metallic 
gold  and  peroxide  of  tin.  Purple  of  Cassius,  when  mixed  with  a 
little  borax  or  some  fusible  glass,  and  applied  to  the  surface  of 
china,  imparts  to  it  a beautiful  rose  or  a rich  j^urple  colour.  It 
is  this  compound  which  is  added  as  the  colouring  material  in  the 
red  glass  of  Bohemia. 

(961)  Characters  of  the  Salts  of  Gold. — The  salts  of  gold 
are  recognised  by  the  brown  precipitate  of  metallic  gold  produced 
ferrous  sulphate  in  their  acidulated  solutions  in  the  absence  of 
free  nitric  acid  ; and  by  the  formation  of  the  purple  of  Cassius  on 
adding  to  the  neutral  solution  a dilute  mixture  of  stannous  and 
stanmo  chloride.  Metallic  tin  yields  the  same  precipitate,  and  is 
a still  more  delicate  test.  Salts  of  gold  are  reduced  to  the  metallic 
state  by  boiling  their  acidulated  solutions  with  a soluble  oxalate 
or  sidphite.  Mercurous  nitrate  also  gives  a dark  brown  precipi- 
tate of  reduced  gold.  All  the  salts  of  gold  are  decomposed  when 
ignited  in  the  open  air. 

(965)  Estimation  of  Gold. — Gold  is  always  estimated  in  the 
metallic  state.  It  may  readily  be  separated  from  all  the  preced- 
ing metals  by  precipitating  its  solution  by  means  of  a solution  of 
ferrous  sulphate,  after  acidulating  it  with  hydrochloric  acid. 
The  precipitate  is  collected  upon  a filter,  ignited,  and  weighed  as 
pure  gold. 


§ lY.  Platinum:  Pt‘^=197T,  or  Pt=98-56.  Sp.  Gr.  21-5. 

(966)  Platinum,  little  silver^  as  its  name  implies,  is  a metal 
which  is  found  in  but  comparatively  few  places : it  was  not  recog- 
nised as  a separate  metal  until  Wood,  an  assayer  of  Jamaica,  in 
ITIl,  pointed  out  its  distinctive  characters.  It  always  occurs  in 
the  native  state,  usually  in  small  flattened  grains,  in  which  it  is 


700 


EXTRACTION  OF  RLATINUM  FROM  ITS  ORES. 


mixed  witli  palladium,  rhodium,  osmium,  ruthenium,  and  iridium, 
— metals  which  are  rarely  found  except  when  associated  with 
platinum.  Occasionally  it  occurs  in  larger  nodules,  frequently 
alloyed  with  gold,  and  traces  of  silver,  and  with  copper,  iron,  and 
lead.  The  deposits  of  platinum  are  for  the  most  part  met  with  in 
alluvial  districts  associated  with  the  debris  of  the  earliest  volcanic 
rocks.  Platinum  is  cliielly  supplied  from  the  mines  of  Mexico, 
of  Brazil,  and  of  the  Ural  Mountains.  It  has  also  been  met  Avith 
in  California  and  Australia.  It  is  separated  by  Avashing,  from  the 
lighter  impurities  contained  in  its  ore. 

Extraction — On  account  of  the  extreme  infusibility  of  pla- 
tinum it  requires  a mode  of  manipulation  which  is  complicjated 
and  peculiar.  1.  The  method  ordinarily  employed  was  contrived 
by  Wollaston: — The  ore,  Avhich  usually  contains  from  75  to  85 
per  cent,  of  platinum,  is  treated  first  with  nitric  acid,  and  then 
with  hydrochloric  acid,  in  order  to  remove  the  more  easily  oxidiz- 
able  metals,  after  which  it  is  digested  at  a moderate  heat  in 
diluted  aqua  regia  as  long  as  anything  is  dissolved,  the  solution 
of  the  platinum  taking  place  very  sloAvly.  It  is  best  therefore 
to  place  tlie  ore  in  hydrochloric  acid  and  add  small  quantities  of 
nitric  acid  at  intervals  to  maintain  the  action,  taking  care  to 
maintain  a sufficient  excess  of  hydrochloric  acid.  The  clear  liquid 
is  then  decanted,  and  the  residue  again  treated  Avith  fresh  acid  as 
long  as  anything  is  dissolved : into  the  mixed  acid  solutions  a solu- 
tion of  sal  ammoniac  in  5 times  its  weight  of  water  is  poured  (41 
parts  of  the  salt  to  100  of  ore) : the  greater  part  of  the  pla- 
tinum is  thus  precipitated  in  the  form  of  a yellow  double  salt 
(2  II^KCl,PtClJ,  which  is  sparingly  soluble.  The  mother-liquor 
still  retains  a portion  of  platinum,  which  is  precipitated  by  means 
of  metallic  iron ; the  black  poAvder  is  redissolved  in  aqua  regia, 
and  again  precipitated  by  the  addition  of  sal  ammoniac,  the  double 
salt  thus  obtained  being  added  to  tlie  first  crop.  The  chloride  of 
platinum  and  ammonium  is  then  washed,  and  heated  to  redness, 
by  wliich  means  the  ammonia  and  chlorine  are  expelled,  leaving 
the  platinum  behind  in  porous  slightly  coherent  masses ; this 
spongy  platinum  is  powdered  in  a wooden  mortar  and  rubbed  into 
a magma  with  water,  in  which  state  it  is  thoroughly  washed ; the 
metallic  particles  soon  subside,  and  the  lighter  impurities  are 
carried  aAvay.*  This  metallic  mud  is  next  poured  into  a some- 
what conical  brass  mould,  closed  below  with  blotting-paper  loosely 
supported  by  a plug ; the  greater  part  of  the  water  drains  off,  after 
Avhich  the  whole  is  subjected  to  the  action  of  a very  powerful  press. 
The  mass,  which  previously  was  of  a dull  grey  colour,  noAV  assumes 
a compact  metallic  appearance,  and  acquires  a specific  gravity  of 
about  10 ; it  is  next  exposed  to  an  intense  heat  in  a Avind  furnace, 
and  the  ingot  is  forged  by  hammering  it  upon  its  tAvo  ends, — 
never  upon  its  sides,  as  if  this  were  done  it  Avould  split.  This 
heating  and  forging  is  several  times  repeated  until  the  mass 

* Platinum  thus  prepared  usually  retains  a small  quantity  of  iridium,  which 
accompanies  the  double  chloride  of  platinum  and  ammonium.  The  platinum  may  be 
freed  from  this  impurity  by  the  method  described  in  paragraph  (991). 


EXTKACTION  OF  PLATINUM. 


701 


becomes  liomogeneous  and  ductile ; it  then  has  a specific  gravity 
of  about  21*5.  Wollaston’s  process  for  working  platinum  depends 
upon  its  property  of  welding  at  very  high  temperatures.  Deville 
and  Debray,  in  their  important  memoir  on  platinum  and  the  metals 
which  accompany  it  {Ann.  de  Chimie^  III.  Ivi.  385),  recommend 
fusion  of  platinum  by  means  of  the  oxyhydrogen  blowpipe,  in  a 
cavity  formed  in  a mass  of  lime,  for  the  purpose  of  freeing  com- 
mercial platinum  from  the  silicon  and  osmium  which  it  always 
contains.'^ 

2. — Deville  and  Debray  have  introduced  an  entirely  new 

* Deville  and  Debray  employ  the  oxyhydrogen  blowpipe  in  the  following  manner, 
for  effecting  the  fusion  of  platinum  and  the  refractory  metals  which  accompany  it. 
The  apparatus  consists  of  the  blowpipe,  c,  fig.  365,  a furnace,  A b d,  and  a crucible, 
G H T.  The  blowpipe  is  composed  of  a 
copper  tube  half  an  inch  in  diameter,  ter- 
minating below  in  a slightly  conical  pla- 
tinum jet  about  an  inch  and  a half  long. 

Within  this  tube,  which  is  supplied  with 
hydrogen  through  the  stopcock,  h,  is  a 
second  copper  tube,  c',  terminated  also  by 
a platinum  nozzle  with  an  aperture  of 
about  a twelfth  of  an  inch  in  diameter. 

The  furnace,  a b d,  consists  of  three 
pieces  of  well-burnt  lime  of  slightly  hy- 
draulic quality,  which  can  be  turned  at  a 
lathe  with  ease.  The  cylinder.  A,  is  about 
2^  inches  thick,  and  is  perforated  with  a 
slightly  conical  tube,  into  which  the  blow- 
pipe fits  accurately,  and  is  allowed  to  pass 
about  half-way  through  the  thickness  of 
the  mass.  A second  somewhat  deeper 
cylinder  of  lime,  b,  is  hollowed  into  a 
chamber  sufficiently  wide  to  admit  the 
crucible  and  leave  an  interval  of  not  more 
than  a sixth  of  an  inch  clear  around  it. 

At  K K are  four  apertures  for  the  escape 
of  the  products  of  combustion. 

The  outer  crucible,  h h,  is  also  made 
of  lime,  but  it  contains  a smaller  crucible, 

I,  of  gas  coke,  provided  with  a cover  of 
the  same  material,  and  in  this  the  sub- 
stance to  be  fused  is  placed,  the  crucible 
resting  on  the  lime-support,  d'.  The  co- 
nical cover,  G,  is  made  of  lime,  and  its 
apex  should  be  placed  exactly  under  the 
blowpipe  jet,  at  a distance  from  it  of  from 
I to  inch. 

The  different  pieces  of  the  furnace  must  be  bound  round  with  thin  iron  wire  to 
support  them  when  they  crack.  The  oxygen  is  admitted  under  a pressure  of  a 
column  of  16  inches  of  water.  The  temperature  is 
gradually  raised  to  the  maximum,  and  in  about  8 min-  Fig.  366. 

utes  from  this  time  the  experiment  is  complete. 

By  employing  a jet  of  mixed  coal-gas  and  oxygen 
(e  q.  Fig.  366)  in  a furnace  of  hme,  a b,  provided  with 
lip  at  D for  pouring,  Deville  and  Debray  succeeded  at 
an  expense  of  about  43  cubic  feet  of  oxygen,  in  melt- 
ing and  refining  in  42  minutes,  2 5 '4  lb.  avoirdupois  of 
platinum,  and  casting  it  into  an  ingot  in  a mould  of 
gas-coke ; and  much  larger  masses  have  since  been 
melted  by  this  method.  Lime  is  so  bad  a conductor 
of  heat,  that,  if  a cup  of  lime  not  more  than  0’8  inch 
thick  be  filled  with  melted  platinum,  the  exterior 
scarcely  rises  beyond  300°  F. 


Fig.  365. 


o 


702 


PEOPEKTIES  OF  PLATINUM. 


method  for  the  extraction  of  platinum  from  its  ores,  of  which  the 
following  is  an  outline : — A small  reverberatory  furnace,  the  bed 
of  which  is  composed  of  a hemispherical  cavity  of  fire-brick,  lined 
with  clay,  is  heated  to  full  redness,  and  a charge  consisting  of 
2 cwt.  of  the  platinum  ore,  mixed  with  an  equal  weight  of  galena, 
is  added  in  small  quantities,  stirring  with  iron  rods  until  the  pla- 
tinum and  lead  ore  have  combined  into  a matt.  A small  quantity 
of  glass  is  thrown  in  to  act  as  fiux,  and  by  degrees  a quantity  of 
litharge  equal  in  weight  to  the  galena  employed  is  added.  The 
sulphur  is  thus  completely  oxidized  and  expelled,  whilst  the  lead 
of  the  galena  and  tlie  litharge  is  reduced  to  the  metallic  state,  when 
it  forms  an  easily  fusible  alloy  with  the  platinum.  The  melted 
mass  is  now  left  completely  at  rest  for  some  time.  The  osmide  of 
iridium  (which  is  not  attacked  at  all  during  the  operation)  gra- 
dually sinks  to  the  bottom  of  the  liquid  alloy,  and  the  upper  por- 
tions of  the  platiniferous  lead  are  cautiously  decanted  from  it  by 
iron  ladles,  and  cast  into  ingot  moulds.  The  residue,  containing 
the  osmide  of  iridium,  is  added  to  a subsequent  melting. 

The  platiniferous  lead  is  then  submitted  to  cupellation  in  the 
ordinary  manner,  and  the  crude  metallic  platinum  left  after  cupel- 
lation is  refined  by  fusion  on  a bed  of  lime,  by  means  of  the  oxy- 
hydrogen  blowpipe : after  undergoing  this  operation  it  furnishes 
platinum,  nearly  pure,  and  very  ductile  and  malleable. 

The  alloy  of  platinum,  iridium  and  rhodium  is  well  adapted  to 
the  preparation  of  crucibles,  for  if  the  proportions  of  the  metals 
be  properly  adjusted,  this  alloy  is  harder  and  resists  a higher  tem- 
perature than  pure  platinum ; at  the  same  time  it  is  less  easily 
attacked  by  chemical  agents.  Such  an  alloy  may  be  obtained 
from  the  crude  platinum  ore  by  simply  fusing  it  by  the  oxyhy- 
drogen  blowpipe  upon  a bed  of  lime  wdth  a quantity  of  lime 
equal  in  weight  to  the  amount  of  iron  in  the  ore.  Palladium 
and  osmium  are  volatilized  during  this  process  of  fusion,  whilst 
the  copper  and  iron  become  oxidized,  and  form  fusible  compounds 
with  the  lime. 

(967)  Properties. — Platinum  is  a white  metal  susceptible  of 
high  lustre,  and  when  pure  is  about  as  hard  as  copper.  In  ducti- 
lity it  rivals  iron,  and  in  tenacity  it  is  inferior  only  to  iron,  cobalt, 
and  nickel,  and  perhaps  copper.  It  resists  the  highest  heat  of  the 
forge ; but  it  may  be  fused  by  the  voltaic  battery  or  by  the  oxy- 
hydrogen  blowpipe,  before  which  it  is  volatilized,  and  is  dispersed 
with  scintillations.  Deville  and  Debray  state  that  it  absorbs  oxy- 
gen, and  if  melted  in  considerable  masses  spits  like  silver  on  rapid 
cooling.  Attempts  to  crystallize  platinum  artificially  have  not 
succeeded,  but  very  perfect  octohedra  have  been  met  with  in  its 
native  beds.  Its  specific  gravity  difters  somewhat  with  the  mode 
of  manipulation  to  which  it  has  been  subjected,  but  it  varies  be- 
tween 21  and  22,  being  (with  the  exception  of  iridium  and  os- 
mium, which  are  equalD  dense)  the  heaviest  form  of  matter  as 
yet  known.  It  expands  less  by  heat  than  any  other  metal,  and 
in  its  power  of  conducting  heat  and  electricity  it  is  much  inferior 
to  gold  and  silver, — in  these  respects  ranking  very  near  to  iron. 


PLATINUM  BLACK USES  AND  ALLOYS  OF  PLATINUM.  703 

Platinum  does  not  undergo  oxidation  in  air  at  any  temperature : 
none  of  the  acids  have  singly  any  effect  upon  it ; aqua  regia  dis- 
solves it  though  but  slowly.  If  heated  to  redness  in  air  in  contact 
with  caustic  alkalies  or  alkaline  earths,  especially  with  hydrate  of 
lithia  or  Avith  baryta,  it  is  corroded,  owing  to  the  formation  of  an 
oxide  which  combines  with  the  alkaline  base.  When  phosphorus 
is  heated  with  spongy  platinum,  combination  between  them  takes 
place  readily.  The  attraction  of  sulphur  for  platinum  is  much 
less  poAverful.  Dry  chlorine  is  without  action  upon  this  metal, 
even  when  aided  by  heat. 

(968)  Platinum  hlach. — Platinum  may  be  obtained  in  a state 
of  subdivision  still  finer  than  that  in  which  it  is  left  on  heating 
the  double  chloride  of  platinum  and  ammonium.  In  this  form  it 
has  the  appearance  of  soot,  and  is  termed  platinum  hlacJc.  It 
may  be  procured  in  this  condition  by  several  methods,  of  which 
one  of  the  most  etficacious  consists  in  dissolving  platinous  chloride 
in  a strong  solution  of  caustic  potash,  and  adding  alcohol  to  the 
hot  liquid  which  is  placed  in  a capacious  v^essel,  and  kept  con- 
stantly stirred ; brisk  effervescence  takes  place,  owing  to  the 
escape  of  carbonic  acid ; the  platinum  is  reduced,  and  is  deposited 
as  a black  poAvder,  which  requires  repeated  washing, — first  with 
alcohol,  next  with  potash,  then  Avith  hydrochloric  acid,  and  lastly 
Avith  water.  Platinum,  in  this  finely  divided  state,  greedily  con- 
denses oxygen  from  the  air,  and  absorbs  many  times  its  bulk 
of  the  gas.  If  moistened  with  alcohol  or  ether  it  imparts  this 
oxygen  to  them,  and  forms  new  compounds,  whilst  the  poAvder 
glows  from 'the  heat  AAdiich  is  extricated.  In  all  its  states,  pla- 
tinum possesses,  in  a marked  degree,  this  property  of  condensing 
gases  upon  its  surface ; and  the  more  finely  it  is  divided,  and 
consequently  the  larger  the  surface  AAdiich  it  presents,  the  more 
striking  is  the  phenomenon. 

a Uses. — The  most  important  applications  of  platinum  are 
to  the  laboratory  of  the  manufacturing  and  experimental 
chemist ; they  depend  upon  its  great  infusibility,  and  its  poAver  of 
resisting  chemical  agents.  Its  introduction  as  a material  for  the 
construction  of  apparatus  employed  by  the  analytical  chemist  has 
contributed  in  no  small  degree  to  the  rapid  progress  of  the  science 
during  the  last  forty  or  fifty  years,  by  conferring  upon  its  experi- 
ments a precision,  neatness,  and  accuracy  till  then  unattainable. 
In  the  concentration  of  oil  of  Autriol,  large  platinum  stills  are 
frequently  employed ; some  of  these  vessels  Aveigh  u])Avards  of 
1000  ounces.  It  is  found  expedient  to  gild  these  vessels  upon  their 
inner  surface,  for,  unless  this  precaution  be  ado])ted,  the  stills 
Avhen  made  of  platinum  prepared  by  Wollaston’s  method,  after  a 
short  time  become  sufficiently  porous  to  alloAV  the  acid  to  transude. 
An  attempt  was  made  in  Dussia  to  enqdoy  platinum  for  coinage, 
but  it  was  found  to  be  inconv^enient,  and  the  ex])eriment  has  been 
abandoned.  Platinum  is  sometimes  used  for  the  touch-holes  of 
foAvling-pieces. 

Alloys. — Platinum  may  be  easily  filloyed  Avith  many  of  the 
more  fusible  metals,  the  combination  generally  taking  ]:)lace  wdth 


70^ 


OXIDES  OF  PLATINUM. 


tlie  extrication  of  liglit  and  lieat.  These  alloys  are  much  more 
fusible  than  pure  platinum  ; care  must  therefore  be  taken  not  to 
heat  the  oxides  of  easily  reduced  metals,  such  as  lead  or  bismuth, 
in  platinum  crucibles,  as  if  the  oxides  should  happen  to  be  reduced, 
the  crucible  would  be  destroyed  by  the  formation  of  a fusible 
alloy.  Most  of  the  platinum  of  commerce  contains  iridium,  which, 
M'ithout  impairing  its  power  of  resisting  chemical  agents,  increases 
its  hardness  and  durability.  It  is  remarkable,  that  though  pure 
platinum  is  perfectly  insoluble  in  nitric  acid,  yet  when  alloyed 
with  10  or  12  times  its  weight  of  silver,  both  metals  are  easily  and 
completely  dissolved  by  the  acid.  An  amalgam  of  platinum  may 
be  formed  by  acting  upon  an  amalgam  of  sodium  with  a neutral 
solution  of  the  double  chloride  of  platinum  and  sodium ; and, 
according  to  Levol,  when  this  amalgam  is  attacked  by  nitric  acid, 
the  platinum  as  well  as  the  mercury  is  partially  dissolved. 

Platinum  enters  into  combination  with  carbon  and  with  silicon : 
sometimes  in  the  fusion  of  ordinary  platinum  wire  before  the  blow- 
pipe, the  globules  of  the  melted  metal  become  covered  with  a film 
of  colourless  glass,  arising  from  the  oxidation  of  the  silicon  and 
tlie  fusion  of  the  resulting  silica.  A brittle  granular  compound  of 
platinum  and  silicon  was  accidentally  obtained  by  Daniell,  owing 
to  the  action  of  silicon  at  a high  temperature  upon  one  of  the 
platinum  bars  of  his  pyrometer.  It  appeared  to  be  formed  by  a 
kind  of  cementation,  the  silicon  being  derived  from  the  clay  of  the 
envelope  in  which  the  bar  was  heated : the  proportion  of  silicon 
amounted  to  1*5  per  cent.  A fusible  compound  of  platinum  with 
boron  was  also  obtained  by  AYohler  and  Deville. 

(970)  Oxides  of  Platinum. — There  are  two  oxides  of  plati- 
num, a protoxide  and  a binoxide.  The  protoxide  {platinous  oxide, 
PtO-  = 213,  or  PtO  = 106-5)  is  procured  by  digesting  platinous 
chloride  in  a solution  of  potash : a dark  olive-green  liquid  is  thus 
obtained,  owing  to  the  solution  of  the  oxide  in  the  excess  of  alkali. 
On  neutralizing  the  solution  with  sulphuric  acid,  a black  hydrated 
protoxide  of  platinum  subsides.  It  is  slowly  dissolved  by  acids, 
forming  unstable  salts  with  them,  and  is  readily  decomposed  by 
heat. 

The  hinoxide  {platinic  oxide,  PtO^  = 229,  or  PtO^  = 111*5) 
has  a strong  tendency  to  combine  with  alkaline  bases ; it  is  there- 
fore prepared  by  adding  to  a solution  of  nitrate  of  platinum  only 
one-half  of  the  quantity  of  carbonate  of  sodium  which  is  necessary 
for  its  complete  precipitation.  It  is  thus  procured  as  a volumin- 
ous brown  hydrate  (PtOj?  ^ 112^)5  Aom  which  water  is  expelled  at 
a gentle  heat,  whilst  the  mass  becomes  darker ; a higher  tempera- 
ture expels  the  whole  of  the  oxygen.  Hydrated  binoxide  of  pla- 
tinum is  soluble  in  solutions  of  potash  and  soda ; the  compounds 
thus  formed  may  be  obtained  in  crystals.  The  soda  compound 
consists  of  Ha^O,  3 PtO^,  6 H^O.  Binoxide  of  platinum  also  enters 
into  combination  with  other  bases,  forming  compounds  most  of 
which  are  insoluble.  The  oxide  is  also  soluble  in  acids,  and  forms 
well  characterized  salts,  the  solutions  of  which  have  a yellowish- 
brown  colour. 


SULPHIDES  AND  CHLOEIDES  OF  PLATINUM.  705 

(971)  Sulphides  of  Platinum. — Platinum  combines  with  sul- 
phur in  two  proportions,  PtS  and  PtS2. 

The  protosuljphide  (PtS)  may  be  obtained  as  a black  precipi- 
tate by  passing  sulphuretted  hydrogen  over  moistened  platinous 
chloride ; it  may  also  be  procured  by  heating  sulphur  with  the 
double  cliloride  of  platinum  and  ammonium,  when  it  assumes  the 
form  of  a grey  powder  of  metallic  appearance,  from  which  the 
sulphur  is  completely  expelled  by  heating  it  in  the  open  air. 

The  bisulphide  (PtS^)  is  best  procured  by  decomposing  the 
double  chloride  of  sodium  and  platinum  by  sulphuretted  hydro- 
gen ; it  falls  as  a dark-brown  powder,  ^hich  becomes  black  dur- 
ing desiccation.  It  is  somewhat  soluble  in  the  sulphides  of  the 
alkaline  metals.  By  ignition  in  closed  vessels  it  is  converted  into 
protosulphide.  When  exposed  to  the  air,  and  gently  heated,  it  is 
j^artially  converted  into  sulphate,  but  at  a higher  temperature  is 
wholly  decomposed,  metallic  platinum  remaining. 

(972)  Chlokides  of  Platinum. — These  correspond  in  number 
to  the  sulphides  and  oxides  of  the  metal. 

In  order  to  procure  the  platinous  chloride  (PtCl2  = 268,  or 
protochloride^  PtCl  = 134),  the  solution  of  platinum  in  aqua  regia 
should  be  evaporated,  and  the  residue  exposed  to  a heat  of  450°, 
so  long  as  any  chlorine  is  expelled ; the  compound  which  remains 
is  platinous  chloride.  It  is  of  an  olive  colour,  and  is  insoluble  in 
water  : it  is  scarcely  acted  upon  by  nitric  or  by  sulphuric  acid ; 
hydrochloric  acid  dissolves  it  when  warmed : and  it  is  dissolved 
easily  by  caustic  potash,  and  by  the  tetrachloride  of  platinum, 
with  which  latter  it  forms  a double  salt,  of  so  deep  a brown 
colour  as  to  appear  opaque  in  a concentrated  solution.  It  forms 
crystallizable  double  salts  with  the  chlorides  of  the  alkaline  metals. 

Platinic  chloride^  or  tetrachloride  (PtCl^  = 339,  or  bichloride 
of  jylatinum^  PtCl^  = 169-5) ; Comp,  in  parts.,  Pt,  58*14  ; Cl, 
41-86. — This  salt  is  obtained  by  dissolving  platinum  in  aqua  Tegia, 
and  evaporating  the  solution  to  dryness  by  means  of  a steam 
heat.*  It  is  a deliquescent  salt,  and  forms  a deep  orange-coloured 
solution  in  water,  from  which  it  may  be  obtained  crystallized  in 
prisms;  it  is  also  dissolved  largely  by  alcohol  and  by  ether. 
VVhen  heated  to  450®  it  loses  half  its  chlorine,  forming  platinous 
chloride,  and  if  the  temperature  be  further  raised,  it  is  completely 
decomposed,  and  metallic  platinum  is  left.  Tetrachloride  of  pla- 
tinum may  easily  be  reduced  to  a platinous  salt  by  transmitting 
sulphurous  acid  through  a boiling  solution  of  the  salt,  containing 
hydrochloric  acid  in  excess ; by  excess  of  sulphurous  acid  the  so- 
lution is  slowly  rendered  colourless,  when  it  contains  platinous 
sulphite  and  free  hydrochloric  acid. 

* In  an  active  laboratory  a number  of  residues  containing  platinum  gradually 
accumulate,  and  these  may  be  turned  to  account  in  the  following  manner: — The 
solutions,  mixed  with  the  precipitates,  are  evaporated  to  dryness,  and  transferred  to 
a clay  crucible,  in  which  they  are  heated  strongly,  with  free  access  of  air,  in  order 
to  burn  off  organic  matters ; after  which  the  residue  is  boiled  with  hydrochloric  acid, 
then  with  water,  and  lastly  with  nitric  acid ; a thorough  washing  with  water  follows. 
The  impurities  having  thus  been  removed,  the  residual  platinum  may  be  converted 
into  tetrachloride  by  means  of  aqua  regia. 

45 


706  BASES  DEKIYED  FKOM  THE  CHLOEmES  OF  PLATIHUM. 

With  other  chlorides,  perchloride  of  platinum  forms  nnmeroiis 
double  salts,  which  are  produced  hj  mixing  the  solutions  of  these 
chlorides  with  that  of  the  tetrachloride,  and  evaporating.  The 
double  chloride  with  potassium  (2  KCl,PtCl4  = 488,  or  KCl,  PtCl^ 
= 244;  sp.  gr.  3 '5 86)  is  a sparingly  soluble  anhydrous  compound, 
which  crystallizes  in  octohedra  ; it  is  insoluble  in  alcohol  and  in 
ether.  This  salt  is  commonly  used  as  a means  of  determining 
analytically  the  quantity  of  potassium  in  a compound  ; 100  parts 
of  this  salt  contain  Pt,  *40‘43  ; K,  15*98,  = as  19*26.  It  is 
decomposed  by  a red  heat,  into  chloride  of  potassium  and  metallic 
platinum.  The  double  chloride  of  p}latinum  and  sodium  (2  NaCl, 
PtCl^,  OH^O,  or  IIaCl,PtCl2,  6 Aq)  crystallizes  in  beautiful  red 
striated  prisms,  which  are  soluble  in  water,  alcohol,  and  ether. 
With  chloride  of  ammonium  a compound  is  formed  (2  H^NCl, 
PtCl^  = 446,  or  H4KCl,PtCl2  = 223)  very  similar  in  appearance  to 
that  with  potassium,  with  which  it  is  isomorphous  : it  is  sparingly 
soluble  in  water,  and  is  insoluble  in  alcohol  and  in  ether.  This 
salt  is  employed  in  analysis  for  determining  the  quantity  of  am- 
monia present  in  solutions  ; 100  parts  of  this  salt  contain,  Pt  44*28, 
and  7*65.  It  is  also  made  use  of  for  separating  platinum 
from  the  other  metals  with  which  it  is  associated,  after  they  have 
been  brought  into  solution  by  treating  the  ore  with  aqua  regia 
(966).  When  the  chloride  of  platinum  and  ammonium  is  ignited, 
the  ammonium  and  chlorine  are  wholly  expelled,  and  pure  plati- 
num remains  in  the  spongy  form. 

(973)  Basic  Ammoniacal  Derivatives  from  the  Chlorides  of 
Platinum. — The  action  of  ammonia  upon  platinous  chloride 
gives  rise  to  the  formation  of  several  remarkable  compound  bases, 
the  composition  of  which  offers  considerable  interest  in  a theoret- 
ical point  of  view.  Magnus  found  that  if  platinous  chloride  be 
dissolved  in  hydrochloric  acid,  the  addition  of  an  excess  of  ammo- 
nia to  the  boiling  solution  causes  the  deposition  of  brilliant,  green, 
acicular  crystals  which  are  insoluble  in  water  and  in  hydrochloric 
acid : they  contain  the  elements  of  1 atom  of  platinous  chloride, 
and  2 of  ammonia  (Pt'^Cl^IIgN’^).  This  compound,  however, 
undergoes  no  change  when  digested  at  ordinary  temperatures  in 
solutions  of  the  caustic  alkalies,  or  in  the  concentrated  acids,  but 
when  boiled  with  them  it  is  slowly  decomposed.  If  digested  in 
diluted  nitric  acid,  one-half  of  the  platinum  is  separated  as 
nitrate,  and  on  evaporating  the  solution,  a salt  is  obtained  crys- 
tallized in  small  flattened  prisms  (PtCl2lIioIl4  2 IIIIO3).  ISTeither 
the  chlorine  nor  the  platinum  can  be  detected  in  this  solution  by 
the  usual  tests.  The  nitric  acid  may  be  displaced  from  it  by 
double  decomposition  with  sulphate,  phosphate,  or  oxalate  of 
sodium,  and  a sparingly  soluble  sulphate,  phosphate,  or  oxalate 
of  the  metal  is  then  formed.  The  base  of  these  salts  (commonly 
called  Groses  salts,  from  the  name  of  their  discoverer)  has  not 
been  isolated. 

Raewsky  discovered  that  if  the  green  salt  of  Magnus  be  boiled 
with  concentrated  nitric  acid,  red  fumes  are  disengaged,  and  a 
different  salt  is  formed,  which  may  be  obtained  in  crystals  on  eva- 


BASES  DEBITED  FROM  THE  CIILOEIDES  OF  PLATmUM.  707 

poration.  The  nitric  acid  may  be  displaced  from  this  compound 
b}^  an  equivalent  quantity  of  oxalic  or  of  carbonic  acid. 

Besides  these  compounds,  other  platinum  bases  derived  from 
ammonia  have  been  obtained,  of  which  the  following  is  a brief 
account. 

Platosamine  / Beisefs  second  base  (Pt'^H4N’2,H20). — This  is  a 
greyish  mass  insoluble  in  water  and  in  ammonia,  which  may  be 
obtained  by  heating  the  hydrate  of  diplatosamine 
2 H^O)  to  230°,  so  long  as  it  gives  off  water  and  ammonia.  It 
combines  with  acids,  and  forms  salts,  most  of  which  are  insoluble, 
and  are  decomposed  on  the  application  of  heat.  Hydi^ochlorate 
of  platosamine  (Pt^'H^N^,  2 HCl)  may  be  obtained  by  heating  the 
chloride  of  the  following  base,  so  long  as  it  gives  off  water  and 
ammonia. 

Diplatosamine  j Beisefs  first  base  (Pt'TIjo^^^,  2 H^O). — This 
substance  may  be  procured  as  a hydrate  in  deliquescent  needles, 
which  are  powerfully  alkaline,  caustic,  and  absorb  carbonic  anhy- 
dride from  the  air.  It  is  usually  isolated  by  decomposing  its  sul- 
j^hate  by  its  exact  equivalent  of  hydrate  of  baryta.  In  order  to 
prepare  its  salts,  the  green  compound  of  Magnus  (Pt2Cl4lIi2MJ  is 
brought  into  solution  by  boiling  it  for  some  hours  with  a solution 
of  caustic  ammonia,  wPen  the  hydrochlorate  of  diplatosamine 
(Pt^TIjolST^,  2 HCl)  is  formed  in  the  liquid  and  crystallizes  easily. 
If  a solution  of  this  salt  be  decomposed  with  an  equivalent  of  sul- 
phate of  silver,  the  sulphate  of  diplatosamine  is  obtained,  and 
may  readily  be  procured  in  crystals  ; the  nitrate  may  be  obtained 
by  similar  means. 

Blatinamine  Gerhardt^s  hase  (Pk^'II^Hj,  4 II2O). — This  com- 
pound may  be  obtained  in  the  form  of  striated  very  brilliant 
rhomboidal  prisms  of  a yellowdsh  colour.  It  is  nearly  insoluble 
in  boiling  water,  is  not  decomposed  by  a boiling  solution  of  pot- 
ash, but  is  readily  dissolved  by  diluted  acids,  and  forms  a large 
number  of  crystallizable,  sparingly  soluble  salts,  which  are  of  a 
yellowish  colour.  Some  of  these  salts  are  neutral,  and  some  are 
acid.  Platin amine  is  usually  obtained  by  adding  ammonia  to  a 
boiling  solution  of  the  neutral  nitrate.  If  chloride  of  platosamine 
be  suspended  in  boiling  water,  and  submitted  to  a current  of 
chlorine,  it  combines  with  chlorine,  and  is  slowly  transformed  into 
hydrochlorate  of  platinamine  (PkHI^H^,  4 HCl),  and  this  by  long 
boiling  with  nitrate  of  silver  is  converted  into  basic  nitrate  of  pla- 
tinamine  (Pd^H^H,,  2 HHO3,  4 II^O). 

Diplatinamine  is  supposed  by  Gerhardt  to  be  the  base  of  the 
salts  of  Gros  and  of  Paewsky ; but  it  has  not  as  yet  been  isolated. 

The  following  table  contains  the  formulae  of  the  principal 
series  of  these  compounds  which  have  been  ascertained  to  exist  :* — 

* The  following  papers  maybe  consulted  upon  this  subject:  Gros,  Ann.  de  Chi- 
mie^  II.  Ixix.  204;  Reiset,  Ih.  III.  xi.  417;  Raewsky,  Ih.  III.  xxii.  278:  Peyrone, 
Liebig's  Annal.  li.  1,  and  Iv.  205 ; Gerhardt,  Comptes  Rendus  des  Travaiux  de  Chimie, 
par  Laurent  et  Gerhardt,  1849,  p.  113,  and  1850,  p.  273 ; Buckton,  Q.  J.  Chem.  Soc. 
V.  213,  and  vii.  22. 

These  different  bases  may  obviously  be  regarded  as  ammonias  in  which  part  of 
the  hydrogeu  in  one  or  two  atoms  of  ammonia  has  been  displaced  by  platinosum. 


708 


BASES  FEOM  THE  CHLOEIDES  OF  PLATLN  LM. 


1.  Salis  of  Plaiosamine  (Eeiset’s  second  base). 


Platosamine PtH^XO 

HTdrocblorate  of  platosa-  ) -d^tt  -sm 

■mineCveUow)....  

Xitrate  of  platosamine PtHaXO.XOp 


Ft’ 2 HCl 
FfH^Xa,  2 HXO,. 


2.  Salis  of  Dipiiiosamine  (Reiset’s  first  base). 
Diplatosamine  (hydrate  of)  PtHeX-2,0,H0  Ft  Hi  0X4,  2 H^O 


PtHsXoQ 


Hydrocblorate  of  diplatosa-  ) 

mine f 

Magnus’s  green  salt PtHeX-iCLPtCl 

Xormal  nitrate  of  diplatosa-  ? q ^q. 


Ft  H1&X4,  2 HCl 
Ft’'HioX4,  2 HCl,'Ft''Cl, 
Ft’  Hi  0X4,  2 HXO, 

^ I so,PtHeX,o,  2 CO3  Ft'’HioX4, 2 H,ee, 

3.  Salts  of  Platinamine  (Grerbardt’s  base). 

Platinamine PtHsXOa  2 HO  Ft’^HaXj,  4 HjO 

X^al  hydrocblorate  of  pla-  [ p^n^;^Q  Ft'^HoX,.  4 HQ 

tinamine ^ ‘ * *• 

Basic  nitrate  of  platinamine  | Ft-HoX^,  2 HXO3,  4 H,e 

Xormal  nitrate RH5XO2,  2 XO5  Ft^^HjXa,  4 HXO3. 

4 Salis  of  Diplaiinamine. 

Fiplatinamine  (not  isolated)  RH^XaOs  FP’^H^4,  2 H2O? 

\ 2 HCl? 

] 2 HS*0„  2 Hi© 

"■p+TI  X”  O \ 

Ft'^H;X4,  3 HX03,  H,e 
5.  Salis  obtained  by  Gros. 

Base  (not  isolated) PtClHfiX^O  Fi'^ClaHioX4,  HjO? 

~ " Fb"H,X4,  4HC1 

Fb"H;X4,  2 HCl,  2 HX0,. 


Xormal  nitrate 

Sesquiaitrate | ^ 


Hydrocblorate* PtClHgXaCl 

Xitrate* \ 


6.  Salis  obtained  by  RaewsJcy  {foirmuUB  douhtfvJ). 

Binitrate  (crystallized) PtaClHiaXiOa,  2 XO5 

Phosphate PtaClHi2X403,P0p,H0 

Bicarbonate R2ClHiaX403,  2 (iOa. 


(974:)  The  perhromvd.e  of  platinum  is  a brown  insolnble 
powder.  Periodide  of  platinum  (Ptl^). — On  adding  iodide  of  po- 
tassium to  a dilute  solution  of  tetrachloride  of  platinum  the  liquid 
assumes  a deep  wine-red  colour ; the  mixture  remains  clear  at  or- 
dinary temperatures,  but  becomes  turbid  and  deposits  a brown 
sparingly  soluble  powder  when  heated. 

Fulminating  platinum  4:  H^O)  is  procured  as  an 

insoluble  black  powder  by  dissolying  the  chloride  of  platinum  and 
ammonium  in  a solution  of  caustic  soda  and  adding  an  excess  of 
acetic  acid,  or  by  precipitating  the  sulphate  with  an  excess  of 
ammonia.  It  may  be  regarded  as  a hydrated  oxide  of  diammo- 

Ft",  or  by  platirUcum,  Ft'’' ; platosamine  and  platinamine  being  formed  upon  the  type 
of  two  atoms  of  hydrated  ammonia  (HgXaHaO)  and  diplatosamine  and  (hplatinamine 
upon  that  of  4 atoms  (Hi  2X4  2 HaO),  as  will  be  rendered  manifest  by  examining  the 
formulae  given  in  the  table. 

* Viewed  by  Gerhardt  as  perhydrochlorate  and  bichloronitrate  of  diplatinamine. 


CHARACTERS  OF  THE  SALTS,  AND  ESTIMATION  OF  PLATINUM.  Y09 

nium  in  wliicli  4 atoms  of  hydrogen  have  been  displaced  by  one 
atom  of  platinum.  Hydrochloric  acid  dissolves  this  compound, 
forming  with  it  a very  soluble  uncrystallizahle  salt : other  acids 
decompose  it  with  formation  of  ammohiacal  salts.  If  suddenly 
heated  to  about  400°  it  explodes. 

The  persulphate  of  platinum  may  be  formed  by  dissolving  the 
oxide  of  platinum  in  dilute  sulphuric  acid,  or  by  treating  the  bi- 
sulphide with  fuming  nitric  acid,  and  heating,  to  expel  the  excess 
of  nitric  acid.  The  pernitrate  may  be  formed  by  decomposing  a 
solution  of  the  persulphate  by  an  equivalent  quantity  of  the  ni- 
trate of  barium ; both  these  salts  yield  insoluble  double  basic  salts 
on  the  addition  of  an  alkali. 

(975)  Characters  of  the  Salts  of  Platinum. — 1.  The  pla- 
tinous  salts  are  unimportant. 

2.  Of  the  platinie  salts  the  tetrachloride  is  the  only  soluble 
compound  of  frequent  occurrence.  These  salts  are  distinguished  by 
the  following  characters.  When  heated  they  are  all  decomposed, 
and  leave  a residue  of  metallic  platinum.  They  have  a brownish- 
yellow  colour  in  solution : with  hydrate  of  potash^  or  with  any  of 
its  salts,  they  give  a yellow  precipitate  of  the  chloride  of  platinum 
and  potassium,  which  is  soluble  in  a large  excess  of  caustic  potash  ; 
hydrate  of  soda  precipitates  a brown  hydrated  oxide  which  is  sol- 
uble in  excess  of  the  alkali : wdth  ammonia^  or  a soluble  salt  of 
ammonium,  a yellow  chloride  of  platinum  and  ammonium  is  pre- 
cipitated, which  is  decomposed  by  heat,  leaving  metallic  platinum. 
Sulphuretted  hydrogen  and  sulphide  of  ammonium  give  a black 
sulphide,  which  is  soluble  in  a large  excess  of  the  sulphides  of 
ammonium  and  of  the  alkaline  metals. 

Solutions  of  the  salts  of  platinum  are  reduced  by  the  mercii- 
rous  nitrate^  but  not  by  ferrous  sulphate.  Stannous  chloride  in 
acid  solutions  produces  a very  deep  brown  solution,  but  yields 
no  precipitate ; iodide  of  potassium  slowly  gives  a brown  preci- 
pitate of  iodide  of  platinum  which  becomes  more  abundant  when 
heated.  The  solutions  of  the  salts  of  platinum  are  readily  re- 
duced to  the  metallic  state  by  means  of  zinc  or  iron.  Oxalic 
acid  exerts  no  reducing  action  upon  the  salts  of  platinum,  which 
may  thus  be  separated  from  those  of  gold ; and  after  the  gold  has 
been  precipitated  in  this  manner,  the  platinum  may  be  thrown 
down  in  the  metallic  form  by  boiling  tlie  liquid  wdth  a soluble 
formiate,  taking  care  first  to  neutralize  the  liquid  by  the  addition 
of  carbonate  of  sodium. 

(976)  Estimation  of  Platinum. — Platinum  may  be  estimated 
either  in  the  metallic  state,  or  in  the  form  of  a double  chloride 
of  platinum  with  potassium  or  ammonium.  Tlie  solutions  from 
which  these  double  salts  are  precipitated  should  be  concentrated  ; 
the  complete  separation  of  the  salt  is  favoured  hy  tlie  addition  of 
alcohol ; and  the  washing  of  the  precipitate  should  be  ]'>erformed 
with  dilute  alcohol.  Platinum  may  thus  be  8e]^arated  from  all 
the  metals  hitherto  described : 100  parts  of  the  double  chloride  of 
platinum  and  potassium  contain  40-43  of  the  metal ; and  100  parts 
of  the  ammoniacal  salt  contain  44*28  of  platinum. 


710 


PALLADIOI. 


§ T.  Palladium  : Pd"= 106*5,  or  Pd= 53*21:.  Sj).  Gr.  11*4 

to  11*8. 

(977)  Palladium  is  one  of  tlie  rare  metals  wliich  occur  chiefly 
in  the  ore  of  platinum,  in  which  it  was  discovered  by  AY ollaston 
in  the  year  1803.  It  usually  forms  from  a half  per  cent,  to 
one  per  cent,  of  these  ores.  According  to  G.  Pose,  palladium  is 
dimorphous,  since  it  is  found  native  in  cubes,  and  in  six-sided 
plates. 

In  order  to  extract  the  metal  from  the  ore  of  platinum,  the 
solution  of  this  ore  in  aqua  regia  is  treated  with  chloride  of  am- 
monium with  a view  to  separate  the  platinum,  as  already  described 
(966),  and  to  the  Altered  liquid,  cyanide  of  mercury  in  solution 
is  added ; a yellowish- white,  flocculent  cyanide  of  palladium  sub- 
sides ; this  is  converted  into  a sulphide  by  heating  it  in  contact 
with  sulphur,  and  the  sulphur  is  subsequently  expelled  by  repeated 
roastings.  Another  source  of  palladimn  is  the  native  alloy  which 
it  forms  with  gold,  and  which  is  found  in  the  Brazilian  mines. 
In  order  to  extract  the  palladium  from  it,  Mr.  Cock  directs  the 
alloy  to  be  fused  with  silver,  and  then  boiled  in  nitric  acid,  by 
which  all  the  metals  except  the  gold  are  brought  into  solution. 
The  decanted  liquid  is  next  mixed  with  a solution  of  common 
salt,  by  which  the  wliole  of  the  silver  is  thrown  down  in  the 
form  of  chloride,  whilst  the  palladium  with  the  other  metals 
(which  consist  principally  of  copper  with  some  lead  and  iron,) 
still  remains  dissolved.  Bars  of  metallic  zinc  are  then  introduced 
into  the  liquid,  and  these  metals  are  precipitated  upon  the  zinc 
in  the  form  of  a black  powder,  consisting  of  reduced  metal.  This 
precipitate  is  washed  and  redissolved  in  nitric  acid,  supersatm’ated 
with  ammonia,  which  dissolves  the  oxides  of  palladium  and  copper, 
while  those  of  iron  and  lead  are  precipitated : the  clear  liquid 
is  now  supersaturated  by  hydrochloric  acid.  Palladium  is  thus 
thrown  down  in  the  form  of  a yellow,  sparingly  soluble  hydi’O- 
chlorate  of  palladamine ; by  ignition  it  is  reduced,  and  aggluti- 
nates, but  does  not  fuse.  A small  quantity  of  palladium  still 
remains  in  solution,  and  may  be  recovered  by  the  introduction 
of  bars  of  iron. 

Palladium  is  a white  hard  metal  possessed  of  considerable 
ductility  and  tenacity.  It  is  not  fusible  in  an  ordinary  wind 
furnace,  but  melts  at  a lower  temperature  than  platinum.  Deville 
and  Debray  state  that,  like  silver,  it  absorbs  oxygen  when  melted, 
and  as  the  metal  cools  the  globule  spits.  Before  the  oxyhydrogen 
blowpipe  it  burns  with  scintillation,  and  if  heated  on  lime  it  is 
slowly  dispersed  in  green  vapours.  It  undergoes  no  change  in 
the  open  air  at  ordinary  temperatures ; but  at  a low  red  heat  it 
becomes  covered  with  an  iridescent  fllm,  owing  to  a superflcial 
oxidation ; on  increasing  the  heat,  the  oxygen  is  expelled,  and  the 
metal  resumes  its  brilliant  surface.  Palladium  is  dissolved  when 
lieated  in  nitric  acid,  or  in  aqua  regia,  but  it  is  acted  upon  by  the 
other  acids  with  difficulty.  AYhen  fused  either  with  acid  sulphate 
of  potassium,  with  nitre,  or  with  the  hydrated  alkalies,  it  is  oxi- 


OXIDES,  SULPHIDES,  AXD  CHLOKEDES  OF  PALLADIUM.  711 

dized.  If  a solution  of  iodine  in  alcohol  be  evaporated  on  a slip 
of  palladium,  a stain  is  left,  by  which  this  metal  is  at  once  dis- 
tinguished from  platinum.  P alladium  combines  readily  with  gold, 
which  is  rendered  brittle  by  its  presence  even  in  small  proportion. 
It  has  a remarkable  power  of  whitening  the  colour  of  gold,  even 
though  present  in  the  mixture  only  in  small  quantity ; and  when 
it  forms  20  per  cent,  of  the  mass,  the  alloy  is  quite  white.  If 
alloyed  with  twice  its  weight  of  silver  it  forms  a ductile  compound 
which  is  not  liable  to  tarnish,  and  is  well  adapted  for  the  con- 
struction of  small  weights.  When  melted  with  8 times  its  weight  of 
tin,  at  a red  heat,  an  alloy  is  formed  (PdgSn^),  which  is  obtained 
in  beautiful  brilliant  lamellae  on  digesting  the  mass  when  cold 
in  hydrochloric  acid.  Palladium  has  been  applied  in  a few  cases 
to  the  construction  of  graduated  scales  for  astronomical  instru- 
ments, for  which,  by  its  whiteness,  hardness,  and  inalterability  in 
air,  it  is  well  adapted. 

(978)  Oxides  of  Palladium. — This  metal  appears  to  form 
three  oxides : a suboxide,  Pd^O,  which  furnishes  a series  of  salts 
resembling  those  of  suboxide  of  copper,  and  which,  according  to 
Kane,  is  obtained  by  heating  the  hydrated  protoxide  to  incipient 
redness  ; a protoxide,  PdO,  which  is  the  base  of  the  ordinary  salts 
of  the  metal ; and  a binoxide,  PdO^. 

11\\Q  protoxide  (PdO=122’5,  or  PdO =61  *2)  may  be  procured 
as  a black  powder,  by  heating  the  nitrate  to  low  redness ; or  it 
may  be  obtained  upon  adding  carbonate  of  potassium  or  of  sodium 
to  its  salts,  as  a dark  brown  hydrate,  soluble  both  in  acids  and  in 
alkalies,  and  from  which  the  water  may  be  expelled  by  heat.  At 
a bright  red  heat  it  loses  its  oxygen. 

The  hinoxide  (PdO^)  is  prepared  by  decomposing  the  solid 
double  chloride  of  palladium  and  potassium  by  a solution  of  caustic 
potash  ; it  forms  a yellowish-brown  hydrate,  which  obstinately 
retains  a portion  of  alkali : it  is  soluble  in  the  alkalies  : by  boiling 
it  with  water  it  is  rendered  anhydrous,  and  is  then  deposited  as  a 
black  powder. 

Sulphide  of  Palladium  (PdS)  may  be  formed  either  directly, 
by  heating  powdered  sulphur  with  palladium  or  by  precipitating 
tlie  salts  of  tlie  protoxide  by  means  of  sulphuretted  hydrogen  ; 
it  forms  a fusible,  greyish- white,  lustrous  mass,  from  which  patient 
roasting  in  air  expels  the  sulphur. 

If  a piece  of  palladium  foil  or  wire  be  held  in  the  flame  of  a 
spirit-lamp,  soot  is  speedily  deposited  in  large  quantity,  the  foil  or 
wire  is  corroded,  and  the  mass  of  soot  is  found  to  contain  palladium 
throughout,  owing  to  the  formation  of  a carbide  of  the  metal. 

(979)  Palladious  chloride^  or  Chloride  of  palladium  (PdCl^,  or 
PdCl)  is  obtained  by  evaporating  to  dryness  a solution  of  ])alladium 
in  aqua  regia ; it  forms  brown  hydrated  crystals  which  become 
black  when  the  water  is  expelled  : if  heated  to  redness  metallic 
palladium  is  left.  Chloride  of  ]>alladium  forms  double  salts  with 
the  soluble  chlorides  ; those  with  potassium  and  ammonium  are 
dark  bottle-green.  AVith  ammonia,  chloride  of  palladium  forms 
a series  of  compounds  analogous  to  those  of  platinum  (973) : one 


712 


SALTS  OF  PALLADIUM. 


of  palladainine^  (PdHey2)0  is  a crystallizable  powerfully 
alkaline  base.  The  perchlo'ride  of  palladium  (PdCl^  or  PdClg) 
exists  in  solution  in  aqua  regia,  but  cannot  be  obtained  in  crystals  : 
it  forms  double  salts  with  the  chlorides  of  the  alkaline  metals  ; the 
double  salt  with  potassium  crystallizes  in  ruby  red  prisms. 

Iodide  of  Palladium  (PdP^SdO'S  or  Pdl=180'2) : Comp,  in 
100  parts  Pd,  30-0  ; I,  TO'O. — This  compound  is  obtained  by  add- 
ing a solution  of  a salt  of  palladium  in  slight  excess  to  one  of  iodide 
of  potassium.  It  is  a black  powder,  insoluble  in  water  but  soluble 
in  ammonia,  and  in  a solution  of  iodide  of  potassium  ; a solution  of 
palladium  is  sometimes  employed  as  a precipitant  for  iodine  when 
it  is  necessary  to  separate  iodine  from  chlorine  and  bromine 
(541).  Iodide  of  palladium  loses  its  iodine  when  strongly  heated. 

Cyanogen  has  a stronger  attraction  for  palladium  than  for  any 
other  metal,  so  that  a salt  of  palladium  will  decompose  even  cya- 
nide of  mercury.  This  cyanide  is  procured  as  a yellowish  precipi- 
tate by  adding  potassium  to  neutral  solutions  of  any  of  the  salts 
of  palladium  ; it  is  soluble  in  ammonia,  in  acids,  and  in  cyanide 
of  potassium  ; it  forms  a series  of  double  cyanides. 

The  Sulphate  of  palladium  (PdSO^,  or  Pd0,S03)  may  be  ob- 
tained by  decomposing  the  nitrate  by  sulphuric  acid,  or  by  dis- 
solving the  oxide  in  sulphuric  acid.  It  is  a deliquescent  salt 
which  forms  a deep  brownish-red  solution ; when  heated  it  loses 
acid,  and  furnishes  a basic  salt. 

The  nitrate  is  formed  by  boiling  nitric  acid  on  palladium  : it 
may  be  obtained  in  rhombic  prisms ; they  are  freely  soluble  in  a small 
quantity  of  water,  and  yield  a deep  reddish-bro^vn  liquid  ; but  on 
being  largely  diluted,  the  normal  salt  is  decomposed,  and  an  in- 
soluble basic  nitrate  is  precipitated.  If  ammonia  in  excess  be 
added  to  the  solution  of  the  nitrate,  an  ammoniacal  nitrate  of 
palladium  may  be  crystallized  from  it  in  rectangular  tables. 

(980)  Characters  of  the  Salts  of  Palladium. — The  proto- 
salts, or  ordinary  salts  of  palladium,  form  either  brown  or  red 
solutions,  which  when  neutral  are  distinguished  by  the  yellowish 
precipitate  of  cyanide  of  palladium,  formed  on  adding  cyanide  of 
mercury.  The  fixed  hydrated  alkalies  precipitate  compounds  of 
palladium  in  the  form  of  a red  or  orange  basic  salt,  which  is  solu- 
ble in  excess  of  the  alkali  by  the  aid  of  heat.  Ammonia  and  its 
carljonate^  when  added  to  a solution  of  palladious  chloride,  give  a 
fiesh-colom’ed  precipitate,  soluble  in  excess  of  ammonia,  titrate 
of  palladium  gives  a brown  precipitate  with  ammonia.  Carbonates 
of  potassium  and  sodium  yield  a brown  precipitate  of  the  hydrated 
oxide,  with  salts  of  palladium.  Iodide  of  potassium  precipitates 
a black  iodide  of  palladiun.  Suljyhuretted  hydrogen  and  sulphide 
of  ammonium  throw  down  a black  sulphide  of  palladium,  insoluble 
in  the  sulphides  of  the  alkaline  metals.  Solutions  of  the  salts  of 
palladium  are  reduced  by  a solution  of  green  sulphate  of  iron ^ and 
by  many  of  the  metals,  the  reduction  being  facilitated  by  heat. 
Stannous  chloride  produces  a dark  brown  precipitate,  which  is 
soluble  in  hydrochloric  acid,  forming  an  intensely  green  solution, 
which  becomes  reddish-brown  on  dilution. 


EHODIDIVI. 


Y13 


Palladium  may  be  separated  from  all  other  metals,  except 
copper  and  lead,  by  the  addition  of  the  cyanide  of  mercury  to  the 
solution  previously  neutralized  by  means  of  carbonate  of  sodium. 
The  cyanide  of  palladium  when  ignited  in  the  air  leaves  metallic 
palladium. 

§ YI.  RHonnjM : Ro'"=104:*3,  or  Ro=:52T6.  Sp.  Gr.  12T. 

(981)  Rhodium  was  discovered  by  Wollaston  in  1803.  It 
usually  forms  about  one-half  per  cent,  of  the  ore  of  platinum ; it 
may  be  extracted  from  the  solution  of  this  ore  in  aqua  regia  after 
the  platinum  and  palladium  have  been  separated  by  the  addition 
of  sal  ammoniac  and  cyanide  of  mercury : the  excess  of  cyanide 
of  mercury  is  then  decomposed  by  acidulating  the  solution  with 
hydrochloric  acid,  adding  common  salt,  and  evaporating  to  dry- 
ness ; the  chloride  of  sodium  thus  forms  double  chlorides  with  all 
the  metals  in  solution  ; the  residue  is  treated  with  alcohol  (of  sp. 
gr.  0*837),  which  dissolves  all  these  double  salts,  except  that  of 
sodium  and  rhodium,  which  remains  behind  as  a red  powder  : this 
is  dissolved  in  water,  and  the  rhodium  thrown  down  in  a pulveru- 
lent form  by  means  of  bars  of  metallic  zinc.  The  chloride  of 
sodium  and  rhodium  may  also  be  decomposed  by  heating  it  in  a 
current  of  hydrogen  gas,  when,  on  crashing  the  mass  with  water, 
the  rhodium  is  left  in  a pulverulent  form. 

Rhodium  is  a white,  very  hard  metal ; when  quite  pure,  it  is 
malleable  after  fusion  upon  lime,  and  it  then  has  a sp.  gr.  of  12*1. 
It  requires  a stronger  heat  to  fuse  it  than  platinum,  and  when 
melted  has  a similar  tendency  to  absorb  oxygen,  and  to  spit  as  the 
globule  sets. 

Deville  says  that  rhodium  furnishes  an  alloy  with  platinum, 
which  is  easily  worked  ; when  the  proportion  of  rhodium  forms  30 
per  cent,  or  upwards  of  the  alloy  it  is  not  attacked  by  aqua  regia. 
When  pure,  rhodium  is  insoluble  in  the  acids,  though  if  alloyed 
in  small  quantity  with  platinum,  copper,  bismuth,  or  lead,  it  is 
dissolved  with  them  in  nitrohydrochloric  acid.  Rhodium  has  a 
considerable  attraction  for  oxygen,  and  may  be  oxidized  by  fusion 
with  a mixture  of  nitre  and  carbonate  of  potassium ; acid  sulphate 
of  potassium  also  oxidizes  the  metal  and  forms  a soluble  double 
sulphate  of  rhodium  and  potassium,  whilst  sulphurous  anhydride 
escapes.  If  heated  in  contact  with  chloride  of  sodium,  in  a cur- 
rent of  chlorine,  a soluble  double  chloride  of  sodium  and  rhodium 
is  produced. 

(982)  Oxides  of  Rhodium.  — Rhodium  has  a considerable 

attraction  for  oxygen  : it  appears  to  form  two  definite  oxides, 
RoO,  and  RO2O3,  besides  some  compounds  intermediate  between 
them.  jprotoxide^  however,  has  not  been  obtained  in  a state 

of  purity. 

Jihodic  oxide,  or  Sesquioxide  of  rhodium  (Ro20j=252*6,  or 
Ro303=128*3). — This  is  tlie  only  salifiable  oxide  of  rhodium  ; it 
may  be  procured  by  heating  rhodium  witli  a mixture  of  nitre  and 
carbonate  of  potassium  ; the  oxide  forms  an  insoluble  compound 


714:  CHARACTERS  OF  THE  SALTS  OF  RHODIUM. 

with  potash,  which  is  to  be  well  washed,  and  decomposed  by 
digestion  with  hydrochloric  acid : the  sesquioxide  is  thus  left  as  a 
greenish-grey  hydrate  which  is  insoluble  in  all  acids. 

Sulphides. — Khodium  forms  two  sulphides,RoS  and  l^o^Sg. 

If  the  metal  be  heated  in  the  vapour  of  sulphur,  the  two  bodies 
unite  with  incandescence,  and  form  i\\Q  protosuljMde,  which  has 
a bluish-grey  colour,  and  fuses  at  a very  high  temperature ; the 
sulphur  burns  off  in  the  open  air,  and  leaves  a forgeable  mass  of 
metallic  rhodium.  The  sesquisulphide  may  be  obtained  in  the 
form  of  a brown  hydrate  by  decomposing  a hot  solution  of  the 
double  chloride  of  sodium  and  rhodium  by  means  of  sulphide  of 
potassium  or  of  sodium. 

Chlorides  of  Khodium. — Three  of  these,  viz.,  KoCl^ ; Ko^Clg ; 
and  K0CI3,  are  stated  by  Berzelius  to  exist,  but  the  last  is  the 
only  one  of  importance. 

Terchloride  of  rhodium  (K0CI3),  or  sesquichloride  (K02CI3), 
is  formed  by  decomposing  the  chloride  of  potassium  and  rhodium 
by  silicofiuoric  acid,  which  separates  the  potassium  as  a gelatin- 
ous silicofluoride  ; the  filtered  liquid  when  evaporated  to  dryness 
leaves  the  terchloride  of  rhodium.  This  chloride  unites  with 
many  of  the  soluble  chlorides  to  form  crystallizable  double  salts, 
which  are  of  a ruby  or  rose  colour  (whence  the  metal  receives  its 
name,  from  p6(^ov,  a rose) : the  sodium  salt  crystallizes  in  cubes  or 
in  octohedra,  which  are  effiorescent  in  the  air  (3  IsraCl,RoCl3, 
9 H^O,  or  3 KaCl,Ko2Cl3,  18  Aq) ; they  are  insoluble  in  alcohol. 
When  terchloride  of  rhodium  is  supersaturated  with  ammonia, 
the  precipitate  formed  at  first  is  redissolved,  and  a characteristic 
yellow  compound,  consisting  of  (K0CI3,  5 H3K)  is  formed  by  boil- 
ing, and  may  be  purified  by  evaporation  and  re-crystallization. 
This  compound  when  ignited,  leaves  pure  rhodium  in  the  form  of 
a powder. 

(983)  Characters  of  the  Salts  of  Khodium. — The  double 
chloride  of  sodium  and  rhodium  is  the  best  known  of  these  com- 
pounds. The  salts  corresponding  to  the  sesquioxide  of  the  metal 
generally  form  rose-coloured  solutions ; they  are  decomposed  by 
iron  or  zinc,  which  causes  a deposit  of  metallic  rhodium.  Hy- 
drates of  potash  and  soda  slowly  occasion  a precipitate  of  yellow 
hydrated  oxide,  which  obstinately  retains  a portion  of  the  alkali ; 
it  is  soluble  in  the  excess  of  the  alkali  as  well  as  in  acids ; if 
alcohol  be  added  to  the  alkaline  solution  a black  precipitate  gradu- 
ally occurs  without  applying  heat.  Iodide  of  potassium  throws 
down  a sparingly  soluble  yellow  iodide  of  rhodium.  Sulphuretted 
hydrogen^  when  the  solution  is  heated,  slowly  forms  a brown 
precipitate  insoluble  in  the  alkaline  sulphides.  The  soluble  sul- 
phites give  a characteristic  pale  yellow  precipitate.  If  the  salts  of 
rhodium  be  heated  in  a current  of  hydrogen,  the  metal  is  readily 
reduced : in  this  form  it  is  insoluble  in  aqua  regia,  but  if  it  be 
fused  with  acid  sulphate  of  potassium,  a double  salt  is  formed 
which  is  soluble  in  water,  with  a pink  colour. 


RUTHENIUM. 


715 


§ YII.  Ruthenium  : 104*2,  or  Ru= 52*11. 

Sp.  Gr.^  from  11  to  11*4. 

(984)  Treatment  of  the  Platimim  residue. — After  the  platinum 
ore  has  been  exhausted  with  aqua  regia,  a residue  is  obtained 
which  frequently  contains  both  titaniferous  iron  and  chrome  iron ; 
hut  its  most  important  constituent  is  an  alloy  in  flat  plates  or 
scales  of  a white  colour  and  metallic  lustre.  This  was  formerly 
considered  to  be  an  alloy  of  osmium  and  iridium.  It  has,  however, 
been  found  to  consist  of  four  metals — viz.,  osmium,  iridium,  ruthe- 
nium, and  a small  quantity  of  rhodium. 

Fremy  in  separating  the  difierent  metals  contained  in  this  res- 
idue avails  himself  of  the  oxidability  of  osmium  and  the  volatility 
of  its  tetroxide.  His  process  is  the  following : — About  3000  grains 
of  the  platinum  residue  placed  in  a porcelain  or  platinum  tube, 
and  heated  to  redness,  is  roasted  in  a current  of  dry  air ; in  the 
portion  of  the  tube  which  projects  from  the  furnace  some  frag- 
ments of  porcelain  are  placed,  and  the  tube  is  connected  with  a 
series  of  glass  flasks  for  the  purpose  of  condensing  the  tetroxide 
of  osmium  as  it  distils  ; in  the  last  flask  a solution  of  caustic  pot- 
ash is  placed  in  order  to  retain  such  portions  of  the  tetroxide  as 
may  have  escaped  condensation  ; and  this  flask  is  connected  with 
an  aspirator,  by  means  of  which  a current  of  atmospheric  air  is 
maintained  through  the  apparatus.  The  air  is  dried,  and  freed 
from  organic  particles  before  it  enters  the  heated  tube,  by  causing 
it  to  pass  through  tubes  filled  with  pumice  moistened  with  sul- 
phuric acid.  During  the  operation  the  osmium  and  ruthenium 
become  oxidized  ; the  tetroxide  of  osmium  condenses  in  beautiful 
needles  in  the  flasks,  and  mechanically  carries  forward  the  binox- 
ide  of  ruthenium,  which  is  deposited  upon  the  fragments  of  por- 
celain in  regular  square  prisms.* 

The  fixed  residue  consists  of  an  alloy  of  iridium  and  rhodium, 
mixed  with  a little  osmium  and  ruthenium.  This  is  to  be  fused 
with  caustic  potash,  by  which  the  oxide  of  ruthenium  is  removed 
and  is  dissolved  out  on  washing  the  fused  mass  with  water.  The 
undissolved  portion  is  ignited  with  four  times  its  weight  of  nitrate 
of  potassium,  and  the  product  is  treated  with  boiling  water,  which 
dissolves  the  osmium,  and  on  cooling  often  deposits  it  in  octohe- 
dral  crystals  as  osmite  of  potassium.  The  residue  now  contains 
only  sesquioxides  of  iridium  and  rhodium  in  combination  witli  pot- 
ash. Aqua  regia,  when  boiled  upon  it,  converts  most  of  the  iri- 
dium into  the  soluble  perchloride  ; a solution  of  chloride  of  potas- 
sium is  added  to  the  liquid,  after  whicli  crystals  of  the  double 
chloride  of  iridium  and  potassium  are  deposited  as  it  cools.  The 
sesquioxide  of  rhodium,  which  is  left  undissolved,  since  it  is  insol- 
uble in  aqua  regia,  is  converted  into  a soluble  double  salt  by 
mixing  it  intimately  with  an  equal  weight  of  chloride  of  sodium, 

* Sometimes  the  osmide  of  iridium  does  not  readily  undergo  oxidation.  In  such 
a case  Deville  fuses  it  with  8 or  10  times  its  weight  of  zinc,  and  heats  it  for  some 
hours  to  full  redness ; he  then  dissolves  out  the  zinc  by  hydrochloric  acid,  which 
leaves  the  platinum  metals,  in  the  form  of  a line  black  powder,  which  is  very  easily 
oxidized  in  a current  of  air. 


716  , 


COMPOUNDS  OF  EUTHENICM OSMIUM. 


and  heating  the  mass  to  dull  redness  in  a cnn’ent  of  dry  chlo- 
rine. 

(985)  Euthentum  is  a metal  which,  in  1845,  was  shown  by  Clans 
to  exist  in  the  ore  of  platinum.  It  is  very  hard,  and  brittle,  and 
is  scarcely  fusible  even  before  the  oxyhydrogen  blowpipe.  The 
melted  metal,  according  to  Deville  and  Debray,  has  a sp.  gr.  of 
from  11  to  IIT.  It  absorbs  oxygen  at  a red  heat,  and  the  oxide 
so  obtained  is  not  decomposed  by  simple  elevation  of  temperature. 
The  metal  is  readily  oxidized  by  fusion  with  nitre,  or  with  caustic 
potash.  Euthenium  accompanies  the  alloy  of  osmium  and  iridium 
in  a proportion  varying  from  3 to  6 per  cent.  ; but  it  is  not  found 
in  the  portion  of  platinum  ore  which  is  soluble  in  aqua  regia.  It 
is  most  easily  obtained  by  Eremy’s  process  (981).  The  binoxide 
of  ruthenium  is  not  volatile  wEen  heated  alone,  but  is  carried  for- 
ward mechanically  by  the  tetroxide  of  osmium,  and  becomes  con- 
densed in  crystals  near  to  the  source  of  heat.  By  heating  this 
oxide  in  a current  of  hydrogen,  the  metal  is  obtained  in  the  form 
of  a dark-grey  powder.  The  metal  forms  an  alloy  with  tin,  Eu 
Sn^,  which  crystallizes  in  cubes  of  perfect  regularity. 

Euthenium  forms  four  compounds  with  oxygen,  EuO;  Eu„0  * 
EuO,;  and  EuO^. 

Ruthenic  anhydride^  or  ruthenic  add  (EuOg),  is  insoluble  in 
water : it  may  be  obtained  by  heating  any  of  the  preceding  oxides 
with  nitre ; the  rutheniate  of  potassium  forms  an  orange-yellow 
solution  in  water.  The  sesquioxide  is  the  most  stable  of  the  oxides 
of  the  metal ; it  is  obtained  in  the  anhydrous  form  by  igniting  the 
metal  in  a current  of  air.  It  is  insoluble  in  the  alkalies : but 
with  acids  it  forms  soluble  salts  which  have  a yellow  colour. 
The  alkalies  precipitate  the  hydi'ated  oxide  (Ru^Og,  3 H^O)  from 
these  solutions  as  a bulky  blackish -brown  powder. 

There  are  three  chlorides  of  ruthenium,  RuClg ; RuCla ; and 
RuCl^.  The  terchloride  is  obtained  by  dissolving  the  sesquioxide 
in  hydrochloric  acid:  on  evaporation  it  yields  a greenish-blue 
deli<'juescent  mass,  which  is  soluble  in  alcohol.  Sidphuretted 
hydrogen  causes  a brown  precipitate  of  sulphide  of  ruthenium  in 
solutions  of  the  terchloride,  leaving  a supernatant  liquid  of  a fine 
blue  colour,  probably  owing  to  the  formation  of  a lower  chloride 
of  the  metal ; this  reaction  is  very  delicate,  and  characteristic  of 
ruthenium.  Metallic  zinc  also  reduces  the  yellow  terchloride  to 
the  blue  bichloride,  and  ultimately  precipitates  the  metal  as  a 
black  powder.  Formiate  or  oxalate  of  sodhtm^  if  boiled  with  salts 
of  ruthenium,  renders  the  solution  colourless,  but  does  not  occa- 
sion any  precipitate  of  reduced  metal.  With  acetate  of  lead  a 
purplish-red  characteristic  precipitate  is  formed.  Cyanide  of  mer- 
cury renders  the  solution  blue,  whilst  a blue  precipitate  is  formed. 
The  caustic  and  carbonated  alkalies  yield  a black  precipitate  of 
the  sesquioxide,  insoluble  in  excess  of  the  precipitant. 

§ YIII.  Osmium:  es=199,  or  Os=r99-41.  Sp,  Gr.  21*4. 

(986)  Osmium  occurs  associated  with  platinum  in  the  form  of 


OSmUM OXIDES  OF  OSMIUM. 


71T 


an  alloy  of  osmium,  iridium,  and  ruthenium.  It  was  discovered 
in  the  ore  of  platinum  by  Tennant,  in  1803.  Osmium  may  be 
obtained  in  the  metallic  condition  by  several  processes.  One  of 
the  simplest  consists  in  treating  volatile  oxide  of  osmium  (OsO^) 
obtained  by  Fremy’s  method  (984)  with  hydrociiloric  acid  and 
metallic  mercury.  Calomel  is  thus  produced  by  the  decomposition 
of  the  mercurous  oxide,  which  is  formed  at  the  expense  of  the 
oxygen  contained  in  the  oxide  of  osmium ; OsO^d-  8 IIg  + 8 HC1= 
Os  + 8 HgCl  + 4 HjO.  The  water  and  the  superfluous  acid  are 
expelled  by  evaporation  to  dryness,  and  on  heating  the  residue  in 
a small  porcelain  retort,  the  excess  of  mercury  and  calomel  are 
driven  off,  leaving  pure  osmium  in  a pulverulent  form.  In  this 
finely  divided  state,  it  emits  the  odour  of  tetroxide  of  osmium, 
when  exposed  to  a moist  atmosphere ; it  takes  iire  when  heated 
in  the  open  air,  and  is  dissolved  by  strong  nitric  acid,  or  by  aqua 
regia,  being  converted  into  tetroxide  of  osmium.  After  ignition, 
however,  it  is  no  longer  soluble  in  the  acids.  The  specific  gravity 
of  osmium  in  the  pulverulent  form  is  about  10,  but  after  it  has 
been  heated  to  the  fusing-point  of  rhodium  in  the  oxyhydrogen 
jet,  it  acquires  a sp.  gr.  of  21 ’4.  In  order  to  obtain  compact 
osmium,  Deville  and  Debray  oxidize  the  alloy  of  osmium  and 
iridium  by  mixing  it  intimately  with  5|-  times  its  weight  of  per- 
oxide of  barium,  heating  it  to  a bright  red  for  2 hours,  after 
which  they  distil  with  a mixture  of  eight  parts  of  hydrochloric 
and  one  of  nitric  acid.  The  tetroxide  of  osmium  which  passes 
over  is  received  into  a solution  of  ammonia,  supersaturated  with 
sulphuretted  hydrogen,  and  boiled.  The  sulphide  of  osmium  is 
separated  by  filtration,  dried  at  a low  temperature,  placed  in  a 
crucible  of  gas-coke,  which  is  enclosed  in  a clay  crucible  and  luted 
down,  and  then  exposed  for  4 or  5 hours  to  a heat  sufficient  to 
melt  nickel.  The  osmium  is  reduced,  and  furnishes  a brittle  mass, 
the  colour  of  which  has  more  of  a bluish  cast  than  that  of  zinc. 
At  a still  higher  temperature  in  the  oxyhydrogen  jet,  at  the  fusing- 
point  of  rhodium,  it  becomes  still  denser.  It  may  be  heated  in 
this  condition  to  the  fusing-point  of  zinc  without  emitting  vapour, 
but  it  takes  fire  at  a higher  temperature.  If  heated  with  7 or  8 
times  its  weight  of  tin  in  a charcoal  crucible  to  a full  red  heat, 
the  osmium  is  dissolved  by  the  tin,  and  crystallizes  out  on  slow 
cooling.  On  treating  the  mass  with  hydrochloric  acid,  the  os- 
mium is  left  as  very  hard  crystalline  powder.  It  may  also  be 
combined  with  zinc,  and  on  dissolving  the  zinc  in  hydrochloric 
acid  the  osmium  is  left  as  an  amorplious  combustible  powder. 
Osmium  appears  to  be  the  least  fusible  of  the  metals.  In  the  oxy- 
hydrogen jet  platinum  is  volatilized,  and  iridium  and  ruthenium 
undergo  fusion,  but  osmium  does  not  melt,  though  it  is  volatilized 
by  the  intense  heat. 

Osmium  differs  remarkably  from  the  other  metals  of  this 
group,  and  presents  more  analogy  with  arsenic  and  antimony  than 
with  the  noble  metals. 

(987)  Five  OxroES  of  Osmium  are  known: — OsO;  Os^Og ; 
OsO, ; OsOj ; OsO,.  The  anhydrous  protoxide  of  osmium  is  of 


OXIDES  OF  OSMITM. 


71 S 

a grev-black.  and  insoluble  in  acids : its  blnish-black  hydrate  is 
soluble  in  hydrochloric  acid,  forming  a deep  indigo-blue  solution 
of  chloride.  OsCl^,  which  absorbs  oxygen  rapidlv,  and  becomes 
converted  into  the  chloride  OsCh.  The  sesquioxide  has  not  been 
isolated:  it  forms  rose-red  uncry stallizable  salts.  The  hinoxide 
is  black.  The  teroxide  possesses  a feebly  acid  character ; it  cannot 
be  isolated,  but  it  forms  a crystalline  compound  with  potassium 
{osmite  of  pota-sdum,  K.OsO^,  2 H.O.  or  KO.OsO.  . 2 Aq),  which 
is  sparingly  soluble.  This  compound  furnishes  a good  source  of 
pure  osmium.  It  is  easily  obtained  by  the  addition  of  a httle 
alcohol  to  a solution  of  the  tetroxide  of  osmium  in  potash : the 
osmite  separates  in  large  rose-coloured  octohedra.  which  are  per- 
manent in  a dry  air,  but  absorb  oxygen  if  moist.  If  this  salt  be 
digested  in  a solution  of  chloride  of  ammonium,  a yeUow  sparingly 
soluble  salt  is  formed  (2  H^XCl.OsO.H^A,).  which,  when  ignited 
in  a current  of  hydrogen,  leaves  pure  osmium. 

Tetroxide  of  osmium^  or  osraic  acid  (OsO^ ; JToh  vol.  ■ ; 
sj?.  gr.  of  vapour,  S’SS » is  the  volatile  compound  which  is  produced 
when  the  metal  is  heated  with  nitre,  or  when  roasted  in  air  : it 
forms  colourless,  acicular.  transparent,  flexible  crystals  which  are 
readily  fusible,  and  are  freely  soluble  in  water  ; it  boils  at 
about  212°,  emitting  an  extremely  irritating  and  deleterious  va- 
pour. with  a pungent  characteristic  odour  somewhat  resembling 
that  of  chlorine  : hence  the  name  of  the  metal  osmium  (from  ocixii, 
odour ) : it  does  not  combine  with  acids  ; but  though  it  unites  with 
the  alkalies,  its  solution  does  not  redden  litmus,  and  its  solutions 
in  the  alkalies  give  olf  tetroxide  when  boiled.  It  produces  a per- 
manent black  stain  upon  the  skin  when  touched,  owing  to  the 
partial  reduction  of  the  metal,  and  gives  a characteristic  blue  pre- 
cipitate when  its  solutions  are  mixed  with  tincture  of  ^alls.  Ac- 
cording to  Fremy.  another  oxide  of  osmium  f)  exists,  but  it 

is  very  unstable  ; it  forms  compounds  with  potash  and  soda  which 
have  a dark-brown  colour ; they  sometimes  crystallize  from  con- 
centrated alkaline  solutions. 

If  the  aqueous  solution  of  tetroxide  of  osmium  be  treated  with 
sulphuretted  hydrogen,  an  immediate  precipitate  of  the  black  hy- 
drated tetra-sidphide  occurs,  which  is  slightly  soluble  in  solutions 
of  the  sulphides  of  the  alkaline  metals.  Four  inferior  degrees  of 
sulphur ation  of  osmium  also  exist ; they  correspond  in  composition 
with  the  oxides.  These  sulphides  are  decomposed  by  prolonged 
ignition,  and  pure  osmium  is  left. 

(9SS » There  are  four  chlorides  of  osrrtium,  viz. — OsCl, : OsCl, ; 
OsCl^ : OsCl^:  the  osmious  suhchloride,  (OsClj)  or  protochloride  ^ 
is  green,  and  sublimes  in  green  needles ; it  is  produced  by  heating 
powdered  osmium  in  a current  of  chlorine  : the  double  salts  which 
it  forms  are  of  a green  colour.  The  osrnic  subchloride  (0sCl,).  or 
bichloride,  is  fonned  in  the  same  way  as  osmious  subchloride,  by 
employing  an  excess  of  chlorine ; it  is  more  volatile,  and  con- 
denses as  a red.  crystalline,  fusible,  deliquescent  powder : both 
this  and  the  preceding  chloride  are  dissolved  by  water,  which  soon 
decomposes  them,  forming  tetroxide  of  osmium  and  hydrochloric 


SALTS  OF  OSmUM miDIUM. 


719 


acid,  and  depositing  metallic  osmium.  Osmic  siibchloride  forms 
with  chloride  of  potassium  a beautiful  sparingly  soluble  red  salt, 
which  furnishes  octohedral  crystals  (2  KCljOsCl^,  or  KCl,OsCl2); 
this  salt  is  obtained  by  heating  a mixture  of  osmium  with  chlo- 
ride of  potassium  in  a current  of  chlorine  : it  is  isomorphous 
with  the  corresponding  platinum  salt,  and  yields  a characteristic 
dark  olive-green  precipitate  with  nitrate  of  silver  (2  AgCljOsCl^ ; 
Claus).  Mercurous  nitrate  gives  with  it  a reddish-brown  preci- 
pitate : tannic  acid  gives  with  it,  when  heated,  a dark-blue 
solution,  and  ferrocyanide  of  potassium,  a chrome-green  liquid, 
passing  into  dark  blue. 

Double  salts  may  also  be  formed  which  contain  both  osmious 
chloride  (OsClg)  and  osmic  chloride  (OsClg). 

A compound  of  nitrogen,  oxygen,  and  osmium  was 

formed  by  Fritsche  and  Struve.  It  may  be  obtained  by  acting  upon 
a mixture  of  caustic  potash  and  ammonia  by  means  of  tetroxide 
of  osmium  : these  chemists  termed  it  osman-osmic  acid.  With  the 
alkalies  it  forms  yellow  crystalline  compounds,  which  detonate  rea- 
dily when  they  are  struck  or  suddenly  heated.  The  potassium  salt 
may  be  represented  by  the  formula,  K20s2]^2^5,  orKO,  OsjNO^. 

The  properties  of  the  salts  of  osmium  have  been  but  incom- 
pletely ascertained.  When  boiled  with  nitric  acid  they  all  evolve 
vapours  of  tetroxide  of  osmium. 

§ IX.  Iridium:  Ir=I97T,  or  Ir=98'56.  Sj).  Gr.  21T5. 

(989)  Iridium  was  discovered  at  the  same  time  as  osmium, 
by  Smithson  Tennant.  It  is  occasionally  found  native  and  nearly 
pure  in  considerable  masses  among  the  Uralian  ores  of  platinum, 
but  it  usually  occurs  combined  with  osmium  as  an  alloy  in  flat 
scales.  Iridium  appears  to  be  dimorphous,  for  it  is  found  crystal- 
lized both  in  cubes  and  in  double  six-sided  pyramids  (G.  Rose). 
In  order  to  obtain  the  metal  in  the  separate  state,  Wohler  recom- 
mends the  powdered  alloy  to  be  intimately  mixed  with  an  equal 
weight  of  finely  powdered  fused  chloride  of  sodium,  and  the  mix- 
ture to  be  heated  to  dull  redness  in  a glass  tube  through  which  a 
current  of  dry  chlorine  is  transmitted  so  long  as  it  is  absorbed. 
The  alloy  is  decomposed  by  the  chlorine  ; double  chlorides  of 
iridium  and  sodium,  and  of  osmium  and  sodium  are  tlius  formed. 
They  are  dissolved  in  boiling  water,  and  are  thus  freed  from  the 
insoluble  portions.  The  solution  is  then  concentrated,  and  the 
liquid  so  obtained  is  mixed  with  nitric  acid  and  distilled ; the 
double  salt  of  osmium  is  decomposed  by  tliis  means,  and  tetroxide 
of  osmium  is  formed,  wdiilst  the  iridium  salt  remains  in  the 
liquid  : the  oxide  of  osmium  being  volatile,  is  expelled  during  the 
distillation.  The  addition  of  chloride  of  ammonium  to  the  concen- 
trated solution  in  the  retort  produces  a precipitate  of  tlie  double 
chloride  of  iridium  and  ammonium,  which,  upon  ignition,  yields 
metallic  iridium.  The  metal,  however,  if  obtained  thus,  is  liable 
to  be  contaminated  with  ruthenium.  It  is  preferable  to  adopt 
Fremy’s  method  of  procuring  the  double  chloride  of  iridium  and 


OXIDES  AXD  CHLOEIDES  OF  mEDITM. 


720 


potassium  (984).  The  salt  may  be  decomposed  by  ignition  in  a 
current  of  hydrogen ; and  the  chloride  of  potassium  may  be  re- 
moved by  washing  with  water,  when  the  iridium  is  left  in  the 
foiTu  of  a finely  divided  powder. 

Iridium  is  a very  hard,  white,  brittle  metal,  which  may  be 
melted  on  lime  by  the  oxyhydrogen  blowpipe,  or  by  the  heat  of 
the  voltaic  current.  It  was  found  to  have  in  its  fused  condition  a 
density  of  21T5  (Deville  and  Debray) ; and  a native  alloy  of  pla- 
tinum and  iridium  even  of  sp.  gr.  22‘6  is  known.  If  heated  in  a 
finely  divided  state  in  the  open  air  it  absorbs  oxygen,  but  if  in 
mass  it  remains  unchanged  by  exposure  to  heat.  In  its  isolated 
form  it  is  unacted  on  by  any  of  the  acids  or  by  aqua  regia ; but 
when  alloyed  with  platinum  it  is  rea<iily  dissolved  by  aqua  regia. 
Pulverulent  iildium.  when  fused  with  nitre  or  with  the  hydrated 
alkalies,  becomes  oxidized,  and  a similar  efiect  is  produced  by 
heating  it  with  acid  sulphate  of  potassium.  Iridium  may  be  ob- 
tained in  a finely  divided  state  by  decomposing  a solution  of  its 
sulphate  by  alcohol : it  then  forms  a black  powder,  which  possesses 
properties  similar  to  those  of  platinum  black  (968). 

(990)  Oxides  of  lEiDirM. — This  metal  forms  three  distinct 

combinations  with  oxygen,  IrO ; ; and  IrO, : they  pass  readily 

one  into  the  other,  and  thus  give  the  variety  of  tints  which  solu- 
tions of  the  salts  of  this  met^  assume.  From  these  changes  of 
colour  the  name  of  iridium,  derived  from  Ins.  the  rainbow,  was 
conferred  on  the  metal. 

The  protoxide  is  obtained  as  a black  anhydrous  powder  by  de- 
composinor  dry  iridioiis  chloride  ( IrCl,)  by  means  of  a concentrated 
solution  of  potash.  It  is  attacked  by  acids  with  difiiculty,  but  is 
dissolved  by  the  alkalies  : the  solution  in  caustic  potash  absorbs 
oxygen  from  the  air,  and  becomes  blue.  Its  solutions  in  the 
acids  have  a dingy  green  colour. 

The  sesqiiioxide  is  the  compound  formed  when  iridium  is  fused 
with  hydrate  of  potash  or  with  nitre,  or  by  heating  the  pulveru- 
lent metal  in  air.  It  is  a bluish-black  powder,  which  is  decomposed 
by  a full  red  heat,  and  is  readily  reduced  by  hydrogen  and  com- 
bustible substances.  This  anhydrous  oxide  is  insoluble  in  acids, 
and  even  in  fused  acid  sulphate  of  potassium.  If  a solution  of 
terchloride  of  iridium  be  boiled  with  a solution  of  caustic  potash, 
oxygen  is  absorbed,  and  an  indis^o-blue  precipitate,  which  is  a 
hydrate  of  the  TAnoxide  of  iridnira  - H^^)  formed 

(Claus).  It  may  be  rendered  anhydrous  by  a gentle  heat.  The 
binoxide  is  but  slowly  dissolved  by  acids : the  hydrochloric  solu- 
tion is  at  first  blue,  it  then  becomes  green,  and,  when  heated, 
changes  to  reddish-brown,  whilst  perchloride  of  iridium  is  formed. 

Three  sulphides  of  iridium  corresponding  to  the  oxides  may 
be  prepared  by  decomposing  the  chlorides  of  the  metal  by  means 
of  sulphuretted  hydrogen. 

Iridium,  like  palla^um,  when  held  in  the  fiame  of  a spirit- 
lamp,  becomes  covered  with  carbonaceous  excrescences,  which 
contain  a considerable  portion  of  metallic  iridium. 

(991)  Chloeides  of  lErorcM. — These  correspond  in  number 


COMPOUNDS  OF  ERIDIUM. 


721 


witli  the  oxides.  They  all  form  donhle  salts  with  the  chlorides 
of  the  alkaline  metals.  According  to  Clans,  the  bichloride  (IrCl„ 
OY  protochloride^  IrCl)  may  he  obtained  in  solution  in  combination 
with  chloride  of  potassium,  if  the  double  salt  of  terchloride  of 
iridium  with  chloride  of  potassium  (3  KCl,IrCl3)  be  treated  with 
a solution  of  the  acid-sulphite  of  potassium,  until  the  green  colour 
has  passed  into  red ; on  evaporating  the  solution  carefully,  red  crys- 
tals of  the  double  salt  (4  KCl,IrCl2  . 2 K2S03,IrS03,  12  H^O)  are 
deposited.  The  terchloride  (hrClg,  or  sesqidchloride^  IraClg)  is  the 
most  stable  of  the  three  chlorides : it  forms  a solution  of  an  olive- 
green  colour ; with  mercurous  nitrate  it  gives  a bright  ochre-yellow 
precipitate  (lrCl3,3  HgCl),  and  a similar  compound  is  formed  with 
nitrate  of  silver,  which  at  first  is  dark-blue,  but  soon  becomes 
colourless : it  forms  salts  with  chloride  of  sodium  and  with  chlo- 
ride of  potassium.  If  dry  chlorine  be  transmitted  over  a mixture 
of  finely  divided  iridium  and  chloride  of  potassium,  a double  salt, 
of  a reddish-black  colour  (2  KCljIrCl^,  or  KCl,IrCl3 ; sp.  gr.  3-546), 
consisting  of  tetrachloride  of  iridium  and  chloride  of  potassium, 
is  formed.  It  may  be  dissolved  in  boiling  water,  and  is  deposited 
in  octohedra  on  evaporating  the  solution ; it  corresponds  in  com- 
position to  the  platinum  salt,  with  which  it  is  isomorphous.  A 
similar  salt  of  sodium  may  be  formed  in  the  same  manner,  by  sub- 
stituting chloride  of  sodium  for  chloride  of  potassium  : it  is  freely 
soluble.  Tetrachloride  of  iridium  forms  a similar  salt  with  sal 
ammoniac,  whicli  possesses  a very  intense  colouring  power,  and 
produces  a dull  brown  solution  even  when  much  diluted.  It  is 
remarkable  that  the  addition  of  caustic  potash  in  small  quantity 
to  this  chloride  converts  it  into  the  olive-green  terchloride.  Tetra- 
chloride of  iridium,  when  heated  with  ammonia,  forms  a series 
of  compound  bases  analogous  to  those  furnished  by  platinum  and 
palladium. 

Claus  considers  that  the  compounds  formerly  described  as  con- 
taining teroxide  and  terchloride  (hexachloride)  of  iridium  were 
really  compounds  of  ruthenium. 

The  salts  of  iridium  have  been  but  incompletely  examined. 

Iridium  is  apt  to  accompany  the  double  chlorides  of  platinum 
with  potassium  and  ammonium.  It  may  be  separated  from  pla- 
tinum by  precipitating  the  two  metals  together,  by  means  of 
chloride  of  potassium : the  precipitate  is  washed,  and  either 
digested  with  cyanide  of  potassium  whicli  dissolves  the  iridium  and 
leaves  the  platinum ; or  it  may  be  fused  with  twice  its  weight 
of  carbonate  of  potassium.  The  platinum  is  liy  tlie  latter  opera- 
tion reduced  to  the  metallic  state,  whilst  the  iridium  remains  in 
the  form  of  sesquioxide.  The  potassium  salts  are  removed  by 
washing,  and  the  platinum  is  redissolved  by  means  of  aqua  regia, 
which  does  not  attack  the  oxide  of  iridium.  This  operation  some- 
times requires  repetition,  as  a portion  of  iridium  may  esca^^e  oxi- 
dation on  the  first  occasion. 

46 


722  CIRCUMSTAi^CES  WHICH  MODIFT  CHEMICAL  ATTKACTIOH. 


CHAPTER  XX. 

OH  SOME  CLRCLTISTAHCES  WHICH  MODIFY  THE  OPEKATIOHS  OF 
CHEMICAL  ATTRACTIOH. 

(992)  Ih  the  first  volnme  of  this  work  an  outline  was  given  of 
the  leading  characters  of  the  most  important  varieties  of  mole- 
cular and  polar  forces,  as  \newed  in  their  simplest  conditions.  In 
the  second  volume  the  attention  of  the  reader  has  hitherto  been 
directed  principally  to  the  results  produced  by  the  exertion  of 
chemical  attraction  in  the  formation  of  the  various  compounds  of 
inorganic  origin,  without  reference  to  the  effects  of  other  forces 
which  may  have  concurred  in  their  production.  It  will,  how- 
ever, now  be  advisable  to  trace  the  influence  exerted  upon  the 
operation  of  chemical  attraction  by  the  co-operation  or  antagonism 
of  elasticity  and  cohesion,  of  adhesion,  and  of  light  and  heat. 
Cases  in  which  the  chemical  decomposition  of  one  substance  by 
another  is  due  simply  to  differences  in  the  degree  of  chemical 
attraction  are  much  less  numerous  than  might  at  first  be  imagined. 
The  displacement  of  one  metal  by  another  from  its  solutions,  such 
as  that  of  silver  by  mercury,  of  mercury  by  copper,  of  copper  by 
lead,  and  of  lead  by  zinc  (7,  4),  furnishes  some  of  the  best 
examples  of  this  kind ; and  similar  instances  are  afforded  by  the 
displacement  of  one  base  by  another  insoluble  base,  as  when 
oxide  of  copper  is  displaced  from  a solution  of  nitrate  of  copper 
by  boiling  it  with  freshly  precipitated  oxide  of  zinc  or  oxide  of 
silver. 

§ I.  IxELEENCE  OF  COHESION,  AdHESION,  AND  ELASTICITY. 

(993)  Influence  of  Cohesion  upon  Chemical  AUraxition. — Since 
chemical  attraction  is  a molecular  force,  which  is  exerted  only 
when  the  particles  of  bodies  are  within  distances  indefinitely 
small,  minute  subdivision  and  diminution  of  cohesion  might  be 
expected  to  favour  its  manifestation,  by  increasing  the  surfaces, 
and  facilitating  the  mutual  contact  of  the  combining  bodies.  It 
will  therefore  be  needless  to  give  more  than  one  or  two  instances 
in  proof  of  this  point : — Iron,  copper,  lead,  and  many  other 
metals,  when  exposed  to  the  atmosphere  in  mass,  are  acted  upon 
very  slowly  by  it,  and  they  gradually  become  converted  into 
oxide  upon  the  surface  : if,  however,  they  be  reduced  to  a finely 
divided  state,  they  are  oxidized  with  such  rapidity  as  often  to 
become  incandescent.  If  iron,  cobalt,  or  nickel  be  reduced  by 
hydrogen  from  its  oxide,  at  a low  red  heat,  it  is  obtained  in  this 
form  : by  the  interposition  of  some  infusible  matter  between  the 
particles  of  the  precipitated  oxide,  as  may  be  effected  by  precipi- 
tating a little  alumina  or  magnesia  along  with  the  oxide,  the 
tendency  to  rapid  oxidation  is  much  increased;  probably  because 
the  cohesion  of  the  fine  particles  of  reduced  metal  is  mechanically 
prevented,  and  the  access  of  the  air  to  each  portion  takes  place 


INFLUENCE  OF  ADHESION,  SOLUTION,  AND  ELASTICITY. 


723 


Vvith  facility.  Copper,  when  precipitated  from  its  solutions  by 
metallic  iron,  or  when  reduced  by  means  of  hydrogen  from  its 
oxide  at  a low  temperature,  often  takes  tire  and  glows  like  tinder, 
when  only  a very  slight  elevation  of  temperature  is  applied  to  it. 
If  a portion  of  tartrate  of  lead  be  exposed  in  a glass  tube  to  a heat 
sufficient  to  char  the  acid,  the  metallic  lead  is  reduced  tlirough- 
out  the  mass  in  a state  of  extreme  division,  and  when  poured  into 
the  air  it  generally  takes  tire,  and  burns  with  scintillations. 

Tlie  opposite  influence,  exercised  by  the  force  of  cohesion,  is 
seen  on  contrasting  the  facility  with  which  disintegrated  carbon 
burns  when  in  the  shape  of  tinder,  with  the  difficulty  which  is 
experienced  in  effecting  the  combustion  of  the  compact  coke 
which  is  deposited  from  coal-gas  upon  the  interior  of  the  iron 
retorts ; and  a decrease  of  combustibility  may  be  traced  through 
all  the  different  forms  of  carbon,  in  proportion  as  their  hardness 
and  density  increase. 

(994)  Influence  of  Adhesion  and  Solution  mi  Chemical  Atti^ac- 
tion. — It  is  mainly  to  the  intimate  subdivision  effected  by  means 
of  solution,  that  this  operation  owes  its  important  influence  in 
facilitating  chemical  combination.  The  force  of  cohesion  amongst 
the  component  particles  of  the  bodies  dissolved  is  balanced  by 
their  adhesion  to  those  of  the  liquid,  and  the  particles  of  the  sub- 
stance in  solution,  being  free  to  move  in  any  direction,  easily  obey 
the  force  of  chemical  attraction. 

The  influence  of  cohesion  in  preventing  chemical  action,  and 
the  manner  in  which  the  force  of  adhesion,  as  displayed  in  the 
production  of  solution,  may  act  in  favouring  chemical  action,  are 
well  exemplifled  by  the  effect  of  nitric  acid  upon  carbonate  of 
barium.  Nitrate  of  barium,  although  soluble  in  water  and  in 
diluted  nitric  acid,  is  not  soluble  in  the  concentrated  acid : when, 
therefore,  concentrated  nitric  acid  is  poured  upon  finely  powdered 
carbonate  of  barium,  it  occasions  but  a slight  effervescence,  which 
speedily  comes  to  an  end,  although  the  acid  may  be  in  large 
excess.  If  the  liquid  be  diluted  with  a small  quantity  of  water, 
a brisk  effervescence  is  temporarily  renewed,  but  again  soon 
ceases  ; on  a further  addition  of  water,  a fresh  effervescence 
occurs,  and  when  the  acid  has  been  diluted  with  8 or  10  times 
its  bulk  of  water,  the  whole  of  the  carbonate  of  barium  is  decom- 
posed and  dissolved. 

For  a similar  reason,  alcoholic  solutions  of  acids  are  witliont 
action  on  the  carbonates,  unless  the  resulting  salt  be  soluble  in 
alcohol.  A mixture  of  tartaric  acid  and  alcohol  will  not  decom- 
pose carbonate  of  potassium.  Hydrochloric  acid  when  dissolved 
in  alcohol  will  not  decompose  carbonate  of  potassium,  but  will 
decompose  carbonate  of  calcium.  An  alcoholic  solution  of  nitric 
acid  decomposes  carbonate  of  calcium,  but  not  carbonate  of 
potassium.  The  tartrates  are  iusoluble  in  alcohol,  so  are  chloride 
and  nitrate  of  potassium,  but  chloride  and  nitrate  of  calcium  are 
dissolved  Iw  alcohol  freely. 

(995)  InflMence  of  Elasticity. — In  the  numerous  instances  in 
which  two  salts  produce  mutual  decomposition,  frequent  examples 


7 '24:  IXFLrEXCE  of  ELASTICITT  ox  CHE:inCAL  ATTEACTIOX. 


are  afforded  of  the  results  produced  by  the  interference  of  other 
forces  with  that  of  chemical  attraction.  The  action  of  sulphate 
of  ammonium  on  carbonate  of  calcium  affords  a case  in  point.  If 
these  two  salts  be  mixed  in  a dry  state,  at  ordinary  temperatures, 
they  do  not  appear  to  act  upon  each  other ; but  if  subjected  to 
tlie  influence  of  a gentle  heat,  a double  decomposition  occurs, 
carbonate  of  ammonium  and  sulphate  of  calcium  are  produced ; 
the  volatile  carbonate  of  ammonium  is  expelled,  and  by  the  aid  of 
the  force  of  elasticity,  it  is  removed  from  the  mixture : -GaOOg  + 
yielding  But  suppose  a solution 

of  sulphate  of  calcium  to  be  mixed  with  one  of  carbonate  of  am- 
monium, the  effects  are  exactly  reversed:  carbonate  of  calcium, 
owing  to  its  insolubility  and  the  predominance  of  cohesion  among 
its  particles,  is  precipitated,  whilst  the  soluble  sulphate  of  am- 
monium remains  in  the  liquid;  and  now  (H^hTj^-GOg-j-OaSO-^ 
become  GaOOg -f  The  chemist  very  often  avails 

himself  of  the  influence  of  elasticity  in  promoting  chemical 
decomposition.  AVhen,  for  example,  an  acid  is  added  to  a salt. 
It  may  decompose  that  salt,  and  its  radicle  take  the  place  of  the 
acid  radicle  previously  in  combination  with  the  basyl,  provided 
that  the  original  acid  can  assume  the  gaseous  form  at  ordinary 
tempjiratures,  or  can  be  converted  into  vapour  at  a temperature 
below  that  required  to  volatilize  the  acid  employed  to  displace  it. 
Carbonic  acid  may  thus  be  displaced  from  the  carbonates  by  solu- 
tions of  all  the  ordinary  mineral  and  vegetable  acids,  except  the 
hydrocyanic  and  hydrosulphuric  acids. 

It  is  upon  this  principle  that  sulphuric  acid,  when  aided  by 
heat,  is  employed  to  displace  the  nitric,  the  hydrochloric,  the 
acetic,  the  formic,  the  butyric,  and  other  volatile  acids  from  their 
salts  by  distillation.  Even  a feebler  but  more  flxed  acid  may 
expel  the  stronger  acids  which  are  more  volatile  than  itself ; oxalic 
acid,  for  example,  if  boiled  with  solutions  of  the  chloride,  expels 
hydrochloric  acid  from  the  liquid  with  facility. 

A remarkable  illustration  of  the  important  influence  exerted 
by  elasticity  in  counteracting  powerful  chemical  attractions,  is 
afforded  in  the  decomposition  of  the  sulphates  themselves,  by 
weaker  acids  at  a high  temperature ; — for  example,  the  action  of 
sulphuric  acid  upon  bases  is  of  the  most  energetic  kind,  whilst 
that  of  boracic  acid,  on  the  contrary,  is  extremely  feeble.  If  a 
solution  of  borax  be  mixed  with  sulphuric  acid,  the  sodium  of  the 
salt  will  change  places  with  the  hydrogen  of  the  sulphuric  acid 
as  it  is  added,  whilst  boracic  acid  will  gradually  be  separated,  and 
if  the  liquid  be  hot  and  not  too  concentrated,  will  be  retained  in 
solution.  Owing  to  the  peculiar  action  of  boracic  acid  on  blue 
litmus,  it  can  be  shown  that  the  two  acids  do  not  divide  the 
sodium  between  them,  for  if  a piece  of  blue  litmus-paper  be  placed 
in  the  liquid,  it  will  exhibit  the  peculiar  wine-red  tint  due  to 
boracic  acid,  until  a quantity  of  sulphuric  acid  exactly  equivalent 
to  the  sodium  contained  in  the  borax  has  been  added ; but  the 
moment  that  this  point  is  reached,  the  lea^t  excess  of  sulphuric 
acid  immediately  reveals  itself  by  the  change  of  the  colour  of  the 


MECHANICAL  AIDS  TO  THE  INFLUENCE  OF  ELASTICITY. 


T25 


litmus  from  diiskj  purplisli-red  to  a briglit  red.  It  is  therefore 
clear  that  boracic  acid  cannot  effect  even  a partial  displacement 
of  snlphnric  acid  from  its  combination  with  sodium  when  the  two 
are  in  solution.  But  it  is  otherwise  at  a red  heat ; if  boracic 
anhydride  be  fused  with  sulphate  of  sodium,  borax  is  produced, 
and  sulphuric  anhydride,  which  is  volatile  at  this  high  tempera- 
ture, is  exjielled  in  the  elastic  form.  Other  acids  and  anhydrides 
which  are  known  to  have  a feebler  attraction  for  bases  than 
sulphuric  acid,  but  which  support  a red  heat  without  experi- 
encing volatilization,  such  as  the  phosphoric  and  silicic  anhy- 
drides, are  also  able  to  decompose  the  sulphates  when  heated 
with  them. 

In  like  manner  when  a base  which  is  fixed  is  heated  with  the 
salt  of  a volatile  base,  the  volatile  base  is  displaced  by  the  more 
fixed  one ; thus  quicldime  or  hydrate  of  potash,  if  heated  with 
the  salts  of  ammonium,  is  converted  into  a salt  of  calcium  or  of 
potassium,  whilst  water  and  gaseous  ammonia  are  expelled : 
2 H,NCl  + eae=eaCl,-fH,e  + 2 H3K 

(996)  The  effect  of  elasticity  in  removing  from  the  sphere  of 
action  one  of  the  components  of  a body  which  is  undergoing  de- 
composition, may  in  some  cases  be  considerably  assisted  by  mechan- 
ical means  ; and  when  the  attractions  of  the  displacing  body,  and 
of  the  substance  displaced  by  it,  for  the  other  constituent  of  the 
compound,  are  nearly  equal,  effects  which  are  in  apparent  oppo 
sition  to  each  other  may  sometimes  be  produced.  For  instance, 
oxide  of  iron,  when  heated  to  redness  in  a current  of  hydrogen 
gas,  is  gradually  reduced  to  the  metallic  state : the  steps  of  the 
process  appear  to  be'these : a sjnall  quantity  of  water  is  formed  ; 
it  immediately  diffuses  itself  in  vapour  into  the  hydrogen,  and  is 
mechanically  carried  away  by  tlie  current  of  this  gas,  which  must 
be  employed  in  considerable  excess  for  tliis  purpose ; and  this  pro- 
cess goes  on  until  tlie  reduction  is  complete.  On  the  other  hand, 
if  metallic  iron  be  heated  in  a current  of  steam,  water  is  decom- 
posed, hydrogen  is  liberated,  and  is  carried  beyond  tlie  reach  of 
chemical  action  upon  the  newly  formed  oxide  of  iron  by  the  excess 
of  the  steam  employed.  In  a similar  manner,  if  a current  of  sul- 
phuretted  hydrogen  be  transmitted  in  large  excess  over  solid  acid- 
carbonate  of  potassium,  aided  by  a gentle  heat,  carbonic  anhydride 
and  water  will  be  displaced  from  the  acid  carbonate,  and  carried 
forward  by  the  excess  of  the  gas,  whilst  sid])hide  of  ])otassiuni 
will  be  formed,  2 KIiee3  + li;S=2  e03  + Iv,B-f2  II^O.  But 
sulphide  of  potassium,  if  dissolved  in  water,  and  subjected  to  a 
current  of  carbonic  anhydride,  will,  in  its  turn,  be  gradually  but 
completely  decomposed  : the  sulphuretted  hydrogen  being  carried 
away  by  the  excess  of  carbonic  aidiydride,  whilst  acid  carbonate 
of  potassium  is  formed  in  the  liquid:  K^S-f  2 OO3-I-2 

+ 2X11003. 

(997)  If  elasticity  be  prevented  by  mechanical  means  from  ex- 
erting its  influence  in  removing  a body  from  contact  with  others 
for  which  it  has  an  attraction,  cond)inations  may  be  obtained 
which  cannot  otherwise  be  procured.  Wohler  {Liel/ufs  Annal. 


726 


ACTION  OF  ACIDS  OX  SALTS  IX  SOLCTIOX. 


IxANV’.  376)  found  tliat  a hydrate  of  sulphuretted  hydrogen  may 
be  obtained  in  colourless  crystals,  if  a portion  of  persulphide  of 
hydrogen,  freed  from  acid,  be  sealed  up  in  a strong  glass  tube  with 
a small  quantity  of  water ; tlie  persulphide  gradually  undergoes 
decomposition  into  crystallized  sulphm*  and  gaseous  sulphuretted 
hydrogen,  which,  at  ordinary  temperatures,  exerts  a pressure  of 
about  17  atmospheres.  Under  these  circumstances  it  combines 
with  water,  and  forms  a crystalline  solid,  which  disappears  with 
effervescence  when  the  tube  is  heated  to  S6°,  but  is  reproduced  on 
cooling.  If  a tube  containing  crystals  of  this  compound  be 
opened,  the  crystals  immediately  disappear  with  brisk  efferves- 
cence. In  other  cases,  the  decomposition  of  compounds  abeady 
formed  may  be  retarded  or  prevented,  by  preventing  the  escape 
of  the  elastic  constituent  by  mechanical  means.  Hydrate  of  chlo- 
rine offers  an  instance  Of  this  kind.  Under  ordinary  circum- 
stances, this  substance  becomes  liquid  at  a few  degrees  above  the 
freezing-point  of  water,  with  escape  of  gaseous  chlorine ; but  if 
the  solid  hydrate  be  sealed  up  in  a glass  tube,  it  remains  solid 
even  when  the  temperature  rises  as  high  as  70°,  the  pressure  of 
chlorine  within  the  tube  retarding  the  decomposition.  Again, 
carbonate  of  calcium  is  decomposed  in  an  open  fire,  at  a red  heat, 
into  carbonic  anhydride  and  quicklime ; but  if  it  be  enclosed  in 
an  iron  tube,  the  mouth  of  which  is  plugged  to  prevent  the  escape 
of  the  acid,  the  carbonate  may  be  melted,  and  on  cooling  it  fur- 
nishes a granular  mass,  which  is  still  carbonate  of  calcium,  and 
has  the  appearance  of  marble  (Sir  J.  Hall). 

(99S)  Action  of  Acids  on  Salts  in  Solution. — 'Wlienever  an 
acid  is  added  to  the  solution  of  a salt  with  the  basyl  of  which  it  is 
capable  of  forming  a soluble  compound,  it  may  be  supposed  to 
produce  a division  of  the  basyl  between  its  own  radicle  and  that 
of  the  acid  with  Avhich  it  was  previously  united,  so  that  two  acids 
and  two  salts  may  be  present  in  the  liquid,  in  some  unknown 
proportions  depending  upon  the  strength  of  the  relative  attrac- 
tions of  the  basyl  for  the  radicles  of  the  two  acids  : — thus,  when 
nitrate  of  potassium  is  mixed  with  sulphuric  acid,  part  of  the 
potassium  may  be  supposed  to  enter  into  combination  with  the 
radicle  of  the  sulphuric  acid,  and  part  to  remain  united  with  that 
of  the  nitric  acid,  while  a portion  of  nitric  acid  will  be  liberated, 
and  will  become  mixed  with  the  uncombined  sulphuric  acid  : for  ex- 
ample, 2 H,se,-fi:Kxe3=2KAe3-fK,se,-f  211X03 -hH,se,. 
The  occurrence  of  such  a decomposition  as  this,  although  pro- 
bable, in  many  cases  does  not  admit  of  direct  proof.  If  an  addi- 
tional force  be  called  into  operation,  such  as  the  development  of 
elasticity  on  the  application  of  heat,  the  more  volatile  acid  may 
I)e  expelled  in  the  form  of  va])0ur,  and  may  thus  be  withdrawn 
from  the  sphere  of  action.  This,  however,  is  no  proof  that 
such  a partition  of  the  basyl  actually  existed  before  the  heat 
was  applied.  In  cases  where  the  attraction  of  the  radicle  of  one 
acid  for  the  basyl  is  very  strong,  whilst  that  of  the  other  is  feeble, 
the  stronger  acid  may  (as  in  the  case  of  sulphuric  acid  and  borax, 
already  cited)  entirely  appropriate  the  basyl  to  itself.  But  where 


ACTION  OF  ACIDS  ON  SALTS  IN  SOLUTION. 


Y2T 


the  two  acids  at  all  approach  each  other  in  chemical  power,  it 
must  be  assumed  that  a division  of  the  basyl  takes  place.  Some- 
times the  occurrence  of  such  a partition  can  be  proved  by  the 
change  of  colour  which  ensues  after  the  mixture  has  been  effected. 
Sulphate  of  copper,  for  example,  is  of  a blue  colour  when  in  solu- 
tion, and  chloride  of  copper  is  green.  If  a solution  of  the  blue 
sulphate  be  mixed  with  hydrochloric  acid,  it  is  evident  that  the 
copper  enters  partially  into  combination  with  the  chlorine  of  the 
hydrochloric  acid,  since  the  solution  assumes  a bright  green  tint ; 

2euse,+4  Hci==euse,+euci,-f  H,se,+2  Hci. 

If  the  basyl  form  an  insoluble  compound  with  the  radicle  of 
the  newly  added  acid,  it  is  possible  to  decompose  the  original  salt 
completely  by  its  means.  If,  for  instance,  a solution  of  nitrate  or 
of  acetate  of  barium  be  mixed  with  sulphuric  acid,  it  may  be  sup- 
posed that  the  barium  divides  itself  between  the  radicles  of  the  two 
acids  in  proportion  to  its  attraction  for  each ; but  the  sulphate  of 
barium  being  insoluble  is  at  once  withdrawn  from  the  mixture, 
and  the  barium  remaining  in  the  original  salt  again  divides  itself 
between  the  radicles  of  the  two  acids ; the  fresh  portion  of 
sulphate  of  barium,  however,  is  immediately  precipitated ; and 
so,  by  a series  of  steps  w^hich,  where  the  chemical  attractions  are 
strong,  succeed  each  other  far  more  rapidly  than  they  can  be 
described, — the  whole  of  the  barium  is  separated  in  the  form  of  an 
insoluble  sulphate,  leaving  the  nitric  or  the  acetic  acid  free  in  the 
solution. 

A very  feeble  acid  may  even  displace  a more  powerful  one 
when  the  compound  which  it  forms  is  insoluble  in  the  menstruum 
in  which  it  is  suspended.  Hydrocyanic  acid  will  separate  nitric 
acid  from  nitrate  of  silver,  owing  to  the  formation  of  the  insoluble 
cyanide  of  silver;  AgH0-3-l-HCy=HH03  + AgCy.  Tartaric  acid 
will  liberate  sulphuric  acid  in  a solution  of  sulphate  of  silver, 
owing  to  the  formation  of  an  insoluble  tartrate  of  silver.  Oxalic 
acid  will  precipitate  oxalate  of  copper  from  a solution  of  chloride 
of  copper  ; and  Pelouze  has  observed  that,  if  a current  of  carbonic 
anhydride  be  transmitted  through  a solution  of  acetate  of  potas- 
sium dissolved  in  alcohol,  acetic  acid  will  be  liberated,  and  car- 
bonate of  potassium,  which  is  insoluble  in  alcohol,  will  be  sepa- 
rated ; but  no  such  change  occurs  in  its  aqueous  solution,  since 
carbonate  of  potassium  is  freely  soluble  in  water.  This  rule, 
however,  is  not  without  exce])tion,  where  one  acid  is  very  power- 
ful and  the  other  is  very  feel)le  ; borate  of  calcium,  for  instance, 
is  an  insoluble  salt,  but  a solution  of  ])oracic  acid  will  not  occasion 
any  ])recipitate  if  mixed  with  one  of  nitrate  of  calcium ; citrate 
and  tartrate  of  calcium  are  also  insoluble  compounds,  but  neither 
solution  of  citric  nor  of  tartaric  acid  occasions  a precipitate  in  one 
of  nitrate  of  calcium. 

In  like  manner,  if  the  acid  originally  present  be  insoluble  in 
water,  it  will  be  separated,  and  the  salt  will  be  decomposed  ; thus, 
on  tlie  addition  of  nitric  acid  to  a solution  of  tungstate  of  ])Otas- 
sium,  the  tungstic  acid  is  pre(u'))itated,  whilst  nitrate  of  ])otassium 
is  retained  in  the  solution ; H-  2 IIHO,= 2 KA -f-  IJ 


72S 


ACTION  OF  BASES  OX  SALTS  EX  SOLUTION. 


(999)  Action  of  Bases  on  Salts  in  Solution. — An  analogous 
decomposition  occurs  if  a quantity  of  some  additional  base  be 
added  to  a saline  solution.  If  the  two  bases  be  soluble,  and  fbe 
salts  which  they  form  be  also  soluble,  the  solution  will  remain 
clear,  and  it  may  be  supposed  that  the  acid  is  divided  between  the 
metals  of  the  two  bases  in  proportion  to  its  attraction  for  each, 
as  when  a solution  of  nitrate  of  barium  is  mixed  with  a solution 
of  caustic  potash  : a mixture  of  nitrate  of  barium  and  nitrate  of 
potassium  with  hydrate  of  baryta  and  hydi’ate  of  potash  is  thus 
obtained ; but  as  hydrate  of  baryta  is  less  soluble  than  hydi’ate  of 
potash,  a portion  of  hydrate  of  baryta  will  be  gradually  deposited 
if  the  solutions  be  in  a concentrated  form.  If  either  of  the  bases 
be  insoluble,  or  form  an  insoluble  salt  with  the  acid,  a complete 
separation  of  the  base  or  of  the  acid  contained  in  the  original  salt 
maybe  effected.  For  example,  the  salts  of  nearly  all  the  metals, 
with  the  exception  of  those  of  the  alkalies  and  of  the  alkaline  earths, 
are  derived  from  metallic  oxides  which  are  not  soluble  in  water  : 
the  addition  of  any  soluble  base,  such  as  potash,  soda,  or  ammonia 
to  their  solutions,  immediately  occasions  the  precipitation  of  the  in- 
soluble oxide.  It  is  in  this  manner  that  such  oxides  are  commonly 
prepared  from  their  solutions ; for  example,  the  oxide  of  zinc,  of 
iron,  of  cobalt,  of  nickel,  of  manganese,  or  of  silver,  may  thus  be 
completely  separated  from  the  acid  by  which  it  was  previously  held 
in  solution;  for  instance,  OoSO^-f 2 K110=0o0,ll20-f K.SO^. 
Solution  of  the  hydrate  either  of  baryta,  of  strontia,  or  of  lime, 
acts  in  a similar  manner,  if  the  acid  be  one  which,  like  the  nitric 
or  the  hydrochloric,  is  capable  of  furnishing  a soluble  compound 
by  its  action  upon  these  bases.  A solution  of  nitrate  of  copper 
may  thus  be  decomposed  by  a solution  of  hydi’ate  of  baryta  ; 
■011 2 X03  -hIIa0,Il20=Sa  2 Fr03-}-0n0,Il20. 

In  a few  cases,  no  precipitation  occurs  even  though  the  oxide 
be  insoluble  ; when,  for  instance,  cyanide  of  mercury  is  mixed  with 
a solution  of  hydrate  of  potash,  no  precipitate  is  produced, 
although  oxide  of  mercury  is  insoluble  in  water. 

If  the  newly  added  base  form  an  insoluble  compound  with  the 
acid,  it  is  wholly  precipitated  by  it ; and  if  the  other  base  be 
soluble,  it  remains  in  the  liquid.  One  of  the  methods  of  forming 
a pure  solution  of  hydrate  of  potash  is  founded  on  this  principle ; 
in  this  experiment,  a solution  of  sulphate  of  potassium  is  mixed 
with  a quantity  of  solution  of  hydrate  of  baryta  exactly  suffi- 
cient to  precipitate  the  whole  of  the  sulphuric  acid;  K^SO^-h 
Sa0,Il20=2  KHO  + fiaSO^ ; and  in  a similar  manner  oxalate  of 
potassium  is  deprived  of  its  oxalic  acid  by  the  addition  of  lime- 
water  to  its  solution,  owing  to  the  formation  of  an  insoluble 
oxalate  of  calcium.  If  the  base  as  well  as  the  salt  which  is 
formed  by  the  addition  of  the  new  base  to  the  acid  be  insoluble, 
it  is  possible  to  precipitate  the  whole  of  both  acid  and  base  from 
the  liquid  simultaneously  ; as  when  a solution  of  hydrate  of  baryta 
is  added  in  re2:nlated  quantities  to  a solution  of  sulphate  of  silver ; 

Ag,se,  -f  fiae,H2e= Ag2e,H2e  -p  fiase,.  ^ 

(1000)  JIutual  Action  of  Salts  in  Solution. — It  is  a rule  almost 


MUTUAL  ACTION  OF  SALTS  IN  SOLUTION. 


729 


without  exception,'^  that  when  sohitions  of  tioo  salts,  cajoable  of 
forming,  hy  mutual  interchange  of  acid  radicles  and  hasyls,  an 
insoluble  or  sjoaringly  soluble  salt,  are  mixed,  the  salts  decompose 
each  other,  and  the  compound  which  is  least  soluble  is  precipitated. 
It  is  in  this  manner  that  the  greater  nmnber  of  insoluble  com- 
pounds are  formed  by  the  process  of  double  decomposition.  Iodide 
of  silver  is  thus  obtained  by  acting  upon  a solution  of  nitrate  of 
silver  with  one  of  iodide  of  jjotassinm;  AgNOg-f  KI  = KNOg 
+ AgI;  and  in  a similar  manner,  if  carbonate  of  manganese  or 
phosphate  of  copper  be  required,  it  may  be  procured  by  mixing  a 
solution  of  chloride  of  manganese  or  of  sulphate  of  copper  with 
one  of  carbonate  of  potassium  or  of  phosphate  of  sodium.  Some- 
times a soluble  compound  may  be  advantageously  procured  in  this 
manner,  as  in  the  ordinary  method  of  preparing  acetate  of  alumi- 
num, in  which  a solution  of  acetate  of  lead  is  mixed  with  one  of 
sulphate  of  aluminum:  sulphate  of  lead  is  precipitated,  and 
acetate  of  aluminum  remains  dissolved;  3 (Pb  2 OgllgOg)  -f- 
Alg  3 SO,  3 PbSO,  -f  Alg  6 O^HgOg.  ^ 

When  two  saline  solutions  are  mixed,  which,  by  the  mutual 
interchange  of  their  acid  radicles  and  basyls,  form  compounds 
also  freely  soluble,  there  is  in  ordinary  cases  no  proof  that  any 
change  occurs,  but  it  is  usually  supposed  that  a mixture  of  four 
different  salts  is  produced.  When,  for  instance,  solutions  of  sul- 
phate of  potassium  and  nitrate  of  sodium  are  mingled,  it  is 
imagined  that  a mixture  of  sulphate  of  potassium  and  sulphate  of 
sodium,  of  nitrate  of  potassium  and  nitrate  of  sodium,  in  un- 
known proportion,  dependent  upon  the  balance  of  the  mutual 
attraction  of  the  acid  radicles  and  basyls,  is  the  result.  In  like 
manner  the  mixture  of  three  salts,  each  containing  a different  rad- 
icle and  a different  basyl,  would  occasion  the  formation  of  nine 
different  salts ; and  the  mixture  of  four  salts,  each  containing  dif- 
ferent acid  radicles  and  different  basyls,  should  produce  sixteen 
different  salts,  provided  that  all  are  capable  of  coexisting  in  solu- 
tion. 

Hence  it  will  be  seen  that  it  is  impossible  to  state  with  cer- 
tainty what  are  the  salts  which  are  present  in  mixture  in  any 
solution  which  contains  a number  of  saline  compounds.  In  the 
analysis  of  a mineral  water,  for  example,  it  is  possible  to  deter- 
mine the  amount  of  each  acid  and  of  each  base  whicli  is  present, 
but  it  is  not  possible  to  say  what  the  salts  really  were  which  were 
brought  into  solution  to  form  the  mineral  water  in  question.  Sul- 
phuric acid,  nitric  acid,  carbonic  and  hydrochloric  acids  may  have 
been  present  amongst  the  acid  constituents,  and  potash,  soda, 
lime,  and  magnesia  amongst  the  bases;  but  it  is  ini])()ssible  to  say 
how  all  those  acids  and  bases  are  distributed  in  the  solution,  kfany 
chemists  allot  the  basyls  to  the  acid  radicles  in  the  order  of  the 
insolubility  of  the  different  salts,  whilst  others  allot  the  strongest 

* When  a solution  of  cyanide  of  mercury  is  mixed  witli  one  of  nitrate  of  silver, 
little  or  no  precipitate  is  produced,  although  cyanide  of  silver  is  a very  insoluble 
compound,  and  cyanide  of  mercury  has  not  the  power  of  forming  a soluble  double 
cyanide  with  it. 


730 


MUTUAL  ACTION  OF  SALTS  IN  SOLUTION. 


bases  to  tlie  strongest  acids.  In  reporting  the  results  of  analysis, 
however,  the  quantities  of  the  separate  anhydrides  and  bases 
should  invariably  be  given  ; in  addition  to  which,  the  analyst,  if 
he  pleases,  can  allot  them  according  to  his  fancy.  Tlie  foregoing 
remarks  may  be  illustrated  by  the  curious  alternate  decompositions 
which  differences  of  solubility  at  different  temperatures  sometimes 
bring  about : a striking  instance  of  this  kind  occurs  in  the  case  of 
a mixture  containing  both  sulphate  of  magnesium  and  common 
salt.  These  salts  occur  mixed  together  on  a large  scale  in  the 
mother-liquor  of  sea-water,  after  the  bay-salt  has  been  separated. 
Four  salts  may  be  formed  by  the  intermixture  of  these  two  com- 
pounds, viz.,  sulphate  of  magnesium,  sulphate  of  sodium,  chloride 
of  magnesium,  and  chloride  of  sodium.  Of  these  four  salts,  chlo- 
ride ot  sodium  is  the  least  soluble  at  the  boiling-point ; if,  therefore, 
the  solution  be  concentrated  by  ebullition,  chloride  of  sodium  is 
separated  in  crystals ; and  as  the  liquid  cools,  the  sulphate  of  mag- 
nesium crystallizes  out.  The  effect,  however,  will  be  different  if 
the  solution  be  allowed  to  evaporate  spontaneously  in  the  open 
air ; at  low  temperatures  the  sulphate  of  sodium  is  the  least  sol- 
uble of  the  four  salts ; and  at  low  temperatures  it  is  the  sulphate 
of  sodium  which  separates  in  crystals  from  the  liquid,  whilst  the 
readily  soluble  chloride  of  magnesium  remains  in  solution  {iiote 
p.  355). 

Upon  a similar  principle  nitrate  of  sodium  is  converted  on  a 
large  scale  into  nitrate  of  potassium,  by  mixing  it  with  chloride 
of  potassium ; on  concentrating  the  solution  by  boiling  it,  chloride 
of  sodium  is  separated  in  crystals,  and  nitrate  of  potassium  crys- 
tallizes out  as  the  liquid  cools : at  low  temperatures  chloride  of 
sodium  is  more  soluble  than  nitrate  of  potassium,  and  the  nitre 
crystallizes  out  nearly  in  a state  of  purity. 

It  may,  in  fact,  be  stated  as  a general  principle,  that  on  con- 
centrating a mixed  solution  by  evaporation,  the  salt  which  is  least 
soluble  at  the  particular  temperature  employed  is  that  which  is 
first  formed. 

In  certain  cases  where  there  is  no  great  difference  in  the  solu-  • 
bility  of  two  salts,  evidence  is  yet  afforded  of  their  mutual  decom- 
position when  the  solutions  are  mixed,  by  the  change  of  colour 
which  then  ensues.  Sulphocyanide  of  potassium,  for  example, 
when  mixed  with  a solution  of  perchloride  of  iron,  so  much 
diluted  as  to  be  colourless,  indicates  by  the  blood-red  solution 
which  it  forms,  that  a mutual  interchange  of  the  components  of 
the  two  salts  has  been  partially  effected.  In  a manner  somewhat 
similar,  when  a solution  of  green  sulphate  of  iron  is  mixed  with 
one  of  acetate  of  sodium,  on  transmitting  a current  of  sulphuret- 
ted hydrogen  through  the  liquid,  the  iron  is  precipitated  in  the 
form  of  a black  sulphide.  This  reaction  could  only  take  place 
owing  to  the  presence  of  ferrous  acetate,  since  a solution  of  fer- 
rous acetate  admits  of  being  thus  decomposed  by  sulphuretted 
hydrogen,  but  one  of  ferrous  sulphate  is  not  so  acted  upon.  The 
entire  quantity  of  iron  may  be  separated  in  this  manner,  for  no 
sooner  is  a certain  proportion  of  the  iron  rendered  insoluble,  than 


INFLUENCE  OF  MASS  ON  CHEMICAL  COMBINATION.  ‘731 

a fresh  portion  of  ferrous  acetate  is  formed ; and  this  formation 
and  decomposition  of  the  salt  continues  so  long  as  any  iron  re- 
mains in  a state  of  solution. 

(1001)  Influence  of  Mass  in  the  Formation  of  Chemical  Com- 
jjouncls. — A curious  question  presents  itself  as  to  the  proportion 
in  which  two  bodies  are  capable  of  thus  mutually  decomposing 
each  other  on  mixture.  When,  for  example,  three  different  bodies, 
A,  B,  and  c,  are  mixed  together,  one  of  wliich,  c,  is  capable  of 
combining  with  either  of  the  other  two,  and  forming  with  them 
compounds,  a c,  b c,  which  in  both  cases  are  soluble,  the  quantity 
of  A and  of  b being  considerably  in  excess  of  c, — will  the  propor- 
tion in  which  o enters  into  combination  with  a and  b,  be  deter- 
mined merely  by  the  strength  of  their  relative  chemical  attraction  ? 
01*  will  the  proportion  in  which  each  of  these  bodies  is  present  also 
influence  the  result  ? It  was  argued  by  Berthollet,  that  not  only 
would  c be  divided  between  a and  b,  but  that  in  proportion  as 
the  quantity  of  one  of  these  bodies,  a,  preponderated  over  the  other 
body,  B,  the  proportion  of  a c in  the  mixture  would  be  increased, 
while,  of  course,  that  of  b o would  be  diminished.  If,  on  the 
other  hand,  the  proportion  of  b were  increased,  the  quantity  of 
the  compound  b c would  be  augmented,  whilst  that  of  a o would 
be  proportionately  lessened,  the  body  c dividing  itself  between  a 
and  B,  in  a proportion  represented  by  the  product  of  its  chemical 
attraction  for  each  of  these  elements  multiplied  into  their  mass. 
Thus  if  a represent  the  mass  of  a,  let  x represent  its  chemical 
attraction  for  c ; if  /3  be  the  mass  of  b,  and  y its  chemical  attrac- 
tion for  c ; then  aa?  : /3?/  : : A c : B 0.  Suppose,  for  example,  a so- 
lution of  nitrate  of  potassium  to  be  mixed  with  more  than  its 
equivalent  of  sulphuric  acid : it  is  generally  conceded  that  the  po- 
tassium divides  itself  between  the  two  acids,  forming  a mixture 
of  sulphate  and  nitrate  of  potassium,  with  free  sulphuric  and 
nitric  acids.  How  if  the  quantity  of  sulphuric  acid  be  increased, 
will  tlie  quantity  of  sulphate  of  potassium  which  is  thus  formed 
be  influenced  by  the  amount  of  sulphuric  acid  which  is  thus 
added  in  excess  ? and  if  so,  to  what  extent  will  this  influence  of 
the  mass  of  the  acid  modify  the  simple  effect  of  chemical  at- 
traction. 

Let  us  imagine,  for  example,  that  a?,  the  attraction  of  sulphuric 
acid  radicle  for  potassium,  = 5,  whilst  y,  that  of  nitric  acid  radicle 
for  potassium,=:4.  When  an  equivalent  of  sulphuric  acid  is  pre- 
sented to  an  equivalent  of  nitrate  of  potassium,  the  mass  a of 
sulphuric  acid=l  ; that  of  the  nitric  acid  (3  = 1 also.  Then  ax: 
/3?/  as  5 : 4.  The  nitrate  will  be  partially  decomposed  : -I  of  the 
potassium  will  enter  into  combination  with  the  sulphuric  acid 
radicle,  whilst  f will  be  united  with  the  nitric,  and  we  shall  have 
in  the  solution  4 (KfiOf  f (2  KNOg),  (IlgSO,)  and  (2  IIAOg). 
But  suppose,  instead  of  adding  1 ecpiivalent  of  sulphuric  acid,  2 
equivalents  be  employed,  whilst  the  proportion  of  the  nitrate 
remains  unaltered  ; the  mass  a of  the  sulphuric  acid  is  now  2,  and 
ax  ; (3j  as  10  : 4.  The  proportion  of  nitrate  of  potassium  will  be 
diminished,  and  there  will  be  (K.^S04),  (2  KNO),  l-j\ 


732 


Gladstone’s  expeeiments  ox  the 


(H^SO,),  and  (2  HXO3)  ; and  if  3 equivalents  of  snlplmric  acid 
be  employed  to  1 of  nitrate  of  potassium,  since  the  mass  a of 
sulplinric  acid  is  now =3  ; ax\  hy  as  15  : 4 ; consequently  the 
proportions  of  the  ingredients  wonidbe  (K,,SOJ,  (2  KXO3), 
2^^  (II3S0,),  and  (2  HXO3) ; the  proportion  of  sulphate  of 
potassium  continuing  to  increase,  though  in  a decreasing  ratio,  for 
every  addition  of  free  sulphuric  acid  to  the  solution. 

(1002)  Gladstone's  Experiments  on  Mass. — Xo  experimental 
solution  of  tliis  problem  was  given  by  Berthollet,  and  the  question 
fell  into  abeyance  ; but  within  the  last  few  years  several  attempts 
have  been  made  with  considerable  success  to  determine  this 
question  quantitatively.  Gladstone  {Phil.  Trans.  1855,  p.  179) 
has  published  a series  of  experiments  in  which  he  has  made  use  of 
the  change  of  colour  which  solutions  of  certain  salts  undergo  on 
mixture  with  each  other  as  a means  of  ascertaining  the  extent  to 
which  this  mutual  decomposition  proceeds  when  ^1  the  products 
remain  in  solution.  The  principle  of  his  experiments  will  be  easily 
understood.  Solutions  of  several  ferric  salts,  such  as  the  ferric 
sulphate,  nitrate,  chloride,  acetate,  citrate,  &c.,  were  prepared  in 
such  a manner  that  each  should  contain  the  same  proportion  of  iron 
dissolved  in  the  same  bulk  of  water  (each  of  the  solutions  employed 
contained  a quantity  of  iron  corresponding  very  nearly  to  1 grain 
of  sesquioxide  of  iron  in  1000  grain  measures  of  water).  A solution 
of  pure  sulphocyanide  of  potassium  was  then  prepared  of  such  a 
strength  that  when  1 measure  of  this  solution  and  4 of  that  of  the 
iron  salts  were  mingled,  the  proportion  of  sulpho cyanogen  should 
be  exactly  sufficient  to  convert  the  whole  of  the  iron  into  sulpho- 
cyanide, if  complete  mutual  decomposition  occurred  : thus  the 
proportions  of  the  two  salts  employed  were  such,  that  it  would  be 
possible  for  exact  mutual  interchange  to  occur  as  represented  in 
the  following  equation  : Fe^G  XO3-I-6  KScy=Fe2Scye-f6  KXO3. 
On  making  the  experiment  in  this  manner,  it  was  found  that  the 
iron  was  never  wholly  converted  into  the  red  salt,  for  the  tint 
was  deepened  by  the  addition  of  more  either  of  the  iron  salt  or  of 
the  sulphocyanide.  In  order  to  obtain  a quantitative  estimate  of 
the  amount  of  these  effects,  definite  measures  of  the  solutions  of  fer- 
ric nitrate  and  of  sulphocyanide  of  potassium  were  mixed  together, 
and  tlie  liquid  so  obtained  was  diluted  with  water  until  it  occupied 
a known,  but  arbitrary  volume.  This  diluted  mixture  furnislied  a 
liquid  of  a certain  depth  of  colour  which  was  employed  as  a standard 
of  comparison.  Another  measure  of  the  solution  of  ferric  nitrate, 
equal  to  that  used  in  the  standard  solution,  was  mixed  with  regulated 
additions  of  the  sulphocyanide  of  potassium,  and  the  liquid  thus 
obtained  was  diluted  with  measured  quantities  of  water  after  each 
addition  of  sulphocyanide,  until,  as  far  as  the  eye  could  distinguish, 
this  solution  had  the  same  depth  of  tint  as  that  employed  as  the 
standard ; it  was  then  assumed  that  the  quantity  of  sulphocyanide 
of  iron  formed  was  proportionate  to  the  bulk  of  the  two  solutions."^ 
Suppose  that  the  standard  solution  occupied  a volume  of  880  mea- 

* Grladstone  found  that  simple  dilution  of  the  sulphocyanide  of  iron  reduced  the 
tint  in  a proportion  greater  than  could  bo  accounted  for  by  mere  dilution ; but  this 


INFLUENCE  OF  I^IASS  ON  CHEMICAL  ATTEACTION. 


733 


snres : it  was  found  that  if  twice  the  quantity  of  the  snlphocya- 
nicle  of  potassium  employed  in  the  standard  liquid  were  made  use 
of  in  the  new  solution,  this  mixture  would  require  dilution  till  it 
occupied  1270  measures.  The  proportion  of  sulphocyanide  of 
iron  formed  in  these  two  cases  was  assumed  to  he  as  880  to  1270, 
or  as  1 to  1*44.  The  excess  of  sulphocyanide  thus  employed  had 
therefore  withdrawn  an  additional  quantity  of  iron  from  its  com- 
bination with  the  nitric  acid. 

In  this  manner  experiments  were  made  witli  quantities  of 
the  sulphocyanide  of  potassium,  progressively  increasing  from 
one-fifth  of  an  equivalent  of  the  sulphocyanide  to  each  equivalent 
of  nitrate  of  iron,  up  to  375  equivalents  of  sulphocyanide  to  1 
equivalent  of  nitrate  of  iron,  and  it  was  found  that  the  quantity 
of  sulphocyanide  of  iron  which  was  formed,  continued  to  increase 
with  every  addition  of  sulphocyanide  of  potassium,  though  the 
effect  of  each  consecutive  addition  became  less  and  less  marked. 

It  was  ascertained,  as  indeed  it  was  to  be  expected,  that  the 
proportions  of  sulphocyanide  of  iron  which  are  formed  by  the 
mixture  of  equivalent  quantities  of  other  salts  of  iron  with  given 
amounts  of  the  sulphocyanide  of  potassium,  vary  with  the  nature 
of  the  acid  radicle  contained  in  the  ferric  salt.  For  example,  it 
was  found  that  when  nitrate  of  iron  was  mixed  with  sulphocyanide 
of  potassium,  in  the  proportion  of  equivalent  quantities  of  each, 
tliat  0*194  of  an  equivalent  of  the  red  salt  was  formed.  When 
an  equivalent  of  ferric  chloride  was  used,  0*173  of  an  equivalent 
was  formed ; when  the  sulphate  was  employed,  0*126  of  an  equi- 
valent was  produced  ; witli  ferric  acetate  0*04  only  was  formed ; 
and  when  citrate  of  iron  was  employed,  the  quantity  of  sulpho- 
cyanide of  iron  which  it  yielded  was  too  small  to  admit  of  being 
estimated.  The  iron  therefore  retained  the  radicles  of  these 
different  acids  with  degrees  of  force  which  vary  inversely  with 
the  quantity  of  sulphocyanide  which  is  formed,  whilst  the  potas- 
sium in  tlie  sulphocyanide  attracted  them  with  a power  in  direct 
proportion  to  these  quantities.  Various  attempts  have  been  made 
to  obtain  relative  numerical  expressions  for  the  force  of  chemical 
attraction  by  which  different  compounds  are  united,  but  they  have 
all  hitherto  failed.  Experiments  conducted  upon  the  principle  of 
those  of  Gladstone  appear  to  offer  the  fairest  prospect  of  solving 
this  interesting  and  important  problem. 

Besides  the  sulphocyanide  of  iron,  Gladstone  examined  a variety 
of  other  coloured  compounds  ; one  of  these  was  the  scarlet  bromide 
of  gold,  which  becomes  yellow  when  mixed  with  the  chlorides  of 
])Otassium  and  sodium,  to  an  extent  varying  with  the  proportion 
in  which  these  salts  are  added ; the  sul])hate  of  quinia,  when  mixed 
with  a soluble  chloride,  bromide,  or  iodide,  also  afforded  similar 
indications,  as  it  loses  fluorescent  character  (110)  in  proportion 
to  the  quantity  of  chloride  or  bromide  with  which  it  is  mixed. 
From  these  and  from  a variety  of  other  experiments  it  appears 
that  when  two  or  more  compounds  in  solution  are  made  to  act 

source  of  error  was  eliminated,  and  was  not  found  to  present  itself  in  other  cases 
which  he  employed  to  test  the  accuracy  of  the  general  conclusion. 


734: 


BOrSEN'S  EXPEKniEXTS  OX  THE 


upon  each  other,  provided  that  the  products  vhich  they  form  hj 
their  mutual  action  are  also  soluble,  the  following  conclusions  may 
be  drawn ; — 1.  That  mutual  interchange  between  the  bodies  which 
are  mixed  takes  place  in  determinate  proportions.  2.  That  these 
proportions  are  independent  of  the  manner  in  which  the  com- 
pounds were  originally  combined : thus,  if  sulphate  of  potassium 
and  ferric  nitrate  be  mixed  in  equivalent  quantities,  the  result  is 
the  same  as  if  nitrate  of  potassium  and  ferric  sulphate  had  been 
employed  in  equivalent  quantities.  This  is  a fundamental  point 
in  these  inquiries  ; but  if  Struve’s  observations  (quoted  by  Graham, 
Elem.  Cliern.  2nd  Ed.  p.  232)  be  correct — viz.,  that  in  the  prepa- 
ration of  mineral  waters,  the  taste  of  the  liquid  varies,  not  only 
according  to  the  natime  of  the  salts,  but  also  according  to  the 
order  in  which  they  are  added — it  cannot  be  a general  law.  3. 
That  these  proportions  are  dependent  partly  upon  the  strength  of 
the  mutual  attractions  of  the  components  for  each  other,  and 
partly  also  upon  the  mass^  or  relative  proportion  of  each  compound 
which  is  present  in  the  mixture.  4:.  That  the  alteration  of  the  mass 
of  any  one  of  these  compounds  alters  the  amount  of  all  the  other 
compounds  which  co-exist  in  the  mixture,  in  a regularly  progres- 
sive ratio ; and  these  quantities  admit  of  being  represented  by 
regular  curves.  In  most  cases  this  adjustment  of  the  relative 
quantities  of  the  different  bodies  takes  place  immediately  that  the 
mixture  is  made. 

(1003)  Experiments  of  Bunsen  and  of  Debus. — The  results 
are  different  if  the  products  of  the  chemical  combination  be  at 
once  removed  from  the  sphere  of  action, — as  by  the  formation 
of  gaseous  compounds,  or  of  an  insoluble  precipitate  when  two 
liquids  are  mixed.  Bunsen  has  investigated  the  results  obtained 
in  some  cases  of  gaseous  combination.  He  found  that  when  a 
mixture  of  hydrogen  and  carbonic  oxide  was  detonated  with 
oxygen  in  quantity  insufficient  for  its  complete  combustion,  the 
oxygen  divided  itself  between  the  two  gases  in  such  a manner 
that  the  quantities  of  water  and  of  carbonic  anhydride  produced 
were  in  very  simple  atomic  relations  to  each  other  {Liebig' s Annal. 
Ixxxv.  137).  He  exploded  together  mixtures  of  oxygen,  hydro- 
gen, and  carbonic  oxide,  in  varying  proportions,  the  hydrogen 
and  carbonic  oxide  being  each  in  considerable  excess  over  the 
oxygen  ; under  such  circumstances  water  and  carbonic  anhydride 
were  formed  ; but  the  quantity  of  carbonic  anhydride  was  greater, 
in  proportion  as  the  carbonic  oxide  preponderated,  according  to 
a certain  law.  Similar  results  were  obtained  by  detonating 
cyanogen  with  a quantity  of  oxygen  insufficient  for  its  complete 
combustion  ; in  such  case  nitrogen  and  a mixtm-e  of  carbonic 
anhydride  and  carbonic  oxide  in  simple  proportions  were  obtained ; 
and  when  a mixture  of  carbonic  anhydride  and  hydrogen  was 
detonated  with  a quantity  of  oxygen  insufficient  for  the  consump- 
tion of  the  hydrogen,  a certain  proportion  of  the  carbonic  anhy- 
dride was  reduced  to  carbonic  oxide,  according  to  the  terms  of 
the  same  law. 

The  following  is  the  law  deduced  by  Bunsen  from  his  experi- 


INFLUENCE  OF  MASS  ON  COMBINATION. 


735 


ments : — 1.  When  two  gaseous  bodies,  a,  b,  are  mixed  with  a 
third  body,  c,  and  fired  by  means  of  the  electric  spark,  the  body 
c takes  from  a and  b quantities  which  always  stand  to  one  another 
in  a simple  atomic  relation  : so  that  for  1 atom  of  a c,  1,  2,  3 or 
4 atoms  of  b c are  produced ; for  2 atoms  of  a c,  3,  or  5,  or  7 atoms 
of  B c are  formed.  If  1 atom  of  the  compound  a c,  and  one  of 
B c be  formed  in  this  manner,  the  mass  of  a may  be  increased  in 
the  presence  of  b,  up  to  a certain  point,  without  any  change  in 
that  atomic  proportion  ; but  if  a certain  limit  be  passed,  the  rela- 
tion of  atoms,  instead  of  being  as  1 : 1,  suddenly  becomes  as  1 : 2, 
or  as  2:3;  and  so  on. 

2.  When  a body,  a,  acting  upon  an  excess  of  any  compound, 
B c,  reduces  it,  so  that  a c is  formed,  and  b is  set  at  liberty ; then — 
if  B in  its  turn  can  reduce  the  newly-formed  compound,  a c — 
the  final  result  is,  that  the  reduced  part  of  a c is  in  simple  atomic 
proportion  to  tlie  unreduced  part.  In  the  case  of  these  reductions 
also,  the  mass  of  one  of  the  ingredients  of  the  mixture  may  be  in- 
creased up  to  a certain  point  without  altering  the  relative  pro- 
portions of  the  compounds  obtained  ; but  if  increased  beyond  this 
limit,  a sudden  alteration  in  the  relative  proportions  of  the  pro- 
ducts occurs  ; but  these  proportions  still  admit  of  being  represented 
by  simple  ratios.  This  second  portion  of  the  law  needs  confir- 
mation by  more  extended  experiments. 

The  following  experiments  illustrate  the  first  part  of  the  fore- 
going law  : — On  exploding  mixtures  of  carbonic  oxide  and  hydro- 
gen with  oxygen,  in  the  following  proportions,  Bunsen  found  that 
the  quantities  of  carbonic  oxide  and  hydrogen  which  were  oxi- 
dized were  in  the  proportions  stated  below  : — 

Mixture  detonated.  Eatio  of  Gases  burned. 


Oxygen. 

Hydrogen 

Carb.  Oxide. 

Hydrogen. 

Carb.  Oxide. 

L... 

. ....10.... 

....20.... 

....79*4.\. 

. .'...1 

: 2 

II. . . . 

10.... 

....20.... 

....44*4... 

2 

: 2 

III. . . . 

10.... 

....20.... 

. ...12T... 

6 

: 2 

lY 

10.... 

....37.... 

....31*5... 

8 

: 2 

These  experiments  show  that,  as  the  proportion  of  carbonic 
oxide  to  the  hydrogen  in  the  mixture  decreased,  the  proportion 
oxidized  on  detonation  decreased  also,  but  it  decreased 
not  gradually,  and  these  proportions  were  found  to  be  uniformly 
the  same  on  repeating  the  detonation  with  the  same  mixture, 
although  the  degree  of  compression  to  which  the  mixture  was 
subjected  during  tlie  detonation  was  considerably  varied  in  differ- 
ent experiments. 

Tlie  following  are  Bunsen’s  principal  experiments  in  support  of 
the  second  part  of  the  foregoing  law  : — When  carbonic  anhydride 
is  driven  over  ignited  charcoal,  it  is  wholly  converted  into  car- 
bonic oxide  ; but  when  steam  is  transmitted  over  ignited  charcoal, 
a mixture  of  hydrogen,  carbonic  oxide,  and  carbonic  anhydride  is 
produced,  in  the  proportion  of  4 volumes  of  hydrogen,  2 of  car- 
bonic oxide,  and  1 volume  of  carbonic  anhydride.  Again,  when 
a mixture  of  cyanogen  with  atmospheric  air  and  oxygen  was  de- 


736 


ADHE5I0X SUEFACE  ACTIOXS. 

tonated  in  tlie  eudiometer  in  the  proportion  of  of  cyanogen  to 
10  of  oxygen."^  the  cyanogen  yielded  3 volumes  of  nitrogen,  2 of 
carbonic  oxide,  and  d of  carbonic  anhydride  : and  when  a mixture 
of  4*07  of  carbonic  anhydride,  33-25  of  hydi*ogen,  and  10  of 
oxygen  was  detonated,  a portion  of  the  carbonic  anhydi*ide  yielded 
oxygen  to  the  hydi'ogen,  and  was  reduced  to  the  state  of  carbonic 
oxide  : 3 volumes  of  carbonic  oxide  being  formed,  wliilst  exactly  2 
volumes  of  carbonic  anhydride  remained  unacted  upon,  although 
a large  excess  of  hydrogen  was  present. 

Debus  an-ived  at  substantially  the  same  results  with  precipi- 
tates as  those  indicated  by  Bunsen  lor  gaseous  mixtures : — ^he  pre- 
cipitated a mixtm*e  of  lime  and  baryta  water,  by  small  pjropor- 
tions  of  a solution  of  carbonic  acid  : and  experiments  upon  a large 
excess  of  a dilute  solution  of  the  mixed  chlorides  of  calcimn  and 
of  barium  to  which  a dilute  solution  of  carbonate  of  sodium  was 
added,  led  to  a similar  result. 

In  the  experiments  of  Bunsen,  it  must  be  recollected  that  the 
first  products  of  the  chemical  combination  are  immediately  re- 
moved from  the  sphere  of  action : carbonic  anhydride,  and  car- 
bonic oxide,  and  water  will  not  mutually  react  upon  each  other ; 
and  in  the  experiments  of  Debus,  the  carbonates  of  the  metals  of 
the  earths  are  insoluble — they  are  therefore  at  once  withdrawn 
from  further  action  upon  the  mixture. 

(1004)  Adhesion. — The  influence  of  adhesion  in  aiding  che- 
mical action  is  often  exeited  by  overcoming  the  opposite  force  of 
elasticity  : this  is  exemplified  by  the  manner  in  which  water 
frequently  favours  the  mutual  action  of  dry  gases  upon  each  other. 
For  example,  stilphurous  anhydride  and  sulphuretted  hydrogen 
may  be  mixed  when  chw  without  acting  upon  each  other,  but  if 
water  be  present,  the  mutual  decomposition  of  the  two  gases  is  the 
result.  In  like  maimer,  when  dry  gaseous  sulphimous  anhydride 
and  dry  peroxide  of  nitrogen  are  mixed  together,  no  combination 
takes  place  between  them  ; the  addition  of  a few  drops  of  water, 
iiowever,  causes  them  immediately  to  condense  and  to  foi*m  the 
white  crystalline  compound  which  has  been  spoken  of  when  treat- 
ing of  the  manufacture  of  sulphuric  acid  (412,  and  note  p.  154). 
If  the  elasticity  of  tliese  gases  be  overcome  by  other  means — if, 
tor  instance,  they  be  liquefied  by  ex]iosiug  them  to  a low  temper- 
ature— combination  occurs  ^vithout  the  intervention  of  moisture. 

TT ater.  by  overcoming  the  self-repulsion  of  tlie  gases,  favours 
their  chemical  action  upon  solid  bodies.  Hydrochloric  acid,  and 
ammonia,  in  their  gaseous  fonn,  generally  exert  comparatively 
little  influence  upon  the  metals  or  upon  their  salts,  although  when 
in  solution  their  action  upon  them  is  rapid  and  powertul. 

Surface  Actio7is. — The  adhesion  of  gases  to  solids  produces 
many  curious  phenomena  : — for  example,  let  a piece  of  charcoal 
be  thoroughly  saturated  with  hydrogen  by  attaching  it  to  the 

* Cranogen  requires  for  the  complete  combustion  of  its  carbon  twice  its  volume 
of  oxygen,  so  that  6’2  of  cyanogen  would  have  required  12'4  instead  of  10  of  oxygen ; 
there  is  therefore  more  oxygen  than  would  suffice  for  the  conversion  of  the  carbon 
into  carbonic  oxide. 


SrKFACE  ACTIONS  OF  PLATINUM. 


737 


negative  wire  of  the  voltaic  battery,  and  employing  it  as  the 
platinode  in  the  decomposition  of  acidulated  water  : this  charcoal, 
if  now  detached  from  the  battery  and  thrown  into  a solution  of 
sulphate  of  copper,  or  of  nitrate  of  silver,  will  effect  the  decompo- 
sition of  these  salts,  and  their  respective  metals  will  be  thrown 
down  upon  the  charcoal  in  the  reduced  state ; the  charcoal  and 
condensed  hydrogen  appearing  to  act  the  part  of  a voltaic  circuit, 
in  which  the  hydrogen  supplies  the  place  of  the  electro-positive 
or  oxidizable  metal,  and  the  charcoal  that  of  the  electro-negative 
metal  or  conducting  plate.  If  a plate  of  platinum,  rendered 
chemically  clean,'^  be  introduced  into  a mixture  of  pure  oxygen 
and  hydrogen,  in  the  proportions  to  form  water,  the  gases  become 
condensed  upon  the  surface  of  the  plate,  and  being  brought  with- 
in the  sphere  of  each  other’s  attraction,  begin  to  unite  ; at  first 
slowly,  but  during  the  act  of  combination  heat  is  extricated,  and 
the  action  proceeds  more  quickly,  until  at  last  the  plate  becomes 
red  hot,  and  an  explosion  of  the  gas  ensues  (Faraday,  Phil. 
Trans. ^ 1831,  p.  55).  By  employing  the  metal  in  a disintegrated 
or  spongy  form,  the  surface  exposed  is  greater,  and  the  action 
much  more  rapid  : the  metal  conducts  away  but  little  of  the  heat 
which  is  generated,  and  soon  becomes  red  hot ; whilst  in  the  con- 
dition of  platinum  black  (968)  tliis  activity  attains  its  maximum. 
On  throwing  a little  of  this  black  powder  into  a mixture  of  oxy- 
gen and  hydrogen  it  immediately  becomes  incandescent,  and  the 
gases  combine  with  a loud  report.  Platinum  may  be  obtained  in 
a convenient  state  of  fine  subdivision  for  experiments  of  this 
nature,  by  moistening  asbestos  with  a solution  of  perchloride  of 
platinum  and  exposing  it  to  a red  heat ; the  chlorine  is  expelled, 
and  a film  of  minutely  divided  platinum  is  left  upon  the  surface 
of  each  fibre  of  asbestos. 

From  its  inalterability  by  ordinary  chemical  agents,  platinum 
in  this  finely  divided  form  has  been  used  to  effect  various  com- 
binations which  cannot  otherwise  readily  be  procured  between 
vaporized  and  gaseous  bodies  : — For  instance,  if  ammonia  be 
mixed  with  atmospheric  air,  and  transmitted  over  spongy  plati- 
num gently  heated,  its  nitrogen  becomes  converted  into  nitric 
acid,  and  its  hydrogen  into  water;  IlgN + 2 : 

but  this  transformation  cannot  be  effected  by  heat,  unless  some 
substance  analogous  to  spongy  platinum  be  used,  since  nitric  acid 
is  decomposed  at  a temperature  which,  under  ordinary  circum- 
stances, is  required  to  effect  the  combustion  of  ammonia.  On  the 
other  hand,  ammonia  may  be  formed  from  tlie  oxides  of  nitrogen, 
by  mixing  them  with  hydrogen  and  transmitting  the  gases  over  pla- 
tinum sponge  gently  heated;  2 KO-f5Il2=:2  Il3ll-h2  Il^O. 
X it  rate  of  ammonium,  when  heated  with  platinum  black,  yields 
nitric  acid,  nitrogen,  and  water,  instead  of  nitrous  oxide ; for 

* This  may  be  effected  by  holding  the  plate  over  the  flame  of  a spirit-lamp  and 
rubbing  it,  when  hot,  with  a stick  of  caustic  potash ; the  potash  is  to  be  maintained 
in  a fused  state  upon  its  surface  for  a second  or  two ; the  alkali  is  then  to  be  washed 
off  completely  in  distilled  water,  and  the  plate  is  to  be  immersed  for  a minute  in  hot 
oil  of  vitriol ; after  which  it  is  to  be  freed  from  adhering  acid  by  immersion  for  a 
quarter  of  an  hour  in  a large  bulk  of  distilled  water. 

47 


738 


STJEFACE  ACTIONS  OF  PLATINUM. 


instance,  5 H.NKOg = 2 HlSTOg  + 4 ^ H2^-  A variety  of  other 

interesting  changes  may  be  effected.  According  to  Ddbereiner, 
(who  first  pointed  out  the  remarkable  power  which  finely  divided 
platinum  possesses  of  effecting  combinations  of  this  kind),  a mixture 
of  cyanogen  and  hydrogen  when  in  contact  with  spongy  platinum 
is  partially  converted  by  the  aid  of  a gentle  heat  into  cyanide  of 
ammonium.  In  a mixture  of  nitric  oxide  and  olefiant  gas,  car- 
bonate of  ammonium  is  produced ; and  in  a mixture  of  the  vapour 
of  alcohol  and  nitric  oxide, — cyanide  and  carbonate  of  ammonium, 
olefiant  gas,  water,  and  a deposit  of  carbon  are  formed.  In  like 
manner,  sulphurous  anhydride  may  be  rapidly  converted  into 
sulphuric  acid,  if  it  be  driven,  in  a moist  state,  mingled  with  air, 
through  tubes  containing  spongy  platinum : this  method  was  even 
proposed  as  a manufacturing  process  for  obtaining  oil  of  vitriol, 
but  it  was  abandoned  in  consequence  of  a gradual  alteration  in 
the  platinum,  by  which  it  is  deprived  of  this  power  of  effecting 
combination.  Platinum  black  produces  with  the  vapours  of  alco- 
hol in  contact  with  atmospheric  air,  a series  of  compounds  which 
are  finally  converted  into  acetic  acid  and  water  ; — 

Alcohol.  Acetic  acid. 

+ H,e. 

For  the  success  of  these  experiments,  it  is  necessary  that  the 
surface  of  the  platinum  be  chemically  clean,  otherwise  the  com- 
bination of  the  gases  does  not  take  place.  Faraday  considers  that 
these  actions  are  owing  to  the  adhesion  of  the  gases  to  the  surface 
of  the  metal,  by  which  the  particles  of  one  gas  are  brought  into 
chemical  contact  with  those  of  the  other.  He  observed  that  the 
admixture  of  small  quantities  of  carbonic  oxide,  or  of  the  vapour 
of  bisulphide  of  carbon,  or  of  olefiant  gas,*  prevented  the  platinum 
from  effecting  the  combination  of  the  oxygen  and  hydrogen,  but 
did  not  deprive  the  metal  of  its  activity,  as  w^as  ascertained  by 
afterwards  plunging  it  into  a mixture  of  pure  oxygen  and  hydro- 
gen. On  the  other  hand,  the  addition  of  sulphuretted  or  of  phos- 
phuretted  hydrogen  to  an  explosive  mixture  of  oxygen  and 
hydrogen,  not  only  prevented  the  combination  from  being  pro- 
duced by  the  platinum,  but  it  effected  such  an  alteration  of  the 
surface  of  this  metal  that  when  it  was  plunged  into  a fresh 
portion  of  mixed  oxygen  and  hydrogen,  no  combination  of  the 
gases  occurred.  Hydrochloric  acid  also  rapidly  destroys  the 
peculiar  properties  of  finely  divided  platinum  ; according  to 
Ddbereiner,  the  preventive  action  of  this  gas  depends  upon  the 
decomposition  of  the  hydrochloric  acid  by  the  oxygen  condensed 
upon  the  platinum  : water  is  formed,  whilst  chlorine  is  liber- 
ated, and  this  chlorine,  by  converting  the  platinum  superficially 
into  chloride,  destroys  its  power ; its  activity,  however,  can  be 

* Grraham  finds  that  in  the  case  of  carbonic  oxide  a gradual  oxidation  of 
the  carbonic  oxide  takes  place,  but  that  this  action  is  much  slower  than  the 
oxidation  of  the  hydrogen:  the  oxidizing  influence  is  wholly  concentrated  on 
the  carbonic  oxide,  and  until  this  gas  is  entirely  oxidated  the  hydrogen  remains  un- 
altered in  the  mixture. 


CATALYSIS. 


Y39 


restored  by  treating  it  with  boiling  oil  of  vitriol.  Hydrochloric 
acid  is  in  this  case  expelled,  and  a small  quantity  of  protoxide 
of  platinum  is  dissolved ; the  metal  is  then  to  be  well  washed  in 
distilled  water. 

(1005)  Other  finely  divided  substances  besides  platinum 
possess  this  property  of  favouring  the  combination  of  oxygen  and 
hydrogen  in  an  inferior  degree  ; even  pounded  glass,  porcelain 
charcoal,  pumice,  and  rock-crystal,  if  warmed  to  600°,  produce 
this  effect.  Finely  divided  palladium,  rhodium,  and  iridium 
also  determine  the  combination  of  oxygen  and  hydrogen  with 
explosion  at  ordinary  temperatures.  Gold  and  silver  efi’ect 
the  combination  of  hydrogen  with  oxygen  qidetly,  at  tempera- 
tures far  below  the  boiling-point  of  mercury  (Dulong  and  The- 
nard).  Metals  which  have  a strong  chemical  attraction  for  oxj^gen 
cannot  be  used,  because  they  immediately  become  oxidized  upon 
their  surface. 

(1006)  Catalysis. — The  remarkable  actions  produced  by  the 
agency  of  finely  divided  platinum  have  in  the  foregoing  para- 
graphs been  attributed  to  the  force  of  adhesion,  which  is  supposed 
to  bring  the  difierent  gaseous  bodies  within  the  sphere  of  mutual 
action ; but  they  were  viewed  by  Berzelius  as  arising  from  a new 
force,  which  he  termed  catalysis^  in  virtue  of  which,  he  says, 
“ Certain  bodies  exert,  by  their  contact  with  others,  such  an  in- 
fluence upon  these  bodies,  that  chemical  action  is  excited  ; com- 
pounds are  destroyed,  or  new  ones  are  formed,  although  the  sub- 
stance by  which  these  actions  are  induced  does  not  take  the 
sliglitest  part  in  these  changes.”  This  catalytic  force,  however, 
is  probably  purely  imaginary : most  of  the  phenomena  which 
liave  hitherto  been  referred  to  its  agency  being  occasioned  by 
several  difierent  causes,  which  often  admit  of  being  distinguished 
from  each  other,  and  which  may,  as  in  the  case  of  the  action 
of  platinum,  be  explained  by  the  active  operation  of  other  known 
forces. 

One  class  of  these  phenomena  is  that  included  under  the  term 
fermentation.  Fermentations  are  peculiar  to  the  products  of  or- 
ganic chemistry  ; such  for  instance,  as  the  change  of  solution  of 
sugar  into  alcohol  and  carbonic  anhydride,  under  tlie  infiuenceof 
yeast : the  change  of  starch  into  sugar  in  the  operation  of  mash- 
ing wort,  or  in  the  germination  of  seeds,  owing  to  the  presence  of 
a peculiar  albuminous  substance  termed  diastase : and  the  grad- 
ual conversion  of  amygdalin,  the  bitter  principle  in  the  bitter 
almond,  into  hydrocyanic  acid,  oil  of  bitter  almonds,  sugar,  and 
formic  acid,  when  it  is  dissolved  in  water,  and  mixed  with  synay[)- 
tase.^  or  the  albuminous  substance  contained  in  the  pulp  of  the  seed. 
In  all  these  cases,  however,  although  the  constituents  of  the 
yeast,  the  diastase,  or  the  synaptase,  do  not  enter  into  the  forma- 
tion of  the  new  products,  yet  these  bodies  disappear  during  the 
change,  and  during  the  whole  time  are  undergoing  a series  of  spe- 
cific alterations,  which  stand  in  intimate  but  as  yet  unexplained 
relation  to  the  metamorphosis  of  the  sugar,  the  starch,  or  the 
amygdalin.  One  of  the  most  remarkable  features  of  these  decom- 


74:0 


Liebig’s  theoey  of  catalysis. 


positions  is  tlie  small  proportion  of  tlie  ferment,  or  catalytic  hody 
as  Berzelius  termed  it,  which  is  required  to  produce  the  change : 
for  instance,  1 part  of  yeast,  calculated  in  its  dry  state,  is  suffi- 
cient to  convert  60  parts  of  sugar  into  alcohol  and  carbonic  anhy- 
dride ; and  a still  smaller  quantity  is  required  in  the  case  of 
diastase,  1 part  of  which  is  able  to  effect  tlie  transformation  of 
more  than  1000  times  its  weight  of  starch  into  sugar.  The 
consideration  of  these  remarkable  metamorphoses  must  however 
be  deferred  until  the  organic  bodies  themselves  have  been  de- 
scribed. 

Liebig’s  theory  of  catalysis  is,  “ that  a body  in  the  act  of  com- 
bination or  decomposition  enables  another  body  with  which  it  is 
in  contact  to  enter  into  the  same  state.  It  is  evident,”  says  he, 
“ that  the  active  state  of  the  atoms  of  one  body  has  an  innuence 
upon  the  atoms  of  a body  in  contact  with  it,  and  if  these  atoms 
be  capable  of  the  same  change  as  the  former,  they  likewise  under- 
go that  change,  and  combinations  and  decompositions  are  the  con- 
sequence. * * * This  inhuence  exerted  by  one  compound  upon 
the  other,  is  exactly  similar  to  that  which  a body  in  the  act  of 
combustion  exercises  upon  a combustible  body  in  its  vicinity; 
with  this  difference  only,  that  the  causes  vdiich  determine  the 
participation  and  duration  of  these  conditions  are  different.” 

These  explanations  have  been  found  insufficient  to  account  for 
the  phenomena  of  fermentation,  as  the  bodies  which  are  under- 
going fermentation  do  not  “enter  into  the  state”  as  the 

particles  of  the  ferment ; though  they  apply  admirably  to  many  of 
the  illustrations  cited  by  Liebig  in  support  of  his  theory.  Amongst 
these  illustrations  is  an  experiment  by  Saussure,  who  observed 
that  moist  woody  fibre,  if  placed  in  contact  with  oxygen,  gradu- 
ally converts  the  oxygen  into  carbonic  anhydride.  On  adding  a 
certain  quantity  of  hydrogen  to  a measured  bulk  of  oxygen, 
which  was  undergoing  this  change,  he  observed  a diminution  in 
the  volume  of  the  two  gases  immediately  after  making  the  mix- 
ture ; a portion  of  oxygen  had  thus  been  caused  to  enter  into  com- 
bination with  the  hydrogen,  and  a true  gradual  combustion  of  the 
hydrogen  had  been  effected,  analogous  to  that  produced  by  plati- 
num, owing  to  its  contact  with  vegetable  matter  which  was  itself 
undergoing  slow  oxidation. 

Again,  it  has  been  observed  in  the  case  of  certain  alloys,  that 
the  compound  is  entirely  soluble  in  an  acid  which  may  be  unable 
to  attack  one  of  the  components  of  the  alloy  when  in  a separate 
form.  Platinum,  for  instance,  is  not  soluble  in  nitric  acid,  but  if 
it  be  alloyed  with  10  or  12  parts  of  silver,  the  acid  dissolves  it 
readily.  In  like  manner,  copper  is  insoluble  in  diluted  sulphuric 
acid  ; but  an  alloy  of  zinc,  nickel,  and  copper  is  readily  dissolved 
by  this  liquid. 

(1007)  Effects  of  Motion  on  Chemical  Attraction. — In  many 
cases  motion  favours  the  manifestation  of  cohesion  in  a remark- 
able manner : for  example,  water  may  be  cooled  below  its  freezing- 
point,  and  may  retain  its  liquid  form  if  it  be  kept  perfectly  motion- 
less, but  on  the  slightest  agitation  it  assumes  the  form  of  ice. 


CATALYSIS CONCUEEmG  ATTEACTIONS.  741 

I 

Again,  if  a solution  of  nitrate  of  silver  be  simply  mixed  witli  hy- 
drochloric acid,  it  will  long  remain  milky ; but  if  the  nitrate  be 
in  excess,  and  the  mixture  be  briskly  shaken  for  about  a minute, 
the  whole  of  the  chloride  of  silver  will  collect  into  dense  tlocculi, 
which  subside  rapidly  and  leave  the  liquid  clear.  In  a somewhat 
similar  manner  motion  favours  the  development  of  chemical  action  : 
— when,  for  example,  a mixture  of  tartaric  acid  and  nitrate  of  po- 
tassium is  made,  no  sign  of  precipitation  will  appear  for  many 
minutes,  if  the  mixture  after  simple  agitation  be  left  at  rest : but 
if  it*  be  briskly  stirred  with  a glass  rod,  an  abundant  deposition 
of  crystals  will  speedily  be  produced.  A similar  effect  is  often 
observed  wdth  other  crystalline  precipitates : the  double  chloride 
of  platinum  and  potassium,  or  of  platinum  and  ammonium,  fre- 
quently does  not  appear  in  dilute  solutions  until  the  mixture  has 
been  briskly  stirred.  If  the  glass  rod  which  is  used  in  stirring 
the  mixture  be  drawn  against  the  side  of  the  vessel  containing  the 
liquid,  the  track  of  the  rod  will  be  rendered  evident  by  the  forma- 
tion of  crystals,  which  are  symmetrically  deposited  on  each  side 
of  this  line.  This  effect  is  particularly  manifested  when  a solu- 
tion of  phosphate  of  sodium  is  added  to  dilute  neutral  solutions 
of  magnesium  containing  ammoniacal  salts  ; the  double  phosphate 
of  ammonium  and  magnesium  takes  many  hours  for  its  complete 
deposition,  unless  the  liquid  be  briskly  stirred. 

Sometimes  when  the  chemical  attractions  which  hold  a com- 
pound together  are  feeble,  or  where  the  components  have  a strong 
tendency  to  assume  the  gaseous  form,  a blow  will  be  sufficient  to 
disturb  the  equilibrium,  and  an  explosion  will  follow.  In  this 
way  chloride  of  nitrogen,  which  is  united  by  feeble  ties,  and  is 
composed  of  bodies  which  naturally  exist  in  the  gaseous  state,  is 
sometimes  decomposed  by  the  mere  fall  of  a drop  of  the  liquid 
to  the  bottom  of  a jar  of  the  solution  in  which  it  is  being  formed. 
The  ordinary  percussion-cap  is  another  instance  of  the  same  kind, 
where  the  nitrogen  in  the  fulminate  suddenly  resumes  its  gaseous 
state  on  the  application  of  a blow.  In  the  latter  case,  and  in 
that  of  the  common  lucifer  match,  it  might  be  supposed  that  the 
heat  evolved  by  the  sudden  compression  attending  the  blow  or 
tlie  friction,  is  the  cause  of  these  detonations ; but  this  explanation 
certainly  cannot  apply  to  the  iodide  of  nitrogen,  which,  if  dry, 
explodes  when  touched  even  witii  a feather.  Fulminating  silver 
is  also  decom])osed  with  explosion  by  causes  equally  slight. 

(1008)  Concurring  Attractions.  — Another  class  of  these  so- 
called  catalytic  phenomena  is  exemplified  in  the  effect  of  the  ad- 
mixture of  oxide  of  copper,  or  oxide  of  manganese,  in  aiding  the 
decomposition  of  chlorate  of  potassium.  Chlorate  of  potassium 
fuses  at  about  950°,  and  when  heated  to  about  700°  it  is  decom- 
])Osed  with  effervescence  and  rapid  evolution  of  oxygen:  when 
mixed  with  about  a fourth  of  its  weight  of  black  oxide  of  copper, 
or  of  oxide  of  manganese,  the  salt  begins  to  be  decomposed  at  a 
temperature  of  between  450°  and  500°  (much  below  its  fusing- 
])oint) ; the  gas  which  is  given  off  in  this  case,  however,  is  always 
accompanied  by  a small  quantity  of  chlorine.  Other  oxides  produce 


74:2 


CATALYSIS CONCUKKING  ATTRACTIONS. 


a similaT  effect,  but  the  temperature  required  varies  with  each 
oxide  : thus,  I find  when  the  chlorate  is  mixed  with  sesquioxide 
of  iron  it  requires  a temperature  of  about  500° ; with  oxide  of 
lead  a somewhat  higher  temperature  is  needed ; whilst  magnesia 
and  oxide  of  zinc  do  not  aid  the  decomposition  of  the  salt  at  all. 

This  remarkable  decomposition  appears  to  admit  of  an  expla- 
nation, suggested  by  Mercer,  in  elucidation  of  other  somewhat 
analogous  actions.  He  supposes,  although  the  cataHtic  body  is 
not  found  to  have  experienced  any  perceptible  alteration  after  the 
decomposition  is  complete,  that  it  acts  by  exerting  a feeble  chem- 
ical attraction  upon  one  of  the  constituents  of  the  compound. 
In  the  case  of  oxide  of  manganese  and  chlorate  of  potassium,  the 
oxide  of  manganese  is  a substance  which  has  an  attraction  for  an 
additional  quantity  of  oxygen,  as  is  evinced  by  the  possibility  of 
forming  manganic  and  permanganic  acids  from  it  by  further  oxi- 
dation. This  tendency,  although  it  does  not  rise  high  enough  in 
the  experiment  before  us  to  produce  the  acids,  may  yet  exert 
sufficient  attraction  upon  the  oxygen  to  facilitate  its  escape. 
Indeed  it  is  not  impossible  that  traces  of  manganic  acid  may  be 
actually  formed,  and  then  decomposed  ; in  which  case  the  forma- 
tion of  the  small  quantity  of  potash,  and  the  liberation  of  the 
chlorine,  which  always  accompanies  the  oxygen,  would  be  ac- 
counted for.  A somewhat  similar  explanation  may  be  applied  in 
the  case  of  the  black  oxide  of  copper  : an  unstable  sesquioxide  of 
this  metal  appears  to  exist : black  oxide  of  copper  therefore  has  a 
feeble  attraction  for  oxygen,  and  though  that  attraction  is  not 
adequate  to  retain  the  oxygen  when  separated  from  the  chlorate 
of  potassium,  it  may  yet  aid  in  effecting  its  liberation  : sesquioxide 
of  iron  is  also  susceptible  in  the  ferric  acid  of  ahigher  but  unstable 
stage  of  oxidation,  and  the  same  holds  good  of  oxide  of  lead; 
hence  these  compounds  facilitate  the  decomposition  of  the  chlorate. 
There  is  no  proof  of  the  existence  of  a hio^her  oxide  either  of 
magnesium,  or  of  zinc,  and  accordingly  we  find  that  scarcely  any 
effect  is  produced  on  heating  these  oxides  with  the  chlorate.  I 
find  also  that  powdered  glass  and  pure  silica  are  equally  inert, 
probably  from  the  same  cause. 

Mercer  observed  that  starch,  which  is  ordinarily  converted  by 
nitric  acid  into  oxalic  acid,  is  entirely  transformed  into  carbonic 
anhydride  if  a salt  of  manganese  be  present ; 2 -GO,  being  formed, 
instead  of  H2O2O4.  Oxalic  acid,  also,  may  be  in  this  manner 
rapidly  converted  into  carbonic  anhydride.  If  an  ounce  of  oxalic 
acid  be  dissolved  in  10  ounces  of  water,  at  180°,  and  1 ounce  of 
colourless  nitric  acid,  sp.  gr.  1-30  be  added,  no  decomposition  of 
the  oxalic  acid  occurs ; but  it  immediately  commences  on  adding 
a small  quantity  of  a solution  of  nitrate  of  manganese,  or  any 
other  manganous  salt.  The  protoxide  of  manganese,  from  its  ten- 
dency to  pa,ss  into  the  state  of  peroxide,  tends  to  deprive  the  free 
nitric  acid  of  oxygen,  and  aids  the  oxalic  acid  to  decompose  this 
acid ; and  the  oxalic  acid  having  a stronger  attraction  for  oxygen 
than  the  protoxide  of  manganese  has,  immediately  approj^riates 
tlie  oxygen  ; the  united  attractions  of  both  being  able  to  acconi- 


CATALYSIS CONCUEEING  ATTEACTIONS. 


743 


plisli  a decomposition  wliicli  could  not  have  been  effected  by  either 
separately.  An  analogous  instance  of  the  effect  produced  by  con- 
curring attractions  of  a more  energetic  kind  is  seen  in  the  power 
possessed  by  chlorine  to  decompose  silica  or  alumina  when  these 
oxides  are  mixed  with  charcoal  (475,  664),  though  neither  chlorine 
nor  charcoal  is  able  separately  to  produce  this  effect  upon  them. 

A similar  result  is  obtained  when  a quantity  of  hydrated  oxide 
of  copper,  or  of  peroxide  of  manganese,  is  thrown  into  a mixture 
of  bleaching  powder  and  water ; on  warming  the  mixture,  oxygen 
is  evolved  abundantly,  and  chloride  of  calcium  is  formed ; the 
oxide  of  copper  or  of  manganese,  by  its  attraction  for  oxygen,  aids 
the  elastic  force  developed  by  heat  in  detaching  the  oxygen  from 
the  chloride  of  lime,  and  the  oxygen,  by  its  elasticity,  escapes  in 
the  gaseous  form  without  combining  with  the  metallic  oxide. 

Gaseous  ammonia  may  be  passed  through  heated  porcelain 
tubes  at  a very  high  temperature,  and  it  will  experience  only  a 
partial  decomposition  ; but  if  the  tube  be  filled  with  finely  divided 
metallic  copper  or  iron,  the  decomposition  takes  place  with  facility 
at  a lower  temperature.  It  appears  that  in  this  case,  the  metals 
act  by  their  attraction  for  nitrogen,  which  is  feeble,  and  that  a 
nitride  of  copper  or  of  iron  is  formed  and  subsequently  decomposed. 
If  iron  wire  be  employed  instead  of  finely  divided  iron,  it  is 
found  to  have  become  superficially  altered  and  brittle  (760).  Pla- 
tinum favours  the  decomposition  of  ammonia  but  slightly,  and 
glass  scarcely  in  any  appreciable  degree. 

Alcohol  when  exposed  to  the  air,  evaporates  without  under- 
going any  chemical  change,  but  if  a quantity  of  caustic  potash  be 
dissolved  in  the  alcohol,  the  alkali  appears  to  enhance  its  attrac- 
tion for  oxygen ; in  consequence  of  which  acetic  and  formic  acids 
are  produced,  and  form  salts  with  the  potash. 

The  decomposition  of  peroxide  of  hydrogen  (485)  by  contact 
with  many  bodies,  which  appear  to  undergo  no  chemical  alteration 
during  the  action,  may  probably  be  referred  to  the  same  cause. 
AVhen,  for  example,  finely  divided  metallic  gold,  silver,  or  plati- 
num, or  black  oxide  of  manganese,  is  placed  in  the  liquid  per- 
oxide, the  latter  is  decomposed,  the  oxygen  being  attracted  by 
the  metal,  wliich,  however,  has  not  sufficient  power  to  retain  it 
in  combination.  A singular  circumstance,  however,  has  been  ob- 
served wlien  oxide  of  gold  or  oxide  of  silver  is  substituted  for  the 
metal  itself;  decomposition  of  the  peroxide  is  produced  by  the 
metallic  oxide,  but  the  oxide  of  gold  or  of  silver  at  the  same  time 
parts  with  its  oxygen,  and  is  reduced  to  the  metallic  state.  A 
similar  reaction  happens  if  an  acid  solution  of  acid-chromate  of 
potassium  be  mixed  with  the  peroxide  of  hydrogen,  the  chromic 
acid  losing  half  its  oxygen  simultaneously  with  the  peroxide  of 
hydrogen. 

Brodie  {Phil.  Trans.  1850,  p.  759,  and  1862,  p.  837),  has 
]uiblished  the  results  of  a series  of  experiments,  showing  that  in 
sucli  decompositions  there  is  a numerical  relation  between  tlie 
quantity  of  the  peroxide  wliich  is  decomposed  and  of  the  metallic 
oxide  wliich  is  reduced.  These  experiments  w^ere  not  confined  to 


CATALYSIS — COXCrURDsG  ATTKACTIOXS. 


7U 


peroxide  of  hydrogen,  but  Tvere  extended  to  peroxide  of  barinm, 
and  peroxide  of  sodium,  whicli  are  much  more  manageable  than 
peroxide  of  hydrogen.  It  was  found  that  when  the  peroxide  is 
mixed  with  water,  and  placed  in  contact  with  oxide  or  with  chlo- 
ride of  silver,  that  both  the  compound  of  barium  and  that  of  silver 
is  decomposed ; baryta,  or  chloride  of  barium,  being  formed,  whilst 
metallic  silver  and  oxygen  gas  are  liberated.  When  a dilute  solu- 
tion of  permanganate  of  potassium  is  mixed  with  an  acid  solution 
of  peroxide  of  hydrogen,  both  compounds  are  decomposed,  the 
permanganate  losing  an  atom  of  oxygen  for  each  atom  of  oxygen 
liberated  from  the  peroxide.  A similar  decomposition  occurs  if 
h}^30chlorite  of  barium  be  substituted  for  permanganate  of  potas- 
sium. Brodie  connects  these  experiments  with  a hypothesis  since 
generally  adopted,  by  which  he  accounts  for  the  simultaneous 
liberation  of  oxygen  from  the  peroxide  of  hydrogen  or  of  barium, 
and  from  the  oxide  of  silver  or  other  oxide  which  undergoes 
decomposition,  and  which  he  applies  to  chemical  decompositions 
generally : he  supposes  that  the  jpartides  of  the  same  element  may, 
in  certain  circumstances,  have  an  attraction  for  each  other : — that, 
for  example,  one  atom  of  the  oxygen  of  the  peroxide  of  barium 
may  be  positive  in  its  relation  to  tlie  oxygen  of  the  oxide  of  silver, 
which  he  supposes  may  be  negative.  In  such  a case  the  two  par- 
ticles of  oxygen  would  mutually  attract  each  other,  and  decom- 
position of  both  the  oxides  would  be  the  result. 

Other  substances  besides  peroxide  of  hydrogen  and  the  alkaline 
peroxides,  exhibit  a similar  susceptibility  to  decomposition  by  con- 
tact with  certain  bodies.  Persulphide  of  hydrogen,  for  example, 
is  immediately  decomposed  by  contact  with  oxides  of  manganese 
and  silver,  and,  like  the  peroxide  of  hydrogen,  it  is  rendered  more 
stable  by  the  addition  of  acids,  while  its  decomposition  is  facili- 
tated by  contact  with  alkalies  (1:29).  The  nitrosulphates  (1:25) 
discovered  by  Pelouze  afibrd  another  instance  of  decomposition 
etfected  by  a body  which  undergoes  no  apjparent  change ; but  this 
decomposition  is  particularly  instructive,  as  it  is  almost  certain 
that  the  body  which  excites  the  decomposition  does  suffer  a real 
chemical  change.  For  example,  the  addition  of  a solution  of  sul- 
phate of  copper  to  a solution  of  nitrosulphate  of  ammonium  causes 
an  immediate  effervescence,  owing  to  the  escape  of  nitrous  oxide. 
This  decomposition  appears  to  be  produced  thus : — on  the  addition 
of  sulphate  of  copper,  the  nitrosulphate  partially  exchanges  basyls 
with  it ; now  so  long  as  the  nitrosulphuric  radicle  is  in  combina- 
tion with  an  alkaline  metal,  the  compound  has  a certain  stability, 
since  the  alkali-metals  appear  by  their  basic  energy  to  preserve 
the  elements  in  equilibrio  ; but  as  soon  as  a salt  with  a weaker 
basyl  is  added,  such  as  the  sulphate  of  copper,  a portion  of  nitro- 
sulphate of  copper  is  formed ; but  the  copper  being  no  longer  able 
to  maintain  this  balance,  the  elements  of  the  compound  arrange 
themselves  in  a new  order : for  instance — 


Xitrosulph  Ammon. 

K 


Sulph.  Copper.  Sulph.  Ammon.  Nitrosnlph.  Copper. 


(ii,x),se3X,o,  + euse,  = (ii.a).3SO,  + ; 


EsFLUENCE  OF  HEAT  UPON  CHEMICAL  ATTRACTION.  Y45 

and  the  nitrosiilphate  of  copper  immediately  breaks  np  into  nitrons 
oxide  and  sulphate  of  copper ; OiiSOgN^O^  becoming  OnSO,  + 
Consequently  sulphate  of  copper  is  found  in  the  liquid  at  the  close 
of  the  reaction  ajpparenthj  unaltered. 

§ II.  Influence  of  Heat  upon  Chemical  Attraction. 

(1009)  The  forces  which  have  as  yet  been  considered  do  not 
manifest  any  specific  effect  in  altering  tlie  amount  of  chemical 
attraction  between  any  two  bodies ; but  it  is  quite  otherwise  in 
the  case  of  heat,  which  exerts  a direct  infiuence  upon  the  degree 
of  attraction.  Elevation  of  temperature  generally  acts  at  once  in 
augmenting  the  tendency  to  combination  between  the  bodies 
which  are  submitted  to  its  infiuence : — for  example,  sulphur  or 
charcoal  may  be  preserved  at  ordinary  temperatures,  in  air  or  in 
oxygen,  without  change,  for  an  indefinite  period  ; but  if  sulphur 
be  heated  to  500°,  and  charcoal  to  a point  a little  below  a red  heat, 
oxidation  commences,  and  proceeds  with  increasing  vigour,  and 
the  phenomena  of  combustion  occur.  But  although  a rise  of 
temperature  exalts  the  action  of  chemical  attraction,  this  tendency 
to  combination  is,  at  the  same  time,  more  or  less  counteracted, 
and  is  sometimes  completely  overcome,  by  the  tendency  to  mutual 
repulsion  which  heat  imparts  to  the  molecules  of  all  substances, 
both  simple  and  compound.  It  not  unfrequently  happens  that  a 
moderate  elevation  of  temperature  produces  combination,  whilst 
a higher  temperature  destroys  the  compound  so  formed.  A good 
instance  of  this  kind  occurs  in  the  action  of  oxygen  upon  mercury ; 
at  ordinary  temperatures  this  metal  shows  no  disposition  to  com- 
bine with  oxygen,  for  it  evaporates  in  air  and  becomes  condensed 
again  in  the  metallic  form  ; but  at  a temperature  approaching 
700°,  or  a little  above  the  boiling-point  of  the  metal,  it  combines 
gradually  with  oxygen  and  becomes  converted  into  the  red  oxide ; 
whilst  at  a heat  short  of  redness  it  is  decomposed  into  gaseous 
oxygen  and  vapour  of  mercury.  Again — baryta  at  a red  heat 
absorbs  a second  atom  of  oxygen,  forming  peroxide  of  barium, 
but  the  second  atom  of  oxygen  is  expelled  by  a full  white  heat, 
and  the  compound  is  reconverted  into  baryta.  A mixture  of 
oxygen  and  hydrogen  may  be  preserved  unchanged  at  ordinary 
temperatures,  but  the  introduction  of  a glass  rod  heated  to  bare 
redness  so  completely  alters  their  mutual  attraction,  that  sudden 
combination  attended  with  explosion  is  the  result.  This  appears 
to  be  as  pure  a case  of  augmentation  of  chemical  attraction  as 
can  be  met  with,  since  both  the  conq)onents  are  thoroughly 
mixed,  and  as  both  are  in  the  gaseous  state,  heat  cannot  in  this 
case  act  by  diminishing  cohesion,  and  so  bringing  their  particles 
into  more  intimate  contact.  Grove,  however,  has  shown  that  in 
the  case  of  this  same  compound  of  oxygen  and  hydrogen  a sudden 
inversion  of  chemical  attraction  takes  ])lace,  for  at  an  intense 
white  heat  water  is  separable  into  its  constituent  gases : by  the 
voltaic  ignition  of  a platinum  wire  under  water,  or  l)y  the  intense 
heat  of  a ball  of  melted  platinum  raised  to  whiteness  by  an  alcohol 


746 


SUSPENSION  OF  CHEMICAL  ATTRACTION  BY  COLD. 


flame  animated  by  a current  of  oxygen,  and  then  plunged  under 
water,  the  two  gases  may  be  separated  from  each  other  and  col- 
lected in  the  gaseous  state  {Phil.  Trans.  1847). 

Sometimes  the  decomposition  efiected  by  elevation  of  tempera- 
ture is  only  partial;  a new  and  more  stable  compound  being 
formed,  which  at  a still  higher  temperature  is  in  its  turn  decom- 
posed : for  example,  olefiant  gas  at  a full  red  heat  loses  half  its 
carbon,  and  is  converted  into  light  carburetted  hydrogen  ; and 
this  gas,  if  subjected  to  a white  heat,  deposits  the  remainder  of  its 
carbon,  whilst  pure  hydrogen  is  liberated.  Chlorate  of  potassium 
at  a moderate  heat  is  decomposed  into  perchlorate,  and  probably 
into  chlorite  of  potassium  : the  latter  salt,  however,  is  immedi- 
ately resolved  into  oxygen  and  chloride  of  potassium ; but  at  a 
higher  temperature  the  perchlorate  in  its  turn  parts  with  its 
oxygen,  and  the  more  stable  chloride  of  potassium  is  the  final 
result,  l^umerous  other  instances  of  this  kind  will  be  presented 
to  the  reader  when -the  products  of  organic  chemistry  are  examined. 

A further  illustration  of  this  point  is  afforded  by  the  difierent 
products  which  are  furnished  by  the  combustion  of  the  same  body 
at  difierent  temperatures.  When  a jet  of  cyanogen  is  burned  with 
a free  supply  of  air,  the  only  products  of  the  combustion  are  car- 
bonic anhydride  and  nitrogen ; but  if  a coil  of  red-hot  platinum 
wire  be  suspended  in  a mixture  of  equal  volumes  of  cyanogen  and 
oxygen,  the  nitrogen  undergoes  oxidation  as  well  as  the  carbon, 
nitric  oxide  being  formed,  as  is  e\ddenced  by  the  appearance  of 
ruddy  fumes,  owing  to  the  combination  of  the  nitric  oxide  with 
free  oxygen.  In  a similar  manner,  ether,  when  burnt  freely  in 
air,  produces  carbonic  anhydride  and  water,  -f- 6 O,  be- 

coming 4 OOj-f-S  H^O;  but  if  a glowing  coil  of  platinum  wire  be 
suspended  in  a mixture  of  the  vapour  of  ether  and  atmospheric 
air,  several  new  products  are  formed,  among  which  are  aldehyd 
and  acetic  acid : — 

Ether.  Aldehyd. 

ejl3  + 0,:3:2ejI^+H,0;  and 

Ether.  Acetic  acid. 

+ 2 o, = 2 -f  H,e. 

(1010)  /Suspension  of  Chemical  Action  hy  Depression  of  Tem- 
perature.— As  chemical  attraction  is  increased,  on  the  one  hand,  by 
elevation  of  temperature,  so,  on  the  other  hand,  it  is  diminished 
by  reduction  of  temperature.  Schrdtter  has  shown  {Chemie.,  vol. 
i.  p.  129)  that,  by  a sufficient  degree  of  cold,  chemical  combination 
may  be  prevented  even  between  bodies  which  at  the  ordinary 
temperature  of  the  air  unite  with  each  other  with  great  energy. 
Chlorine,  for  example,  combines  with  phosphorus,  or  with  finely- 
divided  metallic  antimony  or  arsenicum,  with  such  violence  that 
these  bodies  take  fire  spontaneously  in  an  atmosphere  of  the  gas ; 
but  if  the  chlorine  be  cooled  down  to  — 106°,  by  means  of  a bath 
of  solid  carbonic  anhydride  and  etlier  (196),  it  remains  liquid  at 
the  ordinary  pressure  of  the  air,  and  it  is  then  quite  indifferent  to 


INFLUENCE  OF  LIGHT  ON  CHEMICAL  ATTRACTION.  Y4:7 

the  phosphorus,  the  arsenicum,  or  the  antimony,  provided  these 
substances  be  cooled  to  the  same  temperature  before  they  are 
added  to  the  liquid  chlorine.  When  the  tube  in  which  the  mix- 
ture is  contained  is  withdrawn  from  the  cold  bath,  the  evapo- 
ration of  the  chlorine  occurs  with  sufficient  rapidity  to  preserve 
the  temperature  below  the  point  of  combination  ; but  if  the  free 
escape  of  the  chlorine  be  prevented,  the  temperature  rises,  and 
combination  occurs  with  explosive  violence.  The  mutual  action 
of  chlorochromic  acid  and  alcohol,  of  chlorine  and  ammonia,  of 
iodine  or  of  bromine  and  phosphorus,  and  various  other  actions 
of  a similar  nature,  may  be  prevented  in  the  same  way. 

From  these  experiments,  and  from  those  detailed  in  the  fore- 
going paragraph,  it  appears  to  be  most  probable  that  when  two 
l3odies  have  a chemical  attraction  for  each  other,  there  is  a certain 
range  of  temperature  within  which  they  will  enter  into  combina- 
tion, but  if  the  temperature  be  raised  or  depressed  beyond  a 
certain  limit,  their  mutual  attraction  is  suspended ; and  at  high 
temperatures  the  compound  already  formed  may  be  destroyed. 
The  temperature  most  favourable  for  combination  varies  with  each 
pair  of  bodies,  and  it  seems  to  be  probable  that  there  is  for  each  a 
certain  temperature  at  which  the  maximum  of  attraction  exists, 
and  above  or  below  which  it  decreases. 

§ III.  Influence  of  Light  on  Chemical  Attraction — 
Photography. 

(1011)  Supposed  Influence  of  Light  upon  Crystallization. — It 
is  a familiar  observation,  that  volatile  bodies  which  crystallize 
as  they  are  condensed  after  spontaneous  sublimation, — such  as 
camphor,  naphthalin,  and  Faraday’s  chloride  of  carbon, — if  placed 
in  glass  vessels,  often  collect  upon  the  side  of  the  glass  which  is 
exposed  to  the  light,  whilst  no  crystals  are  deposited  upon  the 
other  side  of  the  vessels.  This  effect,  however,  is  not  confined  to 
crystallizable  substances.  If  a few  drops  of  water  be  placed  at 
the  bottom  of  a bottle,  the  sides  of  which  are  kept  dry,  and  the 
mouth  of  the  bottle  be  closed,  a deposit  of  globules  of  moisture 
will  generally  be  observed  upon  a particular  portion  of  the  side, 
and  often  this  deposit  occurs  upon  the  illuminated  side  of  the 
bottle.  A similar  effect  is  frequently  seen  in  the  vacuum  of  a 
barometer,  globules  of  mercury  being  condensed  upon  the  side  of 
the  tube.  Yt  was  generally  supposed  that  these  effects  were  due 
to  some  subtle  influence  exerted  by  light,  but  Tomlinson  has 
shown  conclusively  that  they  are  simply  owing  to  differences  in 
temperature  ; the  crystals,  or  the  liquid,  becoming  condensed  upon 
that  part  of  the  vessel  which,  from  accidental  circumstances,  is  the 
coldest  {Phil.  Mag.  1862). 

(1012)  Chemical  Actions  of  Light. — The  rays  of  the  sun  are 
not  only  the  great  source  both  of  light  and  heat  to  the  globe  which 
we  inhabit,  but  they  are  constantly  exerting  upon  the  various 
substances  upon  its  surface,  a chemical  influence  of  the  utmost 
importance  to  the  existence  of  animal  and  vegetable  life,  and  to  the 


PHOTO-CHEMICAL  IXDECTIOX. 


71S 

permanence  of  the  present  order  of  creation.  The  occurrence  of 
this  remarkable  chemical  activity  in  the  solar  rays  may  be  shown 
in  various  ways : — ^When  perfectly  dry  chlorine  is  mixed  in  the 
dark  with  hydrogen,  no  chemical  change  takes  place ; if  the  two 
gases  have  been  exposed  separately  to  the  beams  of  the  snn,  and 
have  subsequently  been  mixed  in  the  dark,  they  may  be  pre- 
served in  this  condition  also  without  change,  so  long  as  they 
are  screened  from  the  light ; but  if  the  mixture  be  exposed  to 
diffused  daylight,  it  will  be  observed  that  the  two  gases  begin 
gradually  to  combine,  and  if  they  be  free  from  admixture  with 
uncombined  oxygen  or  excess  of  hydrogen,  sudden  combination 
with  explosion  occurs  when  they  are  exposed  to  the  direct  rays 
of  the  sun.  The  rapidity  with  which  this  combination  occurs  is 
proportioned  to  the  intensity  of  the  light,  and  an  instrument  for 
measuring  the  amount  of  the  action  which  is  produced  by  diffused 
daylight  was  described  by  Draper,  under  the  somewhat  fanciful 
name  of  tlie  tithononieter  (Phil.  2Iag.  Dec.  18d3). 

(1013)  Photo-chemical  Induction. — An  elaborate  investigation 
of  the  circumstances  which  inhuence  the  action  of  light  upon  a 
mixture  of  chlorine  and  hydrogen,  by  Bunsen  and  Roscoe,  will 
be  found  in  the  Phil.  Trans,  for  1857. 

From  these  investigations  it  appears  to  be  probable  that  a 
species  of  induction  precedes  the  chemical  action.  It  was  found 
by  Draper  that  on  exposing  the  explosive  mixture  of  chlorine  and 
hydrogen  to  diffused  daylight,  the  amount  of  condensation  gradu- 
ally increases  for  a few  minutes,  until  it  attains  a maximum,  at 
which  point  the  rate  of  combination  between  the  two  gases  con- 
tinues to  be  uniform  for  ecpial  amounts  of  incident  light.^  Draper 
attributed  this  slow  attainment  of  the  maximum  rate,  to  an  effect 
of  light  upon  chlorine  alone,  in  consequence  of  which  it  was 
gradually  converted  into  a new  and  more  active  modification. 
Bunsen  and  Boscoe,  however,  did  not  find  tliat  either  chlorine  or 
hydrogen,  when  separately  exposed  to  light,  exhibited,  after  they 
had  been  mixed  and  again  exposed,  any  action  different  from 
that  observed  when  the  gases  were  prepared  and  mixed  in  the  dark 
and  then  exposed  to  light ; they  consider  that  the  light  acts  by 
overcoming  certain  resistances  which  oppose  the  combination  of 
the  two  gases;  and  this  peculiar  action  they  term  photo -chemical 
induction.  The  time  which  elapses  before  the  maximum  action, 
due  to  the  light,  is  attained,varies  considerably  in  different  experi- 
ments,— ranging  from  3 or  4 minutes  up  to  10  or  15.  The  more 
intense  the  light,  the  more  rapidly  is  the  maximum  attained,  but 
the  increase  is  in  a greater  ratio  than  the  mere  increase  of  light. 
This  inductive  influence  upon  the  gases  is  not  permanent.  If  they 
are  placed  in  the  dark  for  a short  time,  and  are  afterwards  again 
exposed  to  the  light,  an  interval  of  exposure  similar  to  the  first  is 
required  before  the  maximum  rate  of  combination  is  attained. 

(1014)  Action  of  Light  on  Ilixed  Gasses.  — The  presence  of 
foreign  gases  in  the  mixture  of  chlorine  and  hydrogen  greatly 
diminishes  its  sensitiveness  to  the  action  of  light : the  addition, 
for  example,  of  3 parts  of  hvdrogen  to  1000  of  the  mixture  re- 


ACTION  OF  LIGHT  ON  MIXED  GASES. 


749 


diiced  tlie  rate  of  combination  for  equal  amounts  of  exposure  from 
100  to  37‘8.  The  effect  of  oxygen  is  still  greater ; 5 parts  of  oxy- 
gen in  1000  of  the  mixture  reduced  its  sensitiveness  under  similar 
exposure  from  100  to  9-7,  and  13  parts  of  oxygen  to  2*7.  The 
following  table  shows  the  results  obtained  with  these  and  some 
other  gases, — taking  the  amount  of  condensation  observed  in  equal 
times  with  the  pure  mixture  of  equal  measures  of  chlorine  and 
hydrogen  as  in  all  cases  equal  to  100  : — 

Rate  of  Co7ribination  for  Intervals  of  equal  Exjoosure  to  Light. 


Nature  of  Foreign  Gas. 

Vol.  of  Chlo- 
rine and 
Hydrogen. 

Vol.  of 
Foreign 
Gas. 

Eatio  of 
Condensa- 
tion. 

None 

Hydrochloric  Acid 

Chlorine 

Hydrogen 

Oxygen .... 

1000 

1000 

1000 

1000  . 

1000 

0 

1-3 

] 

( 180 

3 

1 13 

100 

100 

60-2 

50-3 

41*3 

37-8 

9-7 

2-7 

Bunsen  and  Boscoe  found  that  a gas  consisting  of  equal 
measures  of  chlorine  and  hydrogen  could  be  obtained  with  cer- 
tainty, by  the  electrolysis  of  a solution  of  hydrochloric  acid  of 
sp.  gr.  1*148,  if  a sufficient  interval  were  allowed  for  the  liquid  to 
become  saturated  with  the  two  gases.  This  gaseous  mixture  gave 
perfectly  constant  results  for  equal  exposure  to  a light  of  uniform 
intensity,  provided  care  was  taken  to  ensure  the  complete  expulsion 
of  air  from  the  apparatus.  The  constant  source  of  light  which 
they  employed  wvas  that  of  a jet  of  coal-gas,  burned  from  a platinum 
nozzle,  and  connected  with  a special  apparatus  for  regulating  the 
efflux  of  the  gas.  The  coloration  of  the  ff  ame  ])y  a trace  of  foreign 
matter  materially  affected  its  chemical  activity. 

Chlorine  and  carbonic  oxide  gas  also  enter  slowly  into  com- 
bination under  the  influence  of  sunshine.  Two  measures  of  chlo- 
rine and  two  of  carbonic  oxide  in  this  manner  become  condensed 
into  2 measures  ; the  result  is  the  formation  of  the  irritating  pun- 
gent gas  known  as  phosgene  gas  (388),  in  allusion  to  the  mode  of 
its  production.  It  is  remarkable  that  the  direct  union  of  these 
gases  cannot  be  effected  by  any  other  means. 

Organic  chemistry  abounds  with  instances  in  which  combina- 
tions and  decompositions  are  effected  by  chlorine,  under  the  in- 
fluence of  the  solar  ray  : a few  of  these  have  been  mentioned 
when  speaking  of  the  transformations  of  Dutch  liquid  (488).  The 
operation  of  bleaching  linen,  by  exposuro  to  moisture  and  light 
for  several  weeks  during  summer,  is  another  process  which  il- 
lustrates the  influence  of  solar  light  in  the  production  of  chem- 


750 


DEOXIDIZIN-G  rXFLrEXCE  OX  LIGHT. 


ical  clianges.  But  the  chemical  actions  produced  by  the  sun’s 
rays,  which  are  taking  place  unperceived  around  us,  are  of  in- 
finitely greater  importance  than  those  limited  transformations 
which  can  he  effected  in  the  laboratory  or  the  bleach-field ; for  it 
is  upon  these  unobserved,  yet  daily  renewed  alterations,  that  the 
growth  and  renovation  of  the  entire  vegetable  kingdom  is  de- 
pendent. The  great  chemical  eflect  of  light  appears  to  he  that 
of  a powerful  reducing  or  deoxidizing  agent.  Under  the  influence 
of  solar  light,  the  green  parts  of  plants  perform  their  allotted 
function  in  the  purification  of  the  atmosphere,  by  absorbing  and 
removing  carbonic  acid,  in  virtue  of  which  they  fix  the  carbon  in 
their  tissues,  and  thus  supply  themselves  with  food ; by  a similar 
decomposition  of  water  they  obtain  the  hydi’ogen  needed  for  their 
growth,  while  they  return  into  the  aerial  ocean  a portion  of  the 
oxygen  with  which  the  carbon  and  the  hydrogen  were  previously 
in  combination,  and  thus  assist  in  maintaining  that  uniformity  in 
the  composition  of  the  atmosphere  which  is  indispensable  to  the 
healthful  existence  of  animal  life. 

If  solar  light  be  excluded  from  plants,  none  of  these  decompo- 
sitions are  effected ; the  carbonic  acid  escapes  unchanged  into  the 
air,  and  no  fixation  of  carbon  ensues ; the  plant  becomes  pale  and 
succulent,  whilst  its  functions  languish.  Gardeners  take  advantage 
of  this  knowledge  in  order  to  procure  vegetables  of  more  delicate 
flavour  ; by  earthing  up  the  plant,  as  is  practised  with  celery,  or 
by  covering  it  with  a tile  as  in  the  case  of  endive,  or  by  enclosing 
it  in  a bell-jar,  as  is  usual  with  seakale,  the  fight  is  more  or  less 
excluded,  and  the  bleachinor  which  is  desired  in  ves^etables  for  the 

^ > O O 

table  is  produced. 

(1015)  Reducing  Influence  of  Light  on  2Ietcdlic  Salts. — Much 
attention  has,  within  the  last  few  years,  been  given  to  the  study 
of  the  chemical  actions  produced  by  light,  in  consequence  of  the 
beautiful  inventions  of  the  Talbot v])e  and  the  Daguerreotype. 
These  remarkable  processes,  as  well  as  others  of  a somewhat 
similar  character,  appear  to  depend  upon  the  power  which  the 
more  refrangible  rays  of  the  solar  spectrum  possess  of  causing  the 
decomposition  of  the  oxide,  chloride,  or  bromide  of  silver,  and  of 
certain  compounds  of  one  or  two  other  of  the  metals.  This  decom- 
position by  means  of  light,  usually  takes  place  under  the  concur- 
rent influence  of  hydrogen,  or  of  some  metallic  body,  which  acts 
either  by  setting  free  the  silver  or  other  metal,  or  by  producing  a 
lower  oxide,  chloride,  or  other  compound  of  the  metal.  In  other 
cases,  as  with  the  iodide  of  silver,  a molecular,  and  not  a chemical 
change,  appears  to  be  produced  by  exposure  to  fight.  In  this 
case  there  is  no  immediate  change  of  colour,  but  it  may  be  ren- 
dered visible  by  the  reactions  produced  by  the  application  of 
suitable  chemical  reagents  to  the  compound  after  it  has  been  so 
exposed  to  the  solar  ray. 

The  following  instances  of  the  eftfects  of  fight  have  long  been 
observed  by  chemists  : — If  a piece  of  white  silk  be  dipped  into  a 
solution  of  chloride  of  gold,  and  exposed  whilst  in  a moist  state 
to  the  sun’s  light,  the  silk  becomes  green,  then  purple,  and  in 


PHOTOGEAPHIC  PKINTING. 


751 


less  than  an  hour  a film  of  metallic  gold  is  produced  upon  its  sur- 
face. Kitrate  of  silver  in  solution  in  pure  water  undergoes  no 
change  when  exposed  to  the  light,  hut  if  any  organic  matter 
be  added  to  the  liquid,  a black  deposit  is  gradually  formed ; and 
if  the  salt  be  placed  upon  the  surfiice  of  the  skin,  upon  paper,  or 
upon  linen,  the  well-known  blackening  efiect  for  which  it  is  valued 
as  a marking  ink  for  linen  is  produced.  Moist  chloride  of  silver 
retains  its  dazzling  whiteness  if  preserved  in  total  darkness,  but 
it  assumes  a violet  tint,  which  gradually  deepens  in  intensity,  if 
exposed  even  to  the  diffused  light  of  day, — a portion  of  chlorine 
being  liberated  in  the  process. 

(1016)  Photographic  Printing. — The  earliest  experiments  that 
have  been  published  upon  the  production  of  pictures  by  the  action 
of  light,  appear  to  have  been  made  by  Thos.  Wedgwood  and  Davy 
in  the  year  1802.  Wedgwood  moistened  white  paper,  or  white 
leather,  with  a solution  of  nitrate  of  silver,  and  by  its  means 
copied  paintings  on  glass,  and  took  profiles ; but  neither  he  nor 
Davy  was  able  to  devise  any  means  for  preserving  these  pictures 
when  exposed  to  diffused  light. 

The  subject  attracted  but  little  attention  until  the  commence- 
ment of  the  year  1839,  when  Fox  Talbot  made  known  {Phil.  Mag. 
vol.  xiv)  liis  process  of  photogenic  drawing^  which  consisted  in 
soaking  ordinary  writing-paper  in  a weak  solution  of  common  salt, 
and  when  dry,  washing  it  over  upon  one  side  with  a solution  of 
nitrate  of  silver,  consisting  of  1 part  of  a saturated  solution  of  the 
nitrate  with  6 or  8 parts  of  water.  This  operation  was  performed 
by  candle-light,  and  the  paper  was  dried  at  the  fire ; in  this  man- 
ner a film  of  chloride  of  silver,  mixed  with  an  excess  of  nitrate  of 
silver,  was  formed  upon  the  surface  of  the  paper.  Suppose  that 
it  were  desired  to  obtain  a copy  of  an  engraving,  or  of  the  leaf  of 
a tree ; one  of  the  sheets  so  prepared  was  laid  under  the  engraving 
or  the  leaf  which  was  to  be  copied  : the  two  were  pressed  firmly 
together  between  two  plates  of  glass,  and  exposed  to  the  direct 
rays  of  the  sun,  or  even  to  diffused  daylight,  for  a period  of  half 
an  hour  or  an  hour.  The  impression  tlius  obtained  was  a negative 
one,  that  is  to  say,  the  shadows  were  represented  by  lights,  and 
the  lights  by  shadows ; those  portions  of  the  surface  which  had 
been  exposed  to  the  strongest  light  becoming  dark  : in  the  half 
tints,  where  a feebler  light  had  been  transmitted,  the  blackening 
became  less  evident ; and  the  parts  corresponding  to  the  deep 
shadows  in  the  engraving  remained  white.  The  ])ictures  were 
fixed  by  immersing  them  in  a strong  solution  of  common  salt. 
Considerable  improvements  have  l)een  introduced  into  this  process 
since  it  was  first  published,  but,  in  princii)le,  this  operation,  which 
has  been  photograpjhic 2)rinting ^ remains  unchanged. 

A very  good  ])aper  for  this  kind  of  ])rinting  may  be  obtained 
as  follows  : — Prepare  a solution  of  chloride  of  sodium  or  of  chlo- 
ride of  ammonium,  containing  10  grains  of  the  salt  to  each  ounce 
of  water.  If  French  pay)er  (which  is  sized  with  starch)  is  to  be 
used,  it  will  be  improved  by  dissolving  1 grain  of  gelatin  in  each 
ounce  of  the  solution  of  salt.  Pour  this  liquid  into  a flat  shallow 


752 


TALBOTTPE,  OE  CALOTTPE  PEOCE5S. 


dish,  and  having  cut  the  paper  into  pieces  of  a convenient  size, 
take  a sheet  of  it  by  the  two  opposite  corners,  and  bring  it  down 
upon  the  sni’face  of  the  solntion,  so  that  the  middle  of  the  sheet 
shall  be  first  moistened ; then  lower  it  gradually  towards  each  cor- 
ner so  as  to  exclude  air-bubbles.  After  the  lapse  of  a minute  it 
may  be  removed  from  the  solution,  and  hung  up  to  dry.  In  order 
to  render  the  paper  sensitive,  prepare  a solution  of  nitrate  of  sil- 
ver containing  50  grains  of  nitrate  to  the  ounce,  and  lay  the  sheet 
upon  the  sm’face  of  the  solution  in  the  same  manner  as  before  ; 
in  about  three  minutes’  time  the  sheet  may  be  removed  : it  must 
be  raised  by  one  corner  with  a pair  of  forceps  tipped  with  sealing- 
wax,  allowed  to  drain,  and  hung  up  to  dry.  The  process  of  im- 
mersion in  the  silver  bath  and  the  drying  must  be  performed  in  a 
darkened  room. 

Another  sensitive  paper,  which  is  often  used,  may  be  prepared 
by  forming  a solution  which  contains  80  grains  of  nitrate  of  silver 
in  each  ounce  of  distilled  water,  and  adding  caustic  ammonia  until 
the  precipitated  oxide  of  silver  is  almost  redissolved : the  solution 
should  be  preserved  in  a dark  place.  The  paper,  having  been 
previously  salted,  is  excited  by  brushing  it  over  with  this  solution 
by  means  of  a pledget  of  cotton  wool.  The  paper  is  allowed  to 
dry  in  the  dark,  and  should  be  used  immediately. 

In  order  to  protect  the  picture  obtained  upon  either  of  these 
papers  from  the  further  action  of  light,  it  is  now  usual  to  adopt 
the  method  introduced  by  Sir  J.  Herschel,  which  consists  in  soak- 
ing the  picture  in  a solution  of  hyposulphite  of  sodium : this  salt 
combines  with  the  undecomposed  salt  of  silver,  and  renders  it 
soluble : by  washing  the  picture  for  5 or  6 hours  in  water,  which 
should  be  frequently  changed  in  order  to  ensure  the  thorough 
removal  of  the  salts  of  silver  and  of  the  hv|3osulphite,  the  surface 
is  secured  from  further  change  when  exposed  to  light. 

(1017)  TaThotype.  or  Calotype  Process. — In  ISll,  Fox  Talbot 
took  out  a patent  for  the  very  beautiful  process  to  which  his  name 
has  since  been  attached.  In  this  remarkable  operation  the  smTace 
of  the  sheet  of  paper  is  coated  with  iodide  of  silver,  which  is  not 
sensitive  per  se  to  the  action  of  light  if  the  process  of  immersion 
in  iodide  of  potassium  is  the  last  operation  previous  to  washing. 
In  order  to  render  it  sensitive,  it  is  washed  over  with  a mixture 
of  nitrate  of  silver,  with  gallic  and  acetic  acids,  and  then  exposed 
in  the  camera  to  the  object  which  is  to  be  copied.  After  the  lapse 
of  a few  minutes,  (the  time  required  varying  with  the  intensity 
of  the  light,)  the  paper  is  withdrawn  from  the  camera.  Unless 
the  light  has  been  very  strons:,  no  image  is  visible,  or  a mere  out- 
line only,  but  the  compouncl  has  undergone  a change  of  a very 
singular  nature,  for  if  the  blank  sheet  be  protected  from  the  light 
and  washed  over  with  the  mixture  of  nitrate  of  silver  with  gallic 
and  acetic  acids,  on  gently  warming  it  a negative  image  appears 
with  wonderful  distinctness  and  fidelity, — the  portions  which  have 
been  exposed  to  the  strongest  lights  assuming  the  darkest  tints. 
The  development  of  the  image  appears  in  this  process  to  be  due 
to  the  reducing  agency  of  the  gallic  acid,  which  acts  more  rapidlj 


DETAILS  OF  THE  TALBOTYPE  PROCESS. 


T53 


upon  the  nitrate  of  silver  in  contact  with  those  portions  of  the 
iodide  which  have  been  most  freely  exposed  to  the  action  of  light. 
This  dormant  picture  may  be  developed  many  hours  or  even  days 
after  it  was  produced,  if  the  paper  be  preserved  from  the  light. 
It  seems  as  though  the  light,  without  actually  producing  a decom- 
position of  the  particles  of  the  argentine  compound  upon  which 
it  falls,  gives  to  them  a particular  condition  which  predisposes 
them  to  produce  decomposition  in  a reducible  mixture  consisting 
of  nitrate  of  silver  and  gallic  acid.  The  process  may  be  con- 
ducted in  the  following  manner : — 

1.  Preparation  of  the  Iodized  Paper. — A sheet  of  smooth 
writing  paper,  such  as  that  manufactured  by  Turner,  of  Chafford 
Mills,  of  uniform  texture,  and  free  from  stains  and  spots,  is  pinned 
upon  a board  by  two  of  its  corners,  and  brushed  over  uniformly 
with  a solution  of  nitrate  of  silver,  containing  33  grains  of  the 
salt  in  an  ounce  of  distilled  water ; the  solution  is  best  applied  by 
means  of  a brush  consisting  of  a flock  of  cotton  wool  partly  drawn 
through  a glass  tube,  which  furnishes  a convenient  handle : whilst 
the  paper  is  still  moist,  it  is  immersed  in  a bath  of  iodide  of  potas- 
sium, containing  20  grains  of  the  iodide  to  an  ounce  of  distilled 
water,  taking  care  to  avoid  the  occurrence  of  air-bubbles.  In 
about  two  minutes,  or  as  soon  as  the  paper  has  acquired  a uniform 
yellow  colour  throughout,  it  is  transferred  to  a vessel  of  water 
where  it  is  allowed  to  soak  for  two  or  three  hours,  changing  the 
■water  three  or  four  times,  so  as  to  remove  all  the  soluble  salts. 
Each  sheet  of  paper  is  then  to  be  hung  up  separately  and  allowed 
to  dry.  These  operations  may  be  conducted  by  candle-light  or 
in  diffused  daylight.  A stock  of  this  paper  may  be  prepared  and 
kept  for  use. 

2.  Exciting  the  Paper  for  the  Camera. — When  required  for 
the  camera,  prepare  1.  a solution  of  aceto-nitrate  of  silver  (con 
sisting  of  50  grains  of  nitrate  of  silver,  1 ounce  of  water,  and  1|- 
drachm  of  glacial  acetic  acid),  and  2.  an  aqueous  solution  of  gallic 
acid  saturated  in  the  cold.  Add  three  or  four  drops  of  each  of 
these  solutions  to  I drachm  of  distilled  water,  and  then  in  a 
darkened  room  apply  the  mixture  freely  with  a pledget  of  clean 
cotton  wool,  to  the  silvered  surface  of  the  iodized  paper — when 
well  soaked  remove  the  superfluous  portion  witha  sheet  of  clean 
blotting-paper : the  same  sheet  of  blotting-paper  must  not  be 
used  twice  for  this  purpose.  Whilst  still  damp  it  is  to  be  placed 
between  the  glasses  of  the  camera  slide.  It  will  retain  its  white- 
ness for  twelve  hours  or  more. 

3.  Exposure  in  the  Camera. — In  order  to  take  a landscape,  a 
sheet  of  the  prepared  paper  is  exposed  in  the  focus  of  the  camera, 
and  after  the  lapse  of  from  flve  to  lifteen  or  twenty  minutes,  accord- 
ing to  the  amount  of  light,  the  picture  may  be  withdrawn. 

4.  Development. — The  image  is  developed  by  brushing  the 
paper  over,  by  means  of  clean  cotton  wool,  with  a mixture  of  emial 
parts  of  the  solution  of  aceto-nitrate  of  silver  and  gallic  acid.  The 
two  solutions  must  be  mixed  immediately  before  they  are  used,  as 
they  speedily  undergo  mutual  decomposition.  In  a few  minutes 

48 


754 


PHOTOGRAPHY  OX  COLLODIOX. 


the  pictHi’e  gradually  begins  to  appear.  Any  part  of  the  picture 
yrhich  seems  wanting  in  distinctness  may  be  washed  oyer  with  Aesh 
solution  of  aceto-nitrate  of  silyer.  The  deyelopment  should  be 
effected  by  candle-light,  or  in  yellow  light. 

5.  Fixing  the  Impression. — As  soon  as  the  picture  ceases  to 
acquire  distinctness  it  is  to  be  well  washed  with  water,  and  im- 
mersed in  a saturated  solution  of  hyposulphite  of  sodium  till  the 
yellow  tint  of  the  iodide  of  silyer  has  disappeared.  It  is  then  to 
be  washed  thoroughly  for  seyeral  hours  in  clean  water,  frequently 
renewing  the  water.  Unless  all  traces  of  the  hy|)osulphite  of 
silyer  be  remoyed,  the  pictme  will  gradually  lose  its  intensity. 
Fox  Talbot  originally  employed  a solution  of  bromide  of  potas- 
sium for  fixing  these  pictures,  but  tlie  hy]305ulphite  of  sodium  is 
to  be  preferred.  TVIien  di*y,  the  photograph  should  be  waxed  by 
placing  it  between  two  sheets  of  blotting-paper  saturated  with 
white  wax,  and  then  passing  a moderately  heated  smoothing  iron 
oyer  the  whole.  The  negatiye  pictures  thus  obtained  may  be 
employed  to  fimiish  p>ositvce  prints,  or  prints  with  the  lights 
and  shadows  as  they  occur  in  natm*e,  by  Talbot’s  original  ‘ photo- 
genic’ process,  or  by  printing  upon  a second  sheet  of  the  prepared 
Talbotype  paper.* 

(lOiS)  Photography  on  Collodion. — An  important  modification 
of  Talbot's  process  was  introduced  by  Mr.  Ai*cher,  who  substituted 
for  the  iodized  paper  a transparent  film  of  iodized  collodion  spread 
upon  glass  as  the  recipient  of  the  negatiye  pictime.  The  process 
is  thus  rendered  more  certain  and  yery  much  more  rapid,  at  the 
same  time  the  manipulation  is  simplified  whilst  the  positiye 
pictures  obtained  by  transference  of  the  negatiye  impression  are 
much  sharper  in  their  outline.  The  operation  requires  to  be  con- 
ducted ill  a manner  different  fi’om  that  which  is  practised  when 
paper  is  employed.  The  following  is  the  method  to  be  pursued : — 

1.  To prepn,re  the  hath  of  nitrate  of,  silver,  take  of  nitrate  of 
silyer  300  grains,  dissolye  the  salt  in  2 ounces  of  distilled  water, 
and  add  grain  of  iodide  of  potassium  dissoUed  in  half  a di’achm 
of  water ; then  add  drop  by  drop  a solution  of  carbonate  of  potas- 
sium till  a shght  permanent  turbidity  is  produced ; afterwards  add 
distilled  water  until  the  mixture  measimes  10  ounces ; filter  and 
add  2^  minims  of  glacial  acetic  acid.b 

2.  Preparation  of  Solution  of  Collodion. — A solution  of  iodized 
collodion,  which  is  suitable  for  the  formation  of  negatiye  pictures, 
may  be  prepared  as  follows  (Hardwich)  : — Take  of  rectified  ether 

* For  further  details  upon  the  subject  of  photographic  printing,  Ac.,  the  reader  is 
referred  to  Hardwich’s  Manual  of  Photographic  Chemistry. 

f Ordinary  nitrate  of  silver  is  apt  to  contain  a trace  of  nitric  acid,  which  it  is 
desirable  to  neutralize,  because  an  acid  solution  is  much  less  sensitive  to  the  action 
of  light  than  a neutral  one.  It  is  sriU  more  important,  however,  not  to  have  any  alka- 
line reaction,  and  as  carbonate  of  silver  is  slightly  soluble  in  the  nitrate,  the  addition 
of  acetic  acid  is  subsequently  made  to  gmard  against  this : the  iodide  of  potassium  is 
added  in  order  to  saturate  the  bath  with  iodide  of  silver ; if  this  precaution  were  not 
taken,  the  film  of  iodized  collodion  would  be  liable  to  lose  a portion  of  iodide  of 
silver,  since  this  salt  is  also  somewhat  soluble  in  a solution  of  nitrate  of  silver. 

I A suitable  pyroxylin  for  this  purpose  may  be  obtained  in  the  following  manner ; 
— Take  of  oil  of  vitriol  sp.  gr.  1'843,  six  fluid  ounces ; pure  nitrate  of  potassium, 


DETAILS  OF  THE  COLLODION  PROCESS. 


755 


(sp.  gr.  0-725),  and  of  alcoliol  (sp.  gr.  from  0-805  to  0-815)  each 
4 fluid  drachms ; soluble  pyroxylin,  from  4 to  six  grains  ; iodide 
of  potassium  or  ammonium,  2 grains  ; iodide  of  cadmium,  2 grains. 
First  dissolve  the  iodides  in  the  alcohol,  then  add  the  pyroxylin, 
and  lastly  the  ether.  Agitate  the  materials  well,  set  them  aside 
for  twenty-four  hours,  and  then  decant  the  clear  liquid,  which  will 
retain  sufficient  sensitiveness  to  admit  of  being  used  even  at  the 
end  of  a month  after  its  preparation. 

3.  Preparation  of  the  Collodion  Film. — In  order  to  make  use 
of  this  solution,  a plate  of  glass  cut  to  the  size  required  for  the 
camera  (after  being  washed  with  a solution  of  potash  to  free  it 
from  grease,  rinsed  in  water,  dried,  and  wiped  with  a clean  silk 
handkerchief),  is  to  be  held  horizontally  in  the  left  hand,  and  a 
portion  of  the  collodion  is  to  be  poured  steadily  on  the  middle  of 
the  glass,  and  by  slightly  inclining  the  plate  in  difterent  directions, 
made  to  flow  completely  over  the  upper  surface ; the  excess  of  the 
solution  is  immediately  to  be  poured  back  into  the  bottle. 

4.  Exciting  the  Plate  for  the  Camera. — The  nitrate  bath  hav- 
ing been  introduced  into  a trough  of  glass  or  of  gutta  percha  suf- 
ficiently wide  to  allow  the  introduction  of  the  glass  plate  upon 
which  the  collodion  is  spread — the  prepared  plate,  within  half  a 
minute  after  the  film  has  been  poured  off  its  surface,  is  introduced 
into  the  solution  of  nitrate  of  silver ; in  from  two  to  three  min- 
utes’ time  it  is  thoroughly  impregnated  with  iodide  of  silver,  and 
when  withdrawn  from  the  bath  it  will  exhibit  a cream-coloured 
opalescence.  These  operations  must  be  effected  in  a room  illu- 
minated by  light  admitted  through  a yellow  blind,  or  by  the  light 
of  a candle  screened  by  yellow  glass  (1028). 

5.  Exposure  in  the  Camera. — The  prepared  plate  is  to  be  im- 
mediately introduced  into  the  slide  of  the  camera,  in  which  it  is 
to  be  exposed  to  the  object  for  a few  seconds  (from  3 or  4 to  30 
or  40)  according  to  the  nature  of  the  object  and  the  intensity  of  the 
liglit.  The  slide  is  then  withdrawn  from  the  camera,  and  the 
plate,  when  examined  in  the  darkened  chamber,  will  not  be  found 
to  exhibit  any  image. 

().  Developing  the  Image. — A latent  image,  however,  exists^ 
and  it  may  be  developed  by  the  use  of  a liquid  prepared  by  dis- 
solving 1 grain  of  pyrogallic  acid,  10  minims  of  alcohol,  and  from 
10  to  20  minims  of  glacial  acetic  acid,  in  an  ounce  of  distilled 
water.  Half  an  ounce  or  more  of  tliis  liquid  is  to  be  poured  over 
tlie  plate  immediately  after  its  removal  from  the  camera.  The 
negative  image  wliich  is  thus  gradually  develo})ed,  will  be  more 

finely  powdered  and  dried,  3^  ounces  avoirdupois  ; water,  1 fluid  ounce ; dried  cotton 
wool,  60  grains.  Mix  the  acid  and  water,  and  add  the  nitre  gradually,  stirring 
between  each  addition,  until  the  whole  of  the  salt  is  dissolved.  Suffer  the  mixture 
to  cool  to  150"  or  145''  F.,  then  add  the  cotton  wool  in  small  tufts  at  a time,  taking 
care  to  plunge  the  cotton  completely  beneath  the  surface ; cover  it,  and  allow  it  to 
stand  for  ten  minutes.  Then  press  out  the  acid  wuth  a glass  rod  as  completely  as 
possible,  and  throw  the  pyroxylin  into  a large  volume  of  cold  water,  and  wash  for 
half  an  hour;  afterwards  soak  it  well  in  water  for  24  hours ; lastly,  wring  it  out  in  a 
cloth,  and  dry  at  a heat  not  exceeding  100'^  P.  The  substance  tlms  obtained  is  com- 
pletely soluble  in  a mixture  of  ether  and  alcohol.  It  is  essential  to  attend  to  the 
strength  of  the  acid  and  to  the  temperature  employed. 


756 


PHOTOGRAPHIC  ENGEAITNG  AHD  LITHOGRAPHY. 


intense  if  immediately  before  using  the  pyrogallic  solution  an  ad- 
dition be  made  to  it  of  the  same  solution  of  nitrate  of  silver  as  is 
employed  in  the  bath,  in  the  proportion  of  2 drops  to  each  drachm 
of  the  developing  liquid. 

The  exact  reaction  which  occurs  in  this  remarkable  process  is 
not  known.  The  pyrogallic  acid,  however,  is  a substance  which 
has  a strong  tendency  to  combine  with  oxygen ; and  under  the 
conjoined  action  of  iodide  of  silver  and  nitrate  of  silver  (the  pre- 
sence of  the  latter  salt  in  excess  being  necessary  to  the  reaction) 
a portion  of  silver  is  reduced  and  is  deposited  upon  those  parts 
of  the  tilm  which  have  been  exposed  to  the  action  of  light. 

Other  solutions  may  be  employed  for  developing  the  latent 
image.  One  which  answers  very  well  for  this  purpose  consists 
of — crystallized  sulphate  of  iron  from  12  to  20  grains,  glacial 
acetic  acid  20  minims,  alcohol  10  minims,  and  water  1 ounce.  It 
is  not,  however,  so  well  adapted  for  the  production  of  intense 
negatives  as  tlie  pyrogallic  acid.  When  the  picture  is  sufficiently 
distinct  it  must  be  washed  with  clean  water,  and  fixed  by  immers- 
ing it  in  a solution  of  hyposulphite  of  sodium  (1  part  of  the  salt 
to  2 of  water)  till  the  cream-coloured  iodide  of  silver  is  entirely 
removed.  A solution  of  cyanide  of  potassium,  containing  from 
2 to  12  grains  of  the  salt  in  an  ounce  of  water,  may  be  substi- 
tuted for  the  hyposulphite  of  sodium  for  the  purpose  of  fixing  the 
image.  The  picture  is  again  to  be  thoroughly  washed  in  clean 
water ; it  is  allowed  to  dry,  then  heated  before  a fire  until  it  feels 
slightly  warm,  and  the  film  is  protected  from  mechanical  injury 
by  covering  it  with  a coat  of  transparent  spirit- varnish,  by  a mani- 
pulation similar  to  that  employed  in  coating  the  plate  with  collo- 
dion. This  varnished  photograph  may  then  be  employed  for  pro- 
curing positive  pictures  by  means  of  the  sensitive  paper  prepared 
with  chloride  of  silver  upon  Fox  Talbot’s  plan  (1016).  By  em- 
ploying a neutral  nitrate  bath  free  from  all  organic  matter,  and  a 
collodion  which  when  iodized  with  iodide  of  potassium  remains 
very  nearly  colourless,  the  sensitiveness  of  the  film  to  the  action 
of  light  may  be  so  highly  exalted,  that  moving  objects  such  as  the 
waves  of  the  sea,  or  a crowd  of  people,  may  be  successfully  de- 
picted by  the  instantaneous  action  of  light  upon  the  plate. 

(1019)  Alhumenized  Plates. — Hiepce  de  St.  Victor  introduced 
the  employment  of  glasses  coated  with  albumen,  prepared  by 
beating  up  whites  of  eggs  with  1 per  cent,  of  iodide  of  potassium : 
the  liquid  is  to  be  placed  for  12  or  21  hours  in  deep  vessels,  to 
become  clear,  after  which  the  supernatant  liquid  is  to  be  poured 
upon  glass  so  as  to  produce  a uniform  layer ; it  is  then  allowed 
to  dry  for  12  hours,  and  is  fit  for  the  bath  of  nitrate  of  silver. 
Albumenized  glasses  may  be  preserved  for  some  weeks  without 
injury ; they  may  be  excited  by  means  of  Talbot’s  mixture  of 
acetonitrate  of  silver  with  gallic  acid  (1017).  The  image  is  deve- 
loped by  means  of  a solution  of  gallic  acid,  after  the  plate  has 
been  exposed  in  the  camera. 

(1020)  Photographic  Engraving  and  Lithography. — In  the 
year  1827,  Niepce  published  a process  for  obtaining  pictures  by 


PHOTOGEAPHIC  ENGRAVING  AND  LITHOGRAPHY. 


757 


tlie  aid  of  light,  the  basis  of  which  was  the  fact  that  the  bitumen 
of  Judaea,  when  exposed  to  the  sun’s  rays,  becomes  insoluble  in  oil 
of  lavendar,  whilst  those  parts  which  have  remained  in  shadow 
preserve  their  solubility.  This  process  has,  with  some  modifica- 
tion, been  applied  by  Mepce  de  St.  Victor,  the  nephew  of  the 
inventor,  to  the  production  of  engravings  upon  steel.  Powdered 
asphalt  and  a proportion  of  pure  bees-wax  are  dissolved  in  oil  of 
lavender,  and  then  mixed  with  an  equal  volume  of  benzol.  The 
surface  of  the  steel  plate  which  is  to  be  engraved  is  first  carefully 
cleaned  with  whiting  and  water,  after  which  a solution  of  hydro- 
chloric acid  in  20  parts  of  water  is  poured  over  it,  and  the  plate 
is  immediately  washed  and  dried.  The  solution  of  bitumen  is 
then  poured  upon  the  plate  in  a darkened  chamber,  and  dried  by  the 
application  of  a gentle  heat.  A good  'positive  photographic  proof 
is  now  applied  to  the  surface,  covered  with  glass,  and  exposed  for 
a short  time  to  the  action  of  diffused  light.  The  exposed  plate  is 
next  subjected  to  the  action  of  a mixture  of  3 parts  of  rectified 
naphtha  and  1 of  benzol ; the  parts  which  have  not  been  exposed  to 
light  are  gradually  acted  upon  by  this  mixture.  When  the  pro- 
cess of  solution  has  proceeded  far  enough,  the  solvent  is  washed  off 
with  water,  and  the  exposed  parts  of  the  plate  are  ‘ bitten  in’  with 
a mixture  of  1 measure  of  nitric  acid,  sp.  gr.  1*33,  2 measures  of  alco- 
hol, sp.  gr.  0*844,  and  8 measures  of  water.  The  plate  is  then  sub- 
mitted to  the  ordinary  processes  employed  in  aqua-tint  engraving. 

An  important  modification  of  a process  proposed  by  roitevin 
for  producing  lithographs  by  the  aid  of  photography,  has  been  in- 
troduced by  Mr.  Osborne  of  Melbourne.  The  basis  of  this  ope- 
ration is  the  observation  that  a mixture  of  the  anhydro-chromate 
of  potassium  and  gelatin,  when  exposed  to  light,  becomes  insoluble 
in  water.  In  order  to  apply  this  to  practice,  800  grs.  of  gelatin 
and  440  of  acid  chromate  of  potassium  are  dissolved  in  8 ounces 
of  warm  water ; when  cooled  to  about  110°,  2 ounces  of  albumen 
from  perfectly  fresh  eggs  are  added,  ahd  the  whole  is  well  mixed  ; 
the  sheets  of  paper  are  then  coated  with  this  mixture  on  one  side, 
hung  up  to  dry  in  the  dark,  and  are  glazed  by  pressure.  These 
operations  are  conducted  in  a room  illuminated  by  yellow  light. 
Paper  thus  prepared  m^  be  preserved  unaltered  for  a long  time 
if  excluded  from  light.  In  order  to  use  it,  a negative  picture  pre- 
pared in  the  usual  way  is  placed  over  one  of  these  sheets  of 
chromate  paper,  and  exposed  from  half  a minute  to  a minute  in  a 

S)od  light,  with  the  precautions  usual  in  photographic  printing. 

wing  to  the  partial  reduction  of  the  chromic  acid  in  the  parts 
exposed  to  light,  a positive  picture  will  now  be  obtained,  the  parts 
acted  on  by  light  becoming  brown,  whilst  the  screened  portions  re- 
tain their  original  yellow  colour.  When  the  picture  thus  produced 
is  placed  in  water,  the  unchanged  portions  are  easily  washed  away, 
leaving  the  altered  portions  attached  to  the  paper.  In  practice, 
it  is  found  best  to  cover  the  whole  surface  of  the  picture  with  a 
coating  of  lithographic  ink,  and  then  fioat  the  back  of  the  paper 
upon  boiling  water.  After  soaking  for  a short  time  the  surface 
may  be  sponged,  and  the  screened  portion  may  be  completely  re- 


758 


CHKYSOTYPE THE  DAGUEREEOTYPE  PROCESS. 


moved,  leaving  a beantifnlly  defined  positive  impression  of  tlio 
negative  picture.  After  washing  it  with  boiling  water,  the  design 
is,  by  means  of  pressure,  transferred  to  the  lithographic  stone,  and 
the  prints  which  may  be  obtained  from  this  transfer  in  the  usual 
way,  are  remarkable  for  their  sharpness  and  delicacy. 

Yery  nearly  at  the  same  time  as  Mr.  Osborne,  Sir.  H.  James 
made  an  independent  application  of  the  so-called  bichromate  pro- 
cess of  Asser  of  Amsterdam  to  zincography.  The  liquid  which 
he  uses  consists  of  a mixture  of  2 measures  of  a solution  of  acid- 
chromate  of  potassium  (saturated  at  the  boiling-point)  with  1 
measure  of  a solution  of  three  parts  of  gum  arabic  in  4 of  water, 
and  the  transfer  is  made  to  a plate  of  zinc  instead  of  to  the  litho- 
graphic stone.  He  has  applied  the  process  successfully  to  the 
copying  of  old  engravings  and  manuscripts,  as  well  as  to  the 
multiplication  of  maps  and  plants. 

(1021)  Chrysotype. — Other  processes  more  or  less  analogous  to 
the  Talbotype  have  been  contrived : one  of  them  was  invented  by 
Herschel,  and  described  by  him  under  the  name  of  the  chrysotype 
{Phil.  Trans.  1842,  pp.  206,  209) : — Paper  is  washed  over  evenly 
with  a solution  of  ammonio-citrate  of  iron,  of  such  a strength  as 
when  dry  to  produce  a good  yellow  colour.  It  is  placed  in  sun- 
shine in  a camera,  or  under  any  engraving  which  it  may  be 
intended  to  copy;  after  a few  minutes’  exposure  it  is  to  be  re- 
moved, and  instantly  washed  over  with  a neutral  solution  of 
terchloride  of  gold ; a positive  picture  is  thus  developed,  which 
assumes  great  sharpness,  becoming  gradually  deeper  up  to  a 
certain  point ; at  the  instant  when  it  ceases  to  gain  in  intensily 
(this  point  being  easily  seized  by  practice),  the  picture  is-q^ut 
into  pure  water,  and  rinsed  thoroughly,  in  order  to  remove  the 
excess  of  solution  of  gold  ; it  is  then  fixed  with  a solution  of 
iodide  of  potassium,  and  again  washed  to  remove  the  super- 
fluous salts. 

In  this  case  the  ferric  salt,  under  the  influence  of  the  organic 
matter  of  the  paper,  becomes  partially  reduced  to  a ferrous  salt, 
in  the  parts  exposed  to  light ; and  this  ferrous  salt,  when  washed 
over  with  the  solution  of  gold,  precipitates  the  latter  metal  in  the 
reduced  state,  and  thus  gives  rise  to  the  coloured  image.  Water, 
by  removing  the  excess  of  the  salts,  fixes  the  picture,  and  prevents 
it  from  experiencing  further  change  on  exposure  to  light. 

If  ferri cyanide  of  potassium  be  employed  instead  of  chloride  of 
gold,  for  developing  the  picture,  a blue  image  will  be  produced, 
owing  to  the  formation  of  Turnl3ull’s  blue  upon  the  reduced  por- 
tions of  the  salt  of  iron. 

A solution  of  uranic  nitrate  may  be  used  instead  of  the  ammo- 
nio-citrate of  iron,  and  the  picture  may  be  developed  by  means  of 
a solution  of  nitrate  of  silver,  of  chloride  of  gold,  or  of  the  salt  of 
some  other  easily  reducible  metal. 

(1022)  Daguerreotype. — In  the  year  1839,  Daguerre  made 
known  his  beautiful  method  of  obtaining  photographic  pictures 
upon  metallic  plates.  The  essential  parts  of  this  process  are  as 
follows: — A sensitive  film  of  the  iodide  of  silver  upon  a silver 


DETAILS  OF  THE  DAGUEEEEOTYPE  PKOCESS. 


759 


plate  is  exposed  to  the  action  of  light  in  the  camera.  The  latent 
image  is  then  developed  by  exposure  to  the  vapour  of  mercury, 
after  which  the  picture  is  fixed  by  means  of  hyposulphite  of 
sodium. 

1.  Polishing  the  Plate. — For  this  purpose  a polished  sheet  of 
plated  copper  is  taken,  and  cleaned  by  rubbing  it  over  first  wfith 
finely  powdered  tripoli  on  a pledget  of  cotton  moistened  with  a 
few  drops  of  alcohol,  and  afterwards  with  dry  cotton,  until,  when 
breathed  upon,  the  metal  assumes  a uniform  dull  surfiice,  from 
which  the  cloud  disappears  without  showing  any  patches  or  spots ; 
after  this  the  plate  is  carefully  j)olished,  by  means  of  a long 
polishing  board  faced  with  buckskin.  If  this  preliminary  opera- 
tion be  not  carefully  performed,  the  subsequent  steps  will  not 
lead  to  any  satisfactory  result;  the  touch  of  a finger  upon  the 
polished  surface  is  sufficient  to  soil  it. 

2.  Iodizing. — The  plate  is  next  exposed  for  a few  minutes  to 
the  vapour  of  iodine,  till  a thin  yellow^  film  is  produced  uniformly 
over  the  surface.  This  operation  should  be  performed  by  candle- 
light, or  in  a room  furnished  with  a window  supplied  with  yellow 
glass ; the  plate  must  be  protected  from  diffused  daylight. 

3.  Exposure. — If  such  a plate  be  exposed  for  a few  minutes  in 
the  focus  of  a double  achromatic  lens,  adjusted  to  a camera 
obscura  in  such  a manner  that  the  image  of  the  object  to  be 
copied  shall  fall  upon  the  iodized  surface,  it  undergoes  an  altera- 
tion, which,  however,  is  not  perceptible  on  withdrawing  the  plate 
from  the  camera. 

4.  Pevelojjrnent. — But  if  the  plate  be  exposed  for  a few  minutes 
to  the  v^apour  of  mercury,  heated  to  about  140°  F.,  the  latent 
image  gradually  appears,  with  all  the  shadows,  lights,  and  half- 
tints faithfully  reproduced.  Much  of  the  success  depends  upon 
the  proper  length  of  exposure  to  the  action  of  light,  and  in  this 
respect  practice  is  the  best  guide ; if  too  short  a time  be  allowed, 
the  picture  is  dark  and  indistinct ; if  the  light  has  acted  too  power- 
fully, the  shadows  become  metallic  in  a])pearance,  and  ill-defined ; 
and  if  the  action  be  continued  for  a sufficient  length  of  time,  the 
picture  becomes  reverse,  or  negative^  the  shadows  in  such  a case 
being  represented  by  lights,  and  the  lights  by  shadows.  A due 
exposure  to  the  mercurial  vapours  constitutes  an  important  part 
of  the  operation ; for  if  this  exposure  be  insufficient,  the  whites 
liave  a bluish  cast,  and  if  it  be  too  long  continued,  the  blacks  be- 
come indistinct  and  misty. 

Mr.  Goddard,  in  the  year  1841,  discovered  that  the  iodized 
plate  may  be  rendered  veiy  much  more  sensitive  to  the  action  of 
light,  by  exposing  it  for  a few  seconds  to  the  vapour  of  bromine, 
or  of  chloride  of  bromine,  so  as  to  obtain  a mixed  film  of  iodide 
and  bromide  of  silver,  or  of  iodide,  chloride,  and  bromide  of  silver. 
The  process  thus  was  rendered  applicable  to  portraits,  and  the 
operation  could  be  accomplished  in  as  many  seconds  as  it  before 
required  minutes.  The  usual  practice  now  is,  after  having  ob- 
tained an  orange-coloured  film  by  exposure  of  the  silver  plate 
to  the  vapour  of  iodine,  to  expose  it  to  the  fumes  of  bromine 


760 


THEORY  OF  THE  DAGUERREOTYPE  PROCESS. 


from  bromide  of  lime,  until  the  film  assumes  a rose  colour; 
after  which  it  is  a second  time  returned  to  the  iodine  box  for 
a period  equal  to  one-third  of  that  occupied  by  the  first  iodizing. 
The  plate  is  then  exposed  in  the  camera,  after  which  it  is  mer- 
curialized. 

In  order  to  fix  these  pictures,  Daguerre  employed  a solution 
of  hyposulphite  of  sodium,  and  then  washed  the  plates  with 
water.  The  effect  of  the  Daguerreotype  may  be  much  improved 
by  gilding  them  by  the  process  of  Fizeau;  they  are  thus  rendered 
less  liable  to  mechanical  injury,  and  a richer  and  warmer  effect 
is  given  to  the  impression for  this  purpose,  1 part  of  neutral 
chloride  of  gold  and  3 parts  of  hyposulphite  of  sodium  may  be 
dissolved  in  500  parts  of  water : the  plate  having  been  placed  in 
a horizontal  position,  is  to  be  completely  covered  with  a small 
quantity  of  this  liquid,  and  the  plate  is  heated  by  a large  spirit- 
lamp  ffame  until  small  bubbles  appear  on  its  surface.  A thin 
film  of  reduced  gold  is  thrown  down  all  over  the  picture,  and 
by  this  operation  the  shadows  are  deepened  and  the  lights  ren- 
dered more  brilliant.  Finally,  it  must  be  washed  with  distilled 
water,  drained,  and  dried  by  the  application  of  a gentle  heat  to 
the  back  of  the  plate. 

The  following  theory  may  be  off*ered  in  explanation  of  the 
changes  which  occur  during  the  production  of  the  Daguerreotype 
image  : — Under  the  influence  of  light  the  superficial  layer  of 
iodide  of  silver  is  modified  so  as  to  render  it  susceptible  of  decom- 
position. When  the  plate  is  acted  upon  by  the  mercurial  vapour, 
the  iodine  is  driven  to  the  deeper  layer  of  silver,  and  a film  of 
silver  is  liberated  upon  the  surface  of  those  parts  which  have  been 
exposed  to  the  action  of  light,  the  thickness  of  this  film  varying 
with  the  intensity  and  duration  of  the  light.  The  reduced  silver 
combines  with  the  mercury,  and  a film  of  silver  amalgam  is 
formed,  which  varies  in  thickness  with  the  thickness  of  the  silver 
film,  in  consequence  of  which  the  reflected  tints  differ  according 
to  the  varying  thickness  of  this  film : those  parts  of  the  iodized 
plate  which  have  not  been  exposed  to  the  light,  of  couree  do  not 
combine  with  the  mercury.  After  the  plate  has  been  treated 
with  hyposulphite  of  sodium,  the  excess  of  iodide  of  silver  is  re- 
moved, and  the  blacks  consist  of  metallic  silver.  Experiment 
proves  that  those  parts  of  the  plate  immediately  beneath  the 
highest  lights  are  more  deeply  corroded  than  the  others,  by  the 
action  of  the  iodine  which  has  been  driven  inwards  during  the 
process  of  mercurialization. 

In  complete  accordance  with  the  foregoing  explanation  is  a 
curious  fact  first  pointed  out  by  Mr.  Shaw,  that  if  a plate  after  it 
has  received  the  impression  in  the  camera,  but  before  it  has  been 
mercurialized,  be  exposed  to  the  vapour  of  iodine  or  of  bromine 
for  a few  seconds,  the  image  is  completely  effaced,  and  is  no  longer 
producible  by  mercury. 

The  surface  of  the  plate  is  rendered  uneven  by  the  combined 
operation  of  light  and  mercury  upon  it,  so  that  it  admits  of  being 
copied  by  the  process  of  electrotyping  (292).  Impressions  on 


PHOTOGRAPHIC  ACTION  OF  THE  PRISMATIC  SPECTRUM.  761 

paper  have  been  printed  from  an  etched  Daguerreotype  plate,  the 
biting-in  being  produced  by  diluted  nitric  acid,  which  attacks  the 
shadows  (the  reduced  silver),  and  leaves  the  lights  (the  amalgam) 
untouched. 

(1023)  Photogra^hiG  Action  of  the  Prismatic  Spectrum. — If  a 
pure  solar  spectrum,  obtained  by  means  of  a prism  and  lens  of  flint 
glass,  be  allowed  to  fall  upon  a sheet  of  sensitive  paper,  prepared 
% washing  it  over  first  with  common  salt,  and  then  with  nitrate 
of  silver,  it  will  be  speedily  apparent  that  the  chemical  action  is 
not  uniformly  distributed  over  the  luminous  image.  The  maximum 
of  light  falls  in  the  yellow  rays  about  Fraunhofer’s  line  d 
(fig.  367),  whilst  the  maximum  of  chemical  action  occurs  in  the 


Fig.  361. 


blue  portion  of  the  spectrum,  near  the  line  g,  about  one-third  of 
the  distance  between  it  and  the  line  h.  The  blackening  effect 
extends  nearly  as  far  as  f in  the  green,  whilst  it  is  prolonged  be- 
yond the  violet  end  of  the  spectrum  to  a distance  nearly  equal  to 
two-thirds  of  the  length  of  the  luminous  spectrum,  the  chemical 
effect  gradually  shading  off  until  it  becomes  imperceptible ; the 
inaximum  point  of  action,  however,  varies  with  the  preparation 
which  is  used.  When  the  Talbotype  iodized  paper  is  employed, 
the  maximum  blackening  is  found  on  the  extreme  limit  of  the 
violet  rays.  Where  the  bromide  of  silver  forms  the  sensitive  ma- 
terial, the  chemical  action  is  prolonged  towards  the  red  rays,  and 
the  greater  part  of  the  impression  is  of  a uniform  grey  black. 
When  paper  washed  with  chloride  of  gold  is  employed  as  the  sen- 
sitive surface,  the  maximum  effect  is  produced  between  the  green 
and  the  blue  rays,  and  the  chemical  action  does  not  extend  be- 
yond the  violet  extremity  for  more  than  half  the  distance  over 
whicli  tliese  effects  are  produced  upon  the  salts  of  silver.  In  fig. 
367,  1 represents  the  space  occupied  by  the  luminous  spectrum  on 
white  paper ; 2,  the  same  spectrum  thrown  on  a fluorescent  screen, 
viz.,  turmeric  paper, — by  which  it  is  rendered  visible  almost  to 
the  extreme  limit  of  chemical  action ; 3,  the  chemical  spectrum 
on  bromide  of  silver ; 4,  the  Talbotype  spectrum.  Ilerschel, 
Hunt,  and  E.  Becquerel  have  each  succeeded  more  or  less  per- 
fectly in  obtaining  coloured  impressions  of  the  spectrum  upon 
chloride  of  silver,  but  they  have  lieen  unable  to  fix  them.  Iler- 
Bchel  {Phil.  Trans.  1840,  p.  19)  says  that  the  impression  “ was 


TG2 


IXACTITE  SPACES  IX  THE  SPECTREM. 


found  to  be  colom’ed  with  sombre  but  unequivocal  tints,  mutating 
those  of  the  spectrum  itself”  The  coloration  commenced  in  the 
orange  rays.  Beccpierel  appears  to  liave  obtained  more  brilliant 
colours  by  employing  a plate  of  silver  which  had  been  supeidi- 
cially  converted  into  sub-chloride  by  immersing  it  in  diluted 
hydrochloric  acid,  and  then  making  it  the  positive  plate  of  a vol- 
taic battery. 

Inactive  spaces  occur  in  the  chemical  spectrum,  which,  as 
Becquerel  and  Draper  have  shown,  correspond  exactly  with  those 
which  are  found  in  the  visible  spectrum  ; but  tliey  extend  also 
into  the  prolongation  beyond  the  ^dolet  extremity,  and  occim 
there  in  great  number.  These  fixed  lines  may  be  obtained  upon 
Talbot vpe  paper,  or,  still  better,  upon  a surface  of  collodion,  in 
the  following  manner  : — 


Fig  368. 


Let  c,  G (fig.  368),  represent  a camera  which  allows  of  a con- 
siderable range  of  adjustment ; 5 is  a small  slit,  admitting  of 
adjustment,  but  usually  presenting  a Avidth  of  about  0*01  inch, 
through  which  a beam  of  solar  or  other  light  is  either  transmitted 
directly,  or  is  refiected  from  a heliostat,  or  from  a steel  mirror ; I 
is  a quartz  lens  of  from  15  to  30  inches  focal  length ; j?,  a quartz 
prism,  the  axis  of  which  is  perpendicular  to  the  axis  of  the  crys- 
tal, and  the  refracting  faces  of  which  are  worked  so  as  to  cut  the 
optic  axis  of  the  crystal  at  equal  angles.  The  lens  and  prism 
may  indeed  be  made  of  glass  free  from  stride,  but  for  accurate  ob- 
servation they  must  be  constructed  of  rock  crystal : the  distance 
of  the  lens,  Z,  from  the  slit,  5,  is  equal  to  twice  its  focal  length. 
If  the  prism  be  placed  so  as  to  produce  the  minimum  deviation  of 
the  ray,  and  as  close  to  the  lens  as  can  be,  a spectral  image  of  the 
apertirre  will  be  formed,  and  may  be  received  upon  a screen 
placed  at  as  great  a distance  behind  the  lens,  as  s is  in  front  of 
it.  All  the  coarser  lines  of  the  visible  spectrum  may  be  traced 
by  the  unaided  eye,  when  the  spectrum  is  received  on  a screen  of 
ground  glass  : and  if  a sheet  of  turmeric  paper,  or  a block  of  yel- 
low uranium  glass,  be  used,  many  of  the  lines  beyond  the  violet 
are  also  rendered  visible  : by  substituting  a sensitive  surface,  such 


PHOTOGRAPHIC  TRANSPARENCY.  Y63 

as  collodion,  for  tlie  screen  of  white  paper,  a faithful  copy  of  the 
more  refrangible  portion  of  these  lines  may  be  obtained. 

(1024)  It  is  remarkable  that  the  chemical  rays  are  identical 
with  those  which  produce  fluorescence  (110).  If  the  solar  rays 
be  transmitted  through  a layer  of  a concentrated  but  colourless 
solution  of  sulphate  of  quinine,  or  one  of  sesculin  in  ammonia, 
but  little  extra-spectral  prolongation  of  chemical  action  is  pro- 
duced when  this  light  is  allowed  to  fall  upon  a sensitive  surface. 

Again,  if  the  solution  be  removed  and  the  spectrum  be 
received  directly  upon  a screen  of  yellow  uranium  glass,  or  a 
card  coated  with  a particular  phosphate  of  uranium  (Stokes, 
Phil.  Trans.  1862,  p.  602),  a visible  prolongation  of  the  chemical 
ray,  crossed  by  dark  lines  or  inactive  spaces,  is  at  once  rendered 
visible. 

By  varying  the  source  of  light,  the  chemical  powders  of  the 
spectrum  are  varied  also.  The  chemical  action  of  the  flame  of 
the  hydrocarbons,  however  intense  the  light,  is  but  feeble ; that 
of  the  lime-light  is  much  more  marked,  while  that  of  the  electric 
light  between  charcoal-points  greatly  surpasses  either  ; and  these 
results  coincide  exactly  with  their  relative  power  of  exciting  the 
phenomena  of  fluorescence.  ^ 

The  chemical  rays  emitted  by  luminous  objects  vary  greatly 
both  in  quantity  and  in  quality,  some  sources  of  light  emitting 
rays  of  much  higher  refrangibility  than  others.  For  example, 
the  flame  of  ordinary  coal-gas  burned  in  admixture  with  air,  so  as 
to  produce  the  blue  light  of  a smokeless  gas  flame,  gives  out 
scarcely  any  rays  capable  of  affecting  an  iodized  collodion  plate  ; 
whilst  the  same  amount  of  gas,  burned  in  the  ordinary  manner 
for  illumination,  emits  a very  decided  though  limited  amount  of 
rays  capable  of  producing  chemical  action.  The  rays  emanating 
from  the  intensely  hot  jet  of  the  oxyhydrogen  flame,  are  nearly 
without  action  upon  a sensitive  surface  of  collodion  ; whilst  if 
thrown  upon  a ball  of  lime,  though  it  certainly  is  not  hotter  than 
the  burning  jet  of  gas,  the  light  then  emitted  contains  as  large  a 
proportion  of  chemical  rays  as  the  solar  light,  and  of  very  nearly 
the  same  refrangibility.  But  the  most  remarkable  source  of  tlie 
chemical  rays  is  afforded  by  the  light  of  the  electric  spark  or  of 
the  voltaic  arc,  the  chemical  spectrum  of  which  is  three  or  four 
times  as  long  as  the  chemical  spectrum  obtainable  from  the  sun 
itself. 

(1025)  Photographic  Transparency  of  various  Media. — 
Amongst  the  methods  of  testing  tlie  extent  of  chemical  action  of 
any  given  radiant  source,  the  most  convenient  is  that  which  is  de- 
pendent upon  the  extent  of  photograydiic  effect  exerted  upon  a sur- 
face of  collodion  coated  with  iodide  of  silver,  on  which  the  spectrum 
is  allowed  to  fall. 

In  no  case  does  it  appear  that  any  non-luminous  source  can 
emit  chemical  rays  of  sufficient  intensity  to  traverse  ordinary  re- 
fracting media  ; and  amongst  the  rays  given  off  by  various  lumin- 
ous objects,  it  is  found  that  the  chemical  effects  upon  the  collo- 
dion plate  are  not  perceptible  in  those  portions  upon  which  the 


764 


PHOTOGRAPHIC  TRAXSPAREN’CT. 


first  tliree-foHTtlis  of  the  visible  spectrum  has  fallen,  but  they  com- 
mence powerfully  in  the  last  fourth  ; and  in  the  case  of  the  elec- 
tric spark  are  prolonged  to  an  extent  equal  to  between  four  and 
five  times  the  length  of  the  visible  portion. 

In  the  prosecution  of  some  inquiries  upon  the  photographic 
spectra  of  the  metals  in  which  the  author  was  engaged,  it  was  a 
desideratum  to  procure  some  substance  which  should  possess  a 
higher  dispersive  power  than  quartz,  and  which,  whilst  avoiding 
the  double  refraction  of  quartz,  should  yet  allow  the  free  passage 
of  the  chemical  rays.  lie  was  hence  led  to  try  a variety  of  sub- 
stances which,  owing  to  their  transparency  to  light,  might  reason- 
ably be  hoped  to  possess  chemical  transparency  also  ; for  though 
it  was  known  to  those  who  have  studied  the  spectrum,  that  many  col- 
ourless substances  besides  glass  exert  an  absorptive  action  upon  some 
of  these  chemical  rays,  the  subject  had  not  hitherto  received  that 
careful  experimental  examination  which  its  importance  warrants. 

The  inquiry  soon  extended  itself  beyond  the  limits  originally 
proposed,  and  ultimately  embraced  a large  nmnber  of  bodies  in 
the  solid,  liquid,  and  gaseous  conditions  (Phil.  Trans.  1862,  p. 
861).  These  expeiiments  showed  that  although  rock-salt,  fluor- 
spar, water,  and  some  few  other  substances,  are  almost  as  diacti- 
nir  (or  chemically  transparent)  as  quartz,  none  of  these  bodies 
could  be  advantageously  substituted  for  quartz  in  the  construction 
of  the  prisms  and  lenses  requfred  in  the  investigations  in  which 
he  was  engaged. 

Among  the  most  remarkable  results  upon  the  photographic 
transparency  of  bodies  are  the  following  : — 

1.  Colomless  solids  which  are  equally  transparent  to  the  visi- 
ble rays,  vary  greatly  in  permeability  to  the  chemical  rays.  2.  Bo- 
dies which  are  photographically  transparent  in  the  solid  form, 
preserve  their  transparency  in  the  liquid  and  in  the  gaseous  states. 
3.  Colourless  transparent  solids  which  absorb  the  photographic 
rays,  preserve  their  absorptive  action  with  greater  or  less  intensi- 
ty both  in  the  liquid  and  in  the  gaseous  states.  4.  Pure  water  is 
photographically  transparent,  so  that  many  compounds  which  can- 
not be  obtained  in  the  solid  form  suflSiciently  transpai’ent  for  such 
experiments,  may  be  subjected  to  trial  in  solution  in  water. 

The  mode  in  which  the  experiments  were  conducted  was  the 
following  : — The  source  of  hght  employed  was  the  electric  spark 
obtained  between  two  metallic  wires,  generally  of  fine  silver,  shown 
at  e,  Fig.  368,  and  connected  with  the  terminals  of  the  secondary 
'svires  of  an  induction-coil,  into  the  primary  circuit  of  which  was 
introduced  a condenser,  and  into  the  secondary  circuit  a small 
Leyden  jar.  The  light  of  the  sparks  was  then  allowed  to  fall  upon 
the  vertical  slit,  either  before  or  after  traversing  a slice  or  stratum 
of  the  material,  d,  of  which  the  electric  transparency  was  to  be 
tested  ; the  transmitted  light  was  then  passed  tlirough  the  quartz 
prism,  placed  at  the  angle  of  minimum  deviation.  Immediately 
behind  this  was  the  lens  of  rock  crystal,  and  behind  this  at  a suit- 
able distance  the  spectrum  was  received  upon  the  sensitive  surface 
of  collodion.  The  liquids  under  trial  were  contained  in  a small 


PHOTOGRAPHIC  TRANSPARENCY. 


765 


glass  cell  with  quartz  faces,  forming  a stratum  0*75  inch  in  thick- 
ness, which  was  traversed  by  the  rays ; gases  and  vapours  were  in- 
troduced into  tubes  2 feet  long  closed  at  their  extremities  with 
thin  plates  of  polished  quartz.  The  following  tables  exhibit  the 
relative  diactinic  power  of  a few  of  the  various  solids,  liquids,  and 
gases  and  vapours  subjected  to  experiment. 

Photographic  Transparency  op 


Solids. 

Rock  crystal. . . 

Ice 

Fluor-spar 

Topaz 


Borax. 


Liquids,  0'75  in. 

.14 

Water 

Alcohol 

. 63 

.14 

Dutch  liquid 

..36 

.65 

Chloroform 

..26 

,.63 

Benzol 

21 

.63 

Wood-spirit 

, 20 

..62 

Fousel  oil 

.20 

.62 

Oxalic  ether 

. 19 

Glycerin 

.18 

48 

Ether 

16 

.20 

Acetic  acid 

. 16 

.18 

Oil  of  turpentine 

..8 

.18 

Bisulphide  of  carbon . . 

. .6 

..16 

Terchloride  of  arsenic. 

. .5 

Gases  and  Vapours. 


Oxygen 14 

Nitrogen 14 

Hydrogen 14 

Carbonic  anhydride. ..  .14 

Olefiant  gas 66 

Marsh-gas 63 

Hydrochloric  acid 55 

Coal-gas 31 

Benzol  vapour 35 

Hydrobromic  acid 23 

Hydriodic  acid 15 


Sulphurous  anhydride.  .14 
Sulphuretted  hydrogen.  14 
Air,  0-1  in.  pressure. . .14 


The  photographic  image  obtained  upon  the  collodion  plate  com- 
menced in  each  case  at  the  same  point  of  the  spectrum  correspond- 
ing with  a spot  a little  more  refrangible  than  the  line  g.  Calling 
the  line  h 100,  and  numbering  backwards  for  the  less  refrangible 
rays,  the  line  b being  at  84,  the  commencement  of  the  photograph 
in  each  case  is  at  96*5,  and  the  extreme  limit  of  the  most  refran- 
gible rays  170*5. 

Each  photograph  was  obtained  under  circumstanees  varying 
only  in  the  nature  of  the  transparent  medium  through  which  the 
rays  of  the  spark  from  the  silver  points  were  made  to  pass,  before 
they  were  allowed  to  fall  upon  the  collodion  plate.  When  absorp- 
tion occurs,  it  is  almost  always  exerted  upon  the  most  refrangible 
rays ; but  in  the  case  of  the  coloured  gases  and  vapours,  chlorine, 
bromine,  and  iodine,  the  absorption  differs  from  the  general  rule, 
and  is  by  no  means  proportioned  to  the  depth  of  colour.  A 
column  of  chlorine  with  its  yellowish-green  colour  cuts  off  the 
rays  of  the  less  refrangible  extremity  through  fully  two-thirds  of 
the  spectrum  ; the  red  vapour  of  bromine  cuts  off  about  one-sixth 
of  the  length  c>f  the  spectrum,  the  absorbent  action  being  limited 
to  the  less  refrangible  extremity ; whilst  the  deep  violet-coloured 
vapours  of  iodine  allow  the  less  refrangible  rays  to  pass  freely  for 
the  first  fourth  of  the  spectrum ; then  a considerable  absorption 
occurs,  and  afterwards  a feeble  renewal  of  the  photographic  action 
is  exhibited  towards  the  more  refrangible  end. 

In  these  experiments  minute  attention  to  the  purity  of  the 
substances  employed  is  indispensable  : traces  of  foreign  substances 
inappreciable  to  ordinary  modes  of  analysis  occasionally  reveal 
themselves  by  their  absorptive  action  on  the  cliemical  rays. 

Among  the  various  compounds  submitted  to  examination,  the 
fluorides  are  chemically  the  most  transparent ; then  follow  the 
chlorides  of  the  metals  of  the  alkalies  and  alkaline  earths ; the 


766 


PHOTOGEAPHIC  TEANSPAEENCY. 


bromides  are  less  diactinic,  and  tlie  iodides  show  a striking 
diminution  in  this  respect.  The  group  most  remarkable  for  its 
absorptive  power  is  the  nitrates.  Mtric  acid,  whether  simply  dis- 
solved in  water,  or  combined  with  bases,  has  a specific  power  in 
arresting  the  chemical  rays ; the  less  refrangible  portion  it  trans- 
mits freely,  but  intercepts  the  spectrum  abruptly  at  the  same  point, 
whatever  salt  be  employed,  provided  the  base  be  diactinic.  The 
chlorates,  it  may  be  remarked,  are  strongly  diactinic. 

Glass,  even  in  very  thin  layers,  absorbs  the  whole  of  the  more 
refrangible  rays.* 

Diactinic  bases,  when  united  with  diactinic  acids,  usually 
furnish  diactinic  salts ; but  such  a result  is  not  uniform  : the 
silicates  are  none  of  them  as  transparent  as  silica  itself  in  the 
form  of  rock  crystal.  . Again,  hydrogen  is  eminently  diactinic, 
and  iodine  vapour,  notwithstanding  its  deep  violet  colour,  is  also 
largely  diactinic ; but  hydriodic  acid  gas  is  greatly  inferior  to 
either  of  them. 

The  same  substance,  however,  whatever  may  be  its  physical 
form,  whether  solid,  liquid,  or  gaseous,  preserves  its  character ; 
no  chemically  opaque  solid,  though  transparent  to  light,  becoming 
transparent  photographically  by  liquefaction  or  volatilization ; and 
no  transparent  solid  being  rendered  chemically  opaque  by  change 
of  form.  Hence  it  is  obvious  that  this  opacity  or  transparency 
is  intimately  connected  with  the  atomic  or  chemical  character  of 
the  body,  and  not  merely  with  its  state  of  aggregation.  Although 
the  absorption  of  the  chemical  rays  varies  greatly  in  the  different 
gases,  which  therefore  in  their  action  display  an  analogy  to  their 
effects  upon  radiant  heat,  yet  those  gases  which  absorb  the  rays 
of  heat  most  powerfully  are  often  highly  transparent  to  the 
chemical  rays,  as  is  seen  in  the  case  of  aqueous  vapour,  of  car- 
bonic acid,  cyanogen,  and  olefiant  gas,  all  of  which  are  com- 
pound substances,  not  chemical  elements.  Compounds  as  com- 
2)Ounds  do  not  appear  to  act  more  energetically  as  absorbents  than 
simple  bodies. 

The  abrupt  termination  of  the  chemical  spectrum  in  coal-gas 
is  remarkable  : in  that  case  the  absorption  appears  to  be  due,  not 
to  the  permanent  gases,  but  to  the  vapours  of  benzol,  and  other 
heavy  hydrocarbons  that  it  contains. 

In  the  case  of  reflection  from  polished  surfaces,  the  metals 
were  found  to  vary  in  the  quality  of  the  rays  reflected ; gold  and 
lead,  although  not  the  most  brilliant,  reflecting  the  chemical  rays 
Tuore  uniformly  than  the  brilliant  white  surfaces  of  silver  and 
speculum  metal. 

* A hasty  consideration  of  these  experiments  might  lead  to  the  conclusion  that 
lenses  of  quartz,  or  of  water  enclosed  in  quartz,  would  be  far  superior  to  those  of 
glass  in  ordinary  use  by  the  photographer.  This,  however,  is  not  the  fact.  Glass  is 
very  transparent  to  the  less  refrangible  portion  of  the  chemical  rays,  extending 
beyond  the  violet  end  of  the  visible  spectrum  to  a distance  as  much  beyond  the  line 
H as  the  red  end  of  the  spectrum  is  below  it ; and  these  rays  are  precisely  the  most 
abundant  and  powerful  chemical  rays  in  the  solar  spectrum,  which  contains  but  few 
rays  of  a refrangibillty  much  beyond  this  point,  whereas  in  the  electric  arc  these 
highly  refrangible  rays  predominate. 


FLUOEESCENT  ABSORPTION. 


767 


Stokes  {Phil.  Tra/ns.  1862,  p.  606)  has  pursued  this  investiga- 
tion in  a different  manner  : instead  of  photographing  the  spectra, 

Fia.  369. 


Zjv 


Cd 

Stychnia, 

dilute  H2SO4. 

Brucia, 

dilute  H2SO4. 

Morphia, 
dilute  H2SO4. 

Codeia, 

dilute  H2SO4. 

Narcotine, 
dilute  H2SO4. 

Narceia, 

dilute  H2SO4. 

Papaverine, 
dilute  H2SO4. 

Caffein, 

dilute  H2SO4. 

Corydalin, 
dilute  £[2804- 


Piperine,  alcohoL 

.(Esculin, 
dilute  ammonia. 

Phloridzin, 
dilute  ammonia. 

Phloridzin, 
dilute  H2SO4 


Salicin,  water. 


Arbutin,  water. 


he  submitted  them  to  ocular  inspection,  by  receiving  the  invisible 
rays  upon  a fluorescent  screen. 


768 


PHOTOGRAPHIC  SPECTRA  OF  THE  ELEMENTS. 


He  found  that  the  vegetable  alkaloids  and  the  glucosides  are, 
almost  without  exception,  intensely  opaque  for  a portion  of  the 
invisible  rays,  absorbing  them  with  an  energy  comparable,  for  the 
most  part,  to  that  with  which  colouring  matters,  such  as  indigo  or 
madder,  absorb  the  visible  rays.  The  mode  of  absorption  is  also 
generally  highly  characteristic  of  each  compound,  and  frequently 
very  different  in  the  same  body,  according  as  it  is  examined  in  an 
acid  or  an  alkaline  solution.  In  the  examination,  a small  cell, 
with  parallel  faces  of  quartz,  or  sometimes  a wedge-shaped  vessel 
with  its  inclined  faces  also  of  quartz,  was  employed.  The  cell 
being  filled  Avith  the  solvent,  water,  dilute  acid,  dilute  ammonia, 
or  alcohol,  (fcc.,  a minute  quantity  of  the  substance  under  trial  is 
introduced,  and  the  absorptive  effects  exerted  are  watched  as  the 
substance  gradually  undergoes  solution.  Fig.  369,  on  the  fore- 
going page,  is  taken  from  Professor  Stokes’  paper.  The  bold  lines 
of  aluminum,  zinc,  and  cadmium,  are  given  as  points  of  reference  ; 
the  border  on  the  left  is  the  limit  of  the  red  light  visible  on  the 
screen.  The  dotted  line  in  the  figiu-e  for  sesculin  denotes  the 
commencement  of  the  fiuorescence,  which  is  situated  near  the  line 
G of  the  solar  spectrum,  the  luminous  portion  of  which  does  not 
extend  beyond  the  termination  of  the  first  portion  of  the  spectrum 
of  piperine.  Professor  Stokes  remarks  that  in  the  figure  the 
shading  merely  represents  the  general  effect,  the  gradation  of  illu- 
mination not  having  been  registered ; and  although  the  central 
parts  of  the  maxima  of  transparency  are  left  white,  in  reality  there 
is  almost  always  some  absorption.  The  effect  of  acids  and  al- 
kalies on  the  glucosides  presents  one  uniform  feature : when  a 
previously  neutral  solution  is  rendered  alkaline,  the  absorption 
begins  someAvhat  earlier,  when  rendered  acid  somewhat  later,  than 
in  a neutral  solution. 

(1026)  Photographic  Spectra  of  the  Elements. — Equally  inte- 
resting are  the  results  obtained  by  examining  the  spectra  produced 
by  varying  the  nature  of  the  metallic  electrodes  employed  as 
terminals  to  the  secondary  wires  of  the  induction-coil.  Professor 
AYheatstone  showed  many  years  ago  that  the  visible  spectrum  of 
each  metal  is  perfectly  characteristic  when  electro-magnetic  sparks 
are  transmitted  between  two  surfaces  of  the  metal ; and  I have 
found  that  the  same  thing  is  equally  true  of  the  invisible  portion 
of  the  spectrum. 

Even  the  various  gaseous  media  become  so  intensely  heated  by 
the  passage  of  the  electric  spark,  that  they  furnish  photographic 
spectra,  each  of  which  is  characteristic  of  the  body  which  occasions 
it ; and  Avhen  the  electric  discharge  of  the  secondary  coil  becomes 
intensified  by  use  of  the  Leyden  jar,  the  sparks  not  only  produce 
the  spectra  due  to  the  metals,  but  to  the  gaseous  medium  in  which 
the  electrodes  are  immersed ; so  that  a mixed  spectrum  is  the  re- 
sult. The  spectra  produced  by  the  metals  are  characterized  by 
bands  of  which  the  extremities  only  are  visible ; whilst  the  gaseous 
spectra  yield  continuous  lines  which  traverse  the  whole  width  of 
the  spectrum.  When  a compound  gas  is  made  the  medium  of  the 
electric  discharge,  the  spectra  produced  are  those  of  the  elemen- 


ABSORPTION  OF  THE  CHEMICAL  RAYS. 


TGO 

taiy  components  of  the  gas.  It  seems  as  though  at  these  intense 
temperatures  chemical  combinations  were  impossible ; and  at 
temperatures  as  intense  as  those  obtained  in  the  voltaic  arc,  oxygen 
and  hydrogen,  chlorine  and  the  metals  probably  all  coexist  in  a 
separate  form,  though  mechanically  intermingled. 

The  spectrum  produced  by  the  ignition  of  a solid  or  a liquid 
always  yields  a continuous  band  of  light,  containing  rays  of  all 
degrees  of  refrangibility  ; but  the  same  body,  when  converted  into 
vapour,  produces  a spectrum  consisting  of  a series  of  bright  bands 
of  particular  colours,  separated  from  each  other  by  intervals  more 
or  less  completely  dark,  coloured  gaseous  bodies  emitting  rays  of 
certain  definite  refrangibilities  only. 

From  the  striped  character  of  the  photographic  spectra,  it  is 
obvious  that  the  vibrations  are  emitted  from  the  different  metals 
in  the  form  of  vapour,  and  not  merely  in  that  of  detached  parti- 
cles projected  from  the  electrodes  by  disruptive  discharge. 

This  observation  may  give  some  idea  of  the  intensely  high 
temperature  attained  by  the  spark ; since  it  is  observed  that  the 
higher  the  temperature,  the  more  refrangible  are  the  vibrations. 
AVe  are,  indeed,  furnished  in  this  case,  with  a rude,  but  still,  under 
the  circumstances,  with  a valuable  pyrometric  means  of  estimating 
these  exalted  temperatures."^ 

Fig.  370  exhibits  a few  of  the  species  of  the  metals  obtained 
by  the  secondary  spark,  contrasted  with  the  solar  spectrum  trans- 
mitted through  the  same  lens  and  prism  under  similar  circum- 
stances : the  spectra  of  oxygen,  nitrogen,  chlorine,  and  carbonic 
acid,  produced  by  sparks  from  platinum  points,  are  also  given  in 
Fig.  371.  Platinum  has  but  a feeble  spectrum  of  its  own  ; and 
it  does  not  ^pear  in  the  spectra  given  in  this  figure. 

(102Q  Extinction  of  Chemical  Rays. — Bunsen  and  Roscoe 
{Phil.  Trans.  1857,  601)  have  made  experiments  upon  the  ab- 
sorbent power  of  chlorine  upon  the  chemical  rays  which  affect  the 
combination  of  a mixture  of  chlorine  and  hydrogen.  They  find 
that  when  light  passes  through  a medium  in  which  it  excites 

* To  give  an  illustration  of  the  mode  of  applying  the  observation: — The  hottest 
wind-furnace  of  ordinary  construction  yields  a temperature  probably  not  much  ex- 
ceeding 4500°  F.  By  calculations  founded  upon  the  amount  of  heat  ascertained  by 
Andrews  and  others  to  be  emitted  during  the  combustion  of  a given  weight  of  hydro- 
gen, and  the  experiments  of  Regnault  upon  the  specific  heats  of  oxygen,  hydrogen, 
and  steam,  it  has  been  shown  by  Bunsen  that  the  temperature  of  the  oxyhydrogen 
flame  cannot  exceed  14,580®  F.  If  lime  or  sulphate  of  magnesia  be  intioduced  into 
the  oxyhydrogen  jet,  these  incombustible  materials  cannot  be  heated  by  the  burning 
gases  to  a higher  point  than  14,G00  R,  but  the  spectra  obtained  from  those  incandes- 
cent bodies  I found  to  coincide  in  their  photographic  lengths  with  that  of  the  solar 
spectrum.  Hence,  the  temperature  of  the  sun  may  be  approximatively  estimated  to  be 
not  higher  than  that  of  the  oxyhydrogen  (lame.  It  certainly  appears  to  be  far  below 
that  of  the  electric  spark.  Magnesium  in  the  electric  spark  gives  a remarkably 
strong  band  just  beyond  the  limits  of  the  solar  spectrum.  Now  magnesium  is 
as  clearly  proved  to  exist  in  the  solar  atmosphere  as  any  element,  if  we  be  ad- 
mitted to  have  any  such  proof  at  all.  But  unless  a very  long  column  of  air  be 
supposed  to  exert  an  absorbent  action  not  exliibited  in  shorter  ones,  it  is  difficult 
to  avoid  the  conclusion  that  the  temperature  of  the  solar  atmosphere  is  below  that 
generated  by  the  electric  spark,  inasmuch  as  the  special  band  winch  characterizes 
magnesium  at  a high  temperature  in  tlie  electric  spark  is  wanting  in  the  solar 
spectrum. 


49 


770 


PnOTOGRAPHIC  SPECTRA  OF  THE  ELEMENTS. 


Fig.  370. 

ao  100  no  220  230  140  250  ISO  MO  ISO  2»0 


chemical  action,  a quantity  of  light  is  absorbed  proportional  to  the 
chemical  effect  produced.  For  instance,  the  chemical  power  of 
the  light  of  a coal-gas  flame,  of  a certain  intensity  measured  by  its 
activity  in  producing  the  combination  of  chlorine  with  hydrogen, 
was  found  to  be  reduced  to  one-tenth  when  transmitted  through  a 
column  of  chlorine  6*822  inches  in  depth ; if  the  chlorine  were 
diluted  with  an  equal  volume  of  air,  the  length  of  the  column  re- 
quired to  produce  a similar  absorption  was  exactly  double,  or 


LIJifES  m THE  PIIOTOGRAPHTC  SPECTEUM. 


771 


BD  IF 


TtinO 


FtinN 


I^mCO 

•i? 


Fig.  3Y1. 


13*644  inches.  But  when  a mixture  of  equal  volumes  of  chlorine 
and  hydrogen  was  used,  the  depth  of  the  mixture  which  v^as  re- 
quired to  reduce  the  chemical  effect  of  tlie  light  to  one-tenth  of 
its  original  intensity  was  only  9*212  inches  *.  hence  it  appears  that 
a certain  quantity  of  the  active  rays  are  absorbed  during  the  pro- 
duction of  a given  chemical  effect. 

With  light  from  different  sources  analogous  results  were  ob- 
tained, but  the  amount  absorbed  was  found  to  vary  with  the  source 
of  the  light.  For  instance,  the  'diffused  zenith  light  of  a cloud- 
less sky  in  the  morning  w*as  reduced  to  one-tenth  of  its  intensity 
by  transmission  through  1*794  inches  of  chlorine,  and  through 
2*894  inches  of  a mixture  of  chloride  and  hydrogen  ; the  absorbent 
action  of  chlorine  upon  the  chemical  rays  of  diffused  daylight  be- 
ing much  more  energetic  than  on  those  emitted  by  burning  coal- 
gas.  Observations  made  with  evening  light  showed  that  a depth 
of  0*776  inches  of  chlorine  was  sufficient  to  reduce  the  chemical 
power  to  one-tenth  of  that  possessed  by  the  incident  light.  The 
relative  thickness  of  the  stratum  of  chlorine  required  to  produce 
an  equal  reduction  in  the  chemical  power  of  the  incident  light 
was  therefore  the  following  : — 

Inches. 


A flame  of  joal-gas 6’822 

Reflected  zenith  light  (morning) P794 

Reflected  zenith  light  (evening) 0 776 


(1028)  It  was  stated  more  than  50  years  ago  by  Ritter,  and 
the  observation  has  been  confirmed  and  extended  by  ITerschel, 
that  the  two  ends  of  the  spectrum  produce  opposite  chemical  ef- 
fects, though  the  violet  extremity  appears  greatly  to  predominate 
in  power.  If,  for  example,  paper  soaked  in  nitrate  of  silver  be 
partially  blackened  by  exposure  to  diffused  daylight,  and  then 


PHOTOGRAPHIC  EFFECTS  OX  COLOURED  GLASSES. 


i 


submitted  to  tlie  action  of  tlie  solar  spectrum,  the  portion  upon 
which  the  violet  end  falls  speedily  becomes  much  darker,  while 
the  portion  beneath  the  red  rays  assumes  a brick-red  hue.  If  the 
spectrum  be  thrown  upon  white  paper  coated  with  nitrate  of  sil- 
ver, and  dilfused  daylight  be  allowed  at  the  same  time  to  fall  upon 
it,  the  spot  where  the  red  rays  fall  retains  its  whiteness,  while  the 
rest  of  the  paper  speedily  darkens.  It  thus  appears,  that  by  com- 
bining the  influence  of  two  rays  of  different  refrangibilities, 
effects  are  producible  which  cannot  be  obtained  by  either  ray 
separately. 

Paper  soaked  with  nitrate  of  silver  and  blackened  by  the  ac- 
tion of  light,  if  washed  over  with  a solution  of  iodide  of  potassium, 
becomes  gradually  bleached  when  exposed  to  diffused  daylight. 
If  the  solar  spectrum  be  allowed  to  fall  upon  paper  thus  prepared, 
whilst  moist,  and  before  it  has  become  bleached,  the  part  beneath 
the  violet  end  is  quickly  bleached  ; but  this  effect  is  bounded  by 
a sharp  border  in  the  yellow,  while  the  paper  under  the  red  end 
becomes  darker.  The  phenomena  of  phosphorescence  also  exhibit 
similar  opposition  in  the  effects  produced  by  the  opposed  extremi- 
ties of  the  spectrum  (112). 

Claudet  {Phil.  Trams.  ISdT)  found  that  an  iodized  Daguerreo- 
t}q)e  plate,  when  submitted  in  the  focus  of  a camera  to  the  red 
image  of  the  sun  as  seen  through  a London  fog,  became  subse- 
quently whitened  on  exposure  to  the  vapour  of  mercury,  in  all 
parts  except  in  the  track  traversed  by  the  image  of  the  sun — this 
portion  continued  to  be  perfectly  black.  In  another  experiment, 
a plate  was  covered  with  black  lace,  and  exposed  to  diffused 
daylight ; after  a few  minutes’  exposure,  one  half  of  the  plate 
wms  covered  with  an  opaque  screen,  the  other  half  with  a red 
glass,  and  the  exposure  was  continued  for  a short  time  : in  the 
mercury  box  the  red  half  continued  to  be  black,  whilst  on  the 
other  portion  the  image  of  the  lace  was  distinctly  traced.  The 
photographic  effect  at  first  produced  over  the  whole  plate  had  in 
fact  been  neutralized  by  the  red  glass. A pleasing  variation  of 
the  last  experiment  was  made  by  exposing  an  iodized  plate  to  dif- 
fused daylight,  then  covering  it  with  a piece  of  black  lace,  and 
screening  it  with  a red  glass  ; a negative  picture  was  now  deve- 
loped in  the  mercury  box,  the  red  glass  having  destroyed  all  pho- 
tographic action  except  on  those  parts  screened  by  the  lace. 
Orange  and  yellow  glasses  give  similar  results.  After  exposing  a 
plate  to  daylight,  and  then  submitting  it  to  the  action  of  red  glass, 
it  again  becomes  sensitive  to  light,  so  that,  as  Claudet  observes, 
it  is  no  longer  needful  to  prepare  the  plates  in  a dark  chamber, 
since,  if  placed  beneath  a covering  of  red  glass,  they  are  always 
ready  for  immediate  use — even  though  subsequently  to  their  pre- 
paration they  may  have  been  for  some  time  exposed  to  solar  light. 

But  though  the  red  and  yellow  glass  have  the  power  of  com- 

* It  must  be  borne  in  mind  that  all  results  obtained  by  coloured  media  are  liable 
to  ambiguity,  for  it  seldom  happens  that  the  light  transmitted  through  them  is 
homogeneous  (105)  ; the  effects  are  liable  to  become  complicated  from  the  iutermis- 
ture  of  results  produced  by  rays  from  different  parts  of  the  spectrum. 


ACTION  OF  THE  SOLAR  SPECTRUM  ON  VEGETABLE  COLOURS.  7Y3 

pletely  counteracting  the  effect  of  the  radiation  of  the  more 
refrangible  rays,  they  have  a peculiar  effect  of  their  own.  The 
neutralizing  power  of  the  red  ray  is  exerted  more  slowly  than  the 
photographic  effect  of  the  white  light,  nearly  in  the  proportion 
of  100  to  1 ; that  of  the  yellow  ray  was  found  to  he  about  10  to  1. 

From  the  foregoing  remarks,  it  is  evident  that  the  colour  of 
objects  must  exert  a material  influence  upon  the  nature  of  the 
photographic  images  produced.  Reds  and  yellows,  from  the  want 
of  chemical  energy  in  the  less  refrangible  portion  of  the  spectrum, 
will  be  characterized  by  absence  ot  pliotographic  action  in  the 
image,  and  will  be  represented  by  black  spots,  which  often  produce 
singular  disfigurement  in  portraits.  Yellow  freckles,  for  instance, 
on  the  skin  of  the  face  are  accurately  copied,  but  are  depicted 
in  the  portrait  as  black  spots.  Much  judgment  and  knowledge 
are  therefore  required  in  selecting  a dress  of  a colour  which  is 
adapted  to  produce  a suitable  depth  and  contrast  of  tint  in  the. 
photograph. 

(1029)  Action  of  the  Solar  Spectriom  on  Vegetable  Colours. — 
This  subject  has  been  particularly  examined  by  Herschel  {Phil. 
Trans.  1812).  White  paper  coloured  with  various  vegetable  juices 
was  subjected  by  him  to  the  influence  of  the  prismatic  spectrum, 
and  in  some  cases  these  papers  were  washed  over  with  solutions 
of  metallic  salts.  The  following  are  the  most  important  general 
conclusions  which  may  be  drawn  from  these  experiments : — 
1.  That  the  action  of  liglit  is  in  almost  all  cases  of  a nature  to 
obliterate  the  colour ; or  if  it  does  not  entirely  bleach  it,  a fiiint 
residual  tint  is  left,  upon  which  it  has  little  further  action.  The 
older  the  paper  or  the  tincture,  the  more  decided  is  this  residual 
tint,  which  is  probably  the  result  of  an  oxidizing  action  upon  the 
colouring  material,  independent  of  the  action  of  light.  2.  The 
action  is  confined  to  luminous  rays  of  the  spectrum — offering  in 
this  respect  a marked  difference  between  these  actions  and  those 
produced  upon  the  metallic  compounds.  3.  The  rays  which  are 
most  effective  in  destroying  a given  tint  are  in  many  cases  those 
which  are  complementary  (105)  to  the  tint  destroyed.  Orange- 
yellows,  for  instance,  are  bleached  most  powerfully  by  the  blue 
rays : blues  by  the  red,  orange,  and  yellow  rays ; and  purples  and 
pinks  by  the  yellow  and  green  rays. 


CHAPTER  XXI. 

ON  THE  DETERMINATION  OF  THE  COMBINING  NUMBERS  AND  THE 
ATOMIC  WEIGHTS  OF  THE  ELEMENTARY  BODIES. 

(1030)  Aid  derived  from  Analysis  in  filing  the  Atomic  Weight 
of  a Body. — The  determination  of  the  atomic  weight  of  an  elemen- 
tary body  is  an  operation  of  great  delicacy,  and  often  involves 
many  very  difficult  questions.  The  first  object  of  the  chemist  is 


774 


DETERMINATION  OF  ATOMIC  WEIGHTS. 


to  select  some  compound  of  tlie  elementary  body  under  examina- 
tion, the  composition  of  which  is  tolerably  simple,  and  which  can 
readily  be  procured  in  a state  of  purity,  and  in  this  compound  he 
determines  the  proportions  of  each  of  its  components  with  the 
utmost  attainable  precision.  It  is  of  great  importance  that  the 
operations  by  which  these  results  are  obtained  should  be  as  few  in 
number  and  as  simple  and  manageable  as  possible.  It  is  not, 
howeyer,  sufficient  that  three  or  four  different  experiments  con- 
ducted in  the  same  manner  should  giye  uniform  results:  the  mode 
of  analysis  adopted  should,  if  possible,  be  yaried  so  as  to  ayoid 
any  unperceiyed  som’ce  of  error  which  depends  upon  the  process 
employed.  It  is  also  desirable  to  yary  the  compound  upon  which 
the  analysis  is  made.  For  example,  the  atomic  weight  of  a metal 
may  in  some  instances  be  ascertained  by  fixing  the  proportion  of 
oxygen  which  a giyen  weight  of  the  metal  requires  for  its  conyer- 
sion  into  the  state  of  oxide : in  other  cases  the  proportion  of 
oxygen  and  of  metal  can  be  determined  yery  exactly  by  ascertain- 
ing the  loss  of  weight  which  the  oxide  experiences  when  a known 
weight  of  the  pure  oxide  is  heated  in  a current  of  hydrogen.  It 
is,  howeyer,  aclyisable  to  check  these  results,  not  only  by  trials 
upon  diflerent  quantities  of  the  metal  or  of  the  oxide  prepared  at 
different  times,  but  also  (in  order  to  guard  against  the  occurrence 
of  any  unperceiyed  impurity  in  the  substance  under  experiment) 
to  ascertain  if  the  analysis  of  the  chloride,  the  sulphide,  or  some 
other  compound  of  the  metal,  giyes  a similar  numerical  yalue  for 
its  combining  proportion.  These  results  must  be  reduced  by  cal- 
culation to  their  weight  in  va/:uo  (24).* 

(1031)  Aid  derimd  from  Isomorphism^  Specific  Heat^  and 
Combining  Yolurne  of  Yapour. — The  determination  of  the  num- 
bei*s  which  are  assumed  to  represent  the  relatiye  atomic  weights 
of  the  elements,  howeyer,  does  not  rest  simply  upon  the  knowl- 
edge of  the  proportion  in  which  each  element  enters  into  combi- 
nation with  a giyen  amount  of  oxygen  or  of  any  other  simple  body. 
AYhen  a substance  forms  but  a single  combination  with  oxygen, 
the  simplest  hypothesis  respecting  its  composition  is  that  the  com- 
pound so  formed  is  produced  by  the  union  of  single  atoms  of  each 
of  its  components.  Magnesium  and  zinc,  for  example,  each  forms 
but  a single  oxide,  which  is  assumed  to  be  a protoxide, — or  oxide 
each  compound  atom  of  which  contains  1 atom  of  the  metal  to  1 
atom  of  oxygen.  The  nitrates  of  such  oxides,  if  represented  as 
formed  by  the  anhydride  and  the  oxide,  M"0,X,05,  will  contain 
a quantity  of  the  anhydilde  (X^O.),  in  which  the  proportion  of 
oxygen  is  fiye  times  that  of  the  base.  But  it  not  untrequently 
happens  that  the  same  metal  forms  two  oxides,  in  one  of  which  a 
giyen  weight  of  oxygen  combines  with  twice  as  large  a propor- 
tion of  the  metal  as  in  the  other : for  example,  16  parts  of  oxygen 
unite  with  either  63*5  of  copper  to  form  tlie  black  oxide,  or  with 
127  of  the  metal  to  form  the  red  oxide;  and  corresponding  salts 

* Some  idea  of  the  extraordinary  care  required  in  researches  of  this  description 
may  be  formed  by  the  perusal  of  the  admirable  memoir  of  Stas,  in  the  Transactions 
of  the  Brussels  Academy  for  1860. 


AID  DERIVED  FROM  ISOMORPHISM. 


7T5 


may  be  obtained  by  the  reaction  of  each  oxide  with  acids.  In 
like  manner,  16  parts  of  oxygen  form  with  mercury  two  basic 
oxides,  one  containing  200,  the  other  400  parts  of  mercury.  The 
question  to  be  determined  then  is,  which  of  these  numbers  is  to 
be  regarded  as  representing  the  atomic  weight  of  the  metal  ? In 
cases  of  this  kind,  the  judgment  requires  aid  from  analogy,  or 
from  collateral  circumstances,  such  as  the  isomorphism  of  the  body 
with  some  other  analogous  compound  of  known  composition ; the 
circumstance  that  the  specific  heat  of  the  body,  when  multiplied 
into  its  supposed  atomic  weight,  yields  the  same  product  as  that 
obtained  by  multiplying  the  specific  heat  of  some  other  element 
into  its  admitted  atomic  number ; or  the  formation  of  a volume 
of  vapour  from  the  supposed  atomic  weight  which  is  equal  in  bulk 
to  the  volume  of  the  atom  of  hydrogen. 

Such  assistance  is  afforded  in  the  case  of  copper  by  the  iso- 
morphism of  the  compounds  of  the  black  oxide  of  this  metal  with 
corresponding  compounds  of  zinc  and  magnesium.  If  the  oxide 
of  zinc  be  a protoxide,  the  black  oxide  of  copper  is  also  a protoxide, 
and  the  red  oxide  must  be  considered  as  a suboxide. 

Another  character  of  high  importance  is  afforded  by  the  spe- 
cific heat  of  the  metal.  Assuming  the  oxide  of  zinc  to  be  a prot- 
oxide, the  atomic  number  of  the  metal  is  65 ‘0,  and  its  specific 
heat  is  found  to  be  0’0955  ; the  product  of  these  two  numbers  is 
6’206.  The  specific  heat  of  copper  is  0.0951,  and  assuming  the 
black  oxide  to  be  the  protoxide,  the  atomic  weight  of  tlie  metal  is 
63*5 ; the  product  of  these  two  numbers  is  6’039,  or  nearly  the 
same  as  in  the  case  of  zinc ; whereas,  if  the  red  oxide  were  assumed 
to  be  the  protoxide,  it  would  be  double  this  number.  If  the 
numbers  given  upon  pp.  21,  22,  Part  I.,  as  the  atomic  weights  of 
the  elements,  be  multiplied  by  the  specific  heat  of  these  bodies 
in  the  solid  form  (Part  I.  p.  241),  the  products  so  obtained  will 
vary  but  little  from  the  number  6.  Exceptions  occur  in  the  case 
of  carbon,  silicon,  and  boron,  where  allotropic  modifications  inter- 
fere. (See  also  Kopp,  FJiil.  Trans.  1864.) 

In  the  determination  of  the  atomic  weights  of  volatile  bodies, 
assistance  may  be  derived  from  another  character  of  great  impor- 
tance, viz.,  the  density  of  its  vapour.  But  the  force  of  this  argu- 
ment will  be  more  fully  perceived  after  the  various  compounds  of 
organic  chemistry,  of  which  so  large  a proportion  are  volatile, 
have  been  examined. 

It  is  not  safe,  moreover,  to  assume  in  cases  in  which  only  one 
compound  exists  between  an  element  and  oxygen,  that  such  com- 
pound is  necessarily  a protoxide ; aluminum  is  not  known  to 
form  more  than  a single  oxide,  yet  chemists  do  not  hesitate  to 
consider  this  oxide  as  a sesquioxide,  and  in  tliis  judgment  they 
are  guided  by  analogy  : for  example,  those  bodies  which  are  ad- 
mitted to  be  protoxides  are  generally  powerful  bases,  and  neu- 
tralize the  acids  very  completely.  How  alumina  does  not  present 
this  character;  its  salts  have  a powerfully  acid  reaction  and 
taste.  But  the  arguments  of  most  weight  against  the  supi)osition 
that  alumina  is  a protoxide  are  derived  from  the  composition  and 


DATA  FOE  THE  DETEEMIXATIOX  OF  THE 


776 

properties  of  the  oxides  of  iron.  Iron  forms  two  basic  oxides  : 
one  contains  but  two-thirds  of  the  proportion  of  oxygen  which  is 
present  in  the  other.  The  oxide  of  iron  with  the  smaller  propor- 
tion of  oxygen  is  a powerful  base,  and  with  acids  forms  salts 
which  are  isomorphous  with  those  of  magnesia  and  oxide  of  zinc. 
It  is  consequently  regarded  as  a protoxide,  and  the  other  oxide 
is  looked  upon  as  a sesquioxide  ; the  basic  properties  of  the  latter 
are  much  more  feeble,  and  the  salts  which  it  forms  with  acids 
have,  like  the  salts  of  aluminum,  a powerfully  acid  reaction.  Ses 
quioxide  of  iron,  moreover,  furnishes  salts  which  are  isomorphous 
with  those  of  alumina.  An  iron  alum  may  be  obtained  in  octo 
hedral  cr\’stals,  in  which  the  place  of  the  aluminum  is  supplied 
by  that  of  iron  : and  native  sesquioxide  of  iron  is  found  in  forms 
of  the  rhombohedral  system  isomorphous  with  native  almnina  in 
corundmn.  Hence,  if  the  red  oxide  of  iron  be  a sesquioxide,  alu- 
mina must  be  a sesquioxide  also.  Horeover,  the  specific  heat  of 
aluminum  follows  Dulong's  law  if  alumina  be  a sesquioxide,  but 
not  if  it  be  supposed  to  be  a protoxide. 

An  excellent  illustration  of  the  value  of  isomoi*phism  in  these 
cases  is  also  afforded  by  the  oxides  of  chromium.  Until  the  pub- 
lication of  Peligot's  researches  on  this  metal,  only  two  compounds 
of  chromium  with  oxygen  were  known,  viz.,  the  green  oxide,  and 
chromic  anhydride, — the  anhydride  containing  twice  as  much 
oxygen  as  the  oxide.  In  these  two  compounds  the  proportion  of 
oxygen  combined  with  equal  weights  of  chromium  was  as  1 : 2, 
or  as  1^  : 3.  But  there  was  little  difiicultv  in  deciding  that  the 
green  oxide  must  be  regarded  as  a sesquioxide,  for  the  gi’een  oxide 
of  chromium  was  known  to  be  isomorphous  with  the  red  oxide  of 
iron,  both  in  its  uncombined  form,  and  in  the  salts  which  it  yields 
by  action  upon  the  same  acids.  Chromic  anhydi’ide  would  there- 
fore contain  three  atoms  of  oxygen  to  1 atom  of  the  metal.  But 
evidence  still  more  conclusive  of  the  accuracy  of  this  view  is 
afforded  by  the  fact  that  the  chromates  are  isomorphous  with  the 
manganates  : now  the  manganates  are  known  to  contain  I atoms 
of  oxygen,  for  they  are  the  salts  of  the  acid  of  a metal  which 
yields  a basic  oxide  with  a given  weight  of  manganese  containing 
one-fourth  of  the  oxygen  present  in  manganic  acid.  H.MnO^,  and 
which  moreover  is  isomorphous  with  the  protoxide  of  iron.  Finally, 
the  discovery  of  another  oxide  of  chromium,  with  a smaller  pro- 
jDortion  of  oxygen  than  either  of  the  compounds  previously  known, 
fully  vindicated  the  correctness  of  the  foregoing  deductions,  for 
the  new  oxide  was  found  to  contain  one-third  of  the  proportion  of 
oxygen  present  in  chromic  anhydride.  It  also  yields  salts  isomor- 
phous with  the  corresponding  salts  obtained  from  the  protoxide  of 
iron,  and  the  proportion  of  oxygen  which  it  contains  bears  the  same 
relation  to  that  present  in  the  green  oxide  of  chromium  that  the  oxy- 
g<^u  in  the  protoxide  of  iron  does  to  that  in  the  red  oxide  of  iron.  Pe- 
ligot's  new  oxide  therefore  was  the  missing  protoxide  of  chromium. 

(1032^  XumericaJ  Data  from  ichich  the  Equivalents  and 
Atomic  Weights  of  the  Elements  have  been  calculated. 


COMBINmiNG  NUMBERS  OF  THE  ELEMENTS.  TT7 

The  atomic  weights  of  the  elementary  substances  were  first  in- 
vestigated with  precision  by  Berzelius,  and  the  numbers  obtained 
by  him,  with  certain  important  corrections,  are  tliose  at  present 
in  use.  These  researches  of  Berzelius,  combined  with  those  of 
subsequent  cliemists,  particularly  of  Dumas  (Ann.  de  Cliimie^  III. 

i.  5;  viii.  189;  aud  Iv.  129);  of  Pelouze  (Comjptes  Hendns^  xx. 
1047) ; of  De  Marignac  (Bihliotheque  TJniv.  de  Geneve.^  xlvi.) ; of 
Erdmann  and  Marchand  (Journal fiir praM.  (Jlieinie^  xxiii,  xxvi., 
and  xxxiii.) ; and  of  Stas  (Trans.  Brussels  Acadewy^  I860),  have 
furnished  the  following  data,  from  which  the  numbers  given  at 
pp.  17,  18,  and  21,  22,  Part  I.,  Ivdve  been  compiled  : — 

1.  Aluminmrh. — Berzelius  found  that  100  parts  of  tlie  sulphate 
of  aluminum  (Al^  3 SOJ  lost  by  intense  ignition  70*066  of  sulphuric 
acid ; hence  assuming  the  atomic  weight  of  SO^  as  96,  that  of  alumi- 
num (liydrogen  being=l)  is  27*344.  Dumas,  by  determining  the 
amount  of  silver  required  to  precipitate  a given  weight  of  chloride 
of  aluminum  (AljClg),  obtained  numbers,  from  a mean  of  seven  ex- 
periments, indicating  that  the  atomic  weight  of  aluminum  is  27*488. 

2.  Antimony. — The  number  129*03,  assigned  by  Berzelius  to 
antimony,  is  admitted  to  have  been  too  high.  Schneider,  by  re- 
ducing the  native  sulphide  (Sb^Sg)  to  tlie  metallic  form,  obtained 
on  the  average  71*469  per  cent,  of  metal,  which  would  yield  as 
the  combining  number  120*3.  Tlie  experiments  of  Pose  on  the 
chloride  (SbClg)  gave  120*69.  Dexter,  by  oxidizing  the  metal 
with  nitric  acid,  and  converting  the  residue  by  ignition  into 
SbjO^,  obtained  122*34  as  a mean  result ; and  Dumas  by  experi- 
ments upon  the  terchloride  found  the  quantity  of  silver  required 
to  precipitate  the  chloride  indicated  122*0,  as  the  combining  num- 
ber of  the  metal. 

3.  Arsenic. — Pelouze  decomposed  a given  weight  of  chloride 
of  arsenic  (AsClg)  by  means  of  water,  and  determined  the  quan- 
tity of  cliloride  of  silver  which  it  produced  : a mean  of  three  ex- 
periments furnished  75  as  the  atomic  weight  of  arsenic,  a result 
confirmed  by  four  experiments  of  Dumas,  which  gave  it  as  74*95. 

4.  Barium. — Berzelius  found  that  100  parts  of  chloride  of 
barium  (BaCl^),  when  dissolved  in  water,  yielded  112*175  of  sul- 
phate of  barium  (BaSO^),  on  the  addition  of  sulphuric  acid ; and 
that  100  parts  of  the  cliloride  when  mixed  with  a solution  of 
nitrate  of  silver  yielded  138*07  of  chloride  of  silver.  Pelouze, 
by  precipitation  with  silver,  obtained  results  almost  identical : the 
number  calculated  from  the  results  of  Berzelius  for  barium  is 
136*84  ; from  those  of  Pelouze,  137*28.  De  Marignac,  from  a 
series  of  experiments  of  the  same  kind,  checked  by  the  deter- 
mination of  the  barium  as  sulphate,  obtained  the  number  137*16 ; 
and  a mean  of  sixteen  experiments  conducted  in  a similar  manner 
by  Dumas  leads  to  the  number  137*02. 

5.  Bismuth. — 100  parts  of  the  metal  converted  into  nitrate 
and  decomposed  by  heat  in  a glass  vessel,  gave  111*275  of  oxide, 
Bi^O,,  hence  the  atomic  weight  of  bismuth  is  212*86  (Lagerhjelm). 
Dumas,  from  a mean  of  seven  ex})eriments  upon  the  quantity  of 
silver  required  to  precipitate  the  chlorine  from  a given  weight  of 


778 


DATA  FOE  THE  DETEKMINATIOX  OF  THE 


tercKLoride  of  bismuth  (BiClg),  obtained  210 'Sd  as  the  number  for 
this  metal. 

6.  Boron. — According  to  Berzelius,  100  parts  of  borax  lost 
47*1  of  water,  and  yielded  16*31  of  soda,  leaving  for  boracic  an- 
hydride B2O3  (by  difference)  36*59  ; and  Davy  found,  by  the 
direct  combustion  of  boron,  that  100  parts  of  boracic  anhydilde 
contain  32  of  boron  and  68  of  oxygen.  This  would  make  the 
number  for  boron  10*9.  But  the  methods  which  were  employed 
are  admitted  by  Berzelius  not  to  be  such  as  to  warrant  entire  con- 
fidence in  the  accuracy  of  this  number ; and  Deville,  from  his  ex- 
periments upon  the  chloride  and  the  bromide  of  boron,  regards  11 
as  nearer  the  truth. 

7.  Bromine. — De  Marignac  found  that  3*946  grammes  of 
silver,  when  dissolved  in  nitric  acid,  required  4*353  grammes  of 
bromide  of  potassimn  (KBr)  for  its  complete  precipitation  ; and 
15*00  of  silver  converted  into  nitrate  gave  26*11  of  bromide  of 
silver  : taking  the  equivalent  of  silver  at  107*97,  a mean  of  the 
experiments  gives  the  equivalent  of  bromine  as  79*97 ; and  this 
result  has  been  verified  by  Dumas  by  the  decomposition  of  bromide 
of  silver  in  a cm’rent  of  chlorine.  It  may  without  sensible  error 
be  taken  as  80. 

8.  Cadmium. — Stromeyer  found  that  114*352  parts  of  the 
oxide  (-G-dO)  yielded  14*352  of  oxygen  ; from  which  the  atomic 
weight  of  this  metal  is  111*48.  Dumas,  as  a mean  of  six  experi- 
ments upon  the  quantity  of  silver  required  to  precipitate  the 
chlorine  from  a given  weight  of  chloride  of  cadmium  (DdCl,), 
obtained  results  represented  by  the  number  112*24 ; but  the  num- 
bers obtained  in  the  different  experiments  are  not  quite  so  con- 
cordant as  usual. 

9.  Calcium. — Dumas,  by  the  ignition  of  100  parts  of  Iceland 
spar  (-GaOOg)  obtained  56  parts  of  lime,  which  would  make  the 
atomic  weight  of  calcium  exactly  40  ; and  the  mean  of  later  ex- 
periments by  the  same  chemist  upon  the  quantity  of  silver  re- 
quired to  precipitate  a given  weight  of  chloride  of  calcium  (-GaCl^), 
lead  to  the  number,  40*02.  Erdmann  and  Marchand’s  results 
would  make  it  40*06  ; De  Marignac’s,  by  decomposition  of  a 
known  weight  of  the  chloride  of  calcium,  40*21  ; and  those  of 
Berzelius,  by  the  conversion  of  a known  weight  of  pure  lime  into 
sulphate,  would  make  it  40*26.  The  number  40  may  be  safely 
adopted. 

10.  Carhon. — The  determination  of  the  combining  proportion 

of  carbon  formed  the  subject  of  a series  of  laborious  researches  by 
Dumas  and  Stas.  They  burned  graphite,  diamond,  and  charcoal 
in  a current  of  pure  oxygen  with  scrupulous  care.  1*375  grammes 
of  diamond  gave  5*041  of  carbonic  anhydride  ,*  and  the 

mean  of  their  results,  which  agreed  very  closely  with  each  other, 
entitles  us  to  fix  the  atomic  weight  of  carbon  at  12.  Similar  ex- 
periments by  Erdmann  and  l^archand  gave  them  the  number 
12*014 ; and  the  results  obtained  by  Liebig  and  Kedtenbacher 
from  the  combustion  of  the  oxalate  (Ag,^,^^),  the  acetate,  the 
racemate,  and  the  tartrate  of  silver,  correspond  to  12*12,  which 


COMBINING  NUMBERS  OF  THE  ELEMENTS. 


779 


coincides  so  nearly  with  the  number  deduced  from  those  of  Du- 
mas, tliat  these  chemists  themselyes  have  adopted  the  number 
which  he  employs. 

11.  Chlorine. — hJumerous  careful  experiments  have  been  made 
with  a view  to  determine  the  equivalent  of  chlorine.  De  Marignac 
found  that  100  parts  of  chlorate  of  potassium  (KCIO3),  when  de- 
composed by  heat,  left  60*(S39  of  chloride  of  potassium  (KCl) ; 
and  22*032  of  pure  silver  required  15*216  of  chloride  of  potas- 
sium for  its  complete  precipitation.  14*427  of  cliloride  of  potas- 
sium gave  27*749  of  chloride  of  silver  (AgCl).  Berzelius  calcu- 
lates from  these  results  that  the  equivalent  of  chlorine  is  35*46  ; and 
this  coincides  exactly  with  the  recent  elaborate  experiments  of  Stas. 

Maumene,  by  heating  chloride  of  silver  in  a current  of  hydro- 
gen, found  that  100  parts  of  silver  were  united  with  32*856  of 
chlorine.  The  same  chemist  obtained  from  100  parts  of  chlorate 
of  potassium  60*791  of  chloride  of  potassium  : and  from  100  parts 
of  chloride  of  potassium,  he  obtained  by  precipitation  192*75  of 
chloride  of  silver.  These  experiments  furnish  data  from  which 
the  atomic  weights  of  potassium  and  silver  may  be  determined,  as 
well  as  that  of  chlorine,  in  the  manner  following : — 

The  composition  of  chlorate  of  potassium  is  represented  by  the 
formula  KCIO3 ; when  heated  it  gives  off  the  whole  of  its  3 atoms 
of  oxygen.  The  atom  of  chloride  of  potassium  therefore  will  be 
the  quantity  which  is  combined  with  48  parts  (or  3 atoms)  of 
oxygen.  Now,  taking  Maumene’s  result  that  39*209  parts  of  oxy- 
gen are  combined  in  chlorate  of  potassium  with  60*791  of  chloride 
of  potassium,  we  have — 

39*209  : 48 : : 60*791 : a?  (=74*4208,  1 at.  of  KCl). 

If  100  parts  of  chloride  of  potassium  produce  192*75  of  chloride 
of  silver,  1 atom,  or  74*4208,  of  chloride  of  potassium  will  furnish 
1 atom  of  chloride  of  silver.  For — 

100 : 192*75 : : 74*4208 : a?  (=143*446, 1 at.  of  AgCl) ; 

and  132*856  of  chloride  of  silver  contain  32*856  of  chlorine;  con- 
sequently (1  atom  of  chloride  of  silver  containing  1 atom  of  chlo- 
rine), we  find  the  atomic  weight  of  chlorine  as  follows : — 


132*856  : 32*856 : : 143*446  : a?  (=35*476) : 

but  the  atomic  weight  of  chloride  of  silver  being. . . . =143*446 

that  of  silver  is  found  by  deducting  tlie  at.  wt.  of  Cl  = 35*476 


leaving  the  atomic  weight  of  silver =107*970 


and  the  atomic  weight  of  chloride  of  potassium  being  =74*4208 
deduct  from  it  the  atomic  weight  of  chlorine =35*476 


we  obtain  the  atomic  weight  of  potassium =38*9448 

No  material  error  can  therefore  arise  if  the  atomic  weight  ot 

chlorine  be  taken  as = 35*5 

that  of  silver  as =108*0 

and  that  of  potassium  as = 39*0 


780 


DATA  FOE  THE  DETERMIXATIOX  OF  THE 


Dumas  has  also  checked  these  numbers  by  hmming  finely  di- 
vided silver  in  a current  of  perfectly  dry  chlorine.  He  thus  found 
that  108  parts  of  silver  combined  with  35 '505  of  chlorine  as  a 
mean  of  two  experiments. 

12.  Chromium. — The  atomic  weight  of  chromium  was  deter- 
mined by  Berlin,  by  converting  chromate  of  silver  (AggHrOJ  into 
the  chloride ; the  number  calculated  from  this  result  is  52-691; 
and  that  deduced  from  the  reduction  of  the  chromic  anhydride 
(•Gi-Oj)  to  the  sesquioxide  of  chromium,  in  the  same  series  of  expe- 
riments, is  52-51.  Peligot’s  experiments  on  the  acetate  would 
make  it  between  52  and  53-6,  but  he  considers  52-18  as  nearest 
the  truth. 

13.  Cohalt. — Bothoff  found  that  269-2  parts  of  the  protoxide 
of  cobalt  (HoO),  when  converted  into  chloride  (-GoCl^)  by  means 
of  hydrochloric  acid  and  precipitated  by  means  of  nitrate  of  silver, 
gave  1029-9  of  chloride  of  silver  : hence  the  atomic  weight  of 
cobalt  is  58-98.  The  number  59-08  is  the  mean  of  5 experiments 
made  in  a similar  way  by  Dumas.  Schneider,  however,  subse- 
Cjuently,  from  the  decomposition  of  the  oxalate,  obtained  results 
corresponding  to  the  number  60 ; but  the  more  recent  experiments 
of  Bussell  confirm  the  former  number,  and  show  that  the  atomic 
weight  is  identical  with  that  of  nickel. 

11.  Copper. — Berzelius  obtained  from  7-68075  grammes  of 
oxide  of  copper  (HuO),  which  were  reduced  in  a current  of  hydro- 
gen, 6'130T5  of  metallic  copper;  hence  the  atomic  weight  of  the 
metal  is  63-5.  Erdmann  and  Marchand,  by  a similar  method, 
obtained  numbers  which  would  make  it  63-52. 

15.  Fluorine. — Berzelius  found  that  100  parts  of  fiuor-spar 
(HaFo)  when  heated  with  an  excess  of  sulphuric  acid,  yielded  175 
of  sulphate  of  calcium  (HaSOJ.  Louyet,  on  repeating  this  expe- 
riment, obtained  171-361  parts  of  sulphate  of  calcium.  The  equi- 
valent of  fiuorine  deduced  from  this  latter  result  is  19.  {See 
p.  111).  And  these  results  have  been  confirmed  by  Dumas,  who 
made  similar  experiments  upon  the  fiuorides  of  calcium,  potassium, 
and  sodium. 

16.  Glucinnm. — Awdejew  found  that  100  parts  of  the  chlo- 
ride of  this  metal  contained  88-12  of  chlorine ; hence,  if  the  chlo- 
ride be  represented  as  Gl^Clg,  the  combining  number  of  the  metal 
will  be  6-97 ; but  if  the  chloride  be  regarded  as  GClj,  the  atomic 
weight  of  the  metal  is  9-30. 

17.  Gold. — Berzelius,  by  reducing  the  double  chloride  of  gold 
and  potassium  in  a current  of  hydi-ogen,  determined  the  combin- 
ing number  of  this  metal  at  196-66.  By  an  earlier  series  of  ex- 
periments he  found  that  112-9  of  metallic  mercury  precipitated 
93-55  of  gold  from  the  terchloride  (AuClg) ; 3 atoms  of  mercury 
causing  the  precipitation  of  2 atoms  of  gold  : and  assuming  the 
atomic  weight  of  mercirry  to  be  200,  this  would  make  the  nmnber 
for  gold  196-11. 

18.  Hydrogen. — The  equivalent  of  hydrogen  was  determined 
vdth  great  care  by  Dumas,  by  the  method  aheady  described  at 
p.  15.  He  ascertained,  as  a mean  of  nineteen  experiments,  that 


COMBINING  NUMBERS  OF  THE  ELEMENTS. 


781 


8 parts  of  oxygen  combined  with  1’0012  of  hydrogen  to  form 
water ; the  lowest  quantity  which  these  experiments  gave  being 
0*9984,  the  highest  1*0045.  The  quantity  of  water  collected  in 
each  of  these  experiments  was  considerable,  varying  from  230  to 
1100  grains.  Erdmann  and  Marchand  repeated  these  experiments 
with  similar  results.  Berzelius  and  Dulong  concluded,  from 
researches  performed  long  previously  upon  a similar  principle, 
though  on  a smaller  scale,  that  the  quantity  of  hydrogen  united 
with  8 parts  of  oxygen  was  0*9984,  which  coincides  with  the 
lowest  number  obtained  by  Dumas.  It  is  obvious  that  no  appreci- 
able error  can  be  committed  by  assuming  hydrogen  to  possess  an 
atomic  weight  of  1,  that  of  oxygen  being  16,  if  water  be  taken 
as  H2O. 

19.  Iodine. — De  Marignac  determined  the  number  for  iodine 
by  a process  analogous  to  that  which  he  employed  for  chlorine. 
The  atomic  weight  of  iodide  of  potassium  (KI)  he  fixed  at  165*951 ; 
deducting  from  this  38*95,  Maumene’s  number  for  potassium,  we 
obtain  127  as  the  combining  number  of  iodine.  Dumas,  by  two 
experiments  upon  the  iodide  of  silver,  which  he  converted  into 
chloride  by  heating  it  in  a current  of  dry  chlorine,  obtained  the 
same  result. 

20.  Iridium. — Berzelius  deduced  the  number  for  iridium  from 
an  analysis  of  the  chloride  of  iridium  and  potassium  (2  KCl,IrCl4) ; 
his  results  would  make  it  197*12,  which  is  identical  with  the 
number  obtained  for  platinum. 

21.  Iron. — Berzelius  found  that  1*586  grammes  of  pure  iron 
converted  first  into  nitrate,  and  then  into  sesquioxide  by  ignition, 
gave  2*265  of  sesquioxide  (Fe203);  and  Svanberg  and  Norlin,  by 
reducing  sesquioxide  of  iron  in  a current  of  hydrogen,  obtained 
from  35*783  of  sesquioxide,  25*059  of  metallic  iron  ; making  the 
atomic  weight  of  iron  56*08.  Erdmann  and  Marchand,  by  the 
method  last  named,  fixed  the  atomic  weight  at  56*002,  and 
Maumene  has  also  arrived  at  a similar  result  by  dissolving  iron  in 
aqua  regia,  and  precipitating  the  oxide  by  means  of  ammonia. 
Still  more  recently,  Dumas  has  corroborated  the  same  number  by 
decomposing  the  chloride  of  iron  by  means  of  nitrate  of  silver — 
the  mean  of  his  four  experiments  giving  56*14. 

22.  Lead. — 21*9425  grammes  of  oxide  of  lead  (PbO)  were 
reduced  by  Berzelius  in  a current  of  hydrogen,  and  gave  20*3695 
of  metallic  lead ; from  the  mean  of  his  five  experiments,  the 
atomic  weight  of  the  metal  would  be  207*14.  This  result  has  been 
confirmed  by  De  Marignac,  who  ol)tained,  by  the  2)recipitation  of 
5 grammes  of  chloride  of  lean  (BbC]2)  3*8835  of  chloride  of  silver ; 
similar  experiments  by  Dumas  would  make  the  number  for  lead 
207*1,  whilst  from  those  of  Stas  it  would  be  206*912. 

23.  Lithium. — The  number  obtained  by  Berzelius  for  this 
metal,  by  neutralizing  fused  carbonate  of  lithium  (Li2DB3)  with 
sulphuric  acid,  is  probably  inaccurate,  as  the  carbonate  of  lithium 
has  subsequently  been  found  to  lose  a little  of  its  acid  when  melted. 
Mallet  estimates  the  atomic  weight  of  lithium  at  6*97.  Diehl, 
from  an  analysis  of  the  carbonate,  obtained  the  number  7*026 ; 


782 


DATA  FOR  THE  DETERMINATIOX  OF  THE 


and  Troost,  from  tlie  chloride,  obtained  the  number  7*01,  as  well 
as  by  decomposition  of  the  carbonate  by  means  of  silica.  7*00  is 
therefore  the  number  adopted. 

2d.  2Iag7i€shnn. — Berzelius  found  that  100  parts  of  magnesia, 
dissolved  in  pm’e  sulphuric  acid  and  ignited,  gave  293 ’985  of 
sulphate  of  magnesium  (3fgSO^);  hence  the  equivalent  of  mag- 
nesium would  be  25*3;  but  this  result  is  probably  a httle  too 
high. 

Scheerer,  by  ascertaining  the  quantity  of  sulphate  of  barium 
produced  by  a given  weight  of  sulphate  of  magnesium,  determined 
the  number  for  magnesium  at  21:‘22.  The  results  of  Svanberg 
and  Xordonfeldt,  by  the  decomposition  of  the  oxalate  of  magnesium 
(Mg020^,2  II^O)  by  heat,  made  it  21:-7  ; those  by  converting  a 
known  weight  of  magnesia  into  sulphate,  gave  it  as  21:’71: : whilst 
those  of  Marchand  and  Scheerer,  by  ignition  of  the  native  car- 
bonate, inchoated  the  number  21*01:.  Bumas  found  extraordinary 
difficulty  in  procuring  chloride  of  magnesium  quite  free  from  mag- 
nesia. The  mean  of  11  experiments  upon  tlie  precipitation  of  the 
chloride  (MgCl„)  by  nitrate  of  silver  gave  21*6  as  the  combining 
number  of  magnesium.  The  mean  of  these  results  is  21*32. 

25.  2Langane8e, — 1*20775  of  chloride  of  manganese  (MnCh) 
gave  Berzelius  9*575  of  chloride  of  silver;  the  atomic  weight  of 
the  metal,  from  a mean  of  two  such  experiments,  is  55*11.  Dumas, 
as  a mean  of  five  such  experiments  conducted  in  a similar  manner, 
obtained  the  number  51*96. 

26.  ^Lercury. — Erchnann  and Marchand  obtained fromll8*3938 
grammes  of  red  oxide  of  mercmy  (HgO)  109*6308  of  merctrry ; 
a mean  of  five  experiments  gave  200*2  as  the  equivalent  of  the 
metal.  It  may  be  safely  estimated  at  200. 

27.  Molyhdenum. — Berzelius  regarded  the  number  originally 
given  by  himself  for  this  metal,  only  as  an  approximation.  Svan- 
berg and  Struve,  from  an  extensive  series  of  experiments,  consi- 
dered that  the  most  accurate  results  were  obtained  by  roasting  the 
bisulphide  of  molybdenum  in  air,  and  they  conclude  that  100  parts 
of  the  bisulphide  (MoSj)  yield  89*732  of  molybdic  anhycfride 
(M0O3) ; hence,  if  the  equivalent  of  sulphur  be  taken  at  32,  that 
of  molybdenum  will  be  92*12.  Berlin,  from  the  quantity  of 
molybdic  anhydride  left  by  the  salt  (II^X)^02,5  MoO-3,3  H^O,  found 
the  number  for  the  metal  (from  a mean  of  four  experiments)  to 
be  91*96.  Dumas,  however,  by  reducing  crystallized  molybdic 
anhydride  in  a current  of  hydrogen,  found,  as  a mean  of  5 con- 
corciant  experiments,  96  as  the  number  for  this  metal. 

28.  Xickel. — Bothoff  converted  188  parts  of  oxide  of  nickel 
into  chloride  (^iCl^),  and  obtained  from  it  718*2  of  chloride  of 
silver;  the  number  for  nickel  hence  deduced  is  59*08 ; and  Dumas, 
as  a mean  of  5 expenments  on  the  same  plan,  obtained  the 
number  59*02.  Russell  found  it  by  reducing  the  oxide  in  a current 
of  hydrogen  58*738. 

29.  Nitrogen. — De  Marignac,  by  converting  200  grammes  of 
silver  into  nitrate  (AgXOg),  obtained  31-1*891:  of  the  salt ; 11:*110 
of  nitrate  of  silver  required  for  precipitation  6*191  of  chloride 


COMBINING  NUMBERS  OF  THE  ELEMENTS. 


783 


of  potassium ; 10 '339  of  silver  converted  into  nitrate  required 
5*120  of  chloride  of  ammonium  for  complete  precipitation;  the 
mean  result,  as  calculated  by  Berzelius  from  several  experiments 
performed  in  this  manner,  gives  14*004  as  the  number  for  nitrogen. 
Stas,  by  synthetic  experiments  upon  nitrate  of  silver,  fixed  it  at 
14*041 . Anderson,  by  the  decomposition  of  nitrate  of  silver  by 
heat,  concluded  that  the  atomic  weight  of  nitrogen  was  13*95  ; 
and  Svanberg,  from  the  analysis  of  nitrate  of  lead,  obtained  the 
same  result : the  nmnber  for  nitrogen  may  therefore  be  taken 
as  14. 

30.  Osmium. — The  atomic  weight  of  this  metal  was  calculated 
by  Berzelius  from  the  result  obtained  by  heating  the  chloride  of 
osmium  and  potassium  (2KCl,OsCl4)  in  a current  of  hydrogen, 
1*3165  grammes  of  the  salt  leaving  0*401  gramme  of  KCl  and 
0*535  gramme  of  osmium : hence  the  number  for  osmium  may  be 
estimated  at  198*8,  which  agrees  with  the  later  researches  of 
Dmnas. 

31.  Oxygen. — The  atomic  weight  of  oxygen  is  the  fundamental 
one  from  which  all  others  are  calculated.  Beasons  have  already 
been  fully  given  which  lead  to  the  adoption  of  16  as  the  atomic 
weight  of  oxygen,  if  that  of  hydrogen  be  taken  as  1. 

32.  Palladium. — The  number  of  this  metal  rests  upon  the 
authority  of  Berzelius,  who  found,  by  reducing  the  chloride  of 
potassium  and  palladium  (2  KCljPdCl^)  ii^  a current  of  hydrogen, 
that  2*606  grammes  of  the  salt  gave  0*563  gramme  of  chlorine, 
0*851  of  palladium,  and  1*192  of  chloride  of  potassium  : hence  the 
atomic  weight  of  palladium  is  106*48. 

33.  Phosphorus. — According  to  Pelouze,  a solution  of  100 
parts  of  silver  in  nitric  acid  is  required  to  precipitate  the  chlorine 
from  42*74  of  terchloride  of  phosphorus  (PClg) ; the  atomic  weight 
of  phosphorus,  therefore,  would  be  32*02.  Berzelius,  from  the  sil- 
ver reduced  from  sulphate  of  silver  by  a known  weight  of  phos- 
phorus, estimated  the  number  for  phosphorus  at  31*36;  and 
Schrdtter  concludes — from  a mean  of  ten  experiments,  in  which 
phosphorus  was  burned  in  a current  of  dry  air,  and  thus  con- 
verted into  phosphoric  anhydride — that  the  true  atomic  weight 
is  31 ; a result  confirmed  by  careful  experiments  upon  the  terchlo- 
ride by  Dumas,  who  found  it  to  be  31*03. 

34.  Platinum. — Berzelius  found  that  6*981  grammes  of  the 
double  chloride  of  platinum  and  potassium  (2  KCl,PtCl4),  when 
reduced  in  a current  of  hydrogen,  gave  4*957  of  a mixture  of 
platinum  and  chloride  of  potassium ; 2*822  of  this  was  platinum : 
hence  the  number  for  platinum  is  197*12. 

35.  Potassium,. — De  Marignac’s  experiments  on  the  chlorate 
of  potassium  (KCIO3),  (related  when  speaking  of  the  atomic  weight 
of  chlorine)  gave  the  number  for  potassium,  39*1 ; those  of  Mau- 
mene,  38*95:  those  of  Pelouze,  39*14;  and  those  of  Stas,  39*13. 
It  may  tlierefore  be  taken  as  39*1. 

36.  Rhodium,. — 3*146  grammes  of  the  chloride  of  rhodium  and 
potassium  (KCfiRoClg)  when  heated  in  a current  of  hydrogen,  were 
ibund  by  Berzelius  to  furnish  0*912  gramme  of  rhodium,  and  0 515 


784: 


DATA  FOR  THE  DETER:srrN’ATIOH  OF  THE 


gramme  of  chloride  of  potassium ; whence  the  atomic  weight  of 
the  metal  should  he  104:-32. 

37.  Selenium, — 100  parts  of  selenium,  when  heated  in  a current 
of  chlorine,  yield  exactly  279  of  chloride  of  selenimn  (SeCl^),  ac- 
cording to  Berzelius,  “which  would  make  the  atomic  weight  79*32  ; 
hut  the  method  employed  is  not  perfectly  trustworthy.  Dumas, 
hy  modifying  the  method  of  proceeding,  obtained  as  a mean  of 
seven  experiments,  79  •16. 

38.  Silicon. — Berzelius  found  that  100  parts  of  silicon,  when 
oxidized,  yielded  208  parts  of  silica,  which,  if  taken  as  SiO^  would 
give  an  atomic  weight  of  29*62 ; this  appears  to  he  too  high. 
Pelouze  states  that  a solution  of  3*685  parts  of  silver  in  nitric  acid 
precipitated  1*151  of  chloride  of  silicon  (SiCl^),  whence  the  num- 
her  would  he  28*18  ; and  Dumas,  hy  a mean  of  two  experiments 
conducted  on  the  same  principle,  obtained  the  number  28*02. 

39.  Silver. — The  combining  number  of  this  metal  has  been 

repeatedly  determined  with  very  great  care,  as  it  forms  a funda- 
mental datum  in  these  inquiries.  De  Marignac,  by  precipitation 
of  a known  weight  of  silver  from  its  solution  in  nitric  acid,  as 
chloride  (AgCl)  estimates  the  equivalent  as  107*97 ; and  the  ex- 
periments of  Pelouze  and  of  Maumene  agree  almost  exactly  with 
this  result.  Dumas  has  also  confirmed  this  result  by  burning 
finely  divided  silver  in  a current  of  chlorine  gas ; and  the  number 
deduced  by  Stas,  from  his  experiments,  was  107*915.  108  may 

therefore  be  taken  as  the  atomic  weight  of  silver. 

10.  Sodium. — Berzelius  found  that  100  parts  of  chloride  of 
sodium  (27aCl)  gave  by  precipitation  211*6  of  chloride  of  silver  ; 
the  atomic  weight  of  sodium  would  therefore  be  23*17.  Pelouze 
found,  as  a mean  of  three  experiments,  that  100  parts  of  silver 
required  for  precipitation  51*111  of  chloride  of  sodium,  whence 
the  atomic  weight  of  sodium  would  be  22*97.  Dumas,  as  a mean 
of  seven  experiments  of  a similar  kind,  obtained  the  number  23*01 ; 
and  Stas  found  it  to  be  23*05.  It  may  be  taken  as  23. 

11.  Strontium. — The  number  for  this  metal  was  also  obtained 
by  a similar  method,  viz.,  by  ascertaining  the  proportion  of  silver 
which  a given  weight  of  chloride  of  strontium  (SrCl.^)  required  for 
precipitation.  Stromeyer's  experiments  give  the  number  87*31 ; 
De  Marignac’s,  87*51 ; Pelouze’s,  87*68  ; and  the  mean  ot  a nu- 
merous series  of  experiments  by  Dumas,  gives  87*18. 

12.  Sulphur. — The  atomic  weight  of  sulphur  was  estimated 
by  Berzelius  from  the  weight  of  sulphate  of  lead  formed  by  oxidiz- 
ing a known  weight  of  lead  with  nitric  acid,  and  heating  it  vfith 
an  excess  of  sulphuric  acid  till  the  weight  ceased  to  alter.  As  a 
mean  of  three  experiments,  100  parts  of  lead  yielded  116*15  of 
sulphate  of  lead  (PbSO^) ; hence  the  atomic  weight  of  sulphur 
would  be  32*128  ; this  result  was  confirmed  by  converting  chloride 
of  silver  into  sulphide  in  a current  of  dry  sulphuretted  hydrogen. 
Erdmann  and  Marchand,  by  distilling  cinnabar  with  copper  turn- 
ings, obtained  from  100  parts  of  cinnabar  86*213  of  mercury  as 
a mean  of  two  experiments.  This  would  make  the  equivalent  of 
sulphur  exactly  32 — a result  which  agrees  with  those  of  Dumas, 


COMBINING  NUIklBERS  OF  THE  ELEMENTS. 


785 


who  converted  a given  weight  of  silver  into  sulphide,  by  heating 
the  metal  in  the  vapour  of  sulphur.  As  a mean  of  five  such  ex- 
periments, he  obtained  the  number  32*02,  while  Stas  found  it  to 
be  32*0742. 

43.  Tellurium. — 1*5715  gramme  of  tellurium  when  oxidized 

by  nitric  acid  and  heated  till  the  excess  of  nitric  acid  was  expelled, 
left  a residue  of  which  Berzelius  found  to  weigh  1*9365 

gramme  ; hence  the  number  for  tellurium  would  be  128*30.  But 
Dumas,  from  experiments  not  hitherto  published  in  detail,  gives 
figures  which  would  make  it  129. 

44.  Tin. — 100  parts  of  tin,  wdien  oxidized  by  nitric  acid  and 
ignited,  were  found  by  Berzelius  to  yield  127*2  parts  of  peroxide 
(SnOj) ; from  which  the  number  for  tin  would  be  117*64.  Mulder 
states  that  he  obtained  from  100  parts  of  this  metal  127*56  of 
peroxide  of  tin,  which  would  give  the  number  116*1.  Dumas,  on 
repeating  this  experiment,  obtained  the  number  118*06  for  the 
metal,  and  this  result  was  confirmed  by  experiments  on  the  quan- 
tity of  silver  required  for  the  precipitation  of  a known  weight  of 
perchloride  of  tin  (SnCl4).  The  atomic  weight  of  tin  may  there- 
fore be  taken  at  118. 

45.  Titanium. — The  number  for  this  metal  rests  upon  the 
analysis  of  its  perchloride.  Bose  found,  as  a mean  of  four  experi- 
ments, that  100  parts  of  the  perchloride  (TiCl^)  contained  74*46 
of  chlorine,  which  would  give  48*24  as  the  atomic  weight  of  tita- 
nium. Later  experiments  by  Isidore  Pierre,  in  which  0*8215 
gramme  of  TiCl^,  furnished  1*84523  gramme  of  AgCl,  seem  to  fix 
it  at  50*34. 

46.  Tungsten. — The  number  189*28,  calculated  from  the  ex- 
periments of  Berzelius,  was  only  an  approximation.  Schneider, 
on  repeating  the  experiment  of  reducing  tungstic  anhydride 
(WO3),  in  a current  of  hydrogen,  found  that  100  parts  of  the 
anhydride  yielded  79*316  of  the  metal,  and  on  oxidizing  metallic 
tungsten,  and  reconverting  it  into  tungstic  anhydride,  he  found 
79*327  parts  of  metal  furnished  100  of  anhydride  : the  atomic  weight 
of  tungsten  from  the  mean  of  these  results  would  be  184*12.  Mar- 
chand,  by  similar  experiments,  fixed  it  at  184*1  a result  complete- 
ly confirmed  by  Dumas.  It  maybe  taken  as  184.  Persoz, how- 
ever, has  endeavoured  to  show,  though  without  much  probability, 
that  tungstic  anhydride  consists  of  "ILO^,  not  of  WO3,  and  in  such 
case  tlie  atomic  weight  of  tungsten  would  be  153*3.  See  note.,  p.  573. 

47.  Uranium. — Some  doubt  exists  as  to  the  exact  combining 
number  of  this  metal.  Wertheim’s  experiments  on  the  double 
acetate  of  sodium  and  uranium  would  give  118*48  ; and  Ebelmen’s 
on  the  oxalate  118*86  ; but  Pdligot’s  estimate,  which  would  make 
it  120,  is  usually  adopted. 

48.  Vanadium. — The  atomic  weight  of  this  metal  was  deter- 
mined by  heating  vanadic  anhydride  (MO3)  in  a current  of  hydro- 
gen. It  was  thus  reduced  to  the  protoxide.  Berzelius  found  as 
a mean  of  four  experiments,  that  120*927  ])arts  of  the  anhydride 
lost  thus  20*927  of  oxygen.  Hence  the  atomic  weight  of  the  metal 
is  calculated  at  137*1. 

50 


786 


TABLE  OF  COMBINING  NLTklBERS. 


49.  Zinc. — Fa\Te’s  experiments  on  the  analysis  of  the  oxalate 
of  zinc,  and  on  the  quantity  of  hydrogen  which  a given  weight  of 
zinc  liberates  during  its  solution  in  hydrochloric  acid,  would  make 
the  atomic  weight  of  the  metal  66*0  ; and  Jacquelain,  by  the  de- 
composition of  the  nitrate  and  of  the  sulphate  of  zinc  (ZnSO^)  by 
heat,  obtained  results  corresponding  to  the  number  66*24.  The 
original  experiments  of  Berzelius  on  this  metal  lead  to  the  number 
64*5.  Subsequently,  A.  Erdmann  prepared  a pure  oxide  of  zinc, 
mixed  it  with  pure  charcoal  obtained  from  sugar,  and  distilled  the 
zinc  in  a current  of  hydrogen ; he  then  oxidized  the  metal  by 
nitric  acid,  and  converted  it  into  oxide  by  ignition.  The  atomic 
weight  of  zinc,  calculated  from  a mean  of  four  experiments  con- 
ducted in  this  manner,  is  65*04.  The  same  number  is  obtained 
from  the  analysis  of  the  lactate  of  zinc  by  Pelouze. 

50.  Zirconium. — As  a mean  of  six  experiments,  Berzelius  found 
that  100  parts  of  sulphuric  anhydride  (SOg)  required  75*853  of 
zirconia,  in  order  to  form  the  sulphate  of  the  earth.  Fluoride  of 
zirconium  forms  with  fluoride  of  potassium  two  compounds  : in 
one  the  fluorine  is  combined  with  zirconium  and  potassium  in 
equal  quantity ; in  the  other  the  quantity  of  fluorine  combined 
with  zirconium  is  3,  if  that  with  potassium  is  2;  hence  Berze- 
lius considered  that  zirconia  contains  Zr^Og,  and  the  combining 
number  of  the  metal  is  67*18,  but  De  Marignac  has  shown  that 
zirconia  is  more  probably  Zi^Og,  in  which  case  the  number  would 
be  89*5. 

(1033)  Tafjle  of  Comhining  Numhers. — We  may  here  sum  up 
the  foregoing  results,  by  stating  that  the  following  numbers  may 
be  taken,  for  the  purpose  of  calculation,  as  representing  the  atomic 
weights  of  the  elementary  bodies  on  the  hydrogen  scale.  They 
differ  but  very  slightly  from  the  numbers  given  at  pages  21  and 
22  of  Part  I. : — 


Aluminum  .... 

27-5 

Antimony 

122-0 

Arsenic 

75-0 

Barium 

137  0 

Bismuth 

210-0 

Boron 

10-9 

Bromine 

80-0 

Cadmium 

112-0 

Calcium 

40-0 

Carbon 

12-0 

Cerium 

92-0 

Chlorine 

Chromium 

52-5 

Cobalt 

59-0 

Columbium. . . . , 

97-5 

Copper  

63-0 

Didymium 

. ...  96-0 

Fluorine 

19-0 

Glucinum 

9-3 

Gold 196-6 

Hydrogen 1-0 

Iodine 127-0 

Iridium 197-2 

Iron 56-0 

Lanthanum 92-0 

Lead 207-0 

I Lithium 7'0 

I Magnesium 24-3 

1 Manganese 55-0 

Mercury 200*0 

Molybdenum 96-0 

Nickel 59-0 

Nitrogen 14'0 

Osmium 199-0 

! Oxygen 16-0 

j PaUadium 106-5 

Phosphorus 31-0 

Platinum 197-2 


' Potassium 39*1 

' Rhodium 104-2 

Ruthenium 104-2 

Selenium 79-5 

Silicon 2 8 0 

' Silver 108  0 

Sodium 23-0 

Strontium 87-5 

: Sulphur 32-0 

’ Tantalum 137-6 

; Tellurium 129*0 

; Thorinum 119-0 

Tin 118-0 

[ Titanium 50  0 

: Tungsten 184*0 

Uranium 120*0 

, Vanadium 137*0 

' Zinc 65*0 

1 Zirconium 89*5 


(1034)  On  the  Numerical  Relations  of  the  Proportional  Num- 
hers of  the  Elements. — Several  years  ago  Prout  started  the  idea 
that  the  numbers  which  represent  the  combining  proportions  of 


NUMERICAL  RELATIONS  OF  THE  ELEMENTS. 


the  diiferent  elementary  bodies  are  multiples  by  whole  numbers 
of  the  combining  proportion  of  hydrogen ; and  he  attributed  the 
various  cases  of  apparent  departure  from  this  proposition  to  in- 
accuracy in  the  experimental  determinations  of  the  combining 
proportion  of  the  exceptional  bodies.  Since  that  period  an  in- 
creased degree  of  precision  has  been  attained  in  experiments  of 
this  nature,  and  many  of  the  apparent  exceptions  to  Front’s  idea 
have  been  removed. 

Independently  of  the  importance  of  accurate  determinations  of 
these  numbers  for  the  purposes  of  chemical  analysis,  and  for  the 
tracing  out  of  quantitative  relations  between  the  chemical  equiva- 
lents and  certain  physical  properties,  such  as  the  density  and 
specific  heat  of  the  simple  and  compound  bodies,  the  verification 
or  disproof  of  Front’s  hypothesis  acquires  a high  interest  from  its 
connexion  with  the  nature  of  the  elementary  bodies  themselves  ; 
for  if  the  combining  proportions  of  all  the  elements  be  multiples 
by  whole  numbers  of  the  combining  proportion  of  hydrogen,  it  is 
not  absolutely  impossible  that  the  various  bodies  at  present  re- 
garded as  elementary,  may  in  reality  be  compounds  of  a single 
primordial  substance  condensed  in  different  degrees  in  the  various 
so-called  elements. 

If  experiment  justifies  the  hypothesis  of  Front,  it  would  be 
possible  that  the  three  following  propositions  were  true  : — 

a.  Similar  quantities  of  this  one  elementary  principle  might, 
by  variety  in  the  mode  of  their  arrangement,  form  bodies  (at 
present  regarded  as  elementary)  or  radicles  of  equal  atomic  weight, 
but  endowed  with  distinct  properties. 

h.  A radicle  intermediate,  in  properties  and  in  its  combining 
number,  between  two  other  radicles  of  the  same  group,  might  be 
produced  by  the  union  of  half  a molecule  of  the  two  extreme 
radicles. 

G.  And,  finally,  the  supposed  constitution  of  these  radicles  (or 
bodies  at  present  regarded  as  simple)  might  be  assimilated  to  the 
compound  radicles  of  organic  chemistry  of  known  constitution. 
There  would  be,  however,  this  important  distinction  between  the 
radicles  of  mineral  chemistry  and  those  of  organic  origin;  viz., 
that  the  radicles  of  inorganic  chemistry  possess  a stability  indefi 
nitely  greater  than  those  of  the  organic  creation — a stability, 
indeed,  of  such  an  order,  that  the  present  resources  of  analytical 
chemistry  are  insufficient  to  effect  their  decomposition. 

The  probability,  on  the  other  hand,  of  such  views  would  ob- 
viously be  negatived  if  the  elements  exhibited  no  such  multiple 
relation  in  their  equivalents. 

Certain  remarkable  relations  which  exist  between  many  of 
these  numbers  have  been  pointed  out  by  various  chemists.  The 
whole  subject  of  atomic  weights  has  recently  been  submitted  to  a 
careful  revision  by  Dumas  {Ann.  de  Chimie^  III.  Iv.  129).  As 
the  result  of  his  investigations  and  calculations,  Dumas  concludes 
that,  in  a modified  sense.  Front’s  law  is  true'’^' ; and  he  considers 

* Stas,  however,  arrives  at  an  opposite  conclusion.  He  has  lately  published  a 
long  and  most  laborious  series  of  researches,  which  it  appears  almost  impossible  to 


788 


EATIO  OF  PROPORTIONAL  NUMBERS. 


that  the  elementary  bodies,  the  atomic  weights  of  which  he  regards 
as  accurately  known,  may  be  arranged  in  three  groups,  or  rather 
two  groups,  if  the  duplication  of  the  atomic  weights  adopted  in 
this  work  be  followed — viz., 

1.  Bodies  which  are  represented  by  multiples  of  a whole  num- 
ber of  the  atomic  weight  of  hydrogen. 

2.  Multiples  by  the  number  0*5  of  that  of  hydrogen. 

1.  Bodies  which  are  multiples  by  a whole  nmnber  of  the  equi- 
valent of  hydrogen : — 


Hydrogen 1 

Carbon 12 

Nitrogen 14 

Oxygen 16 

Fluorine 19 

Sodium 23 

Silicon 28 

Phosphorus 31 

Sulphur 32 

Calcium 40 

Manganese 55 

Iron 56 

Cobalt 59 

Nickel 59 

Zinc 65 


Arsenic 15 

Bromine 80 

Molybdenum 96 

Silver 108 

Cadmium 112 

Tin 118 

Antimony 122 

Iodine 121 

Tellurium 129 

Barium 131 

Tungsten 184 

Osmium 199 

Mercury 200 

Lead 201 

Bismuth 210 


2.  Multiples  by  0*5  of  the  equivalent  of  hydrogen. 


Aluminum 
Chlorine  . . 
Copper . . . 


21  -5  Selenium. . 

35 '5  Strontium. 

63*5 


19-5 

81-5 


surpass  in  precision.  In  this  memoir  he  gives  the  following  numbers  for  some  of  the 
most  important  elements  (0  = 8): — 


Oxygen. . . 

Silver 

Chlorine  . . 
Potassium. 


8 

101-945 

35-46 

39-13 


Sodium . . 
Nitrogen 
Sulphur  , 
Lead  . . . 


23-05 

14041 

16-0311 

103-456 


These  results  have  been  obtained  in  each  case  by  several  different  processes ; and 
the  differences  between  the  various  numbers  thus  arrived  at  for  the  same  body  are  in 
all  cases  much  smaller  than  the  difference  between  the  mean  result  and  the  whole 
number  required  by  Prout’s  law.  These  numbers  were  obtained  by  operating  with 
balances  of  unusual  delicacy,  and  upon  quantities  much  larger  than  is  customary  in 
researches  of  this  kind — the  quantities  amounting  in  some  cases  to  nearly  a pound 
weight  of  the  materials. 

The  numbers  thus  obtained  do  not  differ  from  those  of  Dumas,  or  indeed  from 
those  in  general  use,  sufficiently  to  affect  any  calculations  of  analyses  founded  upon 
them ; but  from  the  variety  of  methods  employed,  and  the  extraordinary  degree  of 
care  and  precision  with  which  the  experiments  w^ere  made,  the  results  are  of  the 
highest  value  in  relation  to  the  hypothesis  of  Prout. 

M.  Stas  concludes  his  memoir  with  these  words : — 

“ So  long  as  we  adhere  to  the  results  of  experiment  for  the  establishment  of  the 
laws  by  which  matter  is  governed,  we  ought  to  consider  the  law  of  Prout  as  a pure 
illusion,  and  should  regard  the  indecomposable  substances  of  our  globe  as  distinct 
bodies,  having  no  simple  relations  between  their  atomic  weights.  The  undeniable 
analogy  in  properties  which  is  observed  in  certain  of  the  elements  must  be  sought  for 
in  other  causes  than  those  derivable  from  the  relations  in  weight  of  their  acting 
masses.” 

We  cannot  too  jealously  watch  any  twisting  of  experimental  data  to  suit  our 
theories ; and  those  who  are  familiar  with  the  speculations  on  the  numerical  relations 
of  the  atomic  w'eights,  cannot  but  feel  that  the  severe  method  of  induction  from 
facts  has  in  this  case  been  more  than  usually  departed  from  by  the  followers  of  a 
science  which  is  pre-eminently  one  of  experiment. 


EATIO  OF  PKOPOETIONAL  NTJMBEES. 


789 


The  relations  exhibited  between  the  numbers  of  many  of  these 
bodies  which  are  chemically  allied  are  often  very  remarkable : — 

1.  It  has  been  observed  that,  in  several  instances  where  two 
elements  are  in  close  chemical  relation  to  each  other,  they  have 
atomic  weights  which  are  identical ; this  happens,  for  example, 
with  the  following  pairs  of  bodies : — 


Cobalt  and  nickel 59 

Lanthanum  and  cerium 92 

Ehodium  and  ruthenium 104*2 

Platinum  and  iridium 197*2 


2.  In  other  cases  the  ratio  of  the  atomic  weights  is  as  1 to  2 ; 
for  instance : — 


Oxygen...  =:  16  Sulphur...  = 32 

Aluminum.  = 27*5  Manganese.  = 55 

3.  It  has  also  been  stated  that,  w^here  three  elements  belong  to 
the  same  natural  group,  the  atomic  weight  of  the  intermediate 
element  is  frequently  equal  to  the  mean  of  those  of  the  two  ex- 
tremes. This  is  true  in  the  case  of 

Lithium  . = 7 7 + 39*1 

Sodium  . = 23  ; =23*05  ; 

Potassium  = 39  2 


the  number  for  sodium  being  the  arithmetic  mean  of  those  for 
lithium  and  potassium  ; but  this  is  the  only  case  in  which  this  re- 
lation is  rigidly  in  accordance  with  the  experimental  numbers. 
Several  groups  agree  very  nearly  with  such  a supposition,  but  the 
divergence  is,  notwithstanding,  too  great  to  admit  of  being  attri- 
buted to  errors  of  experiment.  For  example  : — 


Calcium  = 40 
Strontium  = 87*5 
Barium  = 137*0 
Sulphur  = 32 
Selenium  = 79*5 
Tellurium  = 129*0 


40  + 87*5 

; =88*5. 

■ 2 

32+129 

; =80*5. 

2 


In  both  these  groups,  the  difference  between  the  experimental 
and  the  calculated  number  of  the  intermediate  elements  amounts 
to  1*0  ; and  it  is  probable  that  this  difference  is  physically  true. 

In  cases  like  the  lithium  and  calcium  groups,  it  has  been 
suggested,  both  by  Pettenkofer  and  by  Dumas,  that  the  relation 
between  the  different  members  of  the  group  may  be  analogous  to 
that  observed  in  bodies  of  organic  origin  which  belong  to  the  same 
homologous  series.  The  reader  who  is  desirous  of  pursuing  this 
speculation  will  find  it  ably  and  clearly  discussed  by  Dumas  in  his 
paper  already  cited  (Ann,  de  Ckimie^  III.  Iv.  164). 


■V  .•,«■•  -v 

’ .jpf  j • >;t'#-‘i^  g*  H K'  fi^v  u'tii #■ ' 


; ' '■^?^rvvj<a6«s,;a;,,; 

:„ . fc'* 


- ,'l  *■  '^i.  ^ Tf ^ ‘^^,*1  Siiil  H 5 ^ ’i  ^ f4f 


INDEX 


Abel’s  mode  of  determining  amount  of 
suboxide  in  copper,  616,  note 
Acetylene,  how  absorbed,  262,  note 
Acid,  antimonic,  596 
“ antimonious,  591 
arsenic,  582 
“ arsenious,  580 
“ auric,  696 
“ bismuthic,  605 
“ boracic,  226 
“ borofluoric,  227 
“ bromic,  127 
“ carbonic,  48  et  seq. 

“ chlorhydric,  101 
“ chlorhydrosulphuric,  160 
“ chloric,  115 
“ chlorocarbonic,  123 
“ chlorochromic,  538 
“ chloromolybdic,  570 
“ chlorosulphuric,  167 
“ chlorotungstic,  576 
“ chlorous,  119 
“ chromic,  534 
“ croconic,  250 
“ cyanic,  257 
“ cyanuric,  258 
“ dithionic  (hyposulphuric),  166 
“ ferric,  517 

“ fluoric  (hydrofluoric),  227 
“ fluosilicic,  221 
“ fulminic,  258 
“ fulminuric,  259 
“ graphic,  60,  note 
“ hydriodic,  130 
“ hydrobromic,  125 
“ hydrochloric  (muriatic),  101 
“ hydrocyanic  (prussic),  253 
“ hydrofluoboric,  228 
“ hydrofluoric,  138 
“ hydrofluosilicic,  221 
“ hydroselenic,  181 
“ hydrosulphuric,  169 
“ hypochlorous,  1 10 
“ hyponitric,  89 
“ hyponitrous,  87 
“ hypophosphorous,  200 
“ hyposulphuric  (dithionic),  166 
“ hyposulphurous,  163 
“ iodic,  132 
“ iodosulphuric,  168 


Acid,  manganic,  545 
“ mellitic,  250 
“ metantimonic,  598 
“ metaphosphoric,  197 
“ metastannic,  558 
“ metatungstic,  67 4 
“ muriatic  (hydrochloric),  101 
“ nitric,  73 
“ nitromuriatic,  107 
“ nitrosulphuric,  168 
“ nitrous,  87 

“ orthophosphoric  (tribasic),  193 
“ osman-osmic,719 
“ osraic,  718 
“ oxalic,  246 

“ oxy muriatic  (chlorine),  136 
“ pentathionic,  167 
“ perchloric,  116 
“ periodic,  134 
“ permanganic,  546 
“ phosphatic,  199 
“ phosphoric,  193 
“ phosphorous,  199 
“ prussic  (hydrocyanic),  253 
“ pyrogallic,  absorption  of  oxygen  by, 
53,  note 

“ pyrophosphoric,  195 
“ rhodizonic,  250 
“ selenic,  180 
“ selenious,  180 
“ silicic,  211 
“ silicO'fluoric,  221 
“ stannic,  559 
“ sulpharsenic,  584 
“ sulpharsenious,  684 
“ sulphantimonic,  600 
“ sulphantiraonious,  599 
“ sulphocarbonic,  175 
“ sulphoxyphosphoric,  205 
“ sulphuric,  163,  157  ' 

“ sulphurous,  149 
“ telluric,  182 
“ tellurous,  182 
“ tetrathionic,  167 
titanic,  666 
“ trithionic,  166 
“ tungstic,  573 
“ vanadic,  578 
Acids,  action  ofj  on  metals,  77 

“ action  of,  on  salts  in  solution,  726 


792 


INDEX. 


Acids,  hydrated,  316 
“ monobasic,  320 
“ nomenclature  of,  3 
“ polybasic,  319,  321 
“ polythionic,  148 
“ sulphazotised,  168 
Adhesion,  influence  of,  on  affinity,  136 
Adit  level,  283 
Adularia,  431 
Aerolites,  489,  note 
Affinity,  see  Chemical  Attraction 
Agate,  211 
Aich’s  alloy,  615 

Air  in  water,  how  estimated,  34,  note 
“ Lavoisier’s  analysis  of,  by  mercury,  11 
“ presence  of,  influence  on  combustion, 
241 

“ weight  of,  21 
Alabaster,  416 
Albite,  437 

Albumen,  use  of,  in  photography,  166 
Algaroth,  powder  of,  601 
Alkali  metals,  289,  326 

“ “ conversion  into  chlorides, 

457 

“ “ estimation  of,  456 

Alkalimeter,  348,  349 
Alkalimetry,  350 

Alkaline  earths,  separation  of,  from 
alkalies,  45l 
Allomerism,  595,  note 
Allotropic  modifications  of  carbon,  69 
“ “ phosphorus,  186 

“ “ sulphur,  145 

Alloys,  general  properties  of,  217 
Alum,  430 

“ concentrated,  430 
“ -schist,  431 
“ -stone,  431 
“ varieties  of,  433 
Alumina,  425 

“ hydrates  of,  426 

“ salts  of  (see  aluminum) 

“ soluble,  426 

Aluminite,  433 
Aluminum,  423 

“ alloys  of,  425 

“ bronze,  425 

“ chlorides  o^  428 

“ fluoride  of,  429 

“ phosphates  ofj  433 

“ silicates  of,  434 

“ sulphates  of,  430 

“ tests  for,  445 

Amalgams,  651 
Amblygonite,  434 
Amethyst,  211 
Amianthus,  455 
Amides,  381,  note 
Amidogeii,  91 

Ammonia,  action  of,  on  salts,  395 
“ -alum,  430 

“ composition  of,  94 

“ conversion  of,  into  nitric  acid, 

91 

“ decomposition  by  chlorine,  95 


Ammonia,  estimation  of,  398 

“ gas,  liquefaction  of,  94 

“ “ preparation  ofj  93 

“ muriate  of,  391 

“ proportion  of,  in  air,  92 
“ “ “ rain-water,  92, 

note 

“ solution  of,  95,  389 

“ solution,  impurities  of,  97 

“ sources  of,  91 

“ table  of  strength  of  .solution,  95 

Ammoniated  bases,  395 
Ammonides,  or  arnmons,  381 
Ammonium,  98,  386,  388 
“ amalgam,  389 

“ carbonates  of,  393 

“ chloride  of,  391 

“ hydrosulphate  of,  390 

“ nitrate  of,  393 

“ phosphates  of,  394 

“ sulphates  of,  392 

“ sulphides  of,  390 

“ tests  for,  398 

Amphibole,  455 
Analcime,  431 

Analysis  of  oxides  by  hydrogen,  46 
Anatase,  565 

Anhydride,  antimonic,  596 
“ arsenic,  582 

“ arsenious,  580 

“ bismuthic,  605 

“ boracic^  224 

“ carbonic,  49 

“ chlorous,  118 

“ chromic,  534 

“ hypochlorous,  109 

“ iodic,  132 

“ molybdic,  569 

“ nitric,  79 

“ nitrous,  81 

“ phosphoric,  192 

“ phosphorous,  199 

“ selenious,  180 

“ sulpharsenic,  584 

“ sulphuric,  159 

“ sulphurous,  148 

“ titanic,  565 

“ tungstic,  512 

“ vanadic,  611 

Anhydrides  distinguished  from  acids,  316 

Anhydrite,  416 

Anhydrochromates,  635 

Anhydro-salts,  323 

Anhydrous,  what,  33 

Antichlore,  360 

Antimoniates,  691 

Antimony,  alloys  of,  594 

“ and  zinc  alloy,  595 

“ bromide  of,  601 

“ butter  of,  601 

“ crocus  of,  593 

“ crude  (sulphide),  693 

“ estimation  of,  602 

“ extraction  of,  593 

“ glass  of,  699 

“ golden  sulphide  of,  600 


INDEX. 


793 


Antimony,  Gore’s  modification  of,  595 
“ iodide  of,  601 

“ oxides  of,  596 

“ oxy sulphide  of,  599 

“ pentachloride  of,  601 

“ persulphide  of,  600 

“ properties  of,  594 

“ separation  of,  from  arsenic  and 

tin,  603 

“ sesquioxide  of,  596 

“ sulphide  of,  599 

“ terchloride  of,  600 

“ tests  for,  602 

“ vermilion,  599 

Antimoniuretted  hydrogen,  598 
Antozone,  22,  note 
Apatite,  422 

Aquafortis  (nitric  acid),  73 
Aqua  regia  (nitromuriatic  acid),  107 
Aqueous  vapour,  amount  of,  in  air,  28 
Aragonite,  417 
Arbor  Dianae,  688 
Argentic  oxide,  681 
Arseniates,  583 
Arsenic,  antidote  for,  587 
“ bromide  of,  586 

“ estimation  of,  592 

“ fluoride  of,  586 

“ hydrides  of,  585 

“ oxides  of,  680 

“ sulphides  of,  583 

“ terchloride  of,  686 

“ teriodide  of,  586 

“ tests  for,  588,  592 

“ white,  580 

Arsenical  nickel,  482 
“ pyrites,  520 

Arsenicum,  578 
Arsenites,  581 
Arseniuretted  hydrogen,  585 
Artificial  siliceous  stone,  216 
Asbestos,  455 
Assay  of  gold,  694 
“ manganese,  544 
“ silver,  672  seq. 

Atacamite,  620 
Atmosphere,  a compound,  11 

“ analysis  of,  27,  note 

“ composition  of,  26 

“ table  of  composition  of,  30 

Atomic  weights,  data  for  determining,  777 
et  seq. 

“ weights  of  elements,  aid  from  ana- 
lysis, 773 

“ weights  of  elements,  numerical  re- 
lations, 788 

“ weights  of  elements,  table  of,  786 
“ weights,  relation  of  specific  heat, 
774 

Atoms  and  equivalents,  2,  note 
Augite,  455 
Aurates,  696 
Azote  (nitrogen),  24 

Ball  Soda,  362 
Baiilla,  361 


Barium,  400 

“ carbonate  of,  403 
“ chloride  of,  402 
“ nitrate  of,  403 

“ oxides  of,  400 

“ peroxide  of,  401 

“ sulphides  of,  402 

“ sulphate  of,  403 

“ silicofluoride  of  403 

“ tests  for,  404 
Baryta,  400 
Baryto-calcite,  418 
Basalt,  437 
Base,  what,  313 
Basic  water,  32 
Basyl,  317 

Bath  for  photographs,  754 
Bauxite,  427 
Bay  salt,  354 
Bell-metal,  556 
Bellows,  action  of,  19 
Berthollet’s  theory  of  effect  of  mass  on 
combination,  731 
Beryl,  445 

Beryllium  (glucinum),  445 
Bessemer’s  process  of  refining  iron,  504 
Bichromate  of  potassium,  use  of,  in  photo- 
lithography, 757 
Binary  compounds,  318 
Binary  theory  of  salts,  315 
Bismuth,  603 

chloride  of,  605 
crystals  of,  604,  note 
estimation  of,  607 
glance,  605 
iodide  of,  606 
nitrates  of^  606 
oxides  of,  605 
sulphide  of,  605 
tests  for,  606 
Bittern,  123,  354 

Bitumen  of  Judaea,  photographic  use  of, 
757 

Black  ash,  362 

‘‘  band  ironstone,  490 
“ flux,  for  arsenical  testing,  587 
“ lead  (graphite),  59 
“ wash,  655 
Blast-furnace,  491 

“ gases  from,  492,  note 
Bleaching,  action  of  light  in,  749 

“ powder  (chloride  of  lime),  112 
Blende,  466 
Block-tin,  553 
Bloodstone,  514 
Bloomery  forge,  505 
Blowpipe,  hydraulic,  245 
“ mouth,  244 

“ oxyhydrogen,  46,  701 

Blue  pill,  651 
“ pots,  60 
“ vitriol,  622 
Bog-iron  ore,  491 
Bole,  436 

Bone  phosphate,  421 
Boracite,  454 


794: 


INDEX. 


Boracic  lagoon^  224 
Borates,  226 
Borax,  369 
Boron,  222 
“ chloride  of,  227 

“ fluoride  of,  227 

“ nitride  of,  228 

Boronatrocalcite,  422 
Boyle’s  fuming  liquor,  390 
Brard’s  process,  testing  building  stones,  420 
Brass,  615 
Braunite,  543 
Bright  white  cobalt,  472 
Brimstone  (sulphur),  143 
Britannia  metal,  556,  594 
Brittleness  of  metals,  274 
Brochanite,  623 

Brodie,  experiments  on  polarity  of  atoms, 
744 

Bromides,  126 

“ metallic,  311 
Bromine,  123 

“ chloride  of,  127 

“ hydrate  of,  125 

Bronze,  557 
Brookite,  565 
Brunswick  green,  620 
Buddie,  285 
Building  stones,  421 

“ Brard’s  mode  of  testing,  420 

Bunsen’s  burner,  239  note 

“ experiments  on  influence  of  mass 

on  aflinity,  734 
Burette,  350 
Burgos  lustre,  697 
Burnett’s  disinfecting  fluid,  466 
Butter  of  tin,  562 
Butylene  (oil  gas),  246 


Cadmium,  468 

“ oxide  of,  469 
“ salts  ofj  469 
“ tests  for,  470 
Calamine,  467 
Calcareous  waters,  417 
Calcedony,  211 
Calcium,  407 

“ carbonate  of,  418 

“ chloride  oC  414 

“ fluoride  of,  415 

“ nitrate  of,  418 

“ oxalate  of,  249 

“ phosphates  of,  421 
“ phosphide  of,  414 

“ silicide  of,  414 

“ sulphate  of,  416 

“ sulphides  of,  413 

“ tests  for,  422 

Calomel,  655 

Calotype  (Talbotype),  752 
Candle,  combustion  ofj  17 
“ flame,  241 
Canton’s  phosphorus,  413 
Carbides,  metallic,  313 
Carbon,  bisulphide  of,  175 
“ chlorides  o^  122 


Carbon,  general  properties  of^  66 

“ its  power  of  promoting  oxidation,  67 
“ natural  sources  of,  57 
Carbonates,  55,  56 
Carbonic  acid,  51 

“ “ composition  o^  55 

“ “ in  water,  estimation  of,  52, 

note 

“ “ precautions  for  breathing  in, 

54 

“ anhydride  (acid),  amount  of,  in 
air,  29 

“ “ “ natural  sources 

of,  51 

“ “ “ preparation  o^ 

48 

“ “ how  estimated,  29 

“ “ synthesis  o^  68 

“ oxide,  69,  73 
Carburets  (carbides),  313 
Camelian,  211 

Cast  iron,  varieties  o^  497-498 
“ steel,  507 
Catalysis,  739 

“ Liebig’s  theory  of,  739 
Caunter  lodes,  282 
Celestine  (sulphate  of  strontium),  406 
Cement,  Keating’s,  417 
“ Keene’s,  417 
“ Martin’s,  417 

“ Portland,  411 

“ Roman,  412 
“ Scott’s,  410 
Cerite,  449 

Cementation  of  steel,  506 
Cerium,  449 
Chalcolite,  485 
Chalk,  417 

Chalybeate  springs,  35,  522 
Char  bon  rou^,  66 
Charcoal,  64 

“ animal,  66 

Chemical  attraction,  influence  of  cohesion 

on,  722 

“ influence  of  elasticity 

on,  723 

“ “ influence  of  mass  on, 

731 

“ “ influence  of  solution 

on,  723 

“ equivalents  (see  atomic  weights) 

“ rays,  extinction  of,  769 

Chessylite,  623 

Chinese  porcelain,  analysis  of,  440 
Chlorate  of  potassium,  catalytic  decompo- 
sition of,  741 
Chlorates,  116 
Chlorides,  101 

“ metallic,  decomposition  of,  310 

“ “ preparation  ofj  309 

“ “ varieties  of,  306 

Chlorimetry,  114 
Chlorine,  98 

“ liquefaction  of,  100 
“ and  hydrogen,  action  of  light  on,  7 48 
“ hydrate  of,  99 


INDEX. 


795 


Chlorine,  peroxide  of,  119 
Chlorite,  438 
Chlorites,  119 
Chloronitric  gas,  107 
Chloronitrous  gas,  108 
Choke-damp,  54 
Chromates,  535 
Chrome  alum,  539 

“ ironstone,  530,  534 

“ yellow,  536 

Chromium,  630 

“ antidote  to  slow  poisoning  by, 

541,  note 

“ chlorides  of,  537 

“ fluorides  of,  538 

“ nitrate  of,  540 

“ nitride  of,  539 

“ oxalates  of,  540 

“ oxides  of,  631 

“ separation  of,  from  alkalies,  542 

“ sesquisulphide  of,  537 

“ sulphates  of,  539 

“ tests  for,  541 

Chrysoberyl,  447 
Chrysolite,  465 
Chrysotype,  758 
Cinnabar,  653 

Clark’s  process  for  softening  water,  4 
Clay,  absorption  of  ammonia  by,  92 
“ analysis  of,  436 
“ ironstone,  490,  523 
Coal,  61 

“ gas,  analysis  of,  267 
“ “ purification  of,  by  oxide  of  iron, 

515 

Coarse  metal,  copper,  610 
Cobalt,  470 

“ ammoniacal  compounds  of,  474 
“ arseniate  of,  478 

“ bloom,  478 

“ bright  white,  472 

“ carbonates  of,  478 

“ chloride  of,  477 

“ estimation  of,  478 

“ glance,  472 

“ Liebig’s  mode  of  separation  from 
nickel,  484 
“ nitrate  of.  477 

“ oxides  of,  472 

“ Rose’s  mode  of  separation  from 
nickel,  471 

“ separation  of,  from  zinc,  480 
“ sesquioxide  of,  474 

“ sulphate  of,  477 

“ sulphides  of,  477 

“ tests  for,  478 

“ tin  white,  472 

Coesia,  386 
Coesium,  384 

“ salts  of^  386 

Cohesion,  influence  of,  on  chemical  action, 
722 

Coke,  62 
Colcothar,  514 

Cold,  effects  in  suspending  chemical  action, 
746 


Cold  short  iron  (phosphuretted),  504 
Collodion,  754 

Colour,  influence  of,  in  photography,  773 
Coloured  glasses,  absorption  of  chemical 
rays  by,  772 

Columbium  (niobium),  667 
Combining  proportions  of  elements,  data 
for  fixing,  776 
Combustion,  its  nature,  17 
“ products  of,  19 
“ quick  and  slow,  18 
“ spontaneous,  18 
Composition  (tin  salt),  562 
Concrete,  412 

Concurring  attractions,  741 
Condy’s  disinfecting  fluid,  548 
Copper,  607 

“ alloys  of,  615 

“ ammoniacal  sulphate  of,  588,  622 
“ antidotes  for,  624 

“ best  selected,  611 

“ black  oxide  of,  617 
“ bromides  of,  622 

“ carbonates  of,  623 

“ chlorides  of,  619 

“ estimation  of,  625 

“ hydride  of,  618 

“ nitrate  of,  623 

“ nitride  of,  618 

“ ores  of,  608 

“ oxides  of,  616 

“ protosulphide  of,  619 
“ phosphide  of,  619 

“ pyrites,  618 

“ quadrantoxide  of,  616 

“ selenide  of,  619 

“ silicide  of,  615 

“ smelting,  610 

“ subiodide  of,  621 

“ sulphate  of,  622 

“ sulphides  of,  618 

“ tests  for,  624 

Copperas,  621 
Coprolites,  421 
Cornish  stone,  435 
Corrosive  sublimate,  656 
Corundum,  425 
Crocus  of  Mars,  514 
Cross  courses,  282 
Cryolite,  429 

Crystals  in  sulphuric-acid  process,  153 
Cubic  nitre,  361 
Cullet  (broken  glass),  373 
Cupellation  of  gold,  694 
“ lead,  629 
“ silver,  672 
Cupreous  chloride,  620 
“ oxide,  616 

Cupric  oxide,  617 
Cuprodiammonium,  620 
Cyaraelid,  258 
Cyanides,  255 
Cyanite,  436 
Cyanogen,  251 

“ chlorides  ot,  260 

“ iodides  of,  261 


INDEX. 


796 

Cyanogen,  liquefaction  ofj  253 
‘ ‘ sulphy drides  of,  2 6 1 

DAGrEREEOTTPE,  T58 
Debus’s  experiments  on  influence  of  mass  | 
on  chemical  attraction,  736 
Decay  of  buildings,  421 
Decimal  salt  solution  for  silver,  675 
Deflagration,  what,  340 
Deliquescence,  what,  33,  note 
Developing  solutions  for  photographs,  751, 
754 

DeviUe’s  lime  furnace,  701 
Devitrification  of  glass,  375 
Dhil  mastic,  635 
Diamond,  58 

“ conversion  of^  into  graphite,  59 
Diaspore.  426 
Didymium,  450 
Diorite,  437 
Diplatinamine,  707 
Diplatosamine,  707 

Displacement,  collection  of  gases  by,  41, 
50,  94 

Disinfecting  fluid,  Burnett’s,  466 
“ “ Condy’s,  548 

Disthene,  436 
Dolerite,  437 
Dolomite,  454 
Drummond’s  light,  47 
Ductility  of  metal^  273 
Dumas’  experiments  on  atomic  weights, 
787 

Dutch  liquid,  331 

“ chlorine  compounds  fi-om,  235 

Dykes,  282 

Earthenware,  438 

Efflorescence,  what,  33 

Elasticity,  influence  of,  on  attraction,  723 

Elayl  (olefiant  gas),  231 

Electric  cable,  heating  of  18,  note 

Elements,  classification  of  7,  8 

“ non-metallic,  table  o^  10 
Emerald,  445 
Emery,  425 
Enamel,  378 
Epsom  salts,  453 
Equivalents  and  atoms,  2,  note 
Erbia,  449 

Etching  on  glass,  139 
Ethiop’s  mineral  653 
Ethylene  (olefiant  gas),  231 
“ bibromide  of,  235 

“ bichloride  of,  231 

“ biniodide  of,  235 
Euehlorine,  121 
Eudiometer,  Cavendish’s,  42 
“ syphon,  447 

Fahlerz,  619 
Fault,  in  raining,  282 
Felspar,  436 
Fermentation,  739 
Fer  oligiste,  490 
Ferrates,  617 


Ferric  oxide,  513 
Ferrocyanogen,  262 
Ferrous  oxide,  513 
Filtering-paper,  ashes  of^  461 
I Filtration,  precautions,  459 
Fine  metal  copper,  610 
Finery  cinder,  504,  524 
Fireclay,  434 
Fire-damp,  237 
Fixed  air  (carbonic  acid),  51 
Fixing  solutions  for  photographs,  753, 
754,  763 

Flame,  high  temperature  of,  237 
Flame,  general  cnaracters  o^  239 
I Flint,  211 
Fluor-spar,  415 

Fluorescent  rays,  also  photographic,  763 
Fluorides,  140 

“ metallic,  312 
Fluorine,  137 

“ combining  number  determined,  140 
Fly-powder,  579 

Formulae,  empirical  and  rational,  6 

Fowler’s  arsenical  solution,  581 

Franklinite,  516 

French  chalk  (steatite),  455 

Fresenius  and  Babo’s  test  for  arsenic,  591 

Fresenius  and  Will,  alkalimetry,  350 

Friction  tubes,  346 

Fuller’s  earth,  436 

Fulminates,  258 

Fur  in  boilers,  how  prevented,  350 
Fuscobaltia,  475 
Fusible  metal,  605,  633 

Gadounite,  449 
Gahnite,  427 
Galena,  637 
Galvanized  iron,  464 
Garnet,  438 
Gases,  analysis  ofj  263 

“ modes  of  distinguishing,  263,  265 
Gas  pipette,  52 
Gay-Lussite,  417 
Gedge’s  alloy,  616 
Gems,  imitations  of,  377 
German  silver,  482 
Gibbsite,  433 
Gilding,  691 

Glacial  phosphoric  acid,  192 
“ sulphuric  acid,  159 
Gladstone’s  experiments  on  influence  of 
mass  on  affinity,  732 
Glass,  371 

“ Bohemian,  372 
“ bottle,  375 
“ coloured,  377 
“ crowa  374 
“ devitriflcation  of,  375 

“ disintegration  of^  379 

“ Faradav’s,  376 
“ flint,  375 

“ gall,  374 

“ Guinand’s,  376 
“ irregular  density  of^  375 
“ of  antimony,  598 


INDEX. 


V97 


Glass,  optical,  376 
“ plate,  373 
“ pots,  377 
“ properties  of,  379 
“ soluble,  369 
“ table  of  analysis  of,  372 
“ window,  374 
Glauberite,  358,417 
Glauber’s  salts,  357 
Glazed  pots,  379 
Glazing  stoneware,  &c.,  443 
Glucina,  445 
Glucinum,  445 
Gneiss,  437 
Gold,  alloys  of,  692 

“ and  sodium,  hyposulphite  of,  166 
“ amalgams,  691 
“ assay  of,  694 
“ bromide  of,  698 
“ chlorides  of,  697 
“ estimation  of,  699 
“ extraction  of,  689 
“ fine,  690 
“ fulminating,  697 
“ iodides  of,  698 
“ leaf,  690 
“ oxides  of,  696 
“ properties  of,  690 
“ parting  from  silver,  693 
“ solder,  694 
“ standard,  693 
“ sulphides  of,  697 
“ suspended,  purple,  698 
“ tests  for,  699 
“ washing,  689 
Gothite,  514 

Graduation  of  brine,  355 
Grain-tin,  553 
Granite,  437 

Graphite  (black-lead),  59 
Graphon,  61,  note 
Green  vitriol,  521 
Greenockite,  469 
Greenstone,  437 
Grey  antimony  ore,  599 
“ copper  ore,  619 
Gros,  platinum  salts  of,  706 
Guano,  ammonia  in,  398 
Guignet,  vert  de,  534 
Gun-metal,  557 
Gunpowder,  342 

“ Karolyi’s  experiments  on, 

343,  note 
“ white,  346 

Gypsum,  416 

Hematite,  490,  514 
Hair  alums,  433 
Halloysite,  436 

Halogens,  general  characters  of,  135 
Haloid  salts,  315 
Hard  snider  for  brass,  616 
Hard  and  soft  water,  36 
Hartshorn,  spirit  of,  392 
Hausmannite,  545 

Heat,  effects  of,  on  chemical  attraction,  746 


Heavy  lead  ore,  636 

“ spar,  (sulphate  of  barium),  403 
Hemming’s  safety  jet,  46 
Hornblende,  455 
Hot  blast  for  iron,  495 
Humboldtite,  524 
Hyacinth,  447 
Hydracids,  314 
Hydrates,  33 
Hydraulic  limes,  410 
Hydrides,  metallic,  313 
Hydrochloric  acid,  action  of,  upon  oxides, 
105 

“ “ impurities  of,  104 

“ “ solution  of,  103 

Hydrocyanic  acid,  tests  for,  256 
Hydrogen,  gaseous  compounds  of,  41 
“ peroxide  of,  228 

“ persulphide  of,  174 

“ phosphides  of,  203 

“ preparation  of,  38 

“ properties  of,  40 

“ purification  of,  46 

Hydrophane,  219 
Hydrosulphates,  172 
Hypochlorides,  112 
Hypophosphites,  201 
Hyposulphites,  163 

Iceland  spar,  417 
Idocrase,  437 
Ilmenium,  667 
Indian  fire,  584 
Iridium,  646 

Ink  for  marking  linen,  686 
lodates,  133 
Iodides,  131,  311 
Iodine,  128 

“ bromides  of,  134 

“ chlorides  ofi  134 

“ estimation  of,  132 

“ tests  for,  129,  132 

Iridium,  719 

“ chlorides  of,  721 
“ oxides  of,  720 

“ separation  from  platinum,  721 

Iron,  action  of  air  and  water  on,  511 
“ alloys  of,  513 
“ alum,  522 

“ ammonio-chloride  of,  521 
“ analysis  of,  529,  530 
“ bar,  510 

“ Bessemer’s  refining,  504 
“ bisulphide  of,  519 
“ bloomery  forge,  605 
“ boiling  of,  502 
“ bromides  of,  521 
“ carbides  of,  498 
“ carbonate  of,  523 
“ case-hardening,  509 
“ cast,  varieties  of,  498 
“ Catalan  forge,  505 
“ chlorides  of,  520 
“ cold  short,  504 
“ effects  of  sulphur  on,  498,  note, 

“ effects  of  wolfram  on,  498 


79S 


rSDEX. 


Iron,  estimation  oC  526 

“ estimation  of  mixed  oxides,  528 
“ heat  produced  by  its  oxidation,  18, 
note 

“ hvdrated  sesquioxide  of,  514 
“ hydride  of,  517 
“ iodide  of,  521 
“ lute,  519 

“ magnetic  oxide  of.  516 
“ magnetic  pyrites,  519 
“ malleable  cast,  500 
“ meteoric,  488 
“ native.  488 
“ nitrates  o^  522 
“ nitride  of^  517 
“ ores  o£  489 
“ oxalates  of,  524 
“ oxides  of,  513 


“ passive,  512 
“ persulphate  o£  522 
“ phosphates  of,  524 
“ phosphide  of,  520 
“ properties  o£  511 
“ puddling,  Calvert  and  Johnson's  ex- 
periments on,  503,  note 
“ pure,  preparation  o^  510 


“ pyrites,  519 
“ r^  short,  513 
“ refining,  500 
“ resin  (oxalate),  524 
“ rusting  of  511 
“ sesquioxide  of,  514 
“ silicates  of  524 
“ smelting,  491-497 
“ sulphate  of  521 
“ sulphides  of,  517 
“ tests  for,  525 

'•  wrought,  how  obtained,  500-505 
“ yearly  produce  of,  497,  wte 
Iserine,  565 
Isomerism.  275 

Isomorphism,  aid  in  fixing  atomic  weights, 


776 


Isomorphous  mixtures,  notation  of,  326 


JiGGiXG  ores,  285 
Juckes’s  smoke-burner,  62 


Kaoux,  435 
Kelp,  357 

Kermes  mineral,  600 
Kernel-roasting  of  copper,  613 
Kieve,  286 

Killas  (clay  slate),  608 
King's  yellow.  5S4 
Kish  (graphite  from  iron),  500 
Kohinoor,  cutting  of  58,  note 
Kupfemickel,  482 

Labradorite.  437 
Lac  sulphuris.  175 
Lake  pigments,  427 
Lampblack,  64 
Lanthanum,  449 
I>apis  lazuli,  443 
Latent  image,  752,  755 


Laughing  gas  (nitrous  oxide),  84 
Lazulite,  434 
Lead,  626 

“ action  of  air  and  water  on,  631 
“ alloys  of  633 
“ borate  of  641 
“ bromide  of  639 
“ carbonate  of  641 
“ chloride  of  638 
“ chlorosulphide  of  639 
“ chromate  of  531,  535 
cupellation  of  629 
“ desUvering  of  628 
“ estimation  of  644 
“ fluoride  of  639 
“ froth  of  631 
“ iodide  of  638 
“ nitrate  of  639 
“ nitrites  of  640 
“ oxides  of  632 
“ oxychloride  of  638 
“ peroxide  of  636 
“ phosphates  of  640 
“ red,  635 
“ refining,  628 
“ shot  633 
“ silicates  of,  641 
“ smelting,  644 
“ sulphate  of  639 
“ sulphite  of  639 
“ tests  for,  643 
Lepidolite,  381,  438 
Leukon,  217 

Light  carburetted  hydrogen.  236 
“ chemical  effects  of  747 
“ of  flames.  241 
‘‘  reducing  eftects  of  750 
“ supposed  effect  of  on  crystalliza- 
tion, 747 

Lime,  chloride  of  (bleaching  powder^ 
112 

“ dead  burnt,  410 
“ hydrate  of  409 

“ hydraulic,  410 

“ salts  of  see  Calcium 
“ use  of  as  manure,  412 
Limekilns.  407 
Limes,  fat  and  poor,  410 
I Limestone,  417 
I Lime-water,  409 

Liquation  of  silver  from  copper,  669 
I Liquefaction  of  cyanogen,  253 
Liquor  potassae,  333 
Litharge,  634 
Lithia.  381 
I Lithium,  381 
i “ carbonate  of  382 
“ chloride  of  382 
“ phosphate  of  382 
“ sulphate  of  382 

“ tests  for,  383 

Litmus,  action  of  acids  on,  318 
Liver  of  sulphur,  336 
Lixivia tion  of  black  ash,  362 
Loadstone.  4S9,  516 
1 Loam,  435 


INDEX. 


^99 


Lodes,  282 
Lucifer  matches,  190 
Lugol’s  solution  of  iodine,  130 
Lunar  caustic,  686 
Luteo-cobaltia,  475 


Magistral,  for  silver  ore,  667 
Magnesia,  452 

“ alba,  454 
“ hydrate  of,  453 

Magnesian  limestone,  421,  454 
Magnesite,  453 
Magnesium,  450 

“ and  potassium,  sulphate  of,  453 
“ borate  of,  464 

“ carbonate  o^  453 

“ chloride  of,  453 

“ estimation  of,  457 

“ nitride  of,  452 

“ nitrate  of,  453 

“ phosphates  of,  454 

“ photographic  use  of,  462 

“ silicates  of,  455 

“ sulphate  of,  452 

“ sulphide  of,  452 

“ tesis  for,  455 

Magnetic  iron  ore,  488,  516 
Magnus’s  green  platinum  salt,  706 
Malachite,  623 
Malleability  of  metals,  273 
Manganates,  545 
Manganese,  542  , 

“ assay  of  oxides  of,  544 

“ black  oxide  of,  544 

“ blende,  548 

“ carbonate  of,  549 

“ chloride  of  548 

“ estimation  of,  550 

“ fluorides  of,  549 

“ isomorphous  relations  of,  550 
“ oxychoride  of,  549 

“ red  oxide  of,  545 

“ separation  from  other  metals, 

660 


“ sesquioxide  of,  543 
“ spar,  649 

“ sulphate  of,  549 

“ sulphides  of,  548 

‘‘  tests  for,  550 

Manganite,  543 
Manganous  oxide,  543 
Margueritte’s  test  for  iron,  529 
Marking  ink,  686 
Marl,  435 
Mars-hgas,  236 
Marsh’s  test  for  arsenic,  589 
Massicot,  634 

Mass,  influence  of,  on  affinity,  731 
Medals  by  compression,  270 
Meerschaum,  455 
Mellite,  250 
Menaccanite,  565 
Mercuramine,  652 

Mercuric  chloride  (corro.  sublim.),  656 
Mercurous  chloride  (calomel),  656 
Mercury,  647 


Mercury,  amalgams  of,  650 

“ ammoniated  derivatives  of,  658 

“ bromides  of,  659 

“ chlorides  of,  665 

“ estimation  of,  663 

“ extraction  of,  647 

“ iodides  of,  659 

“ nitrates  of,  661 

“ nitric  oxide  of,  659 

“ nitride  of,  660 

“ oxides  of;  651 

“ oxychlorides  of,  656 

“ purification  of,  650 

“ sulphates  of,  661 

“ sulphides  of,  653 

“ tests  for,  663 

Metachromic  oxide,  633 
Metals,  action  of,  on  acids,  77 
“ classification  of,  289-294 
“ condition  of,  in  nature,  279 

“ fusibility  of,  275 

“ general  properties  of,  770 
“ hardness  of,  271 
“ in  powder,  271 
“ malleability  of,  273 
“ native,  280 
“ specific  gravity  of,  275 
“ tenacity  of,  271 
“ variable  equivalents  of,  322 
“ volatility  of,  276 
Metameric  compounds,  259 
Metantimoniates,  698 
Metaphosphates,  198,  199 
Metasilicates,  215 
Metastannates,  558 
Metatuugstates,  575 
Meteoric  stones,  489,  note 
Methyl,  hydride  of  (marsh  gas),  236 
Mica,  438 
“ slate,  438 
Microcosmic  salt,  394 
Milk  of  lime,  409 
Mine,  plan  and  sections  of,  283 
Mineral  chameleon,  645 

“ green,  624 

“ veins,  281 

“ waters,  35 

Mining  operations,  283 
Minium,  636 

Mirrors,  silvering  of,  558,  670 

“ “ Liebig’s  mode,  671 

Mispickel,  519 
Moiree  metallique,  556 
Molybdates,  569 
Molybdenum,  567 

“ chlorides  of,  570 

“ oxides  of,  568 

“ sulphides  of,  570 

“ tests  for,  670 


Mordants,  427 
Moroxite,  422 
Mortars  and  cements,  409 
Mosaic  gold,  561 

Motion,  influence  of,  on  chemical  attrac- 
tion, 740 

Mouth  blowpipe,  243,  244 


800 


INDEX. 


Mundic  (iron  pyrites),  519 
Muntz  metai,  616 

Naples  yellow,  598 
Native  metals,  281 
Natron,  361 

Negative  photographs,  151 
Nickel,  arsenical,  482 

“ carbonate  of,  483 

“ chloride  of,  483 

“ estimation  ofj  484 

“ extraction  of,  480 

“ glance,  482 

“ oxides  of,  482 

“ properties  of,  481 

“ sulphate  ofj  482 

“ sulphides  of,  482 

“ tests  for,  484 

Niobium  (columbium),  561 
Nitrates,  81 
Nitre,  338 

“ plantations,  338 
“ refining  of,  340 
Nitric  acid,  action  of,  on  metals,  80 
“ Harcourt’s  method  for,  92 

“ hydrates  of,  19 

“ Pugh’s  method  for,  82,  noie 

“ table  of  strength,  19 

“ tests  for,  82-84 

Nitric  oxide  (deutoxide  of  nitrogen),  85 
Nitrides,  metallic,  312 
Nitrites,  81 
Nitrogen  (azote),  24 

“ bromide  of?,  128 

“ chloride  of?,  121 

“ deutoxide  of  (nitric  oxide),  85 

“ from  nitrite  of  ammonium.  95, 

note 

“ iodide  of?,  135 

“ oxides  of,  13 

“ phosphide  of?,  201 

“ peroxide  of,  89 

“ preparation  of,  25 

“ protoxide  of  (nitrous  oxide),  83 

“ sulphide  of,  118 

Nitrosulphates,  168 
Nitrosyl  (nitric  oxide),  85 
Nitrous  fumes,  condensation  of,  156 

“ oxide  (protoxide  of  nitrogen),  83 
Noble  metals,  table  of,  641 
Nomenclature,  chemical,  1-6 
“ of  acids,  4 

“ of  binary  compounds,  2 

“ of  elements,  2 

“ of  multiple  compounds,  3 

Nordhausen  sulphuric  acid,  159 

Obsidian,  431 

Ochre,  490 

Oil  gas,  246 

Oil  of  vitriol,  151,  159 

Olefiant  gas  (ethylene),  231 

Olivine,  455 

Onyx,  211 

Oolite,  411 

Opal,  211 


Ores,  washing  of,  284 
Orpiment,  584 
Orthoclase,  437 
Orthophosphates,  193 
Orthosilicates,  215 
Osmium,  116 

“ chlorides  ofj  118 

“ oxides  of.  111 

“ sulphides  of,  n 1 

Oxalates,  246 

Oxidating  flame  of  blowpipe,  244 
Oxides,  analysis  of,  by  hydrogen,  46,  4l 
“ metallic,  classes  of,  293,  296 

“ metallic,  decompositions  of,  300 

“ metallic,  preparation  of,  299 

“ varieties  of,  20 

Oxyacids,  314 
Oxychlorides,  325 
Oxychloride,  chromic,  538 

“ of  carbon  (chlorocarbonic 
acid),  123 
Oxycobaltia,  4l5 
Oxygen,  absorption  of,  53,  note 

“ atomic  weight  of,  1 2,  tioie 

“ estimation  of,  301 

“ preparation  of,  14 
“ properties  of,  13 

Oxyhydrogen  furnace,  Deville’s,  101 
“ jet,  46 
Oxysalts,  315 
Ozone,  21 

Packfong,  482 
Painting  on  China,  442 
“ on  glass,  318 
Palladamine,  111 
Palladium,  llO 

“ compounds  of,  711 

“ cyanide  of,  111 

“ oxides  of,  711 

“ tests  for,  112 

Paracyanogen,  259 
Parasulphatammon,  388 
Paratungstates,  512 
Parting  gold  and  silver,  693 
Pa.ssive  state  of  metals,  513 
Paste  for  mock  jewels,  311 
Patent  yellow,  638 
Pattinson’s  desilvering  process,  628 
Pea  iron  ore,  490 
Peacock  copper  ore,  619 
Pearlash,  346 
Pearl  white,  606 
Pegmatite,  435 
Penny’s  test  for  iron,  529 
Pelopium,  561 
Perchlorates,  116 
Permanent  white,  403 
Permanganates,  546 
Petalite,  381,  431 
Petuntze,  437 
Pewter,  556,  595 

Phosgene  (oxychloride  of  carbon),  123 
Phospham,  201 
Phosphates  (tribasic),  194 
Phosphides,  metallic,  313 


INDEX. 


801 


Phosphites,  199  ^ 

Phosphomolybdate  of  sodium,  570 
Phosphorite,  421 
Phosphorus,  185,  188 

“ bromides  of,  206 

“ . group  of  elements,  184 

“ iodides  of,  206 

“ oxide  of,  201 

“ oxychloride  of,  205 

“ perchloride  of  (pentachloride), 
205 

“ red,  or  amorphous,  181 

“ sulphides  of,  207 

“ sulphochloride  of,  205 

‘‘  terchloride  of,  204 

Phosphuretted  hydrogen,  201 
Photo-chemical  induction,  748 
Photographic  collodion,  754 
“ engraving,  756 

“ printing,  751 

“ spectra  of  elements,  768 

“ transparency,  7 63 

Photo-lithographs,  756 
Picrosmine,  455 
Pimple  copper,  611 
Pink  salt  (of  tin),  562 
“ colour,  533 
Pins,  tinning  of,  556 
Pitchblende,  485 
Pipeclay,  435 
Plaster  of  Paris,  416 
Plate  sulphate  of  potassium,  360 
Platinamine,  707 
Plating,  669 
Platinic  oxide,  704 
Platinosum,  708,  note 
Platinous  chloride,  705 
“ oxide,  7 04 

Platinum,  699,  702 

“ alloys  of,  703 

“ amraoniacal  derivatives  of,  706, 

708 

“ black,  703 

“ chlorides  of,  705 

“ condensation  of  gases  by,  703, 

737 

“ estimation  of,  709 

“ extraction,  Deville  and  De- 

bray’s plan,  702 

“ extraction,  Wollaston’s  mode  of, 

700 

“ fulminating,  709 

“ Gros’s  salts,  706 

“ iodide  of,  709 

“ Magnus’s  green  salt,  706 

“ nitrate  of,  709 

“ ore,  treatment  o^  716 

“ oxides  of,  704 

“ properties  of,  702 

“ Raewsky’s  salts,  706 

“ residues,  reduction  of,  705,  note 

“ sponge,  700 

“ sulphides  of,  705 

“ surface  actions  of,  736 

“ tests  for,  709 

Platosamine,  707 


Plumbago  (graphite),  59 
Plumbates,  636 
Plumber’s  solder,  556 
Poling,  copper,  611 
Pollux,  384 
Polyhallite,  417 
Polymeric  compounds,  259 
Porcelain,  438,  440 
Porphyry,  437 
Positive  photographs,  754 
Potash,  332 

“ caustic,  332 

“ hydrate  of,  333 

“ natural  sources  of,  334 
Potashes,  346 
Potassium,  328 

“ anhydrochromate  of,  535 
“ bicarbonate  of,  351 

“ bichromate  of,  535 

“ bisulphate  of,  338 

“ bromide  ot'  337 

“ carbonate  of,  346 

“ chlorate  of,  345 

“ chloride  of,  336 

“ cyanate  of,  257 

“ estimation  of,  351 

“ extraction  of,  from  sea-water,  355, 

note 

“ ferrocyanide  of,  252 
“ fluoride  of,  338 

“ iodide  of,  337 

“ nitrate  of,  338 

“ nitrite  of,  345 

“ oxides  of,  33 1 

“ perchlorate  of,  346 

“ silicofluoride  of,  338 
“ sources  of,  334 

“ sulphate  of,  338 

“ sulphides  of,  334 

“ tests  for,  351 

“ tetroxide  of,  331 

Pot  metal,  633 
Pottery,  440 

Precipitates,  manipulation  of^  450 

Prehnite,  436 

Prussiate  of  potash,  252 

Pressure,  influence  of,  on  combination,  725 

Psilomelane,  644 

Puddling,  501 

Pulvis  fulminans,  345 

Pumice,  438 

Purple  of  Cassius,  699 

Purpureo-cobaltia,  474 

Putty  powder,  658 

Puzzuolana,  410 

Pyrogallic  acid,  for  absorbing  oxygen,  53, 
note 

“ “ for  developing  photo- 

graphs, 755 

Pyrolusite,  544 
Pyrope,  438 
Pyrophorus,  iron,  722 
“ lead,  722 

“ sulphide  of  potassium,  334 
Pyrophosphates,  195 
Pyroxene,  465 


802  IXDEX. 


Pyroxylin,  754,  note 

QuARTATioxof  gold,  693 
Quartz,  211 
Queen’s  metal,  556 
Quicklime,  407 

Rain  water,  34 
Realgar,  583 

Reaumur’s  porcelain,  375 
Red  antimony  ore,  599 
“ lead,  635 
“ phosphorus,  188 
“ silver  ore,  633 
Reducing  flame  of  blowpipe,  243 
Reduction  of  metals,  288 
Reflnery  iron  furnace,  500 
Reinsch’s  test  for  arsenic,  588 
Reiset’s  platinum  bases,  707 
Respiration  a slow  combustion,  19 
Reverberatory  furnace,  287 
Rhodium,  compounds  of,  7 14 
“ tests  for,  714 
Rinman’s  green,  474 
River  water,  35 
Roasting  ores,  28  7 
Rock  crystal,  211 
“ salt,  355 

Rocks,  sedimentary  and  igneous,  281 

Roofing  slate,  438 

Rose  copper,  613 

Roseo-cobaltia,  474 

Rouge,  514 

Rubidia,  384 

Rubidium,  383 

“ salts  of,  384 
Ruby,  425 
Rupert’s  drops,  379 
Rust  of  iron,  19,  511 
Ruthenium,  716 
Rutile,  565 

SAFETT-LAilP,  237 
Sal  alembroth,  656 
“ ammoniac,  391 
“ enixum  (bisulph.  potas.),  338 
“ gem  (rock  salt),  355 
“ prunella  (fused  nitre),  340 
Salt-cake,  359 
Salt  of  sorrel,  246 
Saltpetre,  340 
Salt  radicle,  317 
Salts,  acid,  319 

“ ammoniated,  394 
“ basic,  325 
“ binary  theory  of^  315 
“ double,  323 
“ haloid,  315 

“ in  solution,  action  of  acids  on,  726 
“ “ “ bases  on,  728 

“ “ mutual  action  of,  728 

“ neutral  or  normal,  319 
“ nomenclature  of,  5 
“ of  lemons,  249 
“ of  sesquioxides,  321 
“ of  tin,  562 


Sandiver,  374 
Sapphire,  426 

Sawdust,  a source  of  oxalic  acid,  247,  note 

Scheele’s  green,  582 

Scheelite,  571 

Schlippe’s  salt,  600 

Schlich,  285 

Schlot,  356 

Schweinfurt  green,  582 
Sea  water,  36 
Seleniates,  181 
Selenides,  306 
Selenite,  416 
Selenites,  180 
Selenium,  178 

“ chlorides  of,  181 
Seleniuretted  hydrogen,  181 
Serpentine,  455 
Sesquioxides,  salts  o^  321 
Shot,  633 

Siemen’s  regenerator,  495 
Silica,  211 

“ hydrates  ofj  212 
“ pure,  preparation  of  211 
“ soluble,  212 

Silicates,  215 
suicides,  metallic,  313 
Silicon  (sUicium),  208 
“ bromide  220 

“ chloride  of,  218 

“ crystalline,  209 

“ fluoride  of,  221 

“ hydride  of,  218 

“ hydrochlorate  of  chloride,  220 

“ nitride  of,  218 

“ sulphide  of,  218 

Silicone  (chryseon)  216 
SUico tungstates,  575 
SUver,  acetonitrate  of,  7 53 
“ alloys  of,  671 

“ amalgamation,  American  plan,  667 

“ amalgamation,  Freyberg  plan,  665 

“ ammonio-nitrate  of.  588 

“ assay  by  cupellation,  672-674 

“ “ humid  process,  674-680 

“ Augustin’s  mode  of  extracting, 

667,  7iote 

“ bromide  of,  684 

“ chlorides  of,  683 

estimation  of,  688 
fine,  680 

“ fluoride  of,  685 

“ fulminate  of,  7 58 

“ fulminating,  681 

“ glance,  682 

“ iodide  of,  685 

“ liquation  from  copper,  669 

“ nitrate  of,  686 

“ ores  of,  665 

oxides  of,  681 

“ parting  from  gold  by  sulphuric 

acid,  685 

“ phosphates  of,  686 

“ properties  of,  665 

“ solder,  672 

“ standard,  672 


INDEX. 


803 


Silver,  suboxide  of,  681 
“ sulphate  of,  685 

“ sulphide  of,  682 

“ tests  for,  688 

“ Ziervogel’s  process  for  extracting, 
667,  note 
Silvering,  670 
Slag,  what,  288 
Slags,  iron  furnace,  492 
Slaked  lime,  408 
Slate,  438 

Slip,  in  pottery,  440 
Smalt,  473 

Smelting,  or  reduction,  288 
“ of  copper,  608 

“ of  iron,  491,  seg. 

“ lead,  628 

Smoke,  consumption  of,  61,  62,  note 
Soapstone,  455 
Soap  test,  Clark’s,  419 
Soda,  353 
“ ash,  364 
“ salts,  see  Sodium, 

“ water,  50 
Sodium,  352 

“ aluminate  of,  427 

“ biborate  of,  368 

“ bicarbonate  of,  365 

“ bisulphate  of,  360 

“ bromide  of,  357 

“ carbonate  of,  361 

“ carbonate,  Longmaid’s  process  for, 

365 

“ chloride  of,  354 

“ iodide  of,  357 

“ hyposulphite  of,  163 

“ nitrate  of,  361 

“ oxides  of,  353 

“ phosphates  of,  367 

“ phospho-molybdate  of,  669 

“ sesquicarbonate  of,  365 

“ silicates  of,  369 

“ sulphate  otj  357 

“ sulphides  of,  353 

“ sulphites  of,  360 

“ tests  for,  380 

Solder,  plumbers’,  556 
Solution,  influence  of,  on  affinity,  723 
Spathic  iron  ore,  490 

Spectrum,  chemical  action  of  opposite 
ends,  771 

“ mode  of  photographing,  762 

“ photographic  action  of,  761 

Speciflc  heat,  aid  in  fixing  atomic  weights, 
774 

Specular  iron  ore,  490 
Speculum  metal,  656 
Speiss,  473 
Spelter  (zinc),  461 
Spiegeleisen,  498 
Spinelle,  427 
Spodumene,  381 
Spring  water,  34 
Stalactites,  stalagmites,  418 
Stamping  mill  for  ore,  285 
Standard  silver,  672 


Stannates,  560 
Stannic  chloride,  562 
Stannous  oxide,  658 
“ chloride,  561 
Starch  test  for  iodine,  130 
Stas,  experiments  on  atomic  weights,  788 
Steatite  (soapstone),  455 
Steel,  alloys  of,  507 
“ blistered,  506 
“ cast,  507 
“ cementation  of,  506 
“ nitrogen  in?  507,  woie;  529 
“ shear,  507 
“ tempering  of,  508 
“ tilted,  507 
“ titanium,  507 
Stereochromy,  370 
Sterro-metal,  616 
Stilbite,  436 
Stoneware,  439 
Strass,  377 
Stream  tin,  552 
Stratified  rocks,  281 
Strontia,  405 

Strontianite  (carbonate  of  strontium),  406 
Strontium,  405 

“ salts  of,  405,  406 
Stucco,  417 

Sublimation,  what,  302 
Subsalts,  325 
Sulphammonates,  168 
Sulphantimonites,  600 
Sulphatammon,  388 
Sulphates,  161,  162 
Sulphazates,  168 
Sulphazites,  168 
Sulphazotates,  168 
Sulphhydrates,  304 
Sulphides,  172 

“ decompositions  of,  303 

“ metallic,  varieties  of,  302 

“ preparation  of,  304 
“ soluble  in  sulphide  of  ammo- 

nium, 305 
Sulphitammon,  388 
Sulphites,  151,  152 
Sulphocarbonates,  177 
Sulphocyanogen,  262 
Sulpho-salts,  318 
Sul phoxy phosphates,  205 
Sulphur,  143 

“ extraction  of,  144 

“ chlorides  of,  177 

“ electro-positive  and  electro-nega- 

tive, 146 

“ estimation  of,  305 

“ group,  general  characters  of,  141 

“ iodide  and  bromide,  177 

“ octohedral,  145 
“ oxides  of,  148 

“ oxychloride  of,  177 

“ prismatic,  145 

“ table  of  oxyacids,  148 

“ viscous,  146 

Sulphuretted  hydrogen,  169 
“ waters,  35 


804: 


DJDEX. 


Sulphuric  acid,  153,  157 

“ “ chamber,  155 

“ “ hydrates  of^  160 

“ “ manufacture  of,  155 

“ “ purification  o£  160 

“ “ table  of  strength,  157 

Sulphurous  anhydride,  liquefaction  of,  150 
Sulphury  1,  chloride  of,  167 
Sump  of  mine,  287 
Superphosphates,  194 
Super  saturation  of  sodium,  carbonate,  365 
“ of  Glauber’s  salt,  358 

Surface  actions,  736 
Syenite,  437 


Tabasheer,  220 
Table  of  acidifiable  metals,  551 
alkali-metals,  326 
alkaline  earthy  metals,  400 
“ ammonia  copper  compounds,  621 

“ ammonia  mercury  compounds,  659 

“ ammonia,  strength  of,  95 

‘‘  ammoniated  salts.  395 
“ analyses  of  cast-iron,  499,  500 

“ “ of  China,  440 

“ “of  clay,  436 

“ “ of  gas  from  hot-blast  fur- 

nace, 495 


(< 

li 

H 

u 

il 

ii 

u 

u 

u 

(( 

(( 

u 

u 

u 

u 

(C 

u 

(f 

u 

(( 


il 

u 

u 

a 


u 

u 

a 

u 

if 

(f 

if 


“ of  glass,  372 

“ of  puddled  iron,  501 

“ of  refined  iron,  501 

atomic  weights  of  elements,  786 
basic  salts,  325 
carbonates,  55 

chlorinated  bodies  from  Dutch  li- 
quid, 235 

Clark’s  soap-test,  418 
cobalt  bases,  47  6 
composition  of  atmosphere,  30 
fusing-points  of  metals,  275 
halogens.  135 

hydrochloric  acid,  strength  of,  105 
iron  metals,  47  0 
lead  used  in  assaying,  674 
magnesian  metals,  450 
nitrates,  80 

nitric  acid,  strength  of,  80 
noble  metals,  647 
non-metallic  elements,  10 
olefines,  259 
oxalates,  246 
oxides  of  nitrogen,  73 
phosphorus  group,  184 
photographic  transparency,  765 
platinum  bases,  708 
potash,  strength  of  solution,  333 
products  from  gunpowder,  342 
salts  of  sesquioxides,  321 
silicates,  215 

soda,  strength  of  solution,  353 
specific  gravity  of  metals,  27  5 
sulphates,  161 

sulphides  soluble  in  sulphide  of 
ammonium,  302 
sulphites,  151 
sulphur  group,  141 


Table  of  sulphuric  acid,  strength  of,  157 

“ tenacity  of  metals,  27  2 

“ tungstates,  573 

“ varieties  of  phosphates,  197 

Talbotype  (calotype),  752 
Talc,  455 
Tantalum,  567 
Tartar  emetic,  601 
Tellurium,  181 
Telluretted  hydrogen,  183 
Tempering  of  steel,  508 
Tennantite,  619 
Terbia,  449 

Tetrylene  (oil-gas),  246 
Thallium,  644 

“ oxides  of,  646 

“ salts  ofj  646 

Thenardite,  358 
Thenard’s  lilue,  472 
Thionyl,  chloride  of,  177,  note 
Thorinum,  448 
Thorite,  448 
Tin,  551 
“ alloys  of,  556 
“ binoxide  of,  558 
“ chlorides  o^  561 
“ estimation  of^  563 
“ oxides  of,  558 

“ -prepare  liquor,  560  ' 

“ protoxide  of,  558 
“ sulphides  of^  558 
“ tests  for,  562 
“ tetrachloride  of,  562 
Tincal  (borax),  368 
Tinfoil,  554 
Tinning  copper,  556 
Tinplate,  555 
Tinstone,  558 
Tin- white  cobalt,  472 
Titanates,  566 
Titanium,  564 

“ bisulphide  of,  566 
“ chloride  of,  566 
“ cyanide  of,  564 
“ nitrides  of,  564 
“ oxides  of,  565 

“ tests  for,  566 

Tithonometer,  748 
Topaz,  430 
Touch-paper,  340 
Touchstone,  for  gold,  694,  note 
Trachyte,  437 
Trap,  437 
Travertine,  419 
Triphane  (spodumene),  381 
Triple  phosphate.  455 
Trona,  366 
, Tufa,  420 
I Tungstates.  571 
Tungsten,  571 

“ chlorides  of,  576 

“ oxides  of,  571 

“ oxychloride  of,  576 

“ phosphides  of,  575 

“ sulphides  of,  575 

“ tests  for,  576 


INDEX. 


805 


Turner’s  yellow,  638 
Turpeth  mineral,  661 
Turquoise,  433 
Tutenag,  482 
Tutty,  466 

Type-metal,  594,  633 

Ultramarine,  443 
Uranates,  487 
Uranite,  485 
Uranium,  485 

“ chlorides  of,  487 

“ estimation  of,  487 

“ extraction  of,  485 

“ oxides  of,  486 

“ tests  for,  487 

Uranyl,  487 

Vanadiates  577 
Vanadium,  577 

“ chlorides  of,  578 
“ oxides  of,  577 
Vanning  ore,  286 

Vapour  volume,  aid  in  fixing  atomic 
weights,  774 
Varvicite,  544 

Vegetable  colours,  chemical  action  of  solar 
rays  on,  773 
Vermilion,  653 

“ antimony,  599 
“ humid  process,  654 
Vivianite,  524 

"Wad,  544 
Washing  ores,  284 
“ -bottle,  459 

Waste  gas  from  iron  furnace,  495,  496 
Water-blowpipe,  245 
“ chalybeate,  35 
“ chemical  properties  of,  33 
“ composition  of,  38 
“ distilled,  38 

“ electric  decomposition  of,  38 
“ filtration  of,  36 

“ formed  by  combustion  of  hydrogen, 
42 

“ functions  of,  in  combination,  33 
“ hard  and  soft,  36 
“ of  crystallization,  34 
“ rain,  34 
“ river,  35 


Water,  sea,  36 
“ spring,  34 
“ sulphureous,  35 
“ synthesis  of,  42-46 
“ voltaic  analysis  of,  38 
“ weight  of  cubic  inch  and  foot,  32 
Waters,  natural  varieties  of,  34-38 
“ calcareous,  418 
“ mineral,  35 
Wavellite,  434 
Wedgwood  ware,  439 
White  antimony  ore,  596 
“ gunpowder,  346 
“ lead,  641 
“ precipitate,  658 
“ vitriol,  467 
Wire  drawing,  274 

“ gauze,  action  of,  on  flame,  238 
Witherite  (carbonate  of  baryta),  403' 
Wolfram,  571,  574 
Wood  ashes,  346 
“ charcoal,  64 
Wootz,  508 
Woulfe’s  bottles,  96 

Xantho-cobaltia,  475 

Yellow  ochre,  436 
Yttria,  449 
Yttrium  449 
Yttrotantalite,  449 

Zafpre,  473 
Zeolites,  214,  436 
Zinc,  carbonate  of,  467 
“ chloride  of,  466 
“ extraction  of,  461-464 
“ oxide  of,  465 
“ properties  and  uses  of,  464 
“ purification  of,  464 
“ red  oxide  of,  461 
“ separation  of,  from  alkalies  and  alka- 
line earths,  468 
“ sulphate  of,  466 
“ sulphide  of,  466 
“ tests  for,  467 
“ white,  466 
Zircon,  447 
Zirconia,  447 
Zirconium,  447 


